Help in identifying (Homebrew?) chassis.

[Top Cap]

I have received a 6V6 push pull amp to restore. There is no circuit diagram.
Does anyone recognise the chassis? It uses two CV6 valves for audio amp and phase splitter plus an extra input amp using a single triode L63.
Any ideas for a rectifier? It has a 5V heater winding with HT taken from one of the heater lines so I am guessing on something like a 5Y3.
I guess it's down to drawing out a circuit now and replacing all the metal sleeved 100nF caps that are shoving way too much positive voltages onto the valve grids. Thinks I may re-position the main smoothing block too
Les

[Peter.N.]

Hi Les


I dont recognise it as anything propriotry, that was about the time I started in the business. Looks a fairly standard '50s construction though, except for those wierd valves with the two top caps. The valve at the extreme left of the picture looks suspiciously like a rectifier, but I can't see enough of it to be certain. As HT is, as you say taken from the heater connections it would be a directly heated rectifier, 5U4 comes to mind but there are several types.

Peter.N.

[Herald1360]

It looks like an interesting homebrew!

I can't imagine any commercial outfit using those Daleks in an audio amplifier- I'm sure they were never intended for audio use. The L63 sounds more plausible, though.

I think a 5Y3 would be rather underrated for a p-p pair of 6V6's. HT current for them alone would be around 200mA unless they've been deliberately biassed back. Something like a 5U4 would be better- that can manage around 220mA DC output.

Have fun!

Chris

[paulsherwin]

I agree it looks home made, though somebody has made a good job of it. The two weird valves are E1148s (CV6 is the military designation). This was an early VHF triode which was used in the 'B' (VHF) section of the legendary British military '19 set' transceiver. These radios continued in use as HF transceivers until well into the 1960s but the VHF sections were replaced by more modern equipment soon after WW2. This meant there were huge numbers of E1148s on the market in the 50s, both NOS and ex equipment.

I've never come across them used in an audio amp before but I see no reason why they won't work. I have a basic 1950s signal generator which uses a couple of them, and there were lots of construction projects in 1950s radio mags using them. They look quite pretty when powered up with a very bright heater.

The L63 is just a Marconi clone of the American 6J5 general purpose triode.

Paul

[PJL]

Yes, the CV6 seems an odd choice as they were VHF oscillator valves. They were used in an early 50's hobbiest signal generator I had too presumably still from wartime surplus.

One of the CV6 sockets is bolted on but all the rest are riveted yet the wiring all looks original. There are numerous holes in the front panel that seem to serve no purpose. Possibly an early 50's kit?

[paulsherwin]

Originally Posted by PJL

Yes, the CV6 seems an odd choice as they were VHF oscillator valves. They were used in an early 50's hobbiest signal generator I had too presumably still from wartime surplus.?

There must have been zillions of E1148s knocking around in the 50s. The 19 set alone was made in huge quantities in Britain and Canada (one of its applications was as a tank radio) and lots of E1148s were made in the US and supplied under lend lease. They weren't used in commercial equipment so would have had little demand on the surplus market.

Paul

[G8UWM-MildMartin]

My valve data books suggest nearer 100mA for a pair of P-P 6V6s, and 5Y3s and 5Z4s were commonly used to supply them.

[Top Cap]

Many thanks chaps for the info, an old dog like me had never seen these CV6's before only something similar but bigger and used in VHF output stages. I have attached my trace of the circuit placing a 5U4 as possible rectifier. The circuit is rather basic, no feedback and a crude tone control or should that be top cut .
Apart from the 6V6's and rectifier it looks like the other valves could be replaced with 6J5's. Yes, the rivets on the valve holders had me going for a while but other clues like the use of WD capacitors (definitely surplus) and the attempt to use only a few different resistor values makes me think this came from some radio emporium as a kit. The potentiometers are rather large too, the sort of thing one finds in ex-WD gear. The bad news, apart from heater cathode breakdown on one of the CV6's is that the output transformer winding for V5 appears to be open circuit . Having no real pedigree (the Amp not Me!) I am left with the conclusion that the amp may not be worth rescuing especially as all the caps leak like sieves and probably led to the demise of the tranny. It is fitted into a cabinet and connects to a Jason FM tuner which is next for inspection. Anyone have a spare 6V6 P-P Tranny?
Les

[love kt3]

Hi, ive used 2 230/15v2a xfmrs with the primries in line and sconderies in paralel-to replace 1 pp op xfmr,and it works quite well. those 2 odd valves could be replaced by a 6sn7 or ecc83.there seems to be room on the chasis,and its a pittiy to junk such a unit.

[Baggrus]

I had an amp very similar to this in a suitcase amplifier from the tip in my early days. 2x6L6 and 3xL63 triodes, 2 for amplification and one phaze splitter. Oddly an AZ4 rectifier which may have been a replacement as it certainly doesn't go with the others...
Switched inputs for guitar, mic and accordian using some strange 3 pin sockets like small bulgins. the guitar input was a tv aerial socket which leads me to suspect Vox manufacture.
The HT winding centre tap was o/c so it was stripped for parts. (the choke is still doing service in my Laney)

I think these things were just built from whatever surplus was available to supply the beginnings of the beat group boom of the mid/late 50's.
I think that is what you have.. some small manufacturers "homebrew" supply and demand skiffle group suitcase amp.. minus it's case, unless it has come out of an organ of course.
It should certainly have some punch through a decent 12" speaker of the era.

The early Marshall amplifiers used a very similar circuit with L63's (or ECC83's) and 6V6 class B. That may be a possible source.. just about any dead EL34/6V6 class B guitar amp should make a suitable donor for most parts. What I don't know is if there are any specialist companies still making guitar amp transformers.. There surely must be, because you can still buy Marshall and Laney valve amps new. TVM in Manchester were still in business making valve PA amplifiers last time I checked, and they were very helpful last time I had any dealings with them.