https://golbornevintageradio.co.uk/forum/ Mon, 13 Apr 2026 05:27:41 +0000 MyBB https://golbornevintageradio.co.uk/forum/showthread.php?tid=9529 Sat, 15 Nov 2025 20:28:06 +0000 Mike Watterson]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9529 Quote:John Honniball @anachrocomputer@mastodon.social

#makevember 15: I can't claim that this is an original design idea, but I must've seen it on Mastodon maybe a year ago. Combine two inexpensive drawing compasses into a pair of multimeter probes that can be used one-handed while holding something else in the other hand. https://mastodon.ie/@anachrocomputer@mas...0144406169

Take the two drawing compasses apart.
make one with two pencil holders.
Put the meter probes in the pencil holders.]]> Quote:John Honniball @anachrocomputer@mastodon.social

#makevember 15: I can't claim that this is an original design idea, but I must've seen it on Mastodon maybe a year ago. Combine two inexpensive drawing compasses into a pair of multimeter probes that can be used one-handed while holding something else in the other hand. https://mastodon.ie/@anachrocomputer@mas...0144406169

Take the two drawing compasses apart.
make one with two pencil holders.
Put the meter probes in the pencil holders.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9475 Wed, 30 Jul 2025 08:31:00 +0000 DrStrangelove]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9475
One 150V dc mirror scaled meter out of a JJ instruments piece of kit.

One switchable 15V/75V/150V dc mirror scaled meter ditto.

One 250mA/500mA/1A moving iron ammeter ditto.

Acquired when clearing out The Instrument Store of yore ten or fifteen years ago.

Haven't quite finished the ammeter.

It all came from a complete three phase lab that was moved, installed, then ripped out again.

Must have cost tens of thousands back in the 1970s.

The first of the voltmeters fit the plastic box precisely.

Naturally enough, the second voltmeter was nowhere near as precise & it's fortunate that the now very oval hole is covered. ]]>
One 150V dc mirror scaled meter out of a JJ instruments piece of kit.

One switchable 15V/75V/150V dc mirror scaled meter ditto.

One 250mA/500mA/1A moving iron ammeter ditto.

Acquired when clearing out The Instrument Store of yore ten or fifteen years ago.

Haven't quite finished the ammeter.

It all came from a complete three phase lab that was moved, installed, then ripped out again.

Must have cost tens of thousands back in the 1970s.

The first of the voltmeters fit the plastic box precisely.

Naturally enough, the second voltmeter was nowhere near as precise & it's fortunate that the now very oval hole is covered. ]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9410 Sun, 16 Feb 2025 10:19:03 +0000 sickdear]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9410 https://golbornevintageradio.co.uk/forum/showthread.php?tid=9393 Tue, 14 Jan 2025 13:18:08 +0000 Exiled Yorkshireman]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9393
I found a need for a ferrite core adjustment tool. It has to be the same size as a 1/10 inch or 2.5mm hex (Allen) key. None of my ceramic tools fitted and all my Allen keys are made of ferrous metal. Fortunately I have a 3d printer (Ender 3 Pro) and found a downloadable design on Thingyverse:

https://www.thingiverse.com/thing:5342615

I downloaded the 100mm long one with handle (2.5mm-Allenx100.stl). sliced it with Cura and printed the result with PLA filament. The outcome is not perfect, possibly due to my imperfect heated bed height adjustment, but it fits the cores nicely and is strong enough for the job. I imagine that it would break before a core would. One of the nice features is that it's long enough for deeply recessed cores.

I daresay that someone more skillful than me could design similar tools to fit other cores.

I hope this is useful to someone and apologise if I'm teaching my grandmother to suck eggs.]]>
I found a need for a ferrite core adjustment tool. It has to be the same size as a 1/10 inch or 2.5mm hex (Allen) key. None of my ceramic tools fitted and all my Allen keys are made of ferrous metal. Fortunately I have a 3d printer (Ender 3 Pro) and found a downloadable design on Thingyverse:

https://www.thingiverse.com/thing:5342615

I downloaded the 100mm long one with handle (2.5mm-Allenx100.stl). sliced it with Cura and printed the result with PLA filament. The outcome is not perfect, possibly due to my imperfect heated bed height adjustment, but it fits the cores nicely and is strong enough for the job. I imagine that it would break before a core would. One of the nice features is that it's long enough for deeply recessed cores.

