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Hey ya'll,
I have a blockhead marshall clone up on the bench with an issue that's driving me kind of nuts. It has a plexi style input jack configuration, channel 1 is super quiet and functioning properly, input 1 of channel 2 works, but input 2 of channel 2 has excessive 60hz hum. There are 2.2uH inductors coming off the input jacks and I previously thought one of the inductors was shorted internally since when I put some pressure on it the hum disappeared. It was replaced but the problem persists. I'm starting to think it's a grounding issue since even touching the exterior of the chassis affects the hum. Unfortunately I do not have a schematic, nor does a schematic exist for this amp as far as I know. the grounding of the first channel is connected to the 2nd and then to chassis ground. Any tips on tracking this down? It's stupid even posting here because I can't imagine that the problem is more downstream than V1, but my perspective is becoming unclear on this one. Although I acknowledge 60hz is rarely a symptom of grounding issues.Thank you!
there is a single 250uf cathode bypass for both triodes! The first spot the hum is present on the scope is the plate of V1 which is going to a .022uf cap and then directly to the volume pot for channel 2. V2 and the phase inverter are pulled so I've localized it to V1
I have a blockhead marshall clone up on the bench with an issue that's driving me kind of nuts. It has a plexi style input jack configuration, channel 1 is super quiet and functioning properly, input 1 of channel 2 works, but input 2 of channel 2 has excessive 60hz hum. There are 2.2uH inductors coming off the input jacks and I previously thought one of the inductors was shorted internally since when I put some pressure on it the hum disappeared. It was replaced but the problem persists. I'm starting to think it's a grounding issue since even touching the exterior of the chassis affects the hum. Unfortunately I do not have a schematic, nor does a schematic exist for this amp as far as I know. the grounding of the first channel is connected to the 2nd and then to chassis ground. Any tips on tracking this down? It's stupid even posting here because I can't imagine that the problem is more downstream than V1, but my perspective is becoming unclear on this one. Although I acknowledge 60hz is rarely a symptom of grounding issues.Thank you!
there is a single 250uf cathode bypass for both triodes! The first spot the hum is present on the scope is the plate of V1 which is going to a .022uf cap and then directly to the volume pot for channel 2. V2 and the phase inverter are pulled so I've localized it to V1
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