06-12-2012, 03:11 PM
In another thread I'd mentioned the business about EBL31 valves mostly not being EBL31s at all, but the more plentiful EBL1 side contact valves that have been converted to EBL31s, which - apart from the bases and size of top cap - are electrically identical, including the size of the 'bottle'.
Al ('Skywave') responded, thus, so some extra clarification might be of interest:
Anyone who owns an Ekco A22 will know of the problem of sourcing correctly sized EBL31s. Those on offer from dealers are most certainly converted EBL1s, and because of the method of conversion (fitting an octal valve base over the side contact base rather than removing the original base) are just too tall to fit into an A22 as the valve lies horizontally and the back of the set won't fit on. I dare say that in most other sets where the EBL31 valve was used, the converted valves will fit, but will either need to the top cap changing, or perhaps more easy for most, the top cap clip replacing with the larger diameter one.
It's rather a pity that such an excellent valve - a double diode pentode, which is used in the A22 as AGC, detector, and audio amp - is so scarce.
I first became aware of this problem when my son asked me to restore an A22 which he'd bought from a work colleague. I bought what I thought was an original NOS EBL31 from a major UK valve dealer, only to discover that it was too tall. I checked with several other dealers and asked that they measure the height of the valve and size of the top cap. All were the same.
As a temporary measure to at least get the A22 working, I made a valve base adaptor to enable an EL84 valve to be fitted to take care of the audio amp aspect, with two germanium diodes in the adaptor base. I cross wired the EL84 connections to an octal valve base in the adaptor to suit the EBL31 valveholder connections on the A22 chassis, so that if (as happened some time later) I managed to get a genuine EBL31 valve, I could just remove the EL84/EBL31 adaptor.
(This adaptor design was later published in the BVWS Bulletin).
I've attached a pic of the adaptor alongside a genuine EBL31 and a converted EBL1 as sold by UK dealers as EBL31s. If you look at the octal base, you'll see that it's quite tall as it has to fit over the side contact base. You'll also see the tell tale sign of a join where the octal bases has been glued onto the original base. (Neatly done by the way - possibly even at the factory).
EBL1 valves seem to be slightly more plentiful that EBL31s, though not often much cheaper, so when the opportunity presented itself at the BVWS Golborne Swapmeet in Nov 2010 to buy two N.O.S EBL1s for ten pounds each the temptation proved too great! Partly out of curiosity, partly out of necessity, I wanted to see whether I could convert the valves to EBL31s within the height limitations posed by the Ekco A22. I decided to embark on two approaches – one more radical than the other. The more difficult and intricate option was to cut off the base of the side contact valveholder and to wire an octal base shallow enough for the valve to be identical in height to the EBL31. The easier option was to leave the side contact base intact, and to cross-wire it to an octal base as shallow as possible within the height constraint. I’ll explain those two options, though I only finalised the first one. I also removed the top cap and replaced it with the smaller size as used on the EBL31, and will explain how I achieved that.
Option 1 – removal of part of the EBL1 side-contact base:
The first task was to de-solder the valve pins on the base, which was straightforward enough using a solder sucker and iron. To make sure that each wire was fully de-soldered I used a magnifying glass and wiggled the wires with a pointed modelling knife.
The rest of the operation proved rather more intricate than I’d imagined as I’d wrongly assumed that once a valve holder is removed, the wires would stay in a neat ring, so would be easily identifiable by counting back and forth from the filament wires. Would that life were so simple! Firstly, the wires emerging from the valve do not emerge in a circle, but in a straight line deep within a hollow recess in the glassware at the base of the valve. It is therefore vitally important that as soon as the base has been eased off a little, but while the wires are still in place, each wire is labelled so that when the base is lifted right off, each wire can be identified. I did this by tying some dial cord tightly around each wire and attaching a tag made from masking tape onto each one. How glad I was that I took that precaution because the moment I lifted the base right off, the wires sprang out of place, and apart from the two filament wires, it’s anyone’s guess which wire does what if not labelled! A precaution worth bearing in mind if every anyone wishes to for example replace a cracked or damaged valve base on other valves.