I daresay that someone more skillful than me could design similar tools to fit other cores.

I hope this is useful to someone and apologise if I'm teaching my grandmother to suck eggs.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9357 Thu, 07 Nov 2024 12:00:05 +0000 DrStrangelove]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9357
Practical Electronics October/November 1966: radio remote control by D. Bollen: 

a kalitron transmitter (which I built another example of about 6 years ago & it works).

And a superregen receiver which I built and still couldn't get it to work, instead I built a superhet which did work.

No reason for any of this other than I built "something" back in the late 60s using available bits of scrap & the like & that didn't work either.

So I thought I'd revisit it, being rather better equipped these days than a Hartley 13A scope & an AVO 8.]]>
Practical Electronics October/November 1966: radio remote control by D. Bollen: 

a kalitron transmitter (which I built another example of about 6 years ago & it works).

And a superregen receiver which I built and still couldn't get it to work, instead I built a superhet which did work.

No reason for any of this other than I built "something" back in the late 60s using available bits of scrap & the like & that didn't work either.

So I thought I'd revisit it, being rather better equipped these days than a Hartley 13A scope & an AVO 8.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9304 Sat, 20 Jul 2024 08:56:36 +0000 sickdear]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9304
I'm here to create a Philips pattern generator that has the Philips circle pattern in a variant of this model. I've been trying to find files on GitHub but can't find the Philips circle pattern. I want to create a PM5644 4:3 version similar to the original. Has anyone done it yet?]]>
I'm here to create a Philips pattern generator that has the Philips circle pattern in a variant of this model. I've been trying to find files on GitHub but can't find the Philips circle pattern. I want to create a PM5644 4:3 version similar to the original. Has anyone done it yet?]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9290 Wed, 26 Jun 2024 13:43:07 +0000 Mike Watterson]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9290
Previously I used an isolated PSU with + connected to H+ and Cathode and negative at about 0.7 V, 1.4 V and 2.1V via 1N4007 shunt regulators to the H-.

I sometimes used the bench PSU for 4V and 6.3V valves as the internal heater supply seemed low. I thought this was because the internal is PWM and I had too many ferrites on all the cables.

So recently I removed a lot of ferrites (leaving one small bead per wire), but the 6.3 V still seemed poor. My suspicion then was the IRF1404Z FET driven by push-pull transistor buffer from the CPU. It's about 8 nF gate capacitance and likely needs more than 5V drive on a 33% duty cycle at 19.1V to 6.3V. This became evident when trying to drive an opto-isolater from the drivers. Due to tight THP I couldn't unsolder it so snapped it off. Then the opto-isolater was much better though still not good enough.

The idea of the isolator is so an external PSU up to 120 V can be connected to the +H / Cathode (a fixed +19.1V) and the FET gate drive driven by the isolater. A buffer using a PNP and NPN transistor allows more capacitance to be driven, but has no gain, thus doesn't sharpen the isolated PWM signal. I need 8V to 12V there, so a 74HC74 is no use. I tried a 4049 (not the 4049U) with one gate as inverter and the other 5 gates in parallel and lovely sharp pulse on the scope. Before connecting an IRF740 FET I loaded it with a capacitor. Rise & fall time is sad. I'll recheck capacitor value vs gate capacitance of the IRF740 FET, and change the 8V supply to 12V or more. I found another small transformer. Not sure if my 4049A (not the later more buffered version) is 15V or 18V max. I'll maybe use the 8V one for a floating supply meter with its "OV" referenced to the FET drain to measure heater voltage.

More testing needed.

I'll fit a switch now to select internal or external PSU.]]>
Previously I used an isolated PSU with + connected to H+ and Cathode and negative at about 0.7 V, 1.4 V and 2.1V via 1N4007 shunt regulators to the H-.

I sometimes used the bench PSU for 4V and 6.3V valves as the internal heater supply seemed low. I thought this was because the internal is PWM and I had too many ferrites on all the cables.

So recently I removed a lot of ferrites (leaving one small bead per wire), but the 6.3 V still seemed poor. My suspicion then was the IRF1404Z FET driven by push-pull transistor buffer from the CPU. It's about 8 nF gate capacitance and likely needs more than 5V drive on a 33% duty cycle at 19.1V to 6.3V. This became evident when trying to drive an opto-isolater from the drivers. Due to tight THP I couldn't unsolder it so snapped it off. Then the opto-isolater was much better though still not good enough.

