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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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30th May 2021, 6:07 pm | #1 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
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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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30th May 2021, 6:20 pm | #2 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
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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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30th May 2021, 6:25 pm | #3 |
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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.
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30th May 2021, 6:25 pm | #4 |
Moderator
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Re: Mystery B9A valve
Certainly looks like a TV valve.
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30th May 2021, 7:24 pm | #5 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
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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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30th May 2021, 7:30 pm | #6 |
Dekatron
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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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30th May 2021, 8:19 pm | #7 |
Dekatron
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Location: Croydon, Surrey, UK.
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Re: Mystery B9A valve
They worked very well in power supplies apparently. Another 'workhorse' in a series of popular valves.
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30th May 2021, 11:16 pm | #8 |
Heptode
Join Date: May 2017
Location: Konongo, Ghana
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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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Robert |
31st May 2021, 8:18 am | #9 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
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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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31st May 2021, 8:24 am | #10 |
Heptode
Join Date: May 2017
Location: Konongo, Ghana
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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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Robert |
31st May 2021, 8:55 am | #11 |
Dekatron
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Re: Mystery B9A valve
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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31st May 2021, 4:57 pm | #12 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
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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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31st May 2021, 6:02 pm | #13 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
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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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31st May 2021, 8:20 pm | #14 |
Heptode
Join Date: May 2017
Location: Konongo, Ghana
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Re: Mystery B9A valve
And perhaps the PC500 in your list really is a PD500?
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Robert |
1st Jun 2021, 7:17 am | #15 |
Heptode
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Location: Konongo, Ghana
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Re: Mystery B9A valve
Or a PC900?
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Robert |
1st Jun 2021, 7:35 am | #16 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
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Re: Mystery B9A valve
That's quite likely - a lot of the print is scuffed on a lot of these valves....
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1st Jun 2021, 9:10 am | #17 |
Dekatron
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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. |
1st Jun 2021, 9:36 am | #18 |
Heptode
Join Date: May 2017
Location: Konongo, Ghana
Posts: 513
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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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Robert |
1st Jun 2021, 10:10 am | #19 | |
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Re: Mystery B9A valve
Quote:
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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1st Jun 2021, 10:18 am | #20 |
Dekatron
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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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