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Crackling intermittently on Mission 5e3

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8/18/2003 12:50 PM

Crackling intermittently on Mission 5e3

I just finished my 5e3 project and it worked great. I took the chassis out of the cabinet to shellac the finish. Then put the chassis back in and an intermittent "crackling" began to happen. As soon as it is turned on with standby, crackling is heard at various times. The amp works except for this.

If I tap on the chassis by the input jacks, horrible loud sounds are heard. I tried proding with a plastic prod to try to make the crackling happen . . . no luck. I tried reseating all the tubes . . . still happens.

Any suggestions? Has this happened to you?

Thanks, Jeff

8/18/2003 5:01 PM
quayhog	Make sure your trannies are mounted very tight. Also make sure the bolts through the trannies are tight. If its not that, you have a cold solder connection somewhere or a bad tube. Jonathan

8/18/2003 7:44 PM
Bruce /Mission Amps	Also, check to see if your speaker leads are connected securely... both ends... the chassis jack, 1/4" plug and the speaker itself. Bruce

8/18/2003 7:54 PM
Mike G.	Hi Jeff, my amp had similar symptoms, turned out to be the 12AY7 tube. When I replaced it, no more noises.

8/18/2003 9:15 PM
Todd	I just received a used Mission Tweedy Deluxe today and was going to ask this VERY SAME question. I think I will try some different tubes and look at the speaker set-up. Thanks for the input!

8/19/2003 1:19 PM

The problem has been found. Here is what happened. I tried replacing a known good tube for each of the preamp tubes. The problem persisted. I pulled each preamp tube one at a time then turned the amp on. When I got to V2 (12ax7) the crackling stopped. So, with V2 out of the circuit, no crackling. By the way, when I tapped on the chassis with a plastic prod, I got all sorts of strange sounds, even a radio station at one time. That made me think of a spark gap which was an old way of receiving am radio (right Bruce?). A spark gap meant a bad solder joint. One of the suggestions was to touch up solder joints.

I focused on V2 since it was the one that quieted the amp when it was pulled. I re-soldered all of the pins on the tube socket then put the tubes back in and fired it up . . . no crackling! No am radio, no obnoxious noises. Excellent!

I think the problem was the jumper that I used between two adjacent pins on the socket. I found it very difficult to solder a jumper because when I soldered one end it made the jumper hot enough to melt the other end and it would fall off. Any suggestions?

So the conclusion of this crackling problem was a bad solder joint. I learned a bit about troubleshooting; substituting known good tubes, pulling tubes to isolate the problem. Even the AM radio spark gap clue! Good luck to the others who are searching for their answer. Jeff

8/19/2003 2:01 PM
Aaron	try using a heat sink clamp on the wire somwhere between where you're soldering and the other end which you've already connected to the other tube pin.

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