I'll cut to the chase - the only cure is to replace the bad socket with a good one 
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Child resistant SSE had been exhibiting the typical signs of gain stage tube failure: intermittent noise consisting of random hiss and low level hum, combined with intermittent snaps, crackles, and pops.
Substituting the 12AT7 with known good 12AT7's would cure the symptoms - but only for a short time - the noise would invariably return. The socket looked completely normal - no visible evidence of anything wrong, it held the pins tight.
Reflowing the solder around the tube socket pins did not improve the situation, cleaning the socket with DeOxit did not help, trying to tighten the contacts did not help. The only action that would give some short term respite from the symptoms was manipulation of the tube in the socket - a dead give away of a bad socket. There had only been about four tubes in this socket - half of those subs while troubleshooting the symptoms.
So being tired of this nonsense, last night I bit the bullet and disassembled the thing to replace the socket. Replacing a tube socket is always a royal PITA, the SSE is no better or worse than anything else in this regard. My desoldering tools leave a lot to be desired - a solder sucker and braid ( which I never use ) - two passes on each of the pins had most of the solder gone. At that point I cut the old socket free, heated the stubs and pulled them loose, and then went around the socket one more time to remove the remaining solder, and then soldered in a new socket.
While I had the board off, I replaced the diodes that had failed - the failed diodes were supposed to be 1 amp 1250 PIV parts; I replaced them with more of the same - these should be more than adequate for the task.
I considered pulling the first power supply capacitor to make the power supply LC and lower the voltage a bit, but wound up leaving it alone for now.
Win W5JAG
.Child resistant SSE had been exhibiting the typical signs of gain stage tube failure: intermittent noise consisting of random hiss and low level hum, combined with intermittent snaps, crackles, and pops.
Substituting the 12AT7 with known good 12AT7's would cure the symptoms - but only for a short time - the noise would invariably return. The socket looked completely normal - no visible evidence of anything wrong, it held the pins tight.
Reflowing the solder around the tube socket pins did not improve the situation, cleaning the socket with DeOxit did not help, trying to tighten the contacts did not help. The only action that would give some short term respite from the symptoms was manipulation of the tube in the socket - a dead give away of a bad socket. There had only been about four tubes in this socket - half of those subs while troubleshooting the symptoms.
So being tired of this nonsense, last night I bit the bullet and disassembled the thing to replace the socket. Replacing a tube socket is always a royal PITA, the SSE is no better or worse than anything else in this regard. My desoldering tools leave a lot to be desired - a solder sucker and braid ( which I never use ) - two passes on each of the pins had most of the solder gone. At that point I cut the old socket free, heated the stubs and pulled them loose, and then went around the socket one more time to remove the remaining solder, and then soldered in a new socket.
While I had the board off, I replaced the diodes that had failed - the failed diodes were supposed to be 1 amp 1250 PIV parts; I replaced them with more of the same - these should be more than adequate for the task.
I considered pulling the first power supply capacitor to make the power supply LC and lower the voltage a bit, but wound up leaving it alone for now.
Win W5JAG
Absolutely.
Sometimes they just fall apart from the heat, they can arc, they can be damaged by bent or crooked pins, they can lose tension from too many cycles, there are just a number of ways they can fail.
The one I replaced was definitely bad, but I don't know why. It just was.
Win W5JAG
Sometimes they just fall apart from the heat, they can arc, they can be damaged by bent or crooked pins, they can lose tension from too many cycles, there are just a number of ways they can fail.
The one I replaced was definitely bad, but I don't know why. It just was.
Win W5JAG
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