tube sockets

rebuild my mk 3s last year. i used them for about 9 mouths. Had a speaker problem not electrical the amps were not powered up for about4 mouths. I brought them up slow with a variac listened for a couple hours. The next day powered them up one amp was hiissing unpluged every thing but speakers still hissing swapped speakers still hissing can not hear hiss when playing but comes right back after about 10 to 15 seconds when i stop. noticed the tubes were loser in that amp when rebuilding i used cheaper sockets in that amp got in a hurry looking for problem but may have found it with tube sockets.

Usually a loose or corroded tube socket will cause a crackling sound due to poor connections between the tube pins and socket. There could be a tube socket problem and I recommend cleaning both the tube pins and sockets with a good cleaner such as DeOxit before doing anything else along with re tensioning the contacts in the sockets. There could also be a problem with a noisy resistor especially if they are the carbon composition type. I've run into several of them in the not too distant past or it is also possible that a tube is on the way out.

I am going to replace the sockets. the tubes are 6550we with about 300 hours on them. I bought all the caps from dynakit parts. I will check the caps when i change the sockets I swapped the tubes with the ones from other amp did not change any thing.

Before you replace your sockets, I'd suggest you check the small signal (driver) tubes to be sure they aren't the problem.

It's easy enough to do, just switch the small tubes from one amp to the other and see if the problem follows the tubes.

Found problem the solder traces on the old mk 3 control board burnt next to the 390 cap. Must have got it to hot when i changed that cap. I guess I have the excuse i needed to upgrade the control boards

I was going to put a jumper wire to replace the burnt trace but found the 390 MMF and 12 MMF both open am ordering the vta boards from tubes4hifi .