Help ID this unmarked valve

[Mr Moose]

Hello,

There's a circuit and other info for a PL508 amplifier in this old thread.

https://www.vintage-radio.net/forum/...d.php?t=170827

Yours, Richard

[dougietamson]

Originally Posted by Mr Moose

Hello,

There's a circuit and other info for a PL508 amplifier in this old thread.

https://www.vintage-radio.net/forum/...d.php?t=170827

Yours, Richard

Yes, very interesting.

Here's the schematic downloaded from the original article.

[Leon Crampin]

It looks to me as though the cathodes of the ECC82 driver should be earthed. The bias chain resistor values are unfriendly, and there's no protection for wiper lifting on the adjuster - poor design...

Leon.

[Maarten]

Originally Posted by dougietamson

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.

Keeping in mind those codes aren't etched like the types on some USA valves, but instead printed using a somewhat durable ink, there should be a (possibly wiped out) 3 character code just above the line you spotted. Sometimes it can be read under favourable lighting conditions, maybe even by breathing on the glass.

Heerlen did manufacture colour TV valves well into the 1970's, and since this type of valve (and a 4 character date code) is unlikely to be from 1960, it's almost certainly made in 1970.

[dougietamson]

Originally Posted by Maarten

Keeping in mind those codes aren't etched like the types on some USA valves, but instead printed using a somewhat durable ink, there should be a (possibly wiped out) 3 character code just above the line you spotted. Sometimes it can be read under favourable lighting conditions, maybe even by breathing on the glass.

Heerlen did manufacture colour TV valves well into the 1970's, and since this type of valve (and a 4 character date code) is unlikely to be from 1960, it's almost certainly made in 1970.

The PL508 I bought arrived today, same factory but from 1971. It has the 3 digit code above looks lik I16.
I checked my original one and it has a very faded 6 as above the 4 digit code.

They are identical otherwise.

Photo attached, the 'ne' one is on the right, you can read the codes at the bottom right.

Doug

[Maarten]

That would be t16. I think that's a plausible code for 1970/1971. I know of a t1A from 1973.