My bandmates have two 1979 AC30 Dallas/Rose Morris era Top Boosts. One of them was recently going really low in volume, like ballpark of AC5. I have recapped power section and found out also one bad coupling cap (that may be the reason of the low output).
The tubes are slightly red-plating. They are JJ EL844 which are "lower wattage" versions of EL84. They test around 50% emission so they will be replaced soon...
My plate voltage is 345V measured at the tobe socket with amp working, so seems about right.
One of the 100ohm resistors on the power board was blown, I have replaced it for new 100ohm, but 5W (hope it's ok in this place to have that strong one(?) This is the big lime one on the shot below.
I'm getting 7,3V across the 47ohm cathode resistor.
What confuses me it's 5W 22k resistor (white on the photo below) which on schematics I found is 220k, so ten times more... I'm getting around 113V across it. Should I replace it for 220k? What is the function of this one in AC30s?
The tubes are slightly red-plating. They are JJ EL844 which are "lower wattage" versions of EL84. They test around 50% emission so they will be replaced soon...
My plate voltage is 345V measured at the tobe socket with amp working, so seems about right.
One of the 100ohm resistors on the power board was blown, I have replaced it for new 100ohm, but 5W (hope it's ok in this place to have that strong one(?) This is the big lime one on the shot below.
I'm getting 7,3V across the 47ohm cathode resistor.
What confuses me it's 5W 22k resistor (white on the photo below) which on schematics I found is 220k, so ten times more... I'm getting around 113V across it. Should I replace it for 220k? What is the function of this one in AC30s?
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