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Hello MEF Community,
I have a J-12D (6BK11's & 7591's. The 6BK11's are replaced with NOS 6K11/6Q11's) that seems to play fine except for the lack of the trem effect. I have jumpered over every coupling & cathode cap with the same sizes (one at a time) and none made a difference. I tried to test the resistors (in circuit) in the V1 trem circuit, and all seemed ok. The combo switch & trem control checks out ok.
The schematic on the inside of the back cover shows 175v on one plate (pin 10) of V1 and 2v on the respective cathode (pin4). I measured these pins and got very high voltage readings, 385v & 11v.
Can anyone give me an idea where to start to look for the problem? Could one of the large resistors or a filter cap be the cause? There could be some hum with the volume above 5 or so. The PA cathode cap, 20uf X 25v, measures close to spec.
This amp has had nothing changed or replaced except the pre-amp tubes. I still have one of the original 6BK11's and I tried that in V1 also with no difference.
Any ideas would be appreciated.
The J-12D drawing is at Schematic Heaven.
Scott
I have a J-12D (6BK11's & 7591's. The 6BK11's are replaced with NOS 6K11/6Q11's) that seems to play fine except for the lack of the trem effect. I have jumpered over every coupling & cathode cap with the same sizes (one at a time) and none made a difference. I tried to test the resistors (in circuit) in the V1 trem circuit, and all seemed ok. The combo switch & trem control checks out ok.
The schematic on the inside of the back cover shows 175v on one plate (pin 10) of V1 and 2v on the respective cathode (pin4). I measured these pins and got very high voltage readings, 385v & 11v.
Can anyone give me an idea where to start to look for the problem? Could one of the large resistors or a filter cap be the cause? There could be some hum with the volume above 5 or so. The PA cathode cap, 20uf X 25v, measures close to spec.
This amp has had nothing changed or replaced except the pre-amp tubes. I still have one of the original 6BK11's and I tried that in V1 also with no difference.
Any ideas would be appreciated.
The J-12D drawing is at Schematic Heaven.
Scott
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