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Old 18th Jan 2023, 6:07 pm   #1
dougietamson
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Default Help ID this unmarked valve

This has been puzzling me for a while, what could it be?

Magnoval base, Philips/Mullard 'cross' at the top of the glass, 8Ω across pins 4 & 5

Doug
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Last edited by dougietamson; 18th Jan 2023 at 6:18 pm. Reason: sp
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Old 18th Jan 2023, 6:28 pm   #2
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Smile Re: Help ID this unmarked valve

Hi,
I wonder of it might be an EL93? I have one somewhere here that looks like an EL84, but shorter in stature.
Cheers.
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Old 18th Jan 2023, 6:34 pm   #3
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Default Re: Help ID this unmarked valve

EL508 maybe .Mick.
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Old 18th Jan 2023, 6:38 pm   #4
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Default Re: Help ID this unmarked valve

Hello,
Possibly a PL508?
https://www.radiomuseum.org/tubes/tube_pl508.html
(Or an EL508)
Yours, Richard
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Old 18th Jan 2023, 6:44 pm   #5
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Default Re: Help ID this unmarked valve

At 8Ω cold (?) heater, more likely to be PL508 than EL508.
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Old 18th Jan 2023, 6:45 pm   #6
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Default Re: Help ID this unmarked valve

Quote:
Originally Posted by vinrads View Post
EL508 maybe .Mick.
Yes, looks very similar to the attached photo.

The box of valves I was given that it came from had a few TV/video valves.

Doug
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Old 18th Jan 2023, 6:48 pm   #7
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Default Re: Help ID this unmarked valve

Quote:
Originally Posted by turretslug View Post
At 8Ω cold (?) heater, more likely to be PL508 than EL508.
Measured cold on the minitester
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Old 18th Jan 2023, 7:14 pm   #8
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Default Re: Help ID this unmarked valve

Quote:
Originally Posted by turretslug View Post
At 8Ω cold (?) heater, more likely to be PL508 than EL508.
Quite right EL508 reads 1.2 ohms cold, very cold . Mick.
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Old 19th Jan 2023, 2:40 pm   #9
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Default Re: Help ID this unmarked valve

Mullard PL508 heater measures 8.01Ω using a Keithley 2000 DMM

Rich
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Old 19th Jan 2023, 2:50 pm   #10
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Default Re: Help ID this unmarked valve

For a lot of valves I've found that the hot resistance of the heater will be between 5 to 8 times the cold resistance.

Lawrence.
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Old 19th Jan 2023, 2:57 pm   #11
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Default Re: Help ID this unmarked valve

Quote:
Originally Posted by Marconi_MPT4 View Post
Mullard PL508 heater measures 8.01Ω using a Keithley 2000 DMM

Rich
Thanks for the info.

It's also reassuring the low cost avr mini tester is doing a good job.

From the project page:

"Up to two resistors will be measured with a resolution down to 0.1 ohm. The measurement range is up to 50 Mohm (Megaohm). Resistors below 10 ohm will be measured with the ESR approach and a resolution of 0.01 ohm if a ATmega168/328 is used. Beware: resolution is not accuracy."

Doug
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Old 19th Jan 2023, 4:52 pm   #12
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Default Re: Help ID this unmarked valve

I've tested the valve on my DC-DC buck boost module, I set to 17.04v and the heater draws 300mA, spot on

Now to think of a use for it...
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Old 19th Jan 2023, 5:14 pm   #13
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Default Re: Help ID this unmarked valve

Do you have a socket for it? Those B9D sockets are the first stumbling block.
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Old 19th Jan 2023, 5:42 pm   #14
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Default Re: Help ID this unmarked valve

Quote:
Originally Posted by Richardgr View Post
Do you have a socket for it? Those B9D sockets are the first stumbling block.
I don't, the pins are 0.05" or 1.27mm, I was thinking about buying some PCB headers at the correct size and making a small PCB to hold them.

I checked the pins on some loctal valves and they are all 0.05".

The valve holder attached pic is used to hold a magic eye, might be able to cobble together a bodge job.
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Old 20th Jan 2023, 6:22 am   #15
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Default Re: Help ID this unmarked valve

What are the markings on the glass side wall (partly observed in photo 5 of 5 in post #1?
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Old 20th Jan 2023, 11:23 am   #16
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Default Re: Help ID this unmarked valve

Quote:
Originally Posted by trobbins View Post
What are the markings on the glass side wall (partly observed in photo 5 of 5 in post #1?
Good spot Tim, I stared at the glass for ages trying to find the usual Philips etched (Hydrofluoric acid etching?) codes for type and plant/date.

4 character plant/date = 'right angled triangle' Zero A 2
So the plant is Philips Heerlen
Date is either 2nd week of Jan 1960 or 1970
I'll assume it's 1970 as the valve was designed for colour TVs. ?

No typical 3 character type found.

Doug
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Old 20th Jan 2023, 11:28 am   #17
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Default Re: Help ID this unmarked valve

Quote:
Originally Posted by Richardgr View Post
Do you have a socket for it? Those B9D sockets are the first stumbling block.
Just ordered 2 x B9D chassis mount sockets from Langrex ebay store for £4
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Old 20th Jan 2023, 1:11 pm   #18
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Default Re: Help ID this unmarked valve

Something like a PL508 would work OK as a low-power single-ended audio-amp or even a low-power 1.8/3.5MHz RF power-amplifier in applications where a 5763 or 6BW6 may have originally been specified.

I reckon it would be good for 15 Watts on 80 Metres in Class-C.

TV valves have quite some history in such applications; KW Electronics produced a top-band TX in the 'fifties that used a PL81 as the RF output valve, and the PL509/519 is popular amongst us Hams for use in HF linear-amplifiers, where their ability to handle impressive peak currents helps to prevent 'flat-topping' on modulation peaks.
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Old 20th Jan 2023, 1:22 pm   #19
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Default Re: Help ID this unmarked valve

I was wondering if an EAR 559 clone might be interesting. There is an interesting thread on DiyAudio at the moment on this topic ...
How would you drive an EL509 in enhanced triode mode.
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Old 20th Jan 2023, 2:17 pm   #20
dougietamson
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Default Re: Help ID this unmarked valve

Here's the datasheet attached for the EL508, PL508 is on r-type.org.

http://www.r-type.org/pdfs/pl508.pdf

I've bid 99p on a buddy for the single valve I have.

The free box of valves also came with a NOS PZ30, I tested the heaters on 52v, all good.

Looks like I'll be winding more transformers this year...
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File Type: pdf TELEFUNKEN EL508 p1.pdf (299.5 KB, 17 views)
File Type: pdf TELEFUNKEN EL508 p2.pdf (405.1 KB, 14 views)
File Type: pdf TELEFUNKEN EL508 p3.pdf (216.1 KB, 11 views)
File Type: pdf TELEFUNKEN EL508 p4.pdf (325.3 KB, 14 views)
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