Check your heaters to be at 6.3vac and the value of the cathode resistor on a 63 AC30.
If you run it at 60 cycles and high voltage they have been known to overheat and melt their PTs (well even without 60cycles)
early ones had 82ohm cathode resistor in 63 changed to 47R which, with your frequency of ac and a high voltage can tip you into melted OT.
check you have 68R or 82ohm to be safe
JTM 45/100 build not as loud as original??????
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neikeel
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Ted B
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Re: JTM 45/100 build not as loud as original??????
Actually, the higher frequency (60Hz) isn't an issue. If anything, the shorter period (8.3ms vs 10ms) of 60Hz is easier on the PT and power supply.
The key is proper internal voltages, which can present issues when running older British amps on low voltage taps in the U.S. The Rk 50ohm value shouldn't present issues so long as the voltages are correct, which is why I use a 240V step-up on these shores. Even the RI AC30s have a 50ohm (2 X 100 in parallel) EL84 cathode resistance (320V B+). FWIW, EL84s just seem to sound best when cooking like bacon.
The key is proper internal voltages, which can present issues when running older British amps on low voltage taps in the U.S. The Rk 50ohm value shouldn't present issues so long as the voltages are correct, which is why I use a 240V step-up on these shores. Even the RI AC30s have a 50ohm (2 X 100 in parallel) EL84 cathode resistance (320V B+). FWIW, EL84s just seem to sound best when cooking like bacon.
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neikeel
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Re: JTM 45/100 build not as loud as original??????
That is good to know, must just be the higher ambient temperature in parts of the US that lead to so many melted PTs on your side of the Atlantic (oh and the poor ventilation in JMI AC30s and the preferred sound of roasting EL84s).Ted B wrote:Actually, the higher frequency (60Hz) isn't an issue. If anything, the shorter period (8.3ms vs 10ms) of 60Hz is easier on the PT and power supply.
The key is proper internal voltages, which can present issues when running older British amps on low voltage taps in the U.S. The Rk 50ohm value shouldn't present issues so long as the voltages are correct, which is why I use a 240V step-up on these shores. Even the RI AC30s have a 50ohm (2 X 100 in parallel) EL84 cathode resistance (320V B+). FWIW, EL84s just seem to sound best when cooking like bacon.
Neil
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Ted B
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Re: JTM 45/100 build not as loud as original??????
Actually, that brings up a good point. With any clone amp whose design is such that power tubes run hot and heat accumulation can be a problem, it's never a bad idea to *tastefully* install a small AC computer fan somewhere inside, just to keep air circulating around the power tubes if nothing else.
Some years ago, I bought a cathode biased AC100 (below) at a discount due to the obvious coring of the head box, whereby a large cooling fan was installed by some intrepid soul. At first I was repulsed by that and planned to undo it. Later, I came to my senses and decided that if I was ever going to play the amp, I'd be for the wiser to just leave the bloody thing as is. It works efficiently and quietly, but I'm just glad that I wasn't the one to do it!
Some years ago, I bought a cathode biased AC100 (below) at a discount due to the obvious coring of the head box, whereby a large cooling fan was installed by some intrepid soul. At first I was repulsed by that and planned to undo it. Later, I came to my senses and decided that if I was ever going to play the amp, I'd be for the wiser to just leave the bloody thing as is. It works efficiently and quietly, but I'm just glad that I wasn't the one to do it!