https://golbornevintageradio.co.uk/forum/ Mon, 20 Apr 2026 04:05:06 +0000 MyBB https://golbornevintageradio.co.uk/forum/showthread.php?tid=9411 Sun, 16 Feb 2025 22:03:21 +0000 SVLWinwick]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9411  
If you read my post about the restoration of a GEC AC5, you will realise that this post is related. Briefly, the AC5 was to be used on a regular basis to support historical social events, often with a WWII theme. This is the story of the contemporary extension speaker to be used with that radio.


  WD Speaker cabinet.jpg (Size: 68.34 KB / Downloads: 17)   
  WB logo.jpg (Size: 134.1 KB / Downloads: 19)
 
It’s a W.B. device, vintage circa 1931. It has a Darwins of Sheffield four pole permanent magnet assembly. 


  Darwins magnet.jpg (Size: 95.69 KB / Downloads: 19)

Darwins was principally a cutlery manufacturer but in the late 1920s developed a reputation for producing particularly good permanent magnets for loudspeakers. To put this into perspective, the first patent for a moving coil, permanent magnet speaker was filed in 1921.
 
For any readers not familiar with the intricacies of loudspeaker design, early speakers differ from modern ones in the design of the spider (the bit that connects the speech coil and the bottom of the cone to the frame). The early design has the spider (which is shaped a bit like the Isle of Man legs) on the inside of the speech coil and bolted to the middle of the magnet pole piece. That’s what the nut is that you can see in the centre of this one. 


  Spider nut.jpg (Size: 51.02 KB / Downloads: 20)

This significantly limits the travel of the speech coil and hence the cone and causes a rapid drop-off of response at the bass end. A modern speaker has a spider that is more like a circular accordion which fits around the outside of the coil, connecting it to the speaker chassis. This allows much greater travel and more bass. The spec. that was agreed with broadcasting companies in the early thirties was that speakers should have a flat response from 300Hz to 5000Hz so that orchestral music could be reproduced at an acceptable quality. This one does reasonably well down to 200Hz but drops off sharply at 5000Hz. And it has an odd ‘dead spot’ around 2900Hz that I assume is a resonance issue. However, it sounds pretty respectable now it has been restored.
 
The problem it had was with the suspension, which is at the upper end of the cone. Originally, it was made from chamois leather and over time it has just decayed.


  Suspension damage close.png (Size: 1.38 MB / Downloads: 17)   
  Suspension uncovered.png (Size: 1.44 MB / Downloads: 17)
 
When this happens, the speech coil can touch the pole piece and it causes rattles and eventually, electrical failure. Someone had stuffed a lot of paper around the magnet and under the cone, probably to subdue the rattles.


  Paper wadding.png (Size: 1.47 MB / Downloads: 15)
 
Many people want to preserve speakers of this vintage as near to original as possible, and with care, the rotten chamois can be treated with a liquid rubber solution to restore flexibility and strength. That would be impractical for a speaker that is going to have to work for a living.


  Cone stripped.png (Size: 1.2 MB / Downloads: 16)
 
Fortunately, the cone, speech coil and spider were in good condition, so I replaced the suspension with a modern foam replacement and realigned everything. 


  Suspension fitted.png (Size: 1.48 MB / Downloads: 16)   
  Refitted.jpg (Size: 76.68 KB / Downloads: 19)

There’s a company called North Speaker Parts who sell all sorts of bits and pieces, so it’s just a case of measuring carefully and finding the closest match.


 
This left me with an authentic-sounding and reliable driver. You can hear it in the cabinet by clicking here for music and here for speech.
 
The speech coil has an impedance of 14 ohms but the unit is intended for use with a high impedance extension speaker output like the one on the AC5 which comes straight off the output valve anode via a capacitor. If you have something similar, I strongly recommend you replace the capacitor with a modern, X-type safety capacitor. There is a Ferranti output transformer acting as a matching transformer inside the speaker cabinet. This is original.
 
Once the driver (speaker) had been repaired and cleaned up, the only thing left to be done was some minor attention to the cabinet. Some beading needed regluing and the surface finish was cleaned and sealed. A hole in the cloth covering one of the rear vents was repaired by gluing to fine black netting using spray-on contact adhesive.
 
An advertisement in Wireless Magazine from June 1931 prices it at £8:18:6 which is about £750 in today’s money. So rather like buying a high-end sound bar for your television.]]>  
If you read my post about the restoration of a GEC AC5, you will realise that this post is related. Briefly, the AC5 was to be used on a regular basis to support historical social events, often with a WWII theme. This is the story of the contemporary extension speaker to be used with that radio.


  WD Speaker cabinet.jpg (Size: 68.34 KB / Downloads: 17)   
  WB logo.jpg (Size: 134.1 KB / Downloads: 19)
 
It’s a W.B. device, vintage circa 1931. It has a Darwins of Sheffield four pole permanent magnet assembly. 


  Darwins magnet.jpg (Size: 95.69 KB / Downloads: 19)

Darwins was principally a cutlery manufacturer but in the late 1920s developed a reputation for producing particularly good permanent magnets for loudspeakers. To put this into perspective, the first patent for a moving coil, permanent magnet speaker was filed in 1921.
 
For any readers not familiar with the intricacies of loudspeaker design, early speakers differ from modern ones in the design of the spider (the bit that connects the speech coil and the bottom of the cone to the frame). The early design has the spider (which is shaped a bit like the Isle of Man legs) on the inside of the speech coil and bolted to the middle of the magnet pole piece. That’s what the nut is that you can see in the centre of this one. 


  Spider nut.jpg (Size: 51.02 KB / Downloads: 20)

This significantly limits the travel of the speech coil and hence the cone and causes a rapid drop-off of response at the bass end. A modern speaker has a spider that is more like a circular accordion which fits around the outside of the coil, connecting it to the speaker chassis. This allows much greater travel and more bass. The spec. that was agreed with broadcasting companies in the early thirties was that speakers should have a flat response from 300Hz to 5000Hz so that orchestral music could be reproduced at an acceptable quality. This one does reasonably well down to 200Hz but drops off sharply at 5000Hz. And it has an odd ‘dead spot’ around 2900Hz that I assume is a resonance issue. However, it sounds pretty respectable now it has been restored.
 
The problem it had was with the suspension, which is at the upper end of the cone. Originally, it was made from chamois leather and over time it has just decayed.


  Suspension damage close.png (Size: 1.38 MB / Downloads: 17)   
  Suspension uncovered.png (Size: 1.44 MB / Downloads: 17)
 
When this happens, the speech coil can touch the pole piece and it causes rattles and eventually, electrical failure. Someone had stuffed a lot of paper around the magnet and under the cone, probably to subdue the rattles.


  Paper wadding.png (Size: 1.47 MB / Downloads: 15)
 
Many people want to preserve speakers of this vintage as near to original as possible, and with care, the rotten chamois can be treated with a liquid rubber solution to restore flexibility and strength. That would be impractical for a speaker that is going to have to work for a living.