The idea of the isolator is so an external PSU up to 120 V can be connected to the +H / Cathode (a fixed +19.1V) and the FET gate drive driven by the isolater. A buffer using a PNP and NPN transistor allows more capacitance to be driven, but has no gain, thus doesn't sharpen the isolated PWM signal. I need 8V to 12V there, so a 74HC74 is no use. I tried a 4049 (not the 4049U) with one gate as inverter and the other 5 gates in parallel and lovely sharp pulse on the scope. Before connecting an IRF740 FET I loaded it with a capacitor. Rise & fall time is sad. I'll recheck capacitor value vs gate capacitance of the IRF740 FET, and change the 8V supply to 12V or more. I found another small transformer. Not sure if my 4049A (not the later more buffered version) is 15V or 18V max. I'll maybe use the 8V one for a floating supply meter with its "OV" referenced to the FET drain to measure heater voltage.

More testing needed.

I'll fit a switch now to select internal or external PSU.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9274 Sun, 02 Jun 2024 15:21:03 +0000 Mike Watterson]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9274 The series ballast will use tungsten lamps. The only universally available kind are 26W for ovens, thus rated for up to 360 °C. There may be some old stock regular halogen lamps, or 60W red ones for fireglow effect where the heat makes a disk spin. I do have some 28W halogen cooker hood lamps.

The best way to test really high power valves is in the actual equipment, so I will go with 26W screw in oven lamps.

The most available HT transformer is the 110-120/220-240 isolated shaver outlets. These have a usually a shunt to limit power to under 20W and have good isolation. There is usually a themistor which can be removed. Obviously people can source other transformers or use two transformers back-to-back.

Two cheap FETs used in 500W SMPSUs can be used. They are 1nF to 5nF gate capacitance, but a 10K in series close to the gate is a good idea. A separate +9V (approx, I'll check) supply via a 100K pot will set gate bias to vary shunt current and thus HT after the series lamp(s).

Likely a number of 26W lamps are used in series, or possibly parallel, depending on selection of 150V, 300V or 600V ranges and load. Ideally to test valves you have two duplicate HT circuits.

The 1N4007s will give a nominal +160, +320 and +640V HT with no load. Feeds via 1M, 2M and 4M approx can be used for leakage tests. It can also give a nominal -160. A reversed 1N4148 can regulate to about -110V to -120V assuming a series resistor for under 200uA. A load of a 2M2 Ohm pot is less than 60uA. Perhaps a 1M or even 470K pot is feasible.

The supply for fan and FET bias can be a 9V or 12V transformer, giving between -12V or -24V for grid bias (9V) or about -16 or -32V (12V AC). So zeners for 9.1, and 22V or 12V and 28V could be added.

The 470K to 2M pot(s) can be thus switched to 3 different negative supplies.

Cheap DMMs or panel meters used to display the manually adjusted voltages, and optionally (ideally also) load currents.

There is no explicit HT regulation. Just measure it and adjust the FET bias knob. The negative supply could have the pot calibrated for situations where no or little grid current flows.

Next I will lash up a "breadboard" (a case where a literal one may suit) as I have a good few lamps, FETs, pots, caps, rectifiers, zeners, diodes etc. I'd not trust heatsink insulators at these voltages so the entire of the pair of heatsinks will be live. I've loads of suitable ones off PII style CPUs. Only up to 20W needing cooled, as worst case is HT max / 2 and no external load.]]> The series ballast will use tungsten lamps. The only universally available kind are 26W for ovens, thus rated for up to 360 °C. There may be some old stock regular halogen lamps, or 60W red ones for fireglow effect where the heat makes a disk spin. I do have some 28W halogen cooker hood lamps.

The best way to test really high power valves is in the actual equipment, so I will go with 26W screw in oven lamps.

The most available HT transformer is the 110-120/220-240 isolated shaver outlets. These have a usually a shunt to limit power to under 20W and have good isolation. There is usually a themistor which can be removed. Obviously people can source other transformers or use two transformers back-to-back.

Two cheap FETs used in 500W SMPSUs can be used. They are 1nF to 5nF gate capacitance, but a 10K in series close to the gate is a good idea. A separate +9V (approx, I'll check) supply via a 100K pot will set gate bias to vary shunt current and thus HT after the series lamp(s).

