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

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. :beer:

Re: Help ID this unmarked valve
 

EL508 maybe .Mick.

Re: Help ID this unmarked valve
 

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

Re: Help ID this unmarked valve
 

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

Re: Help ID this unmarked valve
 

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

Re: Help ID this unmarked valve
 

Measured cold on the minitester

Re: Help ID this unmarked valve
 

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

Re: Help ID this unmarked valve
 

Mullard PL508 heater measures 8.01Ω using a Keithley 2000 DMM

Rich

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.

Re: Help ID this unmarked valve
 

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

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...

Re: Help ID this unmarked valve
 

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

Re: Help ID this unmarked valve
 

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.

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?

Re: Help ID this unmarked valve
 

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

Re: Help ID this unmarked valve
 

Just ordered 2 x B9D chassis mount sockets from Langrex ebay store for £4

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.

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.

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...