Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plumcrazyfx on April 17, 2022, 09:52:15 am
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I'm doing some maintenance on a Traynor YBA-1 that never worked since I've owned it. It appears to have had something happen to it at one time that caused the big 10W shared screen resistor to heat up to the point that it melted one of the .1uf coupling caps next to it. So I did basic maintenance of replacing all the electrolytic caps, replacing the screen and dropping resistors, and installing a bias pot. When I was testing voltages I noticed I have voltage on each of the red wires of the power transformer as well as voltage on the connection to the standby switch through the two rectifier diodes.
I don't read any voltage on the other side of the bridge where it connects to the red wire of the output transformer, the filter cap, and one side of the choke. Is this likely a diode issue or can something connected to diodes be causing this behavior.
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Voltage on the STBY switch means the switch contacts are OPEN, maybe because the switch is in STBY mode or the switch has failed or lost it's ground wire connection. Whenever the STBY switch contacts are open there will be no B+ voltage on the + side of the bridge.
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Well, for one thing the Standby switch is physically rotated upside down so, there's that. The switch itself seems to work.
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Well, for one thing the Standby switch is physically rotated upside down so, there's that. The switch itself seems to work.
Doesn't matter if the switch is mounted vertically, horizontally, or even diagonally. Anytime you measure voltage on the switch you will not measure any B+.
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It was upside down so when I thought I was in "Play" it was still on "Standby" which explains the readings. Spun it 180 degrees and all works fine now. Thanks for the help and I'll remember that nugget the next time I get those reading.