Likely a number of 26W lamps are used in series, or possibly parallel, depending on selection of 150V, 300V or 600V ranges and load. Ideally to test valves you have two duplicate HT circuits.

The 1N4007s will give a nominal +160, +320 and +640V HT with no load. Feeds via 1M, 2M and 4M approx can be used for leakage tests. It can also give a nominal -160. A reversed 1N4148 can regulate to about -110V to -120V assuming a series resistor for under 200uA. A load of a 2M2 Ohm pot is less than 60uA. Perhaps a 1M or even 470K pot is feasible.

The supply for fan and FET bias can be a 9V or 12V transformer, giving between -12V or -24V for grid bias (9V) or about -16 or -32V (12V AC). So zeners for 9.1, and 22V or 12V and 28V could be added.

The 470K to 2M pot(s) can be thus switched to 3 different negative supplies.

Cheap DMMs or panel meters used to display the manually adjusted voltages, and optionally (ideally also) load currents.

There is no explicit HT regulation. Just measure it and adjust the FET bias knob. The negative supply could have the pot calibrated for situations where no or little grid current flows.

Next I will lash up a "breadboard" (a case where a literal one may suit) as I have a good few lamps, FETs, pots, caps, rectifiers, zeners, diodes etc. I'd not trust heatsink insulators at these voltages so the entire of the pair of heatsinks will be live. I've loads of suitable ones off PII style CPUs. Only up to 20W needing cooled, as worst case is HT max / 2 and no external load.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9250 Sun, 05 May 2024 18:54:50 +0000 ppppenguin]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9250 Split from https://golbornevintageradio.co.uk/forum...p?tid=9110

In principle you can test a valve with a number of variable power supplies and a number of meters. How many you need depends on the type of valve. You also need a means to connect all these to the correct pins of the valve and try not damage you or anything else while you're doing it. There are also important refinements like making sure the valve doesn't decide to oscillate at some un (insert $deity of choice) ly frequency.

The rest is detail and convenience. From the simplest vintage valve testers to a Tektronix 570 curve tracer they are all making these measurements. With greater or lesser accuracy. With greater or lesser convenience. With greater or lesser detail. Slightly off to one side is the uTracer: https://www.dos4ever.com/uTracer3/uTracer3_pag0.html which uses the cunning trick of pulsing the voltages on the valve's electrodes. This comes with its own set of advantages and disadvantages.

Then there are all the things a valve tester won't tell you such as high frequency characteristics and pulsed power performance.

A big and interesting subject.]]> Split from https://golbornevintageradio.co.uk/forum...p?tid=9110

In principle you can test a valve with a number of variable power supplies and a number of meters. How many you need depends on the type of valve. You also need a means to connect all these to the correct pins of the valve and try not damage you or anything else while you're doing it. There are also important refinements like making sure the valve doesn't decide to oscillate at some un (insert $deity of choice) ly frequency.

The rest is detail and convenience. From the simplest vintage valve testers to a Tektronix 570 curve tracer they are all making these measurements. With greater or lesser accuracy. With greater or lesser convenience. With greater or lesser detail. Slightly off to one side is the uTracer: https://www.dos4ever.com/uTracer3/uTracer3_pag0.html which uses the cunning trick of pulsing the voltages on the valve's electrodes. This comes with its own set of advantages and disadvantages.

Then there are all the things a valve tester won't tell you such as high frequency characteristics and pulsed power performance.

A big and interesting subject.]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9144 Sun, 05 Nov 2023 14:20:47 +0000 Mike Watterson]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9144
https://www.dos4ever.com/uTracerlog7/tub....html#MOT2

I have possibly the original uTracer, with some mods.

Edit:
Better starting point.
https://www.dos4ever.com/uTracerlog7/tub....html#MOT1

Someone mentioned before that a MOT (microwave oven transformer) is useless for anything else. However it seems the MOT can be disassembled and "fixed".]]>
https://www.dos4ever.com/uTracerlog7/tub....html#MOT2

I have possibly the original uTracer, with some mods.

