Hahahahahahahaahahaha
Yeah, compared to the other two nominees, I'd just get a participation trophy.
, maybe related to the old 2-prong power cord. Scared me enough to walk away until I could get inside the amp. Excellent! Very glad this could be helpful! Let us know how it goes.Hey, thanks for all the useful info on the Jet up to now!
~15 years ago, I'd picked up an Ampeg J-12-D for ~$100, intending it as a long-term project amp (with only basic soldering skills!). Cosmetically the amp's in good shape, but with some static/"whooshing" after a few minutes of being played. Also incidentally got a minor buzz by touching the strings of my guitar
Bought replacement tubes from Fliptops, including a pair of 6BK11's and 7591's, and then life intervened for >10 years, and it suddenly turned into a VERY long-term project.
Finally getting back to it now, and the above posts are really useful as I (hopefully) rehab this thing.
My soldering skills are now up to snuff, and some good projects under my belt, but this'll be the first amp project. Appreciate all the good info here as I (carefully) start checking this thing out.
We're attempting to fix a J12D that has a dead tremolo. Has anyone noticed that some the voltages and resistance values shown on the schematic don't relate to the actual product? We're seeing that the plate resistor on V2 input stage on pin #10 is actually 270K, not 120K, and the plate voltage is actually 47VDC, not 150V. Also, there is not a separate 1K resistor in series with the cathode off pin #4. The photos posted here seem to confirm the resistance changes, so this isn't a one-off. Anyway, the tremolo on this unit is non-functional. We can get a few millivolts of oscillator output on the plate of V1, which changes frequency with the pot. The plate voltage is constant at 49V with the switch closed, and 350V with it open. The tubes tests fine, and we've swapped them, with no change. Resistor values are within spec, and we've changed all the .05uF tuning & coupling caps and the 25uF cathode bypass cap. We're obviously missing something.
Yup, we verified via the datasheets. Both tubes were 6K11s. Owner couldn't remember if the tremolo was ever functional with those tubes, which had been installed many years ago. The low mu first section also reduces the overall gain of the preamp. We just obtained a 6AC10 (gain of 62 for all 3 sections) to see if it would function as an oscillator--it did not-BUT, whn installed in the V2 position (Preamp/Driver), the gain increased substantially, as expected. Here's the surprising part.....if we remove V1, the gain drops. This doesn't happen when V2 is also a 6BK11. Appears these tubes are symbiotic. We're going to obtain a second 6AC10 and try them together. All of the 6C10's we've found are approaching 100 bucks, and are just too expensive for this test.