I’d decided that rather than completely removing the side-contact base, that I’d cut around the periphery about 5mm below the point at which the base joined the glass, thus leaving the metalising undisturbed. This proved to be a wise decision. I cut around the periphery of the base with a cutting disk mounted in a small Dremel type drill, very carefully so as to not cut through any wires. The metalising wire which goes to the cathode and G3 connection (which are themselves electrically connected within the valve) was very close to the inside of the valve base and would be all too easy to cut through.
Fitting the new octal base:
Once the severed side-contact base had been lifted off, I slipped coloured sleeving over each wire to identify which of the octal pins they needed to be soldered to. I then obtained an octal valve base from a scrap donor valve and cut the base down to a height of 15mm using the cutting disc. I extended each valve wire by soldering lengths of tinned copper wire to each in turn, then slipping short lengths of sleeving over the wires to obviate the risk of them shorting out to each other when the base was pushed into position to be soldered. The wires were then pushed down into each octal pin according to the EBL31 base requirements. Having made sure that the new octal base married up neatly with the remnant of the side contact base, I mixed some rapid setting two part epoxy glue (‘Araldite Rapid’), applied this to the two valve-base surfaces, pushed the octal base into position and held it there for a minute or two until it was firmly set. I then soldered each octal pin in turn and snipped off the surplus wire ends. That was the ‘business end’ completed, so I turned my attention to the top cap.
Top cap removal and replacement:
I’ve heard various suggestions as to the type of cement used to fit valve bases and top caps to valves, one of which is that it was a paste mixture of shellac and wood-flour. Given that methylated spirits is a solvent of shellac, I thought I’d give that a try. First, I desoldered the top cap to free the wire, gently checking with the point of a modelling knife that it was indeed free. I then inverted the valve and immersed the top cap in a small plastic container filled with methylated spirit and left that to soak overnight. I was pleased and relieved that when I wiggled it, it came free. I scrapped most of the cement away but left some on the glass pip to provide a key for the new top cap. I slipped on the top cap with a generous blob of epoxy cement, and soldered the wire.
Then came for the ‘MOT’ test - the Moment Of Truth! The valve tested fine, so was plugged into my A22, where it passed its test with flying colours. The absolute maximum height of an EBL31 that can be accommodated in the A22 is 128 mm (5 inches) from the valve base to the top of the top cap. A genuine EBL31 valve is 120mm tall (4.75 inches), and my converted EBL1 is 124mm (4.88 inches).
The other option, which I abandoned, was to solder wires onto the EBL1 valve-base and leave it in situ, but cut down an octal based to the lowest height that I could. I then made an insulating disc of 'bubble pack plastic' - the clear think hard plastic often used in packaging. I drilled holes in it, and routed wires from the side contact base to the octal base, then pushed the octal base onto the side contact valve base. Not really a success as it was a little over the 5" maximum height. One day, I might remove the side contact base as with the other one. After all, an EBL31 of the correct height converted from an EBL1 is worth the effort, when the 'big Bertha' so called 'EBL31s' are £25.00 +
There's a pic of the valve base adaptor alongs one a genuine EBL31 and a so called 'EBL31 as sold by dealers.
The second pic is of a genuine EBL31, my converted EBL1, and a tall EBL31 that though it tested fine when I got it, was in a bad way with the metalising flaking off. I gave the metailsed area several coats of conductive silver paint, then sprayed it with red oxide primer, which is a passable match for the original red. I swapped the top cap for a 1/4" one.
The others pics show the steps I took to remove the EBL1 side contact base and fit the octal one - not a job for the fainthearted!
Hope it's of interest.
Al ('Skywave') responded, thus, so some extra clarification might be of interest:
(04-12-2012, 11:55 PM)Skywave Wrote:(04-12-2012, 08:39 PM)Yorkie Wrote: I recall the EBL31s, because they were the genuine correctly sized ones - not those on offer from UK valve dealers which are converted EBL1s. The tell-tale sign is that the converted EBL1s marked as EBL31s have the larger top cap, whereas genuine EBL31s have a 1/4" top cap.
