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One of our Fender Super Sonic amp heads that I had serviced in July came back with static noise issues. I pulled up my service notes from then, to see what I had done....it being one of dozens of amps being scrutinized during preventative maintenance work. All was working fine, then, plate current/balance was fine, just a couple noisy pots that exercised out to be quiet. Never even pulled the chassis out, as nothing then warranted it.
Today, after powering up and plugged into my lab speaker, just pressing down on the top of the cabinet got something excited, to where it growled at me with that excessive-current-flow sound. Tapping and hitting the top of the cabinet sent it off into a tizzy, as did tapping onto both of the 6L6GC power tubes. I removed the driver tube, powered back on, same issue, so it was the power tubes or the tube sockets. Pulled the chassis out and moved it to the service cradle. Hybrid SS/Tube amp...6 preamp / driver tubes, & a pair of 6L6GC power tubes, power suppl PCB, main PCB and front panel/preamp tube PCB. I discharged all the supply caps, then turned it over and removed the power tubes.
Ceramic Octal sockets for the power tubes, using forked-terminals, rather than wrap-around terminals. Rats! I'm not a big fan of the forked-style terminals. I began with my radial scrub brush, dipped in Caig DeOxit and scrubbed all the terminals, then used a wooden Q-tip end to further scrub them. Brass-bristle-brushed the tube pins, and plugged them back in to see if that improved matters. Nope. Just as bad as it was before.
I exercised the tube sockets using the tubes themselves, holding the bear trap claws open....felt like there was sufficient contact force. Tried again, better, but I could still nudge either tube into where it pitched a fit and kept a steady growl coming out of the speaker. Rats!
OK, discharged the supplies again, then looked to see if my tiniest needle-nose pliers would fit into the slots of the ceramic body for loading in the forked terminals. They did JUST fit in. I knew my smallest Wiha bladed screwdriver, which I had filed narrower for this same purpose would fit in, but wanted to see if I could close them up a bit with the pliers. Not quite, but, worked on one terminal at a time, pulling against another opening, as seen in the photo below.
The ceramic tube sockets have slightly wider slot opening in them than this Cinch-Jones Octal socket in the photos, but, this shows the procedure. After drawing the terminals tighter without destroying them, it now required a lot more insertion force to plug the power tubes in. I tried it again. No more static noise or growling....cured it! I was afeared I'd have to replace the bloody sockets for a few moments there.
Other than using those pliers for bread-boarding with 28AWG solid wire between terminals, I rarely use them, since they're not serrated jaws and don't have much grip on things.
Contract noise? That's Contact noise....couldn't correct it after submitting it.
Today, after powering up and plugged into my lab speaker, just pressing down on the top of the cabinet got something excited, to where it growled at me with that excessive-current-flow sound. Tapping and hitting the top of the cabinet sent it off into a tizzy, as did tapping onto both of the 6L6GC power tubes. I removed the driver tube, powered back on, same issue, so it was the power tubes or the tube sockets. Pulled the chassis out and moved it to the service cradle. Hybrid SS/Tube amp...6 preamp / driver tubes, & a pair of 6L6GC power tubes, power suppl PCB, main PCB and front panel/preamp tube PCB. I discharged all the supply caps, then turned it over and removed the power tubes.
Ceramic Octal sockets for the power tubes, using forked-terminals, rather than wrap-around terminals. Rats! I'm not a big fan of the forked-style terminals. I began with my radial scrub brush, dipped in Caig DeOxit and scrubbed all the terminals, then used a wooden Q-tip end to further scrub them. Brass-bristle-brushed the tube pins, and plugged them back in to see if that improved matters. Nope. Just as bad as it was before.
I exercised the tube sockets using the tubes themselves, holding the bear trap claws open....felt like there was sufficient contact force. Tried again, better, but I could still nudge either tube into where it pitched a fit and kept a steady growl coming out of the speaker. Rats!
OK, discharged the supplies again, then looked to see if my tiniest needle-nose pliers would fit into the slots of the ceramic body for loading in the forked terminals. They did JUST fit in. I knew my smallest Wiha bladed screwdriver, which I had filed narrower for this same purpose would fit in, but wanted to see if I could close them up a bit with the pliers. Not quite, but, worked on one terminal at a time, pulling against another opening, as seen in the photo below.
The ceramic tube sockets have slightly wider slot opening in them than this Cinch-Jones Octal socket in the photos, but, this shows the procedure. After drawing the terminals tighter without destroying them, it now required a lot more insertion force to plug the power tubes in. I tried it again. No more static noise or growling....cured it! I was afeared I'd have to replace the bloody sockets for a few moments there.
Other than using those pliers for bread-boarding with 28AWG solid wire between terminals, I rarely use them, since they're not serrated jaws and don't have much grip on things.
Contract noise? That's Contact noise....couldn't correct it after submitting it.
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