  Cone stripped.png (Size: 1.2 MB / Downloads: 16)
 
Fortunately, the cone, speech coil and spider were in good condition, so I replaced the suspension with a modern foam replacement and realigned everything. 


  Suspension fitted.png (Size: 1.48 MB / Downloads: 16)   
  Refitted.jpg (Size: 76.68 KB / Downloads: 19)

There’s a company called North Speaker Parts who sell all sorts of bits and pieces, so it’s just a case of measuring carefully and finding the closest match.


 
This left me with an authentic-sounding and reliable driver. You can hear it in the cabinet by clicking here for music and here for speech.
 
The speech coil has an impedance of 14 ohms but the unit is intended for use with a high impedance extension speaker output like the one on the AC5 which comes straight off the output valve anode via a capacitor. If you have something similar, I strongly recommend you replace the capacitor with a modern, X-type safety capacitor. There is a Ferranti output transformer acting as a matching transformer inside the speaker cabinet. This is original.
 
Once the driver (speaker) had been repaired and cleaned up, the only thing left to be done was some minor attention to the cabinet. Some beading needed regluing and the surface finish was cleaned and sealed. A hole in the cloth covering one of the rear vents was repaired by gluing to fine black netting using spray-on contact adhesive.
 
An advertisement in Wireless Magazine from June 1931 prices it at £8:18:6 which is about £750 in today’s money. So rather like buying a high-end sound bar for your television.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9407 Sat, 15 Feb 2025 17:38:07 +0000 SVLWinwick]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9407  
For my first post here, I thought you may like to hear the story of a rather sad GEC AC5 which now has a new lease of life.

 
The owner of the set has kept it in semi-dry storage since acquiring it some twenty years ago from an elderly relative. Unfortunately, it suffered significant damage to the cabinet from a water leak; most of the electronics were spared, though. He told me that from time to time he has shown people that it ‘works’ but that it now only hums. Our conversation came about because he wants to use the set to support WWII themed social events. So, the challenge was to make it safe, serviceable and reliable. It needed to look good but not necessarily perfect, sound good, be robust enough to transport and to ‘just work’ with minimal attention. For some target events, a low power AM transmitter is used, but for others, Bluetooth capability is needed.
 
Restoration decisions were made with the above expectations in mind. The set was not in original or even 'good enough' condition for preservation of originality to be a consideration. What follows is the summary of the work prepared for the owner:

Initial assessment

Externally, the cabinet is in poor condition with damp-related delamination and missing veneer to the right side, The chrome escutcheon round the tuning dial shows damp-related pitting. All front-facing knobs are present, original and largely undamaged with the usual amount of surface dirt. The rear-facing tone control knob has chipped edges. The shafts of the various controls are rusty. The rear cardboard panel is present and in good condition. The aerial wire is present but in unserviceable condition. The original power connector is present but does not meet modern safety standards.

It was decided to ‘tidy-up’ the cabinet rather than attempt a full restoration. The delamination was treated with PVA, glued and clamped to make sound. Existing veneer was glued where necessary and edges smoothed. The exposed plywood on the damaged side was coloured with walnut stain to more closely match the rest of the cabinet. The original cabinet finish was cleaned and sealed.
The power connector was replaced with a C14 IEC panel-mount inlet. Internal connections were insulated with heat shrink and an embedded 1A slow-blow fuse was incorporated within the shrink-wrapped connection to the mains switch (which was replaced with a double pole switch, switching both live and neutral lines). Earth is connected to the chassis.
The aerial wire was retained but a new flexible ‘tail’ was added to the plug end.

Internally, the cabinet is dirty but undamaged. The speaker cloth has previously been replaced with an (estimated) 1970s common speaker fabric. It is glued in and held with drawing pins. The high voltage cables to the speaker field and output transformer windings are in poor condition representing both a shock hazard (240V at the OP TX) and a fire hazard and will need to be replaced. The high voltage smoothing choke and one high voltage smoothing capacitor have been relocated to a void in the cabinet (they were originally housed securely within the earthed chassis). Because the cabinet back can be easily removed by swivelling three clips (intended to make valve replacement easy), this represents a shock hazard (approx. 75V across the choke and 240V across the capacitor). A solution needs to be found to this (see also comments about the catkin output valve, below). Probably an alternative method of attaching the back cover in a tamper-proof way.

The flexible, multi-strand cables were in poor condition and were replaced, but the solid-core wires were found to be serviceable. Several tags on the speaker connection tag strip were either loose or detached and were resecured. The smoothing choke and capacitor were discarded. The PSU circuit was returned to its design specification with the exception of the choke which was replaced by two 220 ohm wire wound resistors within the under chassis space.
The cabinet back was modified to accommodate three fixing screws. However, all easily accessible high voltages have been removed from the cabinet void or insulated.

The chassis is superficially in good condition with no surface rust apparent. All valves test good for heater continuity. Two valves required rebonding to their bases and one required rebonding of the anode cap. The grid cap and anode cap wires are all unserviceable and will need replacement. The output valve is a Catkin (exposed anode) valve with aged enamel and is thus a shock hazard (nominal 228V). It is easily accessible if the back of the receiver is removed. The tuning mechanism is dirty but operates smoothly. One trimmer on the tuning gang has been unscrewed inappropriately. The tuning scale is badly damaged, possibly by a combination of damp and overheating by the incorrect panel lamp bulbs. It may be possible to stabilise or reproduce. The panel lamp bulbs will need replacing.

At first power-on after restoration, although the mains current draw was not excessive, the HT current draw was nearly twice expected, mostly to the output valve. There was sound for about thirty seconds, then a gradual reduction of volume until silence after two minutes. It is likely that the output valve screen grid was red-plating (can’t be seen in a Catkin). This would be consistent with damage caused by the chronic decline and failure of the power supply noted later. The output valve was replaced with a N42 pentode and operation returned to normal with nominal voltage readings per service manual. The N42 is a glass envelope valve, so its use removed the shock hazard inherent in the original Catkin valve design.
Panel lamps were replaced with bulbs of the correct specification. It is noted, though, that they are significantly under-run (2V vs. 3.5V) and are thus quite dim. This may be why incorrect spec. bulbs had been used previously.

There is evidence of probably four historic repairs. Three repairs are to the power supply circuit (this is not unusual). There is evidence of repair in the 1950s involving the renewal of two of the smoothing capacitors and the smoothing choke. However, the original capacitors were not removed, they were simply bridged, and the replacement choke is of the wrong value (d.c. resistance much too high). There is then a second repair late 1950s/early 1960s when a further smoothing capacitor was replaced with the original being disconnected but left in place. The rectifier valve was replaced probably at this time, but with the incorrect type. It is a serviceable replacement, though. An additional smoothing capacitor was added, probably in the 1970s. It is of an inappropriately high value and was probably an attempt to remove hum. Dates estimated from the date of manufacture of the capacitors. The PSU will be returned to design configuration.

