[Amps] Tentec Centurion arcing problem/question

[Gerhard Marx]

Thanks for the hint (not to use html) Chris

Greetings.  I have a TENTEC Centurion that has worked great for almost 3 decades.
Some month ago a problem started to occure quite frequently: when tuning the amp
with about 30 watts from the xcvr the line fuse (16A house circuit breaker) blows.
I then saw that before this happend, in one of the tubes there started to glow light
at the botton which became brighter and the colour changed to blue. This took about
10 to 15 seconds. Then there was a flash in the tube. It happend all bands.

Meanwhile I replaced both tubes with a another (used) pair and it seems to work ok with
less than 400 watts output.
Before driving the amp with more power I would like to know if the problem observed
can be caused by a bad tube only.
Or could there be other defects causing this arcing ?

mni tnx for ur help es 73 de Gerhard DK6WA