David McGown wrote:
Just read Dave Berning's suggestion, that is the first thing you should try. My comments below are further steps to isolate the problem if not a shorted KT88.
1. Do you have a variac? It is best to start up an amp that has been sitting a long while by starting at a reduced lines voltage and slowly bring up to voltage. This help reform old electrolytic caps.
2. Do you have access to a tube tester (either an emissions tester or transconductance tester). If so, check all tubes for shorts, emissions.
3. Does the amp have a tube rectifier. If so, this could be faulty, so check this (see above)
4. If the amp uses solid state rectification, the turn-on surge could be excessive if the caps are old and leaky after long storage or excessively large. It is possible the capacitors will need replacing.
5. Is there a way to turn on the heaters first to warm up the tubes prior to applying B+ voltage? This helps in getting the tubes up to emission temperature.
6. Is the fuse the correct current value and type for the amp? A fast blow fuse or too small of a fuse will blow on a startup surge. That being said, you do not want to indiscriminately increase the value of the fuse until it doesn't blow.
7. If the amp uses fixed bias (negative bias supply), make sure this is operating. However, if you have badly out of bias tubes (red-plating), this is not likely to cause the amp to immediately blow a fuse.
See my reply above.
Fuses: fast-acting 2A 20mm.
I don’t have an variac. Do u think it is worthwhile based on the symptoms?