My beautiful GZ37 shows some dark/burn on inside glass - but still works fine and the amp biases just fine...

I bought a replacement today (149.00) but the old one (I bought the pair in 2016 and used ever since) very beautiful tubes - and very rare/hard to come by now in this shape - 1962 with the Mullard logo + made in Grt Britain on the glass - I'm going to keep it as a backup.

For a M125 amp where I just run two output tubes (yellow sheet mode + Rubli delay board - bucking transformer) - is it ok to still use this tube or would you chuck it? I asked the same question on AK - the verdict was about 50/50 - most state that a rectifier tube is fairly simple and both sides glow just fine - should be OK to keep using - others were like no way - I think the majority were OK with using it.

My M125 has definitely put this poor tube through its paces - complete red plating/glowing - terrible smells - but the amp has been completely rebuilt since and is now working just fine. I begin rebuild of the second M125 week after next.


Thanks as always!

Back in the day when red plates were a depressingly common occurrence I similarly lit up a GZ37 like a roman candle. Red plate issue is distant memory now thanks to adding AB tech, whereas the latter, well, years later she's still chugging along fine. Put me in the continue to use camp.

LeGrace wrote:Back in the day when red plates were a depressingly common occurrence I similarly lit up a GZ37 like a roman candle. Red plate issue is distant memory now thanks to adding AB tech, whereas the latter, well, years later she's still chugging along fine. Put me in the continue to use camp.  

Thanks LeGrace.

If your output tubes bias OK, continue to use it. GZ37 and GZ33 are very robust.
A little discoloration on inside of the glass is no indicator of the tubes operational condition.

Tubes4ever wrote:If your output tubes bias OK, continue to use it. GZ37 and GZ33 are very robust.
A little discoloration on inside of the glass is no indicator of the tubes operational condition.

Thanks very much.