Valves in Unusual Applications

[Edward Huggins]

Just after the War the were loads of ex WD EF50s and VR65s (SP61) available as surplus - many just on IF strips. Many Radios were designed using these valves in a variety of applications. The notorious PW contributor F. G. Rayer, would often use EF50s/VR65s as output Pentodes in his many utility designs of the early 1950s. These were expressle designed to be built on a very limited budget. Later valves such as the UF89 IF amplifier were used in audio stages as an AF valve. I wonder what other applications Honourable Members can recall of valves being (expediently) used in applications they were not originally designed for?

[Synchrodyne]

Baxandall used a Mazda SP61 VHF pentode in the original version of his feedback tone control. This was chosen to ensure that the anode follower (virtual earth) stage had a high open-loop gain. See Wireless World (WW) 1952 October page 402ff.

Successor to the SP61 was the 6F13 VHF pentode, which Armstrong used in the Baxandall tone control circuit of its BS125 radiogram chassis.

Some TV setmakers used the Philips/Mullard ECL80 as a Band I frequency changer, as recorded in this recent thread: https://www.vintage-radio.net/forum/...d.php?t=140359. Whilst the ECL80 was by design a multi-purpose valve, VHF frequency changing was not in its job description. In the same thread was reported the use of the Mazda 10C1 radio (MF, HF) triode-heptode as a Band I TV frequency changer.

In its HFT111 FM-AM tuner, Pye strapped the EABC80 triode as a diode in order to provide a fourth diode for use as the AM AGC rectifier. Whilst there were certainly some triodes that were specified by their makers for use as diodes, that was not the case for the EABC80. The HFT111 had essentially the same circuit as used for the RF section of the FenMan II FM-AM receiver. But latter had an EBC41 as well as an EABC80, so had an adequate supply of regular diodes.


Cheers,

[slidertogrid]

I don't know if the application would be considered unusual but I was surprised to find that the EY51 made a comeback as a focus rectifier in the Philips G6 in 1967.
The valve as a monochrome set EHT rectifier had long been superseded and the sets using it must have been out of production for nearly a decade so the only market at the time would have been the replacement one and that must have been shrinking rapidly as the sets were scrapped.
It seemed strange that Philips gave it a new lease of life at this late stage, keeping it in production must have been at some cost and considering that the G6 would have been produced in small numbers compared to the previous monochrome market surely it would have been more economic to have designed the focus circuit differently either using a solid state rectifier or a more recent valve.
Assuming that the expected service life of a new colour set was around 8 to 10 years it would mean they would need to keep the valve in production for potential replacements well into the 1970's.
By which time the replacement market must have been small as it would have surely only been for the G6 by then as the great majority of the 1950's mono sets would have been long gone?
Without checking I can't be sure but I think they also used a PCF802 as a reference oscillator valve ?
To me the fact that valves were used in a colour decoder at all seemed a strange thing to do I am pretty sure that all other manufacture's first production colour sets used transistors for the decoder up the CDA stages at least.
I suppose in retrospect I shouldn't have been surprised at all Philips always did do it 'their way' from chassis less valve radios that had to be unknitted for repair to c wrap VHS...
I wonder if it had anything to do with what the design team were smoking...
Rich.

[Synchrodyne]

The Philips/Mullard ECF80/PCF80 had multitudinous “authorized” uses, but even so one may find some that are borderline, or even outliers.

Jason used an ECF80 in its (very simple) Jasonkit JSA2 stereo amplifier. The ECF80 triode was the input stage that was also a Baxandall tone control stage with a small amount of overall gain. The ECF80 pentode was the driver for the EL84 output valve, and within the main feedback loop. Jason made the comment that the ECF80 was primarily an RF valve, and that Mullard did not offer any guarantees about its audio performance. But in this application the signal levels were such that hum was not a problem and having the triode precede the pentode obviated any instability issues.

