this sounds like a dream diagnostic toy for me.
i have a few theories (dont take these to heart without a second opinion)
the power supply caps on modern tube amps is very high. this is because bass noted require more power if the capacitors in the psu start degrading bass is the first thing that goes.
dont hit your amp. ever heard of microphonics? physical vibrations affect tubes.
the extra glowy tube either has a bias issue or is about to die.
if the other channel has the same tube switch the two and see which one glows. this easily rules out the tube or the circuit without any tools.
as for touching your case and it popping.... if the case is grounded when you touch it you alter its magnetic field causing it to emit energy which can translate to interference.
i have a few theories (dont take these to heart without a second opinion)
the power supply caps on modern tube amps is very high. this is because bass noted require more power if the capacitors in the psu start degrading bass is the first thing that goes.
dont hit your amp. ever heard of microphonics? physical vibrations affect tubes.
the extra glowy tube either has a bias issue or is about to die.
if the other channel has the same tube switch the two and see which one glows. this easily rules out the tube or the circuit without any tools.
as for touching your case and it popping.... if the case is grounded when you touch it you alter its magnetic field causing it to emit energy which can translate to interference.
I did switch the tubes, and it turns out it's just that one tube that glows brighter. So you may be right...
The interference theory was one of the first I ruled out, because the crackling doesn't behave anything like static. Pressing hard enough on many places will cause the crackling. The telltale sign is that all music stops during the crackling, and the speaker hits it's excursion limit.
To tell the truth I'm about ready to just rip out all the amp circuitry and start from scratch. There are a number of design choices I don't admire, like the liberal use of Z5U ceramics in the signal path. Switches need cleaned, carbon comp's may have drifted... And soldering anything releases fumes from caked-on dust and nearby plastic. And I should probably replace the tube sockets too. I have sockets pulled from a reel-reel recorder left outside to the Texan elements, whose receptacles aren't dull black like those on this amp.
- keantoken
The interference theory was one of the first I ruled out, because the crackling doesn't behave anything like static. Pressing hard enough on many places will cause the crackling. The telltale sign is that all music stops during the crackling, and the speaker hits it's excursion limit.
To tell the truth I'm about ready to just rip out all the amp circuitry and start from scratch. There are a number of design choices I don't admire, like the liberal use of Z5U ceramics in the signal path. Switches need cleaned, carbon comp's may have drifted... And soldering anything releases fumes from caked-on dust and nearby plastic. And I should probably replace the tube sockets too. I have sockets pulled from a reel-reel recorder left outside to the Texan elements, whose receptacles aren't dull black like those on this amp.
- keantoken
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