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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 1st Jun 2021, 11:53 am   #21
G6Tanuki
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Default Re: Mystery B9A valve

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The designers even went to the extent of having a mains-transformer with a separate 21-volt winding for the PL81's filament.
They could have used the EL81 6.3v version that was used in the Ekco TMB272 TV. I guess there was a massive production of PL81's compared with the EL81 version. J.
An EL81 would probably have been more-expensive; the world was awash with the likes of the PL81 in the late-1950s!

[The TX I remembered was the KW 160 - it used a pair of 6BW6 in the modulator, not two EL84 as I had falsely remembered]
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Old 1st Jun 2021, 2:04 pm   #22
Robert Gribnau
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Default Re: Mystery B9A valve

Looking at these adverts in Practical Wireless (1958 & 1959) there does not seem to be much difference in price. But these are probably prices for end users, so not for producers of TV's.

https://worldradiohistory.com/hd2/ID...8-12-IDX-6.pdf

https://worldradiohistory.com/hd2/ID...9-01-IDX-4.pdf
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Old 1st Jun 2021, 3:30 pm   #23
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Default Re: Mystery B9A valve

I must have been about 12 when I knocked together an audio amplifier with PL81 output, following a circuit in one of the magazines (hence about 1971). I wasn't up for metalwork, so built it on a repurposed perspex implosion screen, mounted on a lid removed from an add-on 78 rpm turntable: it just about worked. Looking online, several designs have employed the PL81 in audio roles, both single-ended and push-pull.

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Old 2nd Jun 2021, 11:00 am   #24
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Default Re: Mystery B9A valve

The PL82 is a nice valve for audio, much like an EL84 but needs 16V or so for the heater.
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Old 2nd Jun 2021, 11:26 am   #25
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Default Re: Mystery B9A valve

I have an old analogue XY flatbed recorder which uses a pair of PL82s in the servo amplifier for each axis. There is, indeed, a 16.5V secondary on each mains transformer to power their heaters.
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Old 2nd Jun 2021, 1:35 pm   #26
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Default Re: Mystery B9A valve

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Originally Posted by Paul_RK View Post
I must have been about 12 when I knocked together an audio amplifier with PL81 output, following a circuit in one of the magazines (hence about 1971). I wasn't up for metalwork, so built it on a repurposed perspex implosion screen, mounted on a lid removed from an add-on 78 rpm turntable: it just about worked. Looking online, several designs have employed the PL81 in audio roles, both single-ended and push-pull.

Paul
Was this "The Teleamp", in an issue of Practical Television (page 308, April 1968 issue)? If so, I too made it.

The circuit employed a Radiospares adjustable high power dropper resistor, an EF80 as the AF preamp and a PY82 half wave mains rectifier.

All "live chassis" too, but with 20nF 750V capacitors isolating the input socket - I bet they're leaky now!
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Old 2nd Jun 2021, 2:34 pm   #27
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Default Re: Mystery B9A valve

I remember as a teenager copying some of the circuit for my 160M tx, but a transformer for the PL81 was too expensive for my schoolboy budget.
Then, around 15 years ago I acquired some used EL81, rememberithe use in hf tx. Not long after I bought a tx, I think it is the KW160, could be the Labgear one though.
Buried behind some test gear at the moment, will need to dig it out sometime.
A lot of used PL81 you see have the black tar like coating inside, but I think all my EL81 still looked clean.
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Old 2nd Jun 2021, 2:45 pm   #28
Paul_RK
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Default Re: Mystery B9A valve

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Originally Posted by dazzlevision View Post
Was this "The Teleamp", in an issue of Practical Television (page 308, April 1968 issue)? If so, I too made it.
Looks and sounds familiar, I'm sure the one I "built" also used one further valve and a rectifier, all common TV types. Then again, I've a feeling the rectifier was octal based, and I don't remember acquiring any copies of PT from that little period: a bundle of late '50s ones came my way, but I wouldn't have bought the magazine new until I was a little (not much) older than eight and three-quarters.

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Old 2nd Jun 2021, 4:43 pm   #29
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Default Re: Mystery B9A valve

EL81 was used in the Pye PTV which had mains transformer and earthed chassis, which
looked similar to the Pye TVT 2788 video monitor.
I have some new in boxes, also EY88 (Philips Australia) indicating their use in the transformer set designs in that continent.
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Old 4th Jun 2021, 6:18 pm   #30
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Default Re: Mystery B9A valve

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Philips used the EL81 in some of their audio amplifiers like the AG9000, EL6401, EL6411 and EL6611. They even made an OTL one, the AG9006, for a 1200 Ohm speaker system (AD5032).

https://nvhrbiblio.nl/schema/Philips_AG9006.pdf
I have an EL6400 amp that uses 2x EL81 for about 20 watts output. It sounds surprisingly good from a pair of supposed not-very-linear line output valves.
Very little background noise and multiple output choice including low impedance and 100v line.
PPP PL81s might be the basis of an economic guitar amp?
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Old 7th Jun 2021, 10:34 am   #31
Maarten
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Default Re: Mystery B9A valve

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The code is B6B2 in a single line, I can't see anything else.

I can't make that into a type using the document....just that it was made in Blackburn in the second week of February 1956.

There must me another line of etching that I can't see, I must try and clean the crud off the envelope!
Given the presence of a day number, I would think it's more likely to be made in 1966.
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