This is one of those very intermittent problems that is hard to reproduce but occurs maybe once every few days. Here's what I do:
1. Guitar lead is already plugged into input 2. Volume set between 1 and 2.
2. Power on the HRD into standby mode.
3. Wait a minute or so and put it out of standby mode.
No sound. (On one occasion there was sound for a few seconds, and then no sound)
1. Adjust volume control on amp. Still no sound.
2. Plug into input 1, and then into the return jack. Still no sound.
3. Plug back into input 2. Still no sound.
But after about a minute or so you can hear the sound coming back, as if it's warming up. After this, the amp is fine. Can play it for hours, no problems.
On a couple of occasions the dropout, and return, of sound has occurred after the amp has warmed up and functioned normally. But this has happened only twice.
I've opened up the amp and I've:
- reseated the power tubes
- checked the bias (fine at 60mv)
- checked fuse is ok
- done a visual check for bad solder joints - looks ok
- checked for heat marks around R78 and R79 - looks ok
Could this be a sign of a bad power tube or something else?
Comments
If you look very carefully at the preamp valves when the amp is silent you should be able to spot it - one valve will have only one filament glowing not two.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
A slow fade-out/fade-in is almost always a filament problem.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
This is such an intermittent problem that I might not be able to reproduce it for some time.
If it's not the filament supply I've seen this problem caused by the muting circuit.
The HRD has a mute circuit that engages when the channels are switched to minimize popping. I've seen intermittent issues with this circuit causing the signal to drop out too.
Yes, that's it. The signal drops out to nothing, and then becomes a very quiet crunchy signal (like just as after you put it standby) and then the signal recovers. And then it's OK after that.
I've been unable to reproduce the problem today, so don't really know where to go from here.
I removed v3 and reseated it. Amp is making a rather worrying rattling sound now...under investigation...
Edit - power tube has developed rattle. Maybe time for a re-tube. The amp is 3 years old, bough s/h.