OK, I did a few searches and if this has been covered already, my apologies - maybe my kewords were wrong. Anyway....
The amp in question is a Rogue 88 (not Magnum build). I've had two filament failures on the same KT88 position/socket, running intriode if that matters. Bought the amp used and the first failure was after one month. I retubed the entire thing and all was fine for another month and one night I hear popping. Inspection shows the same tube position is out. After the failure, fireworks begin in the other 88s (there are four of them) with seemingly random selection. The plate fuse (1/4 amp slow-blo) also blows, sometimes the one of the filament failure side and sometimes both. A couple of the 88s also heat up to the point of the silver top getting dark - ouch. I've also replaced the crispy output resistors to the fuses (100 ohm, 1/2w but replaced with 1w). The problems start once I replace the fuses (guess that makes sense?). Without the plate connected, things are seemingly OK.
Before I fry more of my money, am I missing something simple like a bad socket/finger connection? FYI, I've replaced the bypass caps (don't recall value) and the resistors measure OK. Also, I've replaced the current regulator in the PS (LM317 if I remember?) and the PS seems to be OK. The B+ runs higher than the schematic notes but I attribute this to the 122vac in my house. I tend to overanalyze (EE!!) so I could use a clean perspective. Any advice on modifications to improve the stability of the circuit type is also welcome, but I've already read some good suggestions on the basics.
Many thanks for the anticipated good advice!!
Bob
The amp in question is a Rogue 88 (not Magnum build). I've had two filament failures on the same KT88 position/socket, running intriode if that matters. Bought the amp used and the first failure was after one month. I retubed the entire thing and all was fine for another month and one night I hear popping. Inspection shows the same tube position is out. After the failure, fireworks begin in the other 88s (there are four of them) with seemingly random selection. The plate fuse (1/4 amp slow-blo) also blows, sometimes the one of the filament failure side and sometimes both. A couple of the 88s also heat up to the point of the silver top getting dark - ouch. I've also replaced the crispy output resistors to the fuses (100 ohm, 1/2w but replaced with 1w). The problems start once I replace the fuses (guess that makes sense?). Without the plate connected, things are seemingly OK.
Before I fry more of my money, am I missing something simple like a bad socket/finger connection? FYI, I've replaced the bypass caps (don't recall value) and the resistors measure OK. Also, I've replaced the current regulator in the PS (LM317 if I remember?) and the PS seems to be OK. The B+ runs higher than the schematic notes but I attribute this to the 122vac in my house. I tend to overanalyze (EE!!) so I could use a clean perspective. Any advice on modifications to improve the stability of the circuit type is also welcome, but I've already read some good suggestions on the basics.
Many thanks for the anticipated good advice!!
Bob
