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Hello everyone, long time lurker here. I recently purchased a HiWatt Lead 100R, an amp I've wanted for a while. This particular version is from 1988 and marked "trinity" which just means it has a push/pull gain pot on the front which brings in a bit more gain on the lead channel. This became a standard feature of Hiwatt Lead's not long after this and the "Trinity" tag on the front panel disappeared. It still follows the general schematic of the Lead 100R found on the web, but I can only find the preamp schematic and nothing more. Power section is a quad of EL34's.
Ok, so here's where we are at. The amp came from Indonesia and made no sound when I first plugged it in. I heard a whirring sound a minute or two after turning it on, from the head itself, and as I got closer to inspect, a popping sound which prompted me to immediately turn off the amp. After opening it up, I see it was wired for 100V and I stupidly was running it off of my wall AC's 120V, so that's likely where the problem came from - that said, I would expect to at least have *some* sound come through even if only for the few seconds I strummed the guitar. It did blow a fuse on the rear panel - I can't recall if the fuse blowing turned the amp off or if it was me flipping the switch so quickly after hearing the pop, but either way a fuse was blown.
First things first, I opened it up and corrected the voltage issue. The PT is now connected to the 120V lug, and the PT and HT fuses have been replaced with the correct specs. I also have replaced all 5 preamp tubes with known working ones just in case that is the issue, but I don't think tubes are the problem right now.
I checked voltages on the power and preamp tubes and it appears to be reasonably what I'd expect to see on this style of amp, which is a bit similar to the Marshall split-channel JCM800's like the 2205 and 2210. Same number of tubes, same 3 gain stage with cathode follower design, etc.
When I probe the grids of the power tube with standby off, I do get sound coming through the speakers of the probe touching the grid. However, probing the grid of the phase inverter tube makes no sound - same for any other preamp tube. I was not able to find any burned traces or visually damaged components. I checked for continuity on every resistor and capacitor on the preamp board and I'm not finding any broken components or broken traces. I don't have the tools to verify if a capacitor is working within spec, but if signal goes through it to the other side I would expect to at least have *some* sound so I'll come around to fixing out of spec components once I can get the bare minimum solved here.
My next step was to look into the transformers. I followed the Trinity/Geofex guides online to check on these. Neither the Power or Output transformer seem to have anything wildly out of spec from my probing, but I'll admit I did not remove them from the amp to test. However I would think if the transformers were the problem, I wouldn't get any audio when probing the grids of the power tube - am I wrong?
In short my question is this - if I get sound from probing the grid of the power section, but no sound from the grid of the PI tube, should I still be chasing the transformers as potentially faulty? Or should I strictly be looking for a damaged line somewhere between the preamp/PI and the power section?
I can post pictures if necessary. I appreciate any insight on this. Thanks!
Edit: I also tried some basics - cleaning jacks, plugging directly into the FX return, patching the FX loop, connecting reverb lines together etc - no sound from any of those or combination of them
Ok, so here's where we are at. The amp came from Indonesia and made no sound when I first plugged it in. I heard a whirring sound a minute or two after turning it on, from the head itself, and as I got closer to inspect, a popping sound which prompted me to immediately turn off the amp. After opening it up, I see it was wired for 100V and I stupidly was running it off of my wall AC's 120V, so that's likely where the problem came from - that said, I would expect to at least have *some* sound come through even if only for the few seconds I strummed the guitar. It did blow a fuse on the rear panel - I can't recall if the fuse blowing turned the amp off or if it was me flipping the switch so quickly after hearing the pop, but either way a fuse was blown.
First things first, I opened it up and corrected the voltage issue. The PT is now connected to the 120V lug, and the PT and HT fuses have been replaced with the correct specs. I also have replaced all 5 preamp tubes with known working ones just in case that is the issue, but I don't think tubes are the problem right now.
I checked voltages on the power and preamp tubes and it appears to be reasonably what I'd expect to see on this style of amp, which is a bit similar to the Marshall split-channel JCM800's like the 2205 and 2210. Same number of tubes, same 3 gain stage with cathode follower design, etc.
When I probe the grids of the power tube with standby off, I do get sound coming through the speakers of the probe touching the grid. However, probing the grid of the phase inverter tube makes no sound - same for any other preamp tube. I was not able to find any burned traces or visually damaged components. I checked for continuity on every resistor and capacitor on the preamp board and I'm not finding any broken components or broken traces. I don't have the tools to verify if a capacitor is working within spec, but if signal goes through it to the other side I would expect to at least have *some* sound so I'll come around to fixing out of spec components once I can get the bare minimum solved here.
My next step was to look into the transformers. I followed the Trinity/Geofex guides online to check on these. Neither the Power or Output transformer seem to have anything wildly out of spec from my probing, but I'll admit I did not remove them from the amp to test. However I would think if the transformers were the problem, I wouldn't get any audio when probing the grids of the power tube - am I wrong?
In short my question is this - if I get sound from probing the grid of the power section, but no sound from the grid of the PI tube, should I still be chasing the transformers as potentially faulty? Or should I strictly be looking for a damaged line somewhere between the preamp/PI and the power section?
I can post pictures if necessary. I appreciate any insight on this. Thanks!
Edit: I also tried some basics - cleaning jacks, plugging directly into the FX return, patching the FX loop, connecting reverb lines together etc - no sound from any of those or combination of them
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