Hi David,
Now that is interesting!Back in the early 1960's, I was given an old Philips wireless, model TG170A, which had an EBL31 in it - a wireless and valve which I no longer own.
But I am very sure that the top cap was wider than 0.25 inch. I distinctly recall that it had 'Mullard Pentone' stamped on it. Surely, all those years ago, that was not a 're-housed' EBL1 ?
I am assuming, of course, that your dimensions refer to the diameter of the top cap and not its height above the top of the glass envelope.
Just curious, fascinated.
Al.
Anyone who owns an Ekco A22 will know of the problem of sourcing correctly sized EBL31s. Those on offer from dealers are most certainly converted EBL1s, and because of the method of conversion (fitting an octal valve base over the side contact base rather than removing the original base) are just too tall to fit into an A22 as the valve lies horizontally and the back of the set won't fit on. I dare say that in most other sets where the EBL31 valve was used, the converted valves will fit, but will either need to the top cap changing, or perhaps more easy for most, the top cap clip replacing with the larger diameter one.
It's rather a pity that such an excellent valve - a double diode pentode, which is used in the A22 as AGC, detector, and audio amp - is so scarce.
I first became aware of this problem when my son asked me to restore an A22 which he'd bought from a work colleague. I bought what I thought was an original NOS EBL31 from a major UK valve dealer, only to discover that it was too tall. I checked with several other dealers and asked that they measure the height of the valve and size of the top cap. All were the same.
As a temporary measure to at least get the A22 working, I made a valve base adaptor to enable an EL84 valve to be fitted to take care of the audio amp aspect, with two germanium diodes in the adaptor base. I cross wired the EL84 connections to an octal valve base in the adaptor to suit the EBL31 valveholder connections on the A22 chassis, so that if (as happened some time later) I managed to get a genuine EBL31 valve, I could just remove the EL84/EBL31 adaptor.
(This adaptor design was later published in the BVWS Bulletin).
I've attached a pic of the adaptor alongside a genuine EBL31 and a converted EBL1 as sold by UK dealers as EBL31s. If you look at the octal base, you'll see that it's quite tall as it has to fit over the side contact base. You'll also see the tell tale sign of a join where the octal bases has been glued onto the original base. (Neatly done by the way - possibly even at the factory).
EBL1 valves seem to be slightly more plentiful that EBL31s, though not often much cheaper, so when the opportunity presented itself at the BVWS Golborne Swapmeet in Nov 2010 to buy two N.O.S EBL1s for ten pounds each the temptation proved too great! Partly out of curiosity, partly out of necessity, I wanted to see whether I could convert the valves to EBL31s within the height limitations posed by the Ekco A22. I decided to embark on two approaches – one more radical than the other. The more difficult and intricate option was to cut off the base of the side contact valveholder and to wire an octal base shallow enough for the valve to be identical in height to the EBL31. The easier option was to leave the side contact base intact, and to cross-wire it to an octal base as shallow as possible within the height constraint. I’ll explain those two options, though I only finalised the first one. I also removed the top cap and replaced it with the smaller size as used on the EBL31, and will explain how I achieved that.
Option 1 – removal of part of the EBL1 side-contact base:
The first task was to de-solder the valve pins on the base, which was straightforward enough using a solder sucker and iron. To make sure that each wire was fully de-soldered I used a magnifying glass and wiggled the wires with a pointed modelling knife.
The rest of the operation proved rather more intricate than I’d imagined as I’d wrongly assumed that once a valve holder is removed, the wires would stay in a neat ring, so would be easily identifiable by counting back and forth from the filament wires. Would that life were so simple! Firstly, the wires emerging from the valve do not emerge in a circle, but in a straight line deep within a hollow recess in the glassware at the base of the valve. It is therefore vitally important that as soon as the base has been eased off a little, but while the wires are still in place, each wire is labelled so that when the base is lifted right off, each wire can be identified. I did this by tying some dial cord tightly around each wire and attaching a tag made from masking tape onto each one. How glad I was that I took that precaution because the moment I lifted the base right off, the wires sprang out of place, and apart from the two filament wires, it’s anyone’s guess which wire does what if not labelled! A precaution worth bearing in mind if every anyone wishes to for example replace a cracked or damaged valve base on other valves.