The ECF80 triode was also used as an audio cathode follower in several FM and FM-AM tuners. Typically, the ECF80 pentode would then be used as the FM limiter, in place of say an EF80. Still in the realm of FM tuners, the ECF80 triode was also used as an AFC reactance modulator, often with the pentode as a self-oscillating mixer. I am not sure though that AFC reactance modulator was a listed function for any domestic receiving valves. Probably much rarer, another “DC” function for the ECF80 triode, or rather a pair of them, was as driver for a twin neon FM tuning indicator in the Beam Echo Avantic BM612 FM-AM tuner (which as best I can determine from strong circumstantial evidence, was a clone of the Jason AM/FM2.) In the FM front end of the same tuner, an ECF80 triode was used as the mixer, with the pentode as 1st IF amplifier. Whilst the individual applications were within bounds, their combination was quite unusual. Another unusual combination was found in the Jason JTV2 tuner, with the ECF80 triode as a grounded grid, AGC’d RF amplifier and the pentode as a mixer.


Cheers,

[stevehertz]

Here's mine, a duff KT66 in a turned base as an ornament.

[Herald1360]

The only unusual thing in that picture is tidyness

[turretslug]

This subject has been covered previously, probably most recently,

https://www.vintage-radio.net/forum/...d.php?t=132780

No doubt several sub-headings could be devised- those uses where a designer used genuine imagination, ingenuity and unconstrained thinking to employ a valve in an effective way that the marketing folk and application notes hadn't mentioned, those like the EF50 where, once the war was over, there was an element of "please use these for something before we drown in them", and those where the decision seemed genuinely difficult to rationalise beyond "what were they smoking?"....

I recall at least one VHF signal generator where an EF50 was used as a shunt hum canceller (how are the mighty fallen) and also in a Cossor 'scope as EHT series regulator.

[Sideband]

Originally Posted by Synchrodyne

The Philips/Mullard ECF80/PCF80 had multitudinous “authorized” uses, but even so one may find some that are borderline, or even outliers.

The PCF80 was used as audio amp and audio output stage in at least one Thorn TV, the ECC82 has been used as an output valve in a Derwent TV and the EF80 has been used as an audio output valve in at least one model of TV.

Somewhere I think I've seen an EF91 used as an audio output valve but it may have been a home construction circuit.

The ECL80 used as a VHF mixer is probably the most bizarre! It poses the question 'why'? when there were plenty of 'proper' valves designed for the job....

Originally Posted by Synchrodyne

The ECF80 triode was also used as an audio cathode follower in several FM and FM-AM tuners. Typically, the ECF80 pentode would then be used as the FM limiter, in place of say an EF80.

This is also done in the Leak Troughline FM tuner.

[Nuvistor]

Some of the unusual uses could well have been that they had to use what was easily available, especially in the late 40’s early 50’s when the government focus was on export not home consumption. We still had domestic rationing of food and goods at that time. The circuit designers who had been designing sets for war use were an inventive bunch and that experience would have been carried into civilian life.

It’s not has easy to explain though when those restrictions were no longer in use by the second half of the 1950’s.

[line sync]

Does anyone know if a radio manufacturer ever produced a radio using an EF50 ?
That's a domestic radio not communications sets.

Robin

[turretslug]

There was an early post-war Bush radio (forget the model), a typical example of the posh export or "tea planter" multi-SW band set that used an EF50 RF stage, along with an otherwise conventional line up. Whether they hoped to get brownie points from the use of "radar technology", or whether there was genuine merit in using a low-noise but "straight" valve in place of the usual EF39, EF41 etc. extant candidates, or whether someone simply got a good deal on a ship-load I don't know.

[GrimJosef]

I don't think anyone's yet mentioned the use of banks of TV line output valves wired in parallel in the output stages of output transformerless audio amps (I had a quick look through the Jan 2017 thread on this subject and couldn't spot it in there) https://en.wikipedia.org/wiki/Output_transformerless.

At least one current manufacturer makes a variant of these, with a 6.3V heater, an octal base and no top cap, for just this purpose http://www.jj-electronic.com/en/el509s.

The advantages of doing away with an expensive and often pretty imperfect component are obvious. Unfortunately the disadvantages of deploying high impedance devices to drive low impedance loads turn out to be almost as troublesome which, I guess, is why these designs have never really caught on.

Cheers,

GJ

[Refugee]

I don't think anyone's yet mentioned the use of banks of TV line output valves wired in parallel in the output stages of output transformerless audio amps (I had a quick look through the Jan 2017 thread on this subject and couldn't spot it in there) https://en.wikipedia.org/wiki/Output_transformerless.

