I have a MI-4288-G theater tube amplifier that I am working on.
uses 2 5Z3s, 4 6L6s, and 2 6C5s.
Recapped the entire thing, and had to replace a few open ballast style resistors, probably where someone powered it up with bad lytics.
Anyway. It sounds fine, but the 6L6 at V-6, nearest to the rectifier starts to go cherry red. Sign of overcurrent.
So, i went through and checked the voltage drop across the cathode resistor. All 4 tubes share the same cathode network. 94ohm resistor, somewhere between 29.8v to 30v drop across the resistor when fully warmed up.
Also, when the amp is silent, you can hear some popping/crackling in the speaker when idle.
So i started checking resistors. most of them read a slightly bit high.
I checked all 4 grid resistors, R11, R12, R14, R15 are 47K ohms.
R11 reads 55K
R12 reads 55.1K
R14 reads 50.7K
R15 reads 58K
47ohm plate resistors R24, 25, 26, 27 read as follows:
R24 reads 48.1
R25 reads 41.4
R26 reads 40.7
R27 reads 41.7
Any ideas? some values might seem low, some might seem high. who knows.
Thanks.
uses 2 5Z3s, 4 6L6s, and 2 6C5s.
Recapped the entire thing, and had to replace a few open ballast style resistors, probably where someone powered it up with bad lytics.
Anyway. It sounds fine, but the 6L6 at V-6, nearest to the rectifier starts to go cherry red. Sign of overcurrent.
So, i went through and checked the voltage drop across the cathode resistor. All 4 tubes share the same cathode network. 94ohm resistor, somewhere between 29.8v to 30v drop across the resistor when fully warmed up.
Also, when the amp is silent, you can hear some popping/crackling in the speaker when idle.
So i started checking resistors. most of them read a slightly bit high.
I checked all 4 grid resistors, R11, R12, R14, R15 are 47K ohms.
R11 reads 55K
R12 reads 55.1K
R14 reads 50.7K
R15 reads 58K
47ohm plate resistors R24, 25, 26, 27 read as follows:
R24 reads 48.1
R25 reads 41.4
R26 reads 40.7
R27 reads 41.7
Any ideas? some values might seem low, some might seem high. who knows.
Thanks.