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Old 19th Aug 2019, 7:20 am   #1
Nukeybrown
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Default Valve identity

Pulled from a working set , just cant remember which one lol
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Old 19th Aug 2019, 7:44 am   #2
snowman_al
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Default Re: Valve identity

EL84 (or similar output type 6BQ5 etc.)
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Old 19th Aug 2019, 7:49 am   #3
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Default Re: Valve identity

I've heard that if you freeze valves, it can temporarily reveal the valve markings on the glass envelope.

Never done this myself, but might be worth a try?
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Old 19th Aug 2019, 8:20 am   #4
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Default Re: Valve identity

... should have asked how many pins on the base. 7 or 9?

If it is a Mullard (Philips family) valve there could still be a code round the bottom.
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Old 19th Aug 2019, 9:05 am   #5
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Default Re: Valve identity

If the other valves are "U" types, then UL84
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Old 19th Aug 2019, 11:19 am   #6
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Default Re: Valve identity

Quote:
Originally Posted by snowman_al View Post
If it is a Mullard (Philips family) valve there could still be a code round the bottom.
Yes, etched into the glass so, unlike the other markings, it can't rub off.

Two rows, one identifies the valve type, the second the date and place of manufacture.

Full details - including a translation of the type codes - here: https://frank.pocnet.net/other/Phili...CodeListAB.pdf
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Old 19th Aug 2019, 2:05 pm   #7
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Default Re: Valve identity

Yes I'd say it's an EL/UL84-series. The anode isn't big enough for it to be a 5763.

Sometimes if you breathe on the envelope it can reveal the markings - could this (or rather the condensation that would form on the cold glass) be the same idea as the putting-it-in-a-fridge trick?

Ultraviolet light (from one of those hand-held forged-banknote-detectors) could be worth a try too - residual markings might glow!
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Old 19th Aug 2019, 2:27 pm   #8
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Default Re: Valve identity

I can only see 7 pins - EL90?
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Old 19th Aug 2019, 8:46 pm   #9
Nukeybrown
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Default Re: Valve identity

Can't see any numbers, I have tried with uv lighting. It's a 9 pin. My guess was a UL84 but that was just a guess. Had it for a while so couldn't say which set of valves it came out of.
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Old 19th Aug 2019, 8:54 pm   #10
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Default Re: Valve identity

If they are intact, a check of the heaters cold resistance should indicate whether it's a UL84 or not.

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Old 19th Aug 2019, 9:20 pm   #11
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Default Re: Valve identity

71 ohm cold resistance pins 4 & 5
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Old 19th Aug 2019, 10:17 pm   #12
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Default Re: Valve identity

my EL84's more or less read short when cold, might be a P series?
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Old 20th Aug 2019, 7:11 am   #13
snowman_al
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Default Re: Valve identity

Quote:
Originally Posted by Nukeybrown View Post
71 ohm cold resistance pins 4 & 5
I've just measured a UL84 cold and have 69 ohms.
(Also a couple of UL41s at 70 to 71 ohms - they are 45 volt 0.1 amp heaters same as the UL84)

Checking an EL84 heater resistance, it is less than 1 ohm.

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Old 25th Aug 2019, 1:33 pm   #14
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Default Re: Valve identity

Quote:
Originally Posted by terrykc View Post
Quote:
Originally Posted by snowman_al View Post
If it is a Mullard (Philips family) valve there could still be a code round the bottom.
Yes, etched into the glass so, unlike the other markings, it can't rub off.
Unfortunately, Philips never etched those codes so they can and sometimes are rubbed off. They used a somewhat better ink since it had to survive the chalk print process and then a few years to have proof of warranty.
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Old 26th Aug 2019, 4:15 pm   #15
terrykc
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Default Re: Valve identity

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Originally Posted by Maarten View Post
Unfortunately, Philips never etched those codes so they can and sometimes are rubbed off. They used a somewhat better ink since it had to survive the chalk print process and then a few years to have proof of warranty.
I have seen codes printed on bakelite bases and on the underside of B8A valves but all B7g and B9A valves I've ever seen have had the code etched in the glass and large numbers of valves sold in the UK under the Mullard trademark were manufactured in Dutch factories.
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Old 26th Aug 2019, 5:47 pm   #16
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Default Re: Valve identity

I think what Maarten is saying is that technically, they aren't etched. It's actually an "almost-indelible" ink.
I have seen a few valves where it has partly rubbed off, but that is unusual.
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Old 26th Aug 2019, 7:22 pm   #17
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Default Re: Valve identity

Put 6.3 volts across the heaters and all will be revealed,UL or EL.
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Old 27th Aug 2019, 12:11 am   #18
Nukeybrown
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Default Re: Valve identity

Sorry for the late reply its a UL84 just tried it in a set, works good sounds nice. Thank you
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Old 27th Aug 2019, 2:48 am   #19
Maarten
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Default Re: Valve identity

Quote:
Originally Posted by terrykc View Post
Quote:
Originally Posted by Maarten View Post
Unfortunately, Philips never etched those codes so they can and sometimes are rubbed off. They used a somewhat better ink since it had to survive the chalk print process and then a few years to have proof of warranty.
I have seen codes printed on bakelite bases and on the underside of B8A valves but all B7g and B9A valves I've ever seen have had the code etched in the glass and large numbers of valves sold in the UK under the Mullard trademark were manufactured in Dutch factories.
Please examine more closely. Maybe try to rub it out with some spit or even alcohol on your finger. Etched numbers won't rub out but these will. I've seen it often enough (whenever I get a set in, I make note of all numbers).
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Old 27th Aug 2019, 11:34 pm   #20
Nukeybrown
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Default Re: Valve identity

I will have anther look tomorrow for etched numbers but to be honest im thinking theres none there
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