Mystery valve

[barretter]

Originally Posted by RF Burn

There also seems to be a small structure built above the top mica, reminiscent of the triode in an ECL80 or maybe a diode as in an American valve I once saw (sorry can't remember the type).
So maybe it could be a special, in which case very good luck in getting any info, or one of the latter types of multiple valve that were produced in the dying days like the ECLL80, ECLL800, and other continental (German) types that were made by Mullard for Valvo, Siemens, Telefunken . . .

You can find the data sheets for the valves you mention on www.tubedata.org
(I don't think Mullard made them for the German companies, by the way) but neither of them resemble the mystery valve. I do, however, have several ECL85s which are virtually identical to it.

[radiograham]

This is what I have managed to find out with my valve tester, strange I know but this is how it seems to be. The pinout tallys with a PCL85, 18 volts heater voltage across pins 4 and 5 and the pentode tests as such the difference then is that pin 1 is definitely the junction of the two heaters. 1 and 4 is the triode heater which takes 6.3 volt at 300ma, 1 and 5 is the pentode heater taking 12.6 volt at 300 mA, the two anodes are connected together internally. When you just feed the 6.3 volt heater you can test the triode, when you feed the 12.6volt on its own you can test the pentode.

[G8HQP Dave]

So it appears to be a special, built from a PCL85.

[turretslug]

How curious. Could it have been a niche-purpose modulating, gating or level-shifting valve based on PCL85 structure and jigs to minimise initial investment? Perhaps for a mobile (whether land, air or sea) application where 12.6V nominal heater stringing was needed. There were a few weird and wonderful valves cooked up for machine control interface and computer applications, too. We need that time machine!

[radiograham]

The only clue about these that I have is that the person I bought them from was selling them for his son who was a radio amateur, Am I right in thinking that they must have been used individually by switching in the individual heaters? With the anodes connected together if both heaters were in operation would the two valves be in parallel?

[radiograham]

Originally Posted by ms660

Crazy theory but two anodes strapped together, triode and pentode heaters in series with a pinout connection at their junction.....switchable valves in one envelope?

This is what I thought,operation of triode or pentode by switching the relevant heaters.
Graham.

[Refugee]

Would it be for a two power radio transmitter?

[G8HQP Dave]

Might be more useful in a guitar amp, but this would not have been the original purpose.

[RF Burn]

Originally Posted by turretslug

How curious. Could it have been a niche-purpose modulating, gating or level-shifting valve based on PCL85 structure and jigs to minimise initial investment? Perhaps for a mobile (whether land, air or sea) application where 12.6V nominal heater stringing was needed. There were a few weird and wonderful valves cooked up for machine control interface and computer applications, too. We need that time machine!

I think that this idea is probably closest to the truth, as a lot of developments seem to have been made in the latter valve days for mobile/battery powered valves that could be used on 6/12/24/48 Volt battery supplies and/or be very rugged, these being apparently modifications to standard types in order to save tooling costs especially where the production run was not very high.

A centre tapped heater of 6.3/12.6 Volts suggests to me an ECC81/2/3 heater setup were you wire in series (across the ends) for 12 Volt and parallel (between CT and ends) for 6 Volt supply. I believe that 6 volt batteries were still being used on vehicles at that time (and still are?).

I will not hazard a guess as to the actual intended use for this oddball, suffice to say that as the world of electronics applications was expanding rapidly during that time, it could be almost anything. Only one real clue here, it must have been something worthwhile (or high budget military?) to interest a company like Mullard/Philips . . .

I would forget the amateur radio connection, that is probably just a red herring.

Triode part as a mute function leaving the pentode as the amplifier?

[radiograham]

Just one further comment on this ,Does anyone know when Mullard stopped making valves what happened to all the records of the company,For instance when Blackburn closed was everything dumped or was there any attempt saving anything for historical purposes/posterity.

[Craig Sawyers]

It all is here http://brimaruk.com/menugbvp/great-b...valve-project/ being restored in order to remanufacture valves again.

A lot was scattered overseas - they tracked it down and raised enough money to get it all shipped back.

Craig

[radiograham]

I have seen this venture and hope it comes to fruition, I was wondering about the what must have been the vast amount of documentation in their records, whether any of this was saved from disposal, something like was done with Marconi etc. Graham.

[barretter]

Mullard was completely taken over by Philips in 1928(!) so any documents might be in the Philips Company Archive in Eindhoven. Their email address is:
pca@philips.com
but the problem is you have no designation for the valve. I suggest you scrutinise the valve's bulb with a magnifying glass, possibly with a light behind it which might show up the permanent ink marking of the code (if there is one).

[Thatvalveguy]

Im quite certain that is a PCL805, identical pinout but slightly different guts

[Maarten]

Sometimes it helps to breath a bit on the code. The first line could start with VX for a PCL805 but if it's a development type it could well have another code.

[Radio Wrangler]

Two other possibilities: An oscillator with a built-in reactance valve for FM/AFC? or a training exercise. Someone being trained in development, say, gets to do a design using existing subcomponents and then build it and test it.... then take the result home. I've got a few very oddball items made while in the training school at Rolls Royce. They could get someone who didn't know quite confused. New R&D engineers at HP in the 80's got given a project to do as training. The guy running it used cheap hobbyist counters and function generators as models. The new graduates had to make their own PCB versions of the traced out circuit which they stuck in HP standard cabinets, doing all the schematics, drawings for metal parts, transformers etc. At the end they got to keep the thing. Of course it worked no better than the original bought from a wireless world advertiser. Some of these must be floating around and could cause confusion. I thought that copying another firm's circuit was very dodgy. We should have designed something ourselves for legal reasons, but the guy running the training programme chose this way and said it made an illustration of the difference in price! Who knows what apprentices and trainees made in other firms?

I pre-dated this scheme and just got started straight into designing stuff for real.

David

[GrimJosef]

Originally Posted by Thatvalveguy

Im quite certain that is a PCL805, identical pinout ...

I thought the whole point of this thread was that the mystery valve has a different pinout. The PCL805 has the triode anode connected to pin 1. The mystery valve has a heater tap connected to pin 1. Therefore the mystery valve isn't a PCL805. Or am I missing something ?

Cheers,

GJ

[Maarten]

Originally Posted by Radio Wrangler

Two other possibilities: An oscillator with a built-in reactance valve for FM/AFC? or a training exercise. Someone being trained in development, say, gets to do a design using existing subcomponents and then build it and test it.... then take the result home.

Such a one-off wouldn't have any remains of a manufacturing code on it, though. This mystery valve must at least have been produced as a development type in a somewhat larger trial run, or was possibly from a regular production batch.

A development type wouldn't have had normal type number. It would have been referred to in the documentation (if any) as M<number>PCL or possibly by its manufacturing code.

[radiograham]

Originally Posted by GrimJosef

I thought the whole point of this thread was that the mystery valve has a different pinout. The PCL805 has the triode anode connected to pin 1. The mystery valve has a heater tap connected to pin 1. Therefore the mystery valve isn't a PCL805. Or am I missing something ?

Cheers,

GJ

You are quite right,This is definitely not a standard PCL85/805.The two anodes are connected internally and pin1 is atap on the heater but is not a centretap, The triode section takes 6.3 volt 300ma.The pentode section 12.6 volt 300ma.