[Amps] Rehabbing that dusty old

[Manfred Mornhinweg]

Hi Steve!

> Out of interest, in what way were they too different? 

Totally different date of manufacture, plate looked different (I don't 
remember now what exactly was different), and when I tried them, one 
would take most of the load, the plate getting incandescent even at 
moderate drive.

> Did you get a 
> chance to see if the problem tubes behaved the same in a different amp?

No. But I still have one of the problem tubes here. I kept it to mount 
it on a wooden base! :-)  So it's not too late to run any tests on it.

I suppose that a tube that arcs over - for whatever reason it does so 
the first time - will get some metal evaporated from the arc, and this 
might make it more prone to arcing in the future. I don't know if the 
theory is right, but surely one tube that starts arcing, will keep doing so.

> Manfred mentions his experience being with a Kenwood amp (but not which 
> one). Nichrome might not be a wonder cure, but Henry, Dentron and 
> Measure's suppressors are all more effective than those fitted in a TL922.

Yes, the amp was a TL922.

So, you are proposing that the problem doesn't happen with the Chinese 
tubes simply because they have less gain at VHF? I didn't even think 
about that... I thought the Eimac tubes were just plain gassy! But you 
may well be right.

Manfred.

--------------------------
Visit my hobby homepage!
http://ludens.cl
--------------------------