How is this going to cause the fuse to blow? The speaker jacks are already grounded to the chassis at their bushings. Maybe resoldering the red wire improved the main ground for the filters, but it still doesn't seem to add up...
I fear the worst...
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martin manning
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Re: I fear the worst...
Re: I fear the worst...
Good question. I was always a little unhappy with situations where doing something fixed the problem, but there was no clear way HOW it fixed the problem. There is always this nagging suspicion that it just happened to quit when you did >something< and still lurks there to bite you at the worst possible moment.
I can make up a few scenarios where this would make sense though. Fuse blowing will always involve the power components - the transformers, output tubes, rectifiers and filters, as well as the speaker circuit; the power level is too small back in the preamp circuits for anything except a high frequency oscillation driving an otherwise good power stage to over-dissipate. So finding a fault in the speaker output wiring is at least in the right area.
We would have to know if the speaker jack really is grounded at the chassis, and if so, how well. The OP displays some concerns over wiring. Maybe he did the theoretical right thing and isolated the speaker jacks from the chassis. Maybe it's not really well grounded to the chassis. Maybe chassis-only grounding because of an open speaker return throws the preamp-poweramp into an oscillating tizzy (which is one reason to avoid direct speaker jack grounding; it has happened).
The definitive answer is to have the OP open up the speaker return wire and see if it then causes a fuse to blow after whatever time lag he's been seeing.
I can make up a few scenarios where this would make sense though. Fuse blowing will always involve the power components - the transformers, output tubes, rectifiers and filters, as well as the speaker circuit; the power level is too small back in the preamp circuits for anything except a high frequency oscillation driving an otherwise good power stage to over-dissipate. So finding a fault in the speaker output wiring is at least in the right area.
We would have to know if the speaker jack really is grounded at the chassis, and if so, how well. The OP displays some concerns over wiring. Maybe he did the theoretical right thing and isolated the speaker jacks from the chassis. Maybe it's not really well grounded to the chassis. Maybe chassis-only grounding because of an open speaker return throws the preamp-poweramp into an oscillating tizzy (which is one reason to avoid direct speaker jack grounding; it has happened).
The definitive answer is to have the OP open up the speaker return wire and see if it then causes a fuse to blow after whatever time lag he's been seeing.
Re: I fear the worst...
Wow, ages later but I am now seeing I didn’t respond to the last post. FWIW the speaker jacks are Switchcraft Type 11 mono jacks. They are grounded at their mounting points on the chassis (not isolated from chasss) but I also run a ground wire from the sleeve (?) conductor to a separate ground bolt/screw. This hasn’t ever given me an issue. My thinking is that even though I tighten down the speaker jacks with all my strength when installing it’s a little added security to ground them w/a wire as well.
I have not had any more trouble with the amp blowing fuses, etc. It’s been behaving nicely since last summer.
I have another amp I was just messing w/last night. 18 watt 1x12 combo w/6GK6s as output tubes. Built it about a year and a half ago. Never could get the tone quite right. I built essentuakkybthe same circuit before also using 6GK6s and it sounded so good it was my #1 amp for a while. The culprit turned out to be the output transformer. I used a very old (1930s possibly) GE ‘Musaphonic’ OT that I had for a while. Funny thing is, I had a friend who had an old what he thought was an organ amplifier but in fact was the power block of the same GE Musaphonic that my OT came from. His was an exact match for my OT. After checking voltages, etc I saw that a guitar amp indeed could be constructed within the chassis & using the same iron. It had a bunch of octal tubes so I went ahead (with his consent of course) and built a 5E3 with 6SL7s in place of the 12AY7 & AX7. The end result was awesome, a great sounding amp. That’s what gave me the confidence to go ahead and use the OT in a build. I still think it would sound good in a 5E3, just not in this amp. I got so wrapped up in the swap last night that once I finished the operation I looked up at the clock expecting it to say 11:30, maybe 11:45pm. Nope, 1:30am!
I have not had any more trouble with the amp blowing fuses, etc. It’s been behaving nicely since last summer.
I have another amp I was just messing w/last night. 18 watt 1x12 combo w/6GK6s as output tubes. Built it about a year and a half ago. Never could get the tone quite right. I built essentuakkybthe same circuit before also using 6GK6s and it sounded so good it was my #1 amp for a while. The culprit turned out to be the output transformer. I used a very old (1930s possibly) GE ‘Musaphonic’ OT that I had for a while. Funny thing is, I had a friend who had an old what he thought was an organ amplifier but in fact was the power block of the same GE Musaphonic that my OT came from. His was an exact match for my OT. After checking voltages, etc I saw that a guitar amp indeed could be constructed within the chassis & using the same iron. It had a bunch of octal tubes so I went ahead (with his consent of course) and built a 5E3 with 6SL7s in place of the 12AY7 & AX7. The end result was awesome, a great sounding amp. That’s what gave me the confidence to go ahead and use the OT in a build. I still think it would sound good in a 5E3, just not in this amp. I got so wrapped up in the swap last night that once I finished the operation I looked up at the clock expecting it to say 11:30, maybe 11:45pm. Nope, 1:30am!