There was found to be evidence of a ‘repair’ to the power switch which had failed internally. It had been bypassed by soldering both wires to the same terminal, thus the radio was switched on simply by connecting the mains lead to power. The switch was replaced as described, above.

The fourth repair involved the replacement of a low-voltage electrolytic capacitor that decouples the output valve. This is to be expected in a set of this age.

On dismantling, this capacitor was found to be original but to have failed.

None of the above is unexpected and will be remedied as part of the rebuild. There are two areas where a decision will be needed, though. The cabinet: do we make it look as good as possible without veneering it or do we replace the missing veneer? It’s a big piece. The tuning dial: do we do nothing and leave it as it is; do we attempt to stabilise it by coating it with a lacquer; do we make a reproduction?

It was decided that the only practical solution for the tuning dial was to make a reproduction. The original was scanned into Adobe Illustrator, and traces and separations made. These were printed to acetate with paper used as a diffuser.
 
Emerging issues

All tubular capacitors tested are d.c. leaky (as expected). About half resistors are more than 15% off spec. with some showing evidence of heat damage or damp damage. Three read very high with one open.
The power supply has been significantly reconfigured both physically and electrically. All the additional components will be removed and the circuit returned to design spec. Capacitor packs will be rebuilt with modern internals. All tubular and electrolytic capacitors will be replaced. All resistors will be replaced. This is to ensure reliability given expected regular use.

The original filter capacitor pack was rebuilt using modern components (8uF, 600V vs. 6uF, 450V). The smoothing choke was replaced by two 11W, 220 Ohm wire wound resistors in series, mounted within the chassis body (d.c. resistance of specified smoothing choke is 400 ohms). [use of 11W resistors is overkill. A single 2W resistor was initially used but overheated with the original, faulty output valve and was damaged]

Note that C19 (per GEC service manual) is a potential ‘death cap’. It connects the Catkin anode (228v) to the external extension speaker socket.

C19 was found to have low d.c. resistance, allowing the >200v from the output valve anode to appear across the extension speaker terminals. It has been replaced with a ‘X-cap’ safety capacitor, given the intention to use a contemporary, high impedance extension speaker.

The power switch has failed and has been bypassed.

The power switch was dismantled in an attempt to repair. (It was found that the switch hairspring had a fatigue crack and was weak. The mechanism had been further damaged by the knob being forced, bending the fork. It cannot easily be repaired)

The associated volume potentiometer is very high (7meg vs 500k). It is a conductive-paper-and-compression-ring type. Only suitable NOS replacement available is 10k log carbon track. Track is in a.c. audio line with no d.c. potential across it so 10k should work well.

The replacement switch is double pole so will switch both mains lines. A 1A slow-blow fuse has been incorporated in the live line between the switch and the transformer. This cannot be changed by the user (to ensure that in the case of failure, a technician diagnoses the reason it blew. This is to protect rare and expensive components. A further 0.5A slow-blow fuse has been similarly incorporated in the transformer secondary winding centre-tap line).

The 10k potentiometer was found only to alter tone and not volume when connected according to the original schematic. Since it is a carbon track potentiometer, the circuit was reconfigured to bring one end of the track to d.c. ground, the wiper being taken to the first audio valve grid via a capacitor. It then functioned correctly.

Speaker windings all test good, but the anti-heterodyne coil is intermittent – almost certainly a connection tag issue.

Found to be a fractured solder tag.
+ve HT line to output transformer found to be detached from paxolin support strip.

The ‘Tuneon’ tube does glow and gives some indication of the presence of a carrier. However, it is internally blackened. Replacements are very rare. Given how few radio stations are now broadcasting on the AM bands, there seems little value in replacing it.

A Bluetooth module was incorporated into the Gram circuit. 12V a.c. is derived from a double wound mains transformer connected in parallel with the original mains transformer and housed in the original location of the smoothing choke, within the chassis body. 12V a.c. is taken to a terminal strip inside the cabinet void. This is half-wave rectified and smoothed to deliver about 15V d.c. to the input of a buck converter. The buck converter delivers a stable 5V d.c. to a Bluetooth 5 module. The left and right channel audio from the Bluetooth module is summed to produce a mono output which is delivered between the grid and cathode of the first audio valve, via the volume control. It should be noted that the Bluetooth circuitry is electrically floating and signal ground is above chassis ground by around thirty volts. (This is important if connecting test equipment)

This is AM
This is Bluetooth

Enjoy!]]>  
For my first post here, I thought you may like to hear the story of a rather sad GEC AC5 which now has a new lease of life.

 
The owner of the set has kept it in semi-dry storage since acquiring it some twenty years ago from an elderly relative. Unfortunately, it suffered significant damage to the cabinet from a water leak; most of the electronics were spared, though. He told me that from time to time he has shown people that it ‘works’ but that it now only hums. Our conversation came about because he wants to use the set to support WWII themed social events. So, the challenge was to make it safe, serviceable and reliable. It needed to look good but not necessarily perfect, sound good, be robust enough to transport and to ‘just work’ with minimal attention. For some target events, a low power AM transmitter is used, but for others, Bluetooth capability is needed.
 
Restoration decisions were made with the above expectations in mind. The set was not in original or even 'good enough' condition for preservation of originality to be a consideration. What follows is the summary of the work prepared for the owner:

Initial assessment

Externally, the cabinet is in poor condition with damp-related delamination and missing veneer to the right side, The chrome escutcheon round the tuning dial shows damp-related pitting. All front-facing knobs are present, original and largely undamaged with the usual amount of surface dirt. The rear-facing tone control knob has chipped edges. The shafts of the various controls are rusty. The rear cardboard panel is present and in good condition. The aerial wire is present but in unserviceable condition. The original power connector is present but does not meet modern safety standards.

It was decided to ‘tidy-up’ the cabinet rather than attempt a full restoration. The delamination was treated with PVA, glued and clamped to make sound. Existing veneer was glued where necessary and edges smoothed. The exposed plywood on the damaged side was coloured with walnut stain to more closely match the rest of the cabinet. The original cabinet finish was cleaned and sealed.
The power connector was replaced with a C14 IEC panel-mount inlet. Internal connections were insulated with heat shrink and an embedded 1A slow-blow fuse was incorporated within the shrink-wrapped connection to the mains switch (which was replaced with a double pole switch, switching both live and neutral lines). Earth is connected to the chassis.
The aerial wire was retained but a new flexible ‘tail’ was added to the plug end.

