AcousticBoom
Member
- Messages
- 81
Hey all, I recently bought a JCM 800 4210 (1984 - newer circuit).
A little back story...
First thing I did was replace the electrolytics and give the sockets, jacks and pots a little deoxit. The old tubes would also crackle and pop like cooking bacon when turning the amp on so it was time for new tubes as well. It came with 6550's and decided to put KT66's in it. I bought new production Gold Lion's.
Originally to bias the amp, I had bought a bias scout from tube depot. All my test measurements after assembling the tool came out perfect. However, when I connected it and turned the amp on, it blew the 500mA fuse (slo-blow). From that point I was done with the scout and decided to use the transformer voltage method (70% dissipation if anyone cares to know). Everything was running fine as of this past Saturday. (Edit: I also replaced the tube that was in the scout at the time of the blown fuse with another of the same rating).
Now for the problem I experienced last night...
I haven't had a chance to crank the amp yet and have been playing at slightly-louder-than-bedroom levels (MV cranked and channel volume at 9 o'clock). While in the middle of noodling around, the amp crackles and then loses about half its power. The crackle was similar to a scratchy pot - different than when powering on the old tubes. I played around with the volume and gain knobs, didn't help. I turned off the amp completely, waited a few minutes, and everything came back on OK. It played just fine for the rest of the evening.
Any theories why this might have happened? I would think maybe one of the tubes is bad, but since blowing that fuse, maybe something else got fried in the process? Is it safe to be playing the amp if it does it again? Maybe some suggestions of tests I can do?
Thanks!
A little back story...
First thing I did was replace the electrolytics and give the sockets, jacks and pots a little deoxit. The old tubes would also crackle and pop like cooking bacon when turning the amp on so it was time for new tubes as well. It came with 6550's and decided to put KT66's in it. I bought new production Gold Lion's.
Originally to bias the amp, I had bought a bias scout from tube depot. All my test measurements after assembling the tool came out perfect. However, when I connected it and turned the amp on, it blew the 500mA fuse (slo-blow). From that point I was done with the scout and decided to use the transformer voltage method (70% dissipation if anyone cares to know). Everything was running fine as of this past Saturday. (Edit: I also replaced the tube that was in the scout at the time of the blown fuse with another of the same rating).
Now for the problem I experienced last night...
I haven't had a chance to crank the amp yet and have been playing at slightly-louder-than-bedroom levels (MV cranked and channel volume at 9 o'clock). While in the middle of noodling around, the amp crackles and then loses about half its power. The crackle was similar to a scratchy pot - different than when powering on the old tubes. I played around with the volume and gain knobs, didn't help. I turned off the amp completely, waited a few minutes, and everything came back on OK. It played just fine for the rest of the evening.
Any theories why this might have happened? I would think maybe one of the tubes is bad, but since blowing that fuse, maybe something else got fried in the process? Is it safe to be playing the amp if it does it again? Maybe some suggestions of tests I can do?
Thanks!