Help ID this unmarked valve - UK Vintage Radio Repair and Restoration Discussion Forum

dougietamson · 18th Jan 2023, 6:07 pm

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

Tractorfan · 18th Jan 2023, 6:28 pm

Hi,
I wonder of it might be an EL93? I have one somewhere here that looks like an EL84, but shorter in stature.
Cheers.

vinrads · 18th Jan 2023, 6:34 pm

EL508 maybe .Mick.

Mr Moose · 18th Jan 2023, 6:38 pm

Hello,
Possibly a PL508?
https://www.radiomuseum.org/tubes/tube_pl508.html
(Or an EL508)
Yours, Richard

turretslug · 18th Jan 2023, 6:44 pm

At 8Ω cold (?) heater, more likely to be PL508 than EL508.

dougietamson · 18th Jan 2023, 6:45 pm

Quote:

Originally Posted by vinrads

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

dougietamson · 18th Jan 2023, 6:48 pm

Quote:

Originally Posted by turretslug

At 8Ω cold (?) heater, more likely to be PL508 than EL508.

Measured cold on the minitester

vinrads · 18th Jan 2023, 7:14 pm

Quote:

Originally Posted by turretslug

At 8Ω cold (?) heater, more likely to be PL508 than EL508.

Quite right EL508 reads 1.2 ohms cold, very cold . Mick.

Marconi_MPT4 · 19th Jan 2023, 2:40 pm

Mullard PL508 heater measures 8.01Ω using a Keithley 2000 DMM

Rich

ms660 · 19th Jan 2023, 2:50 pm

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.

dougietamson · 19th Jan 2023, 2:57 pm

Quote:

Originally Posted by Marconi_MPT4

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

dougietamson · 19th Jan 2023, 4:52 pm

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...

Richardgr · 19th Jan 2023, 5:14 pm

Do you have a socket for it? Those B9D sockets are the first stumbling block.

dougietamson · 19th Jan 2023, 5:42 pm

Quote:

Originally Posted by Richardgr

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.

trobbins · 20th Jan 2023, 6:22 am

What are the markings on the glass side wall (partly observed in photo 5 of 5 in post #1?

dougietamson · 20th Jan 2023, 11:23 am

Quote:

Originally Posted by trobbins

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

dougietamson · 20th Jan 2023, 11:28 am

Quote:

Originally Posted by Richardgr

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

G6Tanuki · 20th Jan 2023, 1:11 pm

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.

Richardgr · 20th Jan 2023, 1:22 pm

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.

dougietamson · 20th Jan 2023, 2:17 pm

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...

18th Jan 2023, 6:28 pm	#2
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	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. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

18th Jan 2023, 6:34 pm	#3
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,760	Re: Help ID this unmarked valve EL508 maybe .Mick.

18th Jan 2023, 6:38 pm	#4
Mr Moose Octode Join Date: Jul 2008 Location: Gloucestershire, UK. Posts: 1,043	Re: Help ID this unmarked valve Hello, Possibly a PL508? https://www.radiomuseum.org/tubes/tube_pl508.html (Or an EL508) Yours, Richard

18th Jan 2023, 6:44 pm	#5
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: Help ID this unmarked valve At 8Ω cold (?) heater, more likely to be PL508 than EL508.

19th Jan 2023, 2:40 pm	#9
Marconi_MPT4 Heptode Join Date: Mar 2011 Location: Dorset, UK. Posts: 521	Re: Help ID this unmarked valve Mullard PL508 heater measures 8.01Ω using a Keithley 2000 DMM Rich __________________ To an optimist a glass is half full; a pessimist half empty; an engineer twice as big as need be!

18th Jan 2023, 6:07 pm	#1
dougietamson Hexode Join Date: Mar 2019 Location: Edinburgh, Scotland, UK. Posts: 342	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 Attached Thumbnails Last edited by dougietamson; 18th Jan 2023 at 6:18 pm. Reason: sp

19th Jan 2023, 2:50 pm	#10
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	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.

19th Jan 2023, 4:52 pm	#12
dougietamson Hexode Join Date: Mar 2019 Location: Edinburgh, Scotland, UK. Posts: 342	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...

19th Jan 2023, 5:14 pm	#13
Richardgr Heptode Join Date: Oct 2019 Location: Täby, Sweden Posts: 702	Re: Help ID this unmarked valve Do you have a socket for it? Those B9D sockets are the first stumbling block.

20th Jan 2023, 6:22 am	#15
trobbins Heptode Join Date: Oct 2009 Location: Melbourne Australia Posts: 901	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?

20th Jan 2023, 1:11 pm	#18
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	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. __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.

20th Jan 2023, 1:22 pm	#19
Richardgr Heptode Join Date: Oct 2019 Location: Täby, Sweden Posts: 702	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.