Edit:
Better starting point.
https://www.dos4ever.com/uTracerlog7/tub....html#MOT1

Someone mentioned before that a MOT (microwave oven transformer) is useless for anything else. However it seems the MOT can be disassembled and "fixed".]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9097 Tue, 05 Sep 2023 02:01:28 +0000 joebog1]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9097 I asked some days ago how to post pics. I have worked it out I think !!!.
Starting today, I am building a power supply for an amplifier ( audio ), that I started a few years ago.
This is a bare chassis, and just shows a tin box with some holes innit.
ANYBODY that says there are four without paint have already been told, YES I forgot them when drilling, ( of course NONE of you are guilty of that, ARE you ? ).
So I will start building today, with some hardware. There are four transformers, four chokes, a few electrolytic capacitors, some GEMOVS
( when I was a lad, they were called General Electric Metal Oxide Varistors ),
There are a couple of 105 volt gas regulators too.
Rectification is via high speed fast recovery sand diodes. As I post my progress I will explain what I am doing, and what most of the bits are for.
ANY and ALL critisism or suggestions will be viewed with interest, and will be taken seriously, friendly banter is welcomed.

  Back.jpg (Size: 1.79 MB / Downloads: 35)

  Inside.jpg (Size: 1.88 MB / Downloads: 35)

  Top.jpg (Size: 1.84 MB / Downloads: 35) ]]> I asked some days ago how to post pics. I have worked it out I think !!!.
Starting today, I am building a power supply for an amplifier ( audio ), that I started a few years ago.
This is a bare chassis, and just shows a tin box with some holes innit.
ANYBODY that says there are four without paint have already been told, YES I forgot them when drilling, ( of course NONE of you are guilty of that, ARE you ? ).
So I will start building today, with some hardware. There are four transformers, four chokes, a few electrolytic capacitors, some GEMOVS
( when I was a lad, they were called General Electric Metal Oxide Varistors ),
There are a couple of 105 volt gas regulators too.
Rectification is via high speed fast recovery sand diodes. As I post my progress I will explain what I am doing, and what most of the bits are for.
ANY and ALL critisism or suggestions will be viewed with interest, and will be taken seriously, friendly banter is welcomed.

  Back.jpg (Size: 1.79 MB / Downloads: 35)

  Inside.jpg (Size: 1.88 MB / Downloads: 35)

  Top.jpg (Size: 1.84 MB / Downloads: 35) ]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9025 Tue, 02 May 2023 07:56:24 +0000 CambridgeWorks]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9025 One such item was a ttl based frequency standard with 1MHz, 100KHz and 10Khz switchable outputs. I fabricated an aluminium case, the top and bottom using that blue mottled plastic coated type, often seen on test gear.
It was mains powered and the on off switch was an assembly containing a rocker switch together with neon indicator, this was from a fridge freezer.
Just a few years later I sold it at a junk sale as it was no longer required, nor likely to be.
Around 2010, at a rally, I was rummaging through a junk box under a table and picked it out. It looked slightly familiar, but I just couldn't think why.
Until I saw my callsign in Letraset on the front!
At 50p, I just had to buy it.
Still not of any use to me, but sits in a box somewhere now in my garage. Where it will probably stay, until the Final clearout, maybe ending up in a skip unless asomeone sees my callsign and decides to keep it as a memento?

On another note, an Ekco A22 that I repaired and replaced all out of tolerance components is pride of place on our lounge sideboard. With a minimod in the drawer below, it is used just occasionally, but more for demonstration. My 18 year old grandson just loves it and tells me never to sell it. 
I think he might have a nice surprise one day.....
Rob]]> One such item was a ttl based frequency standard with 1MHz, 100KHz and 10Khz switchable outputs. I fabricated an aluminium case, the top and bottom using that blue mottled plastic coated type, often seen on test gear.
It was mains powered and the on off switch was an assembly containing a rocker switch together with neon indicator, this was from a fridge freezer.
Just a few years later I sold it at a junk sale as it was no longer required, nor likely to be.
Around 2010, at a rally, I was rummaging through a junk box under a table and picked it out. It looked slightly familiar, but I just couldn't think why.
Until I saw my callsign in Letraset on the front!
At 50p, I just had to buy it.
Still not of any use to me, but sits in a box somewhere now in my garage. Where it will probably stay, until the Final clearout, maybe ending up in a skip unless asomeone sees my callsign and decides to keep it as a memento?

