The idling current is meant to be set for 40mA (with the multimeter replacing fuse F2 and F3 for setting per channel). But I get a reading of 60mA on each channel. Twiddling the 200R trimmer makes no difference to the reading at all.
Nothing over-heating or any obvious nasties, and all the front panel lamps light up as they should, so hoping it's a simple fix.
What's been done:
All electrolytics replaced by Panasonic FM types. Signal coupling caps with a mix of polyster & poly-pros. All values the same except C5 which is 470uF as had that to hand. Could that increase have increased the current beyond adjustment range?
The four trimmers have been replaced by Bourns 3386F cermet types. The originals were larger open types, so had to solder longer legs to the wiper pins to make the Bourns ones fit. All checked for continuity & correct orientation. Wondering if these new pots might be to blame and I’ve chosen the wrong types? Resistances are 200R and 30K which appear to match the circuit diagram. Tempted to solder in the old ones again just to see.
All six PSU diodes have been replaced with OnSemi MBR40250G types as I thought the originals looked knackered originally (before I realised the discolouring was 40+ years worth of cigarette smoke - nice!).
The Amp:
The PSU:
Complete circuit diagram at link below (click on the download or magnify icon within Photobucket to get a better look, too big to paste here):
Any help or if I may have made any obvious gaffs please point them out.
Thanks folks.
- John
Last edited by quad2fan; Today at 12:12 PM.
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Amp revamp problems :/
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