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Guild Thunder I farts out when being pushed... PS issues?
Hey All,
I recently purchased this old Guild amp (schematic below) from a local store. Being myself, I took the hood off to see what they did to make it a functional beast again. They said they changed a couple resistors and some caps. To my surprise, the original can caps are still connected, but they replaced the first (separate) cap that comes off the rectifier. They've also added a cathode bypass (100uF, I think?) to the power stage, perhaps to tighten the bass, but this seems like treating the symptom, not the cause... While I do think the power section of a pair of 6GW8's could stand to gain from a little support there, I think the real problem lies elsewhere.
Here's the real issue: When I start playing hard at higher volumes, especially with low notes and chords, the amp spits and sputters like it can't get enough juice.
I have three suspicions as to the cause:
1) bad filter caps -- Bad caps may lead to some of the crackling and hum I had at one point, or that could just be lights (etc.) bleeding to the bench when it's out.
2) weak rectifier tube -- A weak rectifier could be either worn out due to age and use, or simply can't provide for the power-sucking bottom end due to electro-mechanical limitations of the 6CA4.
3) heavily saturated OPT -- The only reason I suspect the OPT is because it seems to be getting a bit warm... warmer than I'd like or even expect. (as a comparison, even my Silvertone 1484 with stock (wimpy) OPT doesnt get that warm after hours of gigging...)
Any ideas on how to really peg the cause without a spray and pray? Thanks,
BR
Guild_Thunder_1_12.pdf
I recently purchased this old Guild amp (schematic below) from a local store. Being myself, I took the hood off to see what they did to make it a functional beast again. They said they changed a couple resistors and some caps. To my surprise, the original can caps are still connected, but they replaced the first (separate) cap that comes off the rectifier. They've also added a cathode bypass (100uF, I think?) to the power stage, perhaps to tighten the bass, but this seems like treating the symptom, not the cause... While I do think the power section of a pair of 6GW8's could stand to gain from a little support there, I think the real problem lies elsewhere.
Here's the real issue: When I start playing hard at higher volumes, especially with low notes and chords, the amp spits and sputters like it can't get enough juice.
I have three suspicions as to the cause:
1) bad filter caps -- Bad caps may lead to some of the crackling and hum I had at one point, or that could just be lights (etc.) bleeding to the bench when it's out.
2) weak rectifier tube -- A weak rectifier could be either worn out due to age and use, or simply can't provide for the power-sucking bottom end due to electro-mechanical limitations of the 6CA4.
3) heavily saturated OPT -- The only reason I suspect the OPT is because it seems to be getting a bit warm... warmer than I'd like or even expect. (as a comparison, even my Silvertone 1484 with stock (wimpy) OPT doesnt get that warm after hours of gigging...)
Any ideas on how to really peg the cause without a spray and pray? Thanks,
BR
Guild_Thunder_1_12.pdf
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