Here is a thread on just such an amp.
http://www.diyaudio.com/forums/tubes...ller-otls.html

[bikerhifinut]

There is a still currently available valve amplifier kit that uses the ECF80 as pentode first stage into a fairly standard "concertina" phase splitter using the triode section. Output was EL84 in PP UL.
I had one (now owned by another forum member) and it was a nice little 10watt (Claimed 15) stereo amp, once I had rectified the "Upgrade" modifications perpetrated by the original owner. It had DC heaters to the ECF80 and the previous owner had substituted Schottkies in the rectifier bridge for the DC heaters and it was bunging way in excess of 7volts up their poor little filaments. I put a pi filter in I think it was about 1 ohm or so can't remember now but I did calculate it and all was well............. after I replaced the gone noisy ECF80s. What was the pentode section similar to gents? I believe some owners could get HF instability issues with this amp and i wonder if it had been designed using a more conventional EF86 pentode and say an ECC82 for the phase splitter would this issue have been reduced by using a specific audio valve in the 1st stage?
Hope thats not off topic in the radio thread, mods please feel free to split it off.

Andy.

[Alistair D]

Originally Posted by Sideband

Somewhere I think I've seen an EF91 used as an audio output valve but it may have been a home construction circuit.

Some versions of the Racal RA17 used an EF91 as the output valve.

Paralleled PL519s were popular in amateur radio circles as a cheap linear amplifier. The name "Skinnier Linear" comes to mind.

Al

[bikerhifinut]

Originally Posted by GrimJosef

I don't think anyone's yet mentioned the use of banks of TV line output valves wired in parallel in the output stages of output transformerless audio amps (I had a quick look through the Jan 2017 thread on this subject and couldn't spot it in there) https://en.wikipedia.org/wiki/Output_transformerless.

At least one current manufacturer makes a variant of these, with a 6.3V heater, an octal base and no top cap, for just this purpose http://www.jj-electronic.com/en/el509s.

The advantages of doing away with an expensive and often pretty imperfect component are obvious. Unfortunately the disadvantages of deploying high impedance devices to drive low impedance loads turn out to be almost as troublesome which, I guess, is why these designs have never really caught on.

Are those similar to the PL509 type used in one of Tim deParavicinis EAR amps GJ?
Although of course that design did use output transformers.
A

[bikerhifinut]

I have an old copy of PW that has a long article featuring the uses of the EF50 and example circuits for just about every application in a radio and a few audio circuits too, preamp, phase splitter, output stages etc. The attraction it seemed was that they could be picked up for pennies (literally) and so were good for amateurs and hobbyists to play around with. I guess someone with enough knowledge could quite easily design and build a good radio using nothing but EF50s. Were not an awful lot of early DIY TV sets made up of EF50?

By the way Edward, why was F G Rayer ( I remember his callsign was G3OGR) "notorious".

A.

[Hartley118]

On the theme of eccentric Philips designs, their EL3425 PA amplifier used 4x EL36 line output valves (top caps & all!) to produce its 70 watts in a rather compact unit. I recall successfully using three EL3425s in the 1960s for an ambiophony artificial reverberation system in a concert hall, an application which needed decent power reserve and refined clipping behaviour.

Martin

[Graham G3ZVT]

Premium Bond winners were originally picked on the whim of nine QS92/10 neon regulators.

https://www.radiomuseum.org/forum/er..._computer.html

[GrimJosef]

Originally Posted by bikerhifinut

... Are those similar to the PL509 type used in one of Tim deParavicinis EAR amps GJ? ...

Are you asking about the JJ EL509S's ? I think they're supposed to be similar except that without the top cap they won't handle the very high anode voltage that a conventional 509 will.

If you're asking about the amps, the only one that I'm familiar with that uses the JJs is this one https://www.stereophile.com/integrat...4ta/index.html. It's beautifully built but its circuit is unusual, to say the least. It is no longer in production and I fear that issues with the long-term stability required of the valves may be a factor in that. It's not strictly an OTL amp because it does have an output transformer.

I've also worked on a true OTL amp which uses PL519s or 509s - it was a Croft Series 3 (4 power valves per channel) referred to in an earlier thread here https://www.vintage-radio.net/forum/...ad.php?t=22251.

Cheers,

GJ