On another note, an Ekco A22 that I repaired and replaced all out of tolerance components is pride of place on our lounge sideboard. With a minimod in the drawer below, it is used just occasionally, but more for demonstration. My 18 year old grandson just loves it and tells me never to sell it. 
I think he might have a nice surprise one day.....
Rob]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9024 Fri, 28 Apr 2023 09:27:24 +0000 Radio Fixer]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=9024
Always use Silicon Rubber Insulated Wire from Phil Marrison who has a stall at BVWS Swap meets He will supply by post if you dont get to those.  ( Message me for his E-mail if you havent got it ).  Its easy strip and doesnt burn with the soldering iron.

Current offering is 0.5mm sq and 0.75 sq with current ratings of 3A and 4.5A.  I use the thin for general radio wiring and the the thicker for heaters, earth and HT.

I had the wire up until now just chucked in a box in a huge tangle.  It actually degrades it because getting a straight piece isnt easy and sharp kinks dont really come out.  So having bought some new stock I made the wire rack.

The key here is the beautiful NEW spools:
PLASTIC SPOOL PLASTIC BOBBIN ABS 100mm x 100mm x 63mm x 16mm, Plastic Bobbin | eBay

At a sensible price and low postage.

Note that I have put two wire colours ( resistor code   ) on each spool.  These come with two holes, top and bottom of each spool face, that pass 16 swg tinned copper with through nicely.   A short piece of this is bent through this, and turned over on the outside, to make a flat loop that holds the wound wire at start and end.  I used some 8mm threaded rod that I had as the spool supports but 15mm copper pipe would also work with a Jubilee Clip each end to fix it.

Thought possibly some Members might be interested


  Wire rack.jpg (Size: 74.44 KB / Downloads: 51)


Gary

  Wire rack 2.jpg (Size: 62.99 KB / Downloads: 50) ]]>
Always use Silicon Rubber Insulated Wire from Phil Marrison who has a stall at BVWS Swap meets He will supply by post if you dont get to those.  ( Message me for his E-mail if you havent got it ).  Its easy strip and doesnt burn with the soldering iron.

Current offering is 0.5mm sq and 0.75 sq with current ratings of 3A and 4.5A.  I use the thin for general radio wiring and the the thicker for heaters, earth and HT.

I had the wire up until now just chucked in a box in a huge tangle.  It actually degrades it because getting a straight piece isnt easy and sharp kinks dont really come out.  So having bought some new stock I made the wire rack.

The key here is the beautiful NEW spools:
PLASTIC SPOOL PLASTIC BOBBIN ABS 100mm x 100mm x 63mm x 16mm, Plastic Bobbin | eBay

At a sensible price and low postage.

Note that I have put two wire colours ( resistor code   ) on each spool.  These come with two holes, top and bottom of each spool face, that pass 16 swg tinned copper with through nicely.   A short piece of this is bent through this, and turned over on the outside, to make a flat loop that holds the wound wire at start and end.  I used some 8mm threaded rod that I had as the spool supports but 15mm copper pipe would also work with a Jubilee Clip each end to fix it.

Thought possibly some Members might be interested


  Wire rack.jpg (Size: 74.44 KB / Downloads: 51)


Gary

  Wire rack 2.jpg (Size: 62.99 KB / Downloads: 50) ]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8912 Thu, 20 Oct 2022 21:13:27 +0000 AdrianPH]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8912
This will be for a modulator, the plan was to use part of the circuit as used in an old military radio as I have the mod driver transformer out of it, unfortunately the interstage transformer was toast.
Anyway here is the circuit from the available online manual.

  mod1.png (Size: 660.49 KB / Downloads: 56)

The area that has me baffled is 2V2, the HT is 250 Volts, The cathode bias resistor is made up of a 1K2 and a 2K7 to give 3K9 total, with the grid bias taken off at the junction of the two resistors via a 330K resistor.

In a later section of the manual it lists the voltage on the Cathode of 2V2 as being 10.5 Volts.

  mod2.png (Size: 146.2 KB / Downloads: 56)

So this would put the grid bias at -3.2 Volts with respect to the cathode?   The valve is a CV136 or EL91 and OK with 240 Volts across the valve rather than 250 I would not expect to see much difference in I_c but according to the spec sheets at -3.2 grid bias, 250 Volts on screen and anode, the anode current I_a should be around 55mA and not the 2.7 mA suggested by a cathode voltage of 10.5.
Considering the screen current I_g2 should be around 2.3 mA, then there is only 0.4mA of Anode current in the manual?