Internally, the cabinet is dirty but undamaged. The speaker cloth has previously been replaced with an (estimated) 1970s common speaker fabric. It is glued in and held with drawing pins. The high voltage cables to the speaker field and output transformer windings are in poor condition representing both a shock hazard (240V at the OP TX) and a fire hazard and will need to be replaced. The high voltage smoothing choke and one high voltage smoothing capacitor have been relocated to a void in the cabinet (they were originally housed securely within the earthed chassis). Because the cabinet back can be easily removed by swivelling three clips (intended to make valve replacement easy), this represents a shock hazard (approx. 75V across the choke and 240V across the capacitor). A solution needs to be found to this (see also comments about the catkin output valve, below). Probably an alternative method of attaching the back cover in a tamper-proof way.

The flexible, multi-strand cables were in poor condition and were replaced, but the solid-core wires were found to be serviceable. Several tags on the speaker connection tag strip were either loose or detached and were resecured. The smoothing choke and capacitor were discarded. The PSU circuit was returned to its design specification with the exception of the choke which was replaced by two 220 ohm wire wound resistors within the under chassis space.
The cabinet back was modified to accommodate three fixing screws. However, all easily accessible high voltages have been removed from the cabinet void or insulated.

The chassis is superficially in good condition with no surface rust apparent. All valves test good for heater continuity. Two valves required rebonding to their bases and one required rebonding of the anode cap. The grid cap and anode cap wires are all unserviceable and will need replacement. The output valve is a Catkin (exposed anode) valve with aged enamel and is thus a shock hazard (nominal 228V). It is easily accessible if the back of the receiver is removed. The tuning mechanism is dirty but operates smoothly. One trimmer on the tuning gang has been unscrewed inappropriately. The tuning scale is badly damaged, possibly by a combination of damp and overheating by the incorrect panel lamp bulbs. It may be possible to stabilise or reproduce. The panel lamp bulbs will need replacing.

At first power-on after restoration, although the mains current draw was not excessive, the HT current draw was nearly twice expected, mostly to the output valve. There was sound for about thirty seconds, then a gradual reduction of volume until silence after two minutes. It is likely that the output valve screen grid was red-plating (can’t be seen in a Catkin). This would be consistent with damage caused by the chronic decline and failure of the power supply noted later. The output valve was replaced with a N42 pentode and operation returned to normal with nominal voltage readings per service manual. The N42 is a glass envelope valve, so its use removed the shock hazard inherent in the original Catkin valve design.
Panel lamps were replaced with bulbs of the correct specification. It is noted, though, that they are significantly under-run (2V vs. 3.5V) and are thus quite dim. This may be why incorrect spec. bulbs had been used previously.

There is evidence of probably four historic repairs. Three repairs are to the power supply circuit (this is not unusual). There is evidence of repair in the 1950s involving the renewal of two of the smoothing capacitors and the smoothing choke. However, the original capacitors were not removed, they were simply bridged, and the replacement choke is of the wrong value (d.c. resistance much too high). There is then a second repair late 1950s/early 1960s when a further smoothing capacitor was replaced with the original being disconnected but left in place. The rectifier valve was replaced probably at this time, but with the incorrect type. It is a serviceable replacement, though. An additional smoothing capacitor was added, probably in the 1970s. It is of an inappropriately high value and was probably an attempt to remove hum. Dates estimated from the date of manufacture of the capacitors. The PSU will be returned to design configuration.

There was found to be evidence of a ‘repair’ to the power switch which had failed internally. It had been bypassed by soldering both wires to the same terminal, thus the radio was switched on simply by connecting the mains lead to power. The switch was replaced as described, above.

The fourth repair involved the replacement of a low-voltage electrolytic capacitor that decouples the output valve. This is to be expected in a set of this age.

On dismantling, this capacitor was found to be original but to have failed.

None of the above is unexpected and will be remedied as part of the rebuild. There are two areas where a decision will be needed, though. The cabinet: do we make it look as good as possible without veneering it or do we replace the missing veneer? It’s a big piece. The tuning dial: do we do nothing and leave it as it is; do we attempt to stabilise it by coating it with a lacquer; do we make a reproduction?

It was decided that the only practical solution for the tuning dial was to make a reproduction. The original was scanned into Adobe Illustrator, and traces and separations made. These were printed to acetate with paper used as a diffuser.
 
Emerging issues

All tubular capacitors tested are d.c. leaky (as expected). About half resistors are more than 15% off spec. with some showing evidence of heat damage or damp damage. Three read very high with one open.
The power supply has been significantly reconfigured both physically and electrically. All the additional components will be removed and the circuit returned to design spec. Capacitor packs will be rebuilt with modern internals. All tubular and electrolytic capacitors will be replaced. All resistors will be replaced. This is to ensure reliability given expected regular use.

The original filter capacitor pack was rebuilt using modern components (8uF, 600V vs. 6uF, 450V). The smoothing choke was replaced by two 11W, 220 Ohm wire wound resistors in series, mounted within the chassis body (d.c. resistance of specified smoothing choke is 400 ohms). [use of 11W resistors is overkill. A single 2W resistor was initially used but overheated with the original, faulty output valve and was damaged]

Note that C19 (per GEC service manual) is a potential ‘death cap’. It connects the Catkin anode (228v) to the external extension speaker socket.

C19 was found to have low d.c. resistance, allowing the >200v from the output valve anode to appear across the extension speaker terminals. It has been replaced with a ‘X-cap’ safety capacitor, given the intention to use a contemporary, high impedance extension speaker.

The power switch has failed and has been bypassed.

The power switch was dismantled in an attempt to repair. (It was found that the switch hairspring had a fatigue crack and was weak. The mechanism had been further damaged by the knob being forced, bending the fork. It cannot easily be repaired)

The associated volume potentiometer is very high (7meg vs 500k). It is a conductive-paper-and-compression-ring type. Only suitable NOS replacement available is 10k log carbon track. Track is in a.c. audio line with no d.c. potential across it so 10k should work well.

The replacement switch is double pole so will switch both mains lines. A 1A slow-blow fuse has been incorporated in the live line between the switch and the transformer. This cannot be changed by the user (to ensure that in the case of failure, a technician diagnoses the reason it blew. This is to protect rare and expensive components. A further 0.5A slow-blow fuse has been similarly incorporated in the transformer secondary winding centre-tap line).

The 10k potentiometer was found only to alter tone and not volume when connected according to the original schematic. Since it is a carbon track potentiometer, the circuit was reconfigured to bring one end of the track to d.c. ground, the wiper being taken to the first audio valve grid via a capacitor. It then functioned correctly.

Speaker windings all test good, but the anti-heterodyne coil is intermittent – almost certainly a connection tag issue.

Found to be a fractured solder tag.
+ve HT line to output transformer found to be detached from paxolin support strip.

The ‘Tuneon’ tube does glow and gives some indication of the presence of a carrier. However, it is internally blackened. Replacements are very rare. Given how few radio stations are now broadcasting on the AM bands, there seems little value in replacing it.

