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Old 30th May 2021, 6:07 pm   #1
mole42uk
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Default Mystery B9A valve

In a box of miscellaneous pulls, I find this strange beastie which bears no identity. It is a B9A base with a top cap and a peculiar internal construction.

Any ideas?
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Old 30th May 2021, 6:20 pm   #2
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Default Re: Mystery B9A valve

It's most likely to be a PL81 or 81A tv line output valve. Or the 6.3V heater version EL81.
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Old 30th May 2021, 6:25 pm   #3
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Default Re: Mystery B9A valve

My first thought was a line output valve, it is. Amazing bits of technology, all that power handling in such a small space.
 
Old 30th May 2021, 6:25 pm   #4
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Default Re: Mystery B9A valve

Certainly looks like a TV valve.
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Old 30th May 2021, 7:24 pm   #5
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Default Re: Mystery B9A valve

Most definitely a PL or EL81 line output valve...and I would say that it's more likely a PL81 since they were far more common than the EL version. The 'A' version had limited use in some portable sets. The internal structure shows ceramic supports.

See http://www.r-type.org/exhib/aaa0359.htm
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Old 30th May 2021, 7:30 pm   #6
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Smile Re: Mystery B9A valve

Hi,
I have a valve DC to AC inverter for use on board ship. It uses six of these in parallel push-pull. They are PL81s with series heaters and an ECC82 oscillator.
Cheers, Pete.
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Old 30th May 2021, 8:19 pm   #7
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Default Re: Mystery B9A valve

They worked very well in power supplies apparently. Another 'workhorse' in a series of popular valves.
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Old 30th May 2021, 11:16 pm   #8
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Default Re: Mystery B9A valve

Can you make out the code near the base of the valve? If it is a factory code of Mullard/Philips/etc., the code can tell you if is an EL81 or a PL81: http://www.r-type.org/pdfs/ref4110.pdf
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Old 31st May 2021, 8:18 am   #9
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Default Re: Mystery B9A valve

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!
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Old 31st May 2021, 8:24 am   #10
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Default Re: Mystery B9A valve

Most of the time the codes are in two lines. It seems that the first line of the code on your valve is wiped off. The first "B" in the part "B6B2" indicates that your valve is made by Mullard, Blackburn.
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Old 31st May 2021, 8:55 am   #11
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Default Re: Mystery B9A valve

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Originally Posted by mole42uk View Post
I must try and clean the crud off the envelope!
That brown staining will be internal. Most of them ended up like that. Doesn't mean to say that it's no good though.

A bright light might help to reveal the markings. Failing that, hook pins 4&5 up to a 6 volt supply and see if the heater lights. If not then it will be a PL which requires 21 volts.
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Old 31st May 2021, 4:57 pm   #12
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Default Re: Mystery B9A valve

That's sorted. 6V didn't do much except draw 200mA, 20V gave me a nice heater glow....

PL81 it is.

Most of the pulls in this box seem to be TV types. Here's a list if anyone's interested:
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Old 31st May 2021, 6:02 pm   #13
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Default Re: Mystery B9A valve

Hmm, there is no such valve (as far as I am aware) as an EB86. It might be an EF86. If in doubt, please post a picture.....
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Old 31st May 2021, 8:20 pm   #14
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Default Re: Mystery B9A valve

And perhaps the PC500 in your list really is a PD500?
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Old 1st Jun 2021, 7:17 am   #15
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Default Re: Mystery B9A valve

Or a PC900?
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Old 1st Jun 2021, 7:35 am   #16
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Default Re: Mystery B9A valve

Quote:
Originally Posted by Sideband View Post
Hmm, there is no such valve (as far as I am aware) as an EB86. It might be an EF86. If in doubt, please post a picture.....
That's quite likely - a lot of the print is scuffed on a lot of these valves....
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Old 1st Jun 2021, 9:10 am   #17
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Default Re: Mystery B9A valve

As well as use in TV scan-circuits and DC-to-AC inverters, there was at least one commercially-prodced 1950s ham-radio transmitter for Top-band that used a PL81 as the PA stage (with, from memory, a pair of EL84 modulating it).

The designers even went to the extent of having a mains-transformer with a separate 21-volt winding for the PL81's filament. I guess it turned out cheaper to have an extra winding which allowed the use of a 'commodity' TV valve, rather than sticking with 6.3V and using a more-traditional (and probably more costly) RF valve like a 2E26 or a TT11.
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Old 1st Jun 2021, 9:36 am   #18
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Default Re: Mystery B9A valve

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
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Old 1st Jun 2021, 10:10 am   #19
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Default Re: Mystery B9A valve

Quote:
Originally Posted by G6Tanuki View Post
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.
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Old 1st Jun 2021, 10:18 am   #20
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Default Re: Mystery B9A valve

I had an old Marconi sig gen used an EL81 I think it had an easy life ,it looked new when I scrapped the unit , Mick.
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