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I bought it a couple of months ago; when it arrived, it had a 100uf/450V cap at the rectifier output and a 20uf/450V tied to one leg of the rectifier's 5V heater supply ... the leg where the DC taken.
Schematic: http://www.schematicheaven.com/gibsonamps/ga30rv.pdf
I straightened out the caps, put in a known-good 6087/5Y3 in, and a new 6V6 cathode bypass cap. Turned it on for a few minutes and the bypass cap blew ... put it on the bench and, through a variac, I get 355VAC on each secondary and a whopping 425VDC out of the rectifier; 4.7VAC on the heaters. The schematic secondary is 320VAC and the expected rectifier output is 330VDC. The PT looks original; says 23-P on top. Have drawn the actual power supply and wiring is as the schematic. I've tried 3 different rectifiers; the one that shipped with the amp, the 6087/5Y3, and another known-good bench 5Y3.
At one point, the rectifier was glowing bright orange and the 6V6s glowing blue; ????????
This 5Y3 data sheet: http://www.tubebooks.org/tubedata/HB...t_1/5Y3-GT.PDF seems to suggest that chokes and capacitors at the filter input are mutually exclusive ... one or the other but not both ... the GA30 schematic has both ... as does the amp.
The NJ7P 5Y3 data here: NJ7P Tube Database Search indicates that at 350VAC, the expected output is 360VDC ... I have way more than that.
The 6.3V and 5V windings are ok; maybe this particular amp was late in the production cycle and got a bumped-up transformer but if a 5Y3 can live with 355VAC, I'd just as soon put a dropping resistor at its output but don't know how to calculate what value would yield about 330VDC. Even if the 5Y3 can survive the higher AC, it would mean that all the other taps on the DC rail are higher than design. If I'm stuck with the PT, I think it would be simpler to drop the rectifier's output than it would redesign the bias and all the rest of it.
Hum:
In either standby or on, the amp hums ... not volume dependent. The polarity switch is gone, 3-wire cord in, ground wire landed under a transformer bolt, and both HV and heater center taps grounded together at same point as filter caps. Schematic has odd way of shorting (?) the output at the power switch; anybody see anything wrong with running a wire to ground from the X/Y connections on the switch?
Thank you; John
Schematic: http://www.schematicheaven.com/gibsonamps/ga30rv.pdf
I straightened out the caps, put in a known-good 6087/5Y3 in, and a new 6V6 cathode bypass cap. Turned it on for a few minutes and the bypass cap blew ... put it on the bench and, through a variac, I get 355VAC on each secondary and a whopping 425VDC out of the rectifier; 4.7VAC on the heaters. The schematic secondary is 320VAC and the expected rectifier output is 330VDC. The PT looks original; says 23-P on top. Have drawn the actual power supply and wiring is as the schematic. I've tried 3 different rectifiers; the one that shipped with the amp, the 6087/5Y3, and another known-good bench 5Y3.
At one point, the rectifier was glowing bright orange and the 6V6s glowing blue; ????????
This 5Y3 data sheet: http://www.tubebooks.org/tubedata/HB...t_1/5Y3-GT.PDF seems to suggest that chokes and capacitors at the filter input are mutually exclusive ... one or the other but not both ... the GA30 schematic has both ... as does the amp.
The NJ7P 5Y3 data here: NJ7P Tube Database Search indicates that at 350VAC, the expected output is 360VDC ... I have way more than that.
The 6.3V and 5V windings are ok; maybe this particular amp was late in the production cycle and got a bumped-up transformer but if a 5Y3 can live with 355VAC, I'd just as soon put a dropping resistor at its output but don't know how to calculate what value would yield about 330VDC. Even if the 5Y3 can survive the higher AC, it would mean that all the other taps on the DC rail are higher than design. If I'm stuck with the PT, I think it would be simpler to drop the rectifier's output than it would redesign the bias and all the rest of it.
Hum:
In either standby or on, the amp hums ... not volume dependent. The polarity switch is gone, 3-wire cord in, ground wire landed under a transformer bolt, and both HV and heater center taps grounded together at same point as filter caps. Schematic has odd way of shorting (?) the output at the power switch; anybody see anything wrong with running a wire to ground from the X/Y connections on the switch?
Thank you; John
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