A Bluetooth module was incorporated into the Gram circuit. 12V a.c. is derived from a double wound mains transformer connected in parallel with the original mains transformer and housed in the original location of the smoothing choke, within the chassis body. 12V a.c. is taken to a terminal strip inside the cabinet void. This is half-wave rectified and smoothed to deliver about 15V d.c. to the input of a buck converter. The buck converter delivers a stable 5V d.c. to a Bluetooth 5 module. The left and right channel audio from the Bluetooth module is summed to produce a mono output which is delivered between the grid and cathode of the first audio valve, via the volume control. It should be noted that the Bluetooth circuitry is electrically floating and signal ground is above chassis ground by around thirty volts. (This is important if connecting test equipment)

This is AM
This is Bluetooth

Enjoy!]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9103 Mon, 18 Sep 2023 09:34:16 +0000 boater sam]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9103
The Murphy B485 is finally working and re-assembled. Not fully home into the Neohide ( thanks for the information ) case, it may need to come out again one day! I have cut the bottom of the case so that it can be pushed out from the bottom.

It did not submit to full working order without an eleventh hour struggle. Replacing C18 had restored reception on Long wave and improved the Medium wave reception, I had become tired of listening to just Gold. Now there were plenty of the remaining stations coming in loud and clear. A quick tweak to the RF trimmers improved the aerial response and put the stations in the correct place on the tuning dial.

I refitted the battery holder pockets on the aluminium bar across the chassis and replaced the loudspeaker. I noted that the loudspeaker is a bit special, 25 Ohm, had not noticed that in the service instructions.
A quick power up before fitting the top and the case halves produced no reception! Tapping and wriggling the battery carrier made no difference so I took it out again and intermittent reception was restored.

The ends of this carrier fits into slots in the chassis sides. One end just touched the sleeved lead of one of the transistors, moving this ever so slightly stopped reception. Not a dry joint but another rusted through transistor lead inside sleeving. These steel wires are really terrible, they break at the slightest touch and rust worse than an Austin 1100.
Extending the remaining lead restored reception once more.

Re-assembled, re-cased and suited,  I have declared the radio  restored to working order. Hopefully it will stay this way for a reasonable time.

So a radio with many oddities and difficulties for the repairer, terrible access to some components,  unusually the sole AF117 transistor is still in good working order!

Replaced 7 electrolytic capacitors, 2 resistors to gain access, 2 AF126 output transistors and rusted leads on 2 other transistors. Phew!
Of course there are no PP1 batteries any more. I use 8 AA cells in 2 battery holders as a replacement.]]>
The Murphy B485 is finally working and re-assembled. Not fully home into the Neohide ( thanks for the information ) case, it may need to come out again one day! I have cut the bottom of the case so that it can be pushed out from the bottom.

It did not submit to full working order without an eleventh hour struggle. Replacing C18 had restored reception on Long wave and improved the Medium wave reception, I had become tired of listening to just Gold. Now there were plenty of the remaining stations coming in loud and clear. A quick tweak to the RF trimmers improved the aerial response and put the stations in the correct place on the tuning dial.

I refitted the battery holder pockets on the aluminium bar across the chassis and replaced the loudspeaker. I noted that the loudspeaker is a bit special, 25 Ohm, had not noticed that in the service instructions.
A quick power up before fitting the top and the case halves produced no reception! Tapping and wriggling the battery carrier made no difference so I took it out again and intermittent reception was restored.

The ends of this carrier fits into slots in the chassis sides. One end just touched the sleeved lead of one of the transistors, moving this ever so slightly stopped reception. Not a dry joint but another rusted through transistor lead inside sleeving. These steel wires are really terrible, they break at the slightest touch and rust worse than an Austin 1100.
Extending the remaining lead restored reception once more.

Re-assembled, re-cased and suited,  I have declared the radio  restored to working order. Hopefully it will stay this way for a reasonable time.

So a radio with many oddities and difficulties for the repairer, terrible access to some components,  unusually the sole AF117 transistor is still in good working order!

Replaced 7 electrolytic capacitors, 2 resistors to gain access, 2 AF126 output transistors and rusted leads on 2 other transistors. Phew!
Of course there are no PP1 batteries any more. I use 8 AA cells in 2 battery holders as a replacement.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9003 Tue, 28 Mar 2023 05:23:19 +0000 boater sam]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9003
  Its here   https://www.youtube.com/watch?v=UbNBGVW1n0Y 

His "blobby" soldering technique appals me as a purist and soldering with valves still in the connecter is a recipe for disaster.
He obviously has never seen "cheat" twisted wire capacitors before.

Replacing the original capacitors but not saving the paper labels is a shame, it would be so much better with restuffed capacitors or at least disguised to look original.

He seems not to understand how IF transformers work either.

Perhaps I am too much a perfectionist but to me it is a mess, certainly not restored, more like ruined.

Part 2 is the speaker repair and horror of horrors, Bluetooth installed.  When I have recovered a bit  I may watch that from behind the sofa in case it becomes too scary.]]>
  Its here   https://www.youtube.com/watch?v=UbNBGVW1n0Y 

His "blobby" soldering technique appals me as a purist and soldering with valves still in the connecter is a recipe for disaster.
He obviously has never seen "cheat" twisted wire capacitors before.

Replacing the original capacitors but not saving the paper labels is a shame, it would be so much better with restuffed capacitors or at least disguised to look original.

He seems not to understand how IF transformers work either.

Perhaps I am too much a perfectionist but to me it is a mess, certainly not restored, more like ruined.

Part 2 is the speaker repair and horror of horrors, Bluetooth installed.  When I have recovered a bit  I may watch that from behind the sofa in case it becomes too scary.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8991 Tue, 14 Mar 2023 17:51:11 +0000 catch29]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8991 Six MA-12's
Three S-99's
Two USC-1's
Love that valve sound. I need to pay for all this restoration so I'm selling off my 'tranny' collection.
I acquired some months ago a faulty Rotel RX-604. I replaced the caps on the circuit protection board and gave it a test on some cheap disposable speakers, AH! life!, bit of hum so opened up again and started replacing leaky looking caps. I stopped after a couple as the track was lifting from the board, I probably had the iron too hot. Anyway, patched it up and gave it a good test connecting it on spkrs A & B to Kef 104's & Concerto's and wound the volume up.
Well, now after a week I'm still astonished at how good it sounds, clear, sweet, and a bass low and tight.
I'm unsettled!, have I missed something?.
Yours, Judas.]]> Six MA-12's
Three S-99's
Two USC-1's
Love that valve sound. I need to pay for all this restoration so I'm selling off my 'tranny' collection.
I acquired some months ago a faulty Rotel RX-604. I replaced the caps on the circuit protection board and gave it a test on some cheap disposable speakers, AH! life!, bit of hum so opened up again and started replacing leaky looking caps. I stopped after a couple as the track was lifting from the board, I probably had the iron too hot. Anyway, patched it up and gave it a good test connecting it on spkrs A & B to Kef 104's & Concerto's and wound the volume up.
Well, now after a week I'm still astonished at how good it sounds, clear, sweet, and a bass low and tight.
I'm unsettled!, have I missed something?.
Yours, Judas.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8903 Sun, 09 Oct 2022 21:39:54 +0000 boater sam]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8903
In the pile  of sets to be renovated or completely restored are a few cream Bush DAC90A radios. Unfortunately all have the small heat cracks over the dropper common with these sets.
Picking one at random, the selection was one that looked completely untouched, complete with the mains lead and the hallowed plug, good clear tuning glass scale, all undamaged knobs and an undamaged back.

