112 RD65 bias issue after service
Hi all.
I have an RD2165 GD2 on the bench at the moment. I’ve just done a full recap (all electrolytics), and replaced the driver transistors, but I now cannot seem to get any bias current.
I’ve been over the work I’ve done and can’t see any errors. What would cause voltages to appear correct, but no cathode current on output tubes? Thoughts?
I’m very comfortable with tube electronics, but solid state stuff is still an area I’m learning.
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2 years 1 monthI meant to come back and
I meant to come back and update.
Despite having been over and over my work, it turns out I had made an accidental solder bridge between two pads, it just happened to look factory, so it took me a long while to pick up the mistake. Does anyone have board layouts for these amps? The schematic is great for understanding the circuit, but a layout diagram would’ve had me solve this issue in 5 minutes, not 5 hours!
In any case, the amp is sounding better than ever. The new driver transistors are much more closely matched than the old ones, so the bias is almost exact between both output tubes. The noise floor is so low that I thought it still wasn’t working, until I played a chord.
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10 years 9 months
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So, I had a chance to
So, I had a chance to investigate further today. I have a short somewhere in the low voltage section. Being a 240V export amp, the low voltage supply is fused, and it’s just vaporising the fuses on power on.
So, maybe one of the driver transistors I used as replacements is bad? I can’t see any other solution really. I’ve been through the whole board looking for possible accidental solder bridges, or carbon shorts etc. and cleaned the whole board up with IPA and a tooth brush, but the problem persists.
So either, I applied too much heat with the iron, or one of the mounting screws isolating grommets didn’t do it’s job. That’s my thinking anyway.
Thoughts?