Now the manual also states using a meter with 1,000 Ohms per Volt and I am guessing a 25 or 30 Volt range to take the measurement, so the true Cathode Voltage may be around 12 Volts with -3.5 Volts Grid bias but the spec sheet for the valve would still put that at 50mA anode current.

  mod3.png (Size: 299.69 KB / Downloads: 56)

I can not build the circuit as the transformer 2T2 is duff. But even with a 1K resistor in there I could not get the values to work out.
So I am confused as to what I have wrong, or, if the manual is wrong, if I have neglected something like space charge across the 330K resistor adding some more negative bias.

So please assist if you can and say what I have wrong/missed etc.

Adrian]]>
This will be for a modulator, the plan was to use part of the circuit as used in an old military radio as I have the mod driver transformer out of it, unfortunately the interstage transformer was toast.
Anyway here is the circuit from the available online manual.

  mod1.png (Size: 660.49 KB / Downloads: 56)

The area that has me baffled is 2V2, the HT is 250 Volts, The cathode bias resistor is made up of a 1K2 and a 2K7 to give 3K9 total, with the grid bias taken off at the junction of the two resistors via a 330K resistor.

In a later section of the manual it lists the voltage on the Cathode of 2V2 as being 10.5 Volts.

  mod2.png (Size: 146.2 KB / Downloads: 56)

So this would put the grid bias at -3.2 Volts with respect to the cathode?   The valve is a CV136 or EL91 and OK with 240 Volts across the valve rather than 250 I would not expect to see much difference in I_c but according to the spec sheets at -3.2 grid bias, 250 Volts on screen and anode, the anode current I_a should be around 55mA and not the 2.7 mA suggested by a cathode voltage of 10.5.
Considering the screen current I_g2 should be around 2.3 mA, then there is only 0.4mA of Anode current in the manual?

Now the manual also states using a meter with 1,000 Ohms per Volt and I am guessing a 25 or 30 Volt range to take the measurement, so the true Cathode Voltage may be around 12 Volts with -3.5 Volts Grid bias but the spec sheet for the valve would still put that at 50mA anode current.

  mod3.png (Size: 299.69 KB / Downloads: 56)

I can not build the circuit as the transformer 2T2 is duff. But even with a 1K resistor in there I could not get the values to work out.
So I am confused as to what I have wrong, or, if the manual is wrong, if I have neglected something like space charge across the 330K resistor adding some more negative bias.

So please assist if you can and say what I have wrong/missed etc.

Adrian]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8836 Thu, 14 Jul 2022 19:59:42 +0000 AdrianPH]]> https://golbornevintageradio.co.uk/forum/showthread.php?tid=8836
Looking at the board, it is a bit of a Frankenstein, with trimmer caps strapped to allow for adjustment, wires bridging sections etc.


  pic1.jpg (Size: 466.57 KB / Downloads: 29)
  pic2.jpg (Size: 405.92 KB / Downloads: 29)

But it works and has been a very satisfying little project.

6 x 9 Volt battery for HT 4.4 mA HT current.
3 x 1J18B valves, 1 for local Osc, mixer and RF amp.  1 for IF stage and 1 for driving a speaker, 1 Ge diode for detector.

if anyone knows of a Ki-cad library that includes the rod valves I could draw out a circuit.

Inspiration came from http://www.hi-ho.ne.jp/ux-45/russian.html   now if only I could get things that small?

Adrian]]>
Looking at the board, it is a bit of a Frankenstein, with trimmer caps strapped to allow for adjustment, wires bridging sections etc.


  pic1.jpg (Size: 466.57 KB / Downloads: 29)
  pic2.jpg (Size: 405.92 KB / Downloads: 29)

But it works and has been a very satisfying little project.

6 x 9 Volt battery for HT 4.4 mA HT current.
3 x 1J18B valves, 1 for local Osc, mixer and RF amp.  1 for IF stage and 1 for driving a speaker, 1 Ge diode for detector.

if anyone knows of a Ki-cad library that includes the rod valves I could draw out a circuit.

Inspiration came from http://www.hi-ho.ne.jp/ux-45/russian.html   now if only I could get things that small?

Adrian]]>