I’d decided that rather than completely removing the side-contact base, that I’d cut around the periphery about 5mm below the point at which the base joined the glass, thus leaving the metalising undisturbed. This proved to be a wise decision. I cut around the periphery of the base with a cutting disk mounted in a small Dremel type drill, very carefully so as to not cut through any wires. The metalising wire which goes to the cathode and G3 connection (which are themselves electrically connected within the valve) was very close to the inside of the valve base and would be all too easy to cut through.
Fitting the new octal base:
Once the severed side-contact base had been lifted off, I slipped coloured sleeving over each wire to identify which of the octal pins they needed to be soldered to. I then obtained an octal valve base from a scrap donor valve and cut the base down to a height of 15mm using the cutting disc. I extended each valve wire by soldering lengths of tinned copper wire to each in turn, then slipping short lengths of sleeving over the wires to obviate the risk of them shorting out to each other when the base was pushed into position to be soldered. The wires were then pushed down into each octal pin according to the EBL31 base requirements. Having made sure that the new octal base married up neatly with the remnant of the side contact base, I mixed some rapid setting two part epoxy glue (‘Araldite Rapid’), applied this to the two valve-base surfaces, pushed the octal base into position and held it there for a minute or two until it was firmly set. I then soldered each octal pin in turn and snipped off the surplus wire ends. That was the ‘business end’ completed, so I turned my attention to the top cap.
Top cap removal and replacement:
I’ve heard various suggestions as to the type of cement used to fit valve bases and top caps to valves, one of which is that it was a paste mixture of shellac and wood-flour. Given that methylated spirits is a solvent of shellac, I thought I’d give that a try. First, I desoldered the top cap to free the wire, gently checking with the point of a modelling knife that it was indeed free. I then inverted the valve and immersed the top cap in a small plastic container filled with methylated spirit and left that to soak overnight. I was pleased and relieved that when I wiggled it, it came free. I scrapped most of the cement away but left some on the glass pip to provide a key for the new top cap. I slipped on the top cap with a generous blob of epoxy cement, and soldered the wire.
Then came for the ‘MOT’ test - the Moment Of Truth! The valve tested fine, so was plugged into my A22, where it passed its test with flying colours. The absolute maximum height of an EBL31 that can be accommodated in the A22 is 128 mm (5 inches) from the valve base to the top of the top cap. A genuine EBL31 valve is 120mm tall (4.75 inches), and my converted EBL1 is 124mm (4.88 inches).
The other option, which I abandoned, was to solder wires onto the EBL1 valve-base and leave it in situ, but cut down an octal based to the lowest height that I could. I then made an insulating disc of 'bubble pack plastic' - the clear think hard plastic often used in packaging. I drilled holes in it, and routed wires from the side contact base to the octal base, then pushed the octal base onto the side contact valve base. Not really a success as it was a little over the 5" maximum height. One day, I might remove the side contact base as with the other one. After all, an EBL31 of the correct height converted from an EBL1 is worth the effort, when the 'big Bertha' so called 'EBL31s' are £25.00 +
There's a pic of the valve base adaptor alongs one a genuine EBL31 and a so called 'EBL31 as sold by dealers.
The second pic is of a genuine EBL31, my converted EBL1, and a tall EBL31 that though it tested fine when I got it, was in a bad way with the metalising flaking off. I gave the metailsed area several coats of conductive silver paint, then sprayed it with red oxide primer, which is a passable match for the original red. I swapped the top cap for a 1/4" one.
The others pics show the steps I took to remove the EBL1 side contact base and fit the octal one - not a job for the fainthearted!
Hope it's of interest.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
