Looks like it's sorted - been on for a couple of days without problems. The quiescent current in the other amp was 60mA on the positive rail - and that includes the current drawn by the speaker protection circuit and relay. This seems low to me, but I've set it to the same.
it is a bit on the low side.
But unless you want the last 0.001% of distortion reduction, its fine.
We used to bias bipolars to between 5mA and 20mA..FETS a bit more.
Shouldn't need relays though. Bad design that.
Not really any other way in those days - the relay drops out if there is a large DC offset on the output. Also prevents witch on thump.
It appears the original blow out was caused by shorting the output.
'witch' on thump you can eradicate by careful design*.
And DC offset on the output is a sign that the amp is borked anyway.
Quite. And 50 volts of DC will quickly 'bork' a moving coil speaker. Hence the speaker protection circuitry. Speakers cost more to repair than the odd output transistor.
In my experience, DC coupled SS power amps are a PITA. Unless you change every semicon you're gonna hit trouble. Leastways, that's what I always needed to do. You change what you're convinced is screwed, switch it on, bang. ditto ditto Change the lot, usually ok. Testing PN junctions with an AVO or testing forward volts drop got nowhere. I'm going back a year or two tho but (40 odd).
We used to be knee deep in those things but rarely did I use one. Mostly used bench psu's.
They're certainly not cheap. Scuse my previous nick, sock trouble ;)
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