A quick look around revealed that the drive cord was intact and moving the needle, the on/off volume control had a decent click but the wave change switch felt very odd, lacking end of travel stops and a bit crunchy feeling.

Making a start by taking the back and knobs off, filthy chassis out, all valves are in and no previous repairs seen. All waxy capacitors present along with much soot and thick black dust everywhere
The wave change switch is definitely broken, there is no detent ball bearing.
Connecting some power via the limiter initially, no bangs, no shorts, produced reception on long wave only even when positioning the switch carefully in the right place for medium wave.  Cut the badly crumbled speaker wires to get the cabinet out of the way to safety.

To remove these switches is involved. The tuning spindle is in the way and two of the five wires on the switch are on top amongst the cord drive, difficult to get to without melting the cord. 
The easy way I have found is to drop the spring off the hook on the tuning drum, slip the cord off the pulley at the other end of the needle slide and slip it off the tuning spindle. Then remove the chassis front to back brace, one locating stud and two 6BA nuts and bolts, remove the tuning spindle bracket, three 6BA nuts and bolts and front bearing plate, two more 6BA screws.  This allows the switch to be removed from the bracket, which is slotted, unsoldering the five wires in the process.

Examining the switch, it has one crunched up contact finger which accounts for the lack of medium wave, and the brass ball retainer is bent out stopping the switch passing the tuning spindle, and sideways. Bit of a mangled mess. The ball is long gone of course.  Checking I find I have some 4mm balls which would seem to be the size that will work.
Carefully reshaping the switch contact and the ball retainer allowed a new ball to be fitted. Not a quick job. Greased and oiled, the switch now works, the ball stops the spindle turning past the two end stops.

Just got to put it all back together, very fiddly with these nuts and bolts with grip washers, get the cord drive back on the spindle and pulleys, re-hooking the spring using a fishing line loop to pull it into place, sounds easy but it isn't. Remembered to solder the wires back on as the assembly was manoeuvred back into place.
New speaker wires fitted and powered up, it works fine on both wavebands. Not running it too long as those waxy caps will need to go.

Tidy up, four hours to do a simple but fiddly repair. Not even changed any capacitors yet, no wonder the radio and TV repair trade has gone.]]>
In the pile  of sets to be renovated or completely restored are a few cream Bush DAC90A radios. Unfortunately all have the small heat cracks over the dropper common with these sets.
Picking one at random, the selection was one that looked completely untouched, complete with the mains lead and the hallowed plug, good clear tuning glass scale, all undamaged knobs and an undamaged back.

A quick look around revealed that the drive cord was intact and moving the needle, the on/off volume control had a decent click but the wave change switch felt very odd, lacking end of travel stops and a bit crunchy feeling.

Making a start by taking the back and knobs off, filthy chassis out, all valves are in and no previous repairs seen. All waxy capacitors present along with much soot and thick black dust everywhere
The wave change switch is definitely broken, there is no detent ball bearing.
Connecting some power via the limiter initially, no bangs, no shorts, produced reception on long wave only even when positioning the switch carefully in the right place for medium wave.  Cut the badly crumbled speaker wires to get the cabinet out of the way to safety.

To remove these switches is involved. The tuning spindle is in the way and two of the five wires on the switch are on top amongst the cord drive, difficult to get to without melting the cord. 
The easy way I have found is to drop the spring off the hook on the tuning drum, slip the cord off the pulley at the other end of the needle slide and slip it off the tuning spindle. Then remove the chassis front to back brace, one locating stud and two 6BA nuts and bolts, remove the tuning spindle bracket, three 6BA nuts and bolts and front bearing plate, two more 6BA screws.  This allows the switch to be removed from the bracket, which is slotted, unsoldering the five wires in the process.

Examining the switch, it has one crunched up contact finger which accounts for the lack of medium wave, and the brass ball retainer is bent out stopping the switch passing the tuning spindle, and sideways. Bit of a mangled mess. The ball is long gone of course.  Checking I find I have some 4mm balls which would seem to be the size that will work.
Carefully reshaping the switch contact and the ball retainer allowed a new ball to be fitted. Not a quick job. Greased and oiled, the switch now works, the ball stops the spindle turning past the two end stops.

Just got to put it all back together, very fiddly with these nuts and bolts with grip washers, get the cord drive back on the spindle and pulleys, re-hooking the spring using a fishing line loop to pull it into place, sounds easy but it isn't. Remembered to solder the wires back on as the assembly was manoeuvred back into place.
New speaker wires fitted and powered up, it works fine on both wavebands. Not running it too long as those waxy caps will need to go.

Tidy up, four hours to do a simple but fiddly repair. Not even changed any capacitors yet, no wonder the radio and TV repair trade has gone.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8849 Fri, 29 Jul 2022 14:31:59 +0000 Bushbaby]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8849 I recently could not resist buying this Marshall amplifier cabinet (Marshall Class 5 - single EL84 with 2 x ECC83's) as a project. It was advertised as a "dummy' cabinet but looked original and I managed to negotiate a price of £60 which I thought was cheap considering it was one with red tolex material being quite rare. The person I bought it from had no idea whether it had a proper chassis or any board etc but I took it as read that it may not have anything inside.

When it arrived, on examining this the chassis is marked as 'dummy" but it is a real model and it does have a circuit board which is the same as the one as the one in my other Class 5 that my late mother bought me on my 50th birthday (near 13 years ago). The challenge I have, hence ask for some advice/thoughts is that the chassis appear to be designed for a later board (which cannot be purchased and are never seen anywhere for sale) where the valve are positioned at the edge of the chassis (see the photo below). The board I have has the valve positioned on the rear of the board and as such have holes drilled in the middle of the chassis to position them. The reason for the change was to do with a major rattling issue with this amp which eventually led to it being sold as a head and cabinet and not a combo, which had the issues.

I don't want to spend masses of time working on this one at the moment so what I have been thinking is:
- can I use the board I have (yes, it looks a wee bit cheap!) and position the valves at the edge of the chassis by adding appropriate leads from where the valve socket mounts in the middle of the board outwards?
- drill holes in the middle of the chassis and mount the bard with no changes as it stands with no modification?
- prepare a handwired board and modify the whole thing albeit my expertise here is very weak indeed (I can't seem to understand still(!!??) how to convert a schematic into a circuit board layout). I've look everywhere and cannot find anyone or anything that explains this in easy terms.

Thanks in advance for any help.

