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In the Forum: Melquiades Amplifier
In the Thread: R22
Post Subject: Please check for shorts and mistakes before investing in another transformerPosted by JJ Triode on: 1/2/2022
Domidaw, you wrote:
The photo shows the capacitor c10. Its minus is connected to ground, its plus goes to the output transformer,
According to the schematic it is the grounded (minus) end of C10 that should connect to one side of the output transformer's secondary winding. The purpose of this connection is simply to establish a ground reference for the speaker circuit. This side of the output secondary should also connect to one speaker terminal, probably the black one; the other side of the output secondary should connect only to the red output terminal, nothing else. The output transformer primary winding is of course in series with the output tube plate.
The plus end of C10 should connect to R22 and to the output transformer primary winding (perhaps this is what you meant) with the other end of the output primary going to the output tube plate. However, between the plus end of C10 and the output primary you should have that small resistor R21 whose voltage drop enables you to calculate the true current through the output tube. I urge you to measure this while the amplifier is running, to see where the current is going.
Maybe I am misunderstanding how that capacitor is supposed to be connected, but in your photo I see plus signs "+" on the opposite end from where you have R22 connected. Anyway, other tests you might do include the following:
1. With the amplifier turned off and all capacitors drained of energy, measure the DC resistance (after all transients go down) from the connection point of R22 and C10 to ground. It should be nearly infinite, but I still suspect a short here.
2. With the output tube out of the socket, measure the DC resistance from the tube's plate to cathode, to make sure is in not shorted internally.
3. With the amplifier off and all capacitors drained, and the output tube out of the socket, measure the DC resistance between the socket cathode and plate pins, to make sure there is no short at the socket or through its connections to other parts.
I emphasize again that there has to be some path to ground for the excess current through R22 when the amplifier is on, and that path needs to be identified. There is no way a 20% excess voltage at the power supply should be causing a 300% excess current through the output tube.
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