Rob

  red 5 cab 2.jpeg (Size: 365.07 KB / Downloads: 40)

  Class 5 dummy chassis.jpg (Size: 243.67 KB / Downloads: 40)

  class 5 front panel rear valves.jpg (Size: 232 KB / Downloads: 43)

  board 1 class 5.jpg (Size: 222.58 KB / Downloads: 42)

  board 2 Class 5.jpg (Size: 225.24 KB / Downloads: 42) ]]> I recently could not resist buying this Marshall amplifier cabinet (Marshall Class 5 - single EL84 with 2 x ECC83's) as a project. It was advertised as a "dummy' cabinet but looked original and I managed to negotiate a price of £60 which I thought was cheap considering it was one with red tolex material being quite rare. The person I bought it from had no idea whether it had a proper chassis or any board etc but I took it as read that it may not have anything inside.

When it arrived, on examining this the chassis is marked as 'dummy" but it is a real model and it does have a circuit board which is the same as the one as the one in my other Class 5 that my late mother bought me on my 50th birthday (near 13 years ago). The challenge I have, hence ask for some advice/thoughts is that the chassis appear to be designed for a later board (which cannot be purchased and are never seen anywhere for sale) where the valve are positioned at the edge of the chassis (see the photo below). The board I have has the valve positioned on the rear of the board and as such have holes drilled in the middle of the chassis to position them. The reason for the change was to do with a major rattling issue with this amp which eventually led to it being sold as a head and cabinet and not a combo, which had the issues.

I don't want to spend masses of time working on this one at the moment so what I have been thinking is:
- can I use the board I have (yes, it looks a wee bit cheap!) and position the valves at the edge of the chassis by adding appropriate leads from where the valve socket mounts in the middle of the board outwards?
- drill holes in the middle of the chassis and mount the bard with no changes as it stands with no modification?
- prepare a handwired board and modify the whole thing albeit my expertise here is very weak indeed (I can't seem to understand still(!!??) how to convert a schematic into a circuit board layout). I've look everywhere and cannot find anyone or anything that explains this in easy terms.

Thanks in advance for any help.

Rob

  red 5 cab 2.jpeg (Size: 365.07 KB / Downloads: 40)

  Class 5 dummy chassis.jpg (Size: 243.67 KB / Downloads: 40)

  class 5 front panel rear valves.jpg (Size: 232 KB / Downloads: 43)

  board 1 class 5.jpg (Size: 222.58 KB / Downloads: 42)

  board 2 Class 5.jpg (Size: 225.24 KB / Downloads: 42) ]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8848 Tue, 26 Jul 2022 15:51:26 +0000 boater sam]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8848
I acquired 2 of these 1959/1960 radios, not my usual requirement as I try to avoid ac/dc sets unless a bit special and these are a bit late for me.

Both were complete, one a little scratched about the white painted front. I had a friend who wanted a valve FM radio for his father so I cleaned up and checked out the better one for him.

The usual capacitor replacements were made, a working set of valves fitted and it worked well on all wave bands.  It was dispatched with son for father's birthday.

The other set was a bit more challenging. Part of the mains dropper resistor was open circuit and a large ceramic tube resistor had been hung on the wiring beneath the chassis. I figured that this would be better above the chassis as it would get more cooling air flow.
There were a few nasty previous repairs to be put right and the "twiddler" had been at the trimmers and coil cores. A full realignment sorted it however and it worked fine.
The chassis was put back in the cabinet, back refitted with new screws as the originals were missing and put on soak test on the bench.

Distracted by a 'phone call and a call of nature it was some time before I returned to find the set still working but blazing merrily!
Without panicking, pulling the mains plug out and using a CO2 extinguisher quelled the blaze but not before the set was well and truly ruined.

Inspection revelled that  probably excess heat from the extra resistor due to a smoothing capacitor going short had melted the highly flammable plastic tuning scale until it had drooped down and come into contact with the resistor. The resultant flames had set fire to wiring and the Bakelite cabinet.

The stink of burning Bakelite took weeks to disappear and the fumes caused a film of rust to appear on any exposed metal and tools in the workshop. I don't know what harmful gasses the fumes contained but they could not have been healthy.

So one BC402 a total right off. And a lot of cleaning up it caused too.

The other radio returned some time later smashed to pieces, it had been dropped from a fair height.  Another BC402 total right off!

I don't want to see another  GEC BC402 ever, the only radio that has ever set on fire in the workshop.]]>
I acquired 2 of these 1959/1960 radios, not my usual requirement as I try to avoid ac/dc sets unless a bit special and these are a bit late for me.

Both were complete, one a little scratched about the white painted front. I had a friend who wanted a valve FM radio for his father so I cleaned up and checked out the better one for him.

The usual capacitor replacements were made, a working set of valves fitted and it worked well on all wave bands.  It was dispatched with son for father's birthday.

The other set was a bit more challenging. Part of the mains dropper resistor was open circuit and a large ceramic tube resistor had been hung on the wiring beneath the chassis. I figured that this would be better above the chassis as it would get more cooling air flow.
There were a few nasty previous repairs to be put right and the "twiddler" had been at the trimmers and coil cores. A full realignment sorted it however and it worked fine.
The chassis was put back in the cabinet, back refitted with new screws as the originals were missing and put on soak test on the bench.

Distracted by a 'phone call and a call of nature it was some time before I returned to find the set still working but blazing merrily!
Without panicking, pulling the mains plug out and using a CO2 extinguisher quelled the blaze but not before the set was well and truly ruined.

Inspection revelled that  probably excess heat from the extra resistor due to a smoothing capacitor going short had melted the highly flammable plastic tuning scale until it had drooped down and come into contact with the resistor. The resultant flames had set fire to wiring and the Bakelite cabinet.

The stink of burning Bakelite took weeks to disappear and the fumes caused a film of rust to appear on any exposed metal and tools in the workshop. I don't know what harmful gasses the fumes contained but they could not have been healthy.

So one BC402 a total right off. And a lot of cleaning up it caused too.

The other radio returned some time later smashed to pieces, it had been dropped from a fair height.  Another BC402 total right off!

I don't want to see another  GEC BC402 ever, the only radio that has ever set on fire in the workshop.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8666 Sat, 04 Dec 2021 15:54:13 +0000 Radio Fixer]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8666

First You Tube video (golbornevintageradio.co.uk)

But at least I can send the article off to the BVWS Bulletin.
 
The pushbuttons gave me a lot of trouble.  Chassis and out twice, including the difficult Cap holding the dial.  Alas but still one sticks down.  So later it will have to all come out again and see what's going on.  Problem is that it is hard to see what's going on..  Reckon to strip the spare chassis topside, then mount the fingers and actuating arms and see how that gets on.   Should be able to see better.   Its possible that the pushbutton shaft has been bent
 
Oh! what fun....but that's Philips for you.  Don't  take 'em on if you haven't got staying power.

Cabinet came up really well from what it was.  All worm treated ...

I wanted to post two pics but Full Edit isnt like it used to be and I cant load them?

Gary]]>

First You Tube video (golbornevintageradio.co.uk)

But at least I can send the article off to the BVWS Bulletin.
 
The pushbuttons gave me a lot of trouble.  Chassis and out twice, including the difficult Cap holding the dial.  Alas but still one sticks down.  So later it will have to all come out again and see what's going on.  Problem is that it is hard to see what's going on..  Reckon to strip the spare chassis topside, then mount the fingers and actuating arms and see how that gets on.   Should be able to see better.   Its possible that the pushbutton shaft has been bent
 
Oh! what fun....but that's Philips for you.  Don't  take 'em on if you haven't got staying power.

Cabinet came up really well from what it was.  All worm treated ...

I wanted to post two pics but Full Edit isnt like it used to be and I cant load them?

Gary]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8569 Sat, 18 Sep 2021 14:08:12 +0000 Mike Watterson]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8569 valve gear restore I did. Time flies, over a year ago!]]> valve gear restore I did. Time flies, over a year ago!]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8498 Mon, 26 Jul 2021 11:12:13 +0000 skyclad]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8498 https://golbornevintageradio.co.uk/forum/showthread.php?tid=7778 Sun, 26 Jan 2020 20:08:59 +0000 Bushbaby]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=7778 I've had an opportunity this weekend to return to another project I had on the go. I bought this old 1963 (or there abouts) old instrument amplifier some while ago. Since these pics were taken I've removed and replaced all the Hunts caps, the plessey red/black electrolytics and the resistors that were well and truly out of spec. I'm now stuck as the output volume is very low indeed and heavily distorted but its not a pleasant musical distortion by any means. Being just a person that can follow instructions to build electrical equipment or to replace parts, my electronic technical knowledge is very much lacking with regard to problem solving. I have checked valve pin voltages on the ECC83, EL84 & EZ80 and all appears ok. I have reformed the smoothing cap too.

I am stuck what to do next?

Kindest Regards

Rob





  shaftesbury 519.jpg (Size: 263.12 KB / Downloads: 14)
  519.1.jpg (Size: 229.67 KB / Downloads: 31)
  519.2.jpg (Size: 513.24 KB / Downloads: 20)
  519.3.jpg (Size: 323.13 KB / Downloads: 15)
  519.4.jpg (Size: 178.93 KB / Downloads: 17) ]]> I've had an opportunity this weekend to return to another project I had on the go. I bought this old 1963 (or there abouts) old instrument amplifier some while ago. Since these pics were taken I've removed and replaced all the Hunts caps, the plessey red/black electrolytics and the resistors that were well and truly out of spec. I'm now stuck as the output volume is very low indeed and heavily distorted but its not a pleasant musical distortion by any means. Being just a person that can follow instructions to build electrical equipment or to replace parts, my electronic technical knowledge is very much lacking with regard to problem solving. I have checked valve pin voltages on the ECC83, EL84 & EZ80 and all appears ok. I have reformed the smoothing cap too.

I am stuck what to do next?

Kindest Regards

Rob





  shaftesbury 519.jpg (Size: 263.12 KB / Downloads: 14)
  519.1.jpg (Size: 229.67 KB / Downloads: 31)
  519.2.jpg (Size: 513.24 KB / Downloads: 20)
  519.3.jpg (Size: 323.13 KB / Downloads: 15)
  519.4.jpg (Size: 178.93 KB / Downloads: 17) ]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=7689 Mon, 04 Nov 2019 18:14:41 +0000 Bushbaby]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=7689 I think I'm going to be in need of some help. I've just mad a silly offer on an old guitar amp (spares/repair) and it was accepted! I have to say I know very little about these early Charlie Watkins amps. I've yet to collet it but I've attached some pics.

Thanks

Rob

  s-l500.jpg (Size: 48.76 KB / Downloads: 46)

  s-l1600 (1).jpg (Size: 75.76 KB / Downloads: 64) ]]> I think I'm going to be in need of some help. I've just mad a silly offer on an old guitar amp (spares/repair) and it was accepted! I have to say I know very little about these early Charlie Watkins amps. I've yet to collet it but I've attached some pics.

Thanks

Rob

  s-l500.jpg (Size: 48.76 KB / Downloads: 46)

  s-l1600 (1).jpg (Size: 75.76 KB / Downloads: 64) ]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=7425 Thu, 02 May 2019 12:42:30 +0000 beamcurrent]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=7425
The Trust's project is well underway and the object of this post is to raise awareness of MCR21 and to gather support and funding.

Our Trust has 4 trustees and we have formed a “CIO”, a registered Charitable Incorporated Organisation, and more information is on the MCR21 website.
As NVCF  is soon, it forms a convenient meeting point to discuss and explain this project. This forum has a wide and knowledgeable readership (blatant plug) and it is hoped that information about the early BBC history of MCR21 (1963-1975) could be obtained or even original bits of equipment found!  Wish List Link.

We also need to raise funds and to this end donations of unwanted equipment, that is unrelated to broadcasting, would be welcome to be sold at later events.

I should state, to clarify my position, that at the NVCF event I will be working on the bring and buy stall to raise funds for the BVWTM in Dulwich. Whilst our CIO, the Broadcast Television Technology Trust has similar objectives in the broadcast field it is unrelated and independent organisation.

Brian Summers

  mcr-350.jpg (Size: 28.37 KB / Downloads: 23)

  OB Vehicles 1963 - 65 Scan0014.jpg (Size: 193.61 KB / Downloads: 26)

  pye mcr type 4013 sm 2000.jpg (Size: 1.35 MB / Downloads: 26) ]]>
The Trust's project is well underway and the object of this post is to raise awareness of MCR21 and to gather support and funding.

Our Trust has 4 trustees and we have formed a “CIO”, a registered Charitable Incorporated Organisation, and more information is on the MCR21 website.
As NVCF  is soon, it forms a convenient meeting point to discuss and explain this project. This forum has a wide and knowledgeable readership (blatant plug) and it is hoped that information about the early BBC history of MCR21 (1963-1975) could be obtained or even original bits of equipment found!  Wish List Link.

We also need to raise funds and to this end donations of unwanted equipment, that is unrelated to broadcasting, would be welcome to be sold at later events.

I should state, to clarify my position, that at the NVCF event I will be working on the bring and buy stall to raise funds for the BVWTM in Dulwich. Whilst our CIO, the Broadcast Television Technology Trust has similar objectives in the broadcast field it is unrelated and independent organisation.

Brian Summers

  mcr-350.jpg (Size: 28.37 KB / Downloads: 23)

  OB Vehicles 1963 - 65 Scan0014.jpg (Size: 193.61 KB / Downloads: 26)

  pye mcr type 4013 sm 2000.jpg (Size: 1.35 MB / Downloads: 26) ]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=7348 Sun, 10 Mar 2019 21:22:03 +0000 Beardyman]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=7348