silverface twin bias arrangement

[jim]

A kid brought me this trainwreck of an amp to fix up for him.  Got it working.  Bias draws only about 20ma/5881 max. The two pairs are balanced.  I haven't seen this CBS bias arrangement in person until
now. Its a blend of fixed bias and cathode bias--you can see the bypass caps off to the side.  The amp is loud but I feel it could be louder.   It has a nice crunch at "10" but decent headroom otherwise.  My feeling is to leave it alone at this point for this kid since money is an issue. What do you think? Is 20ma OK for this arrangement? I feel it should be a little louder.  Jim

[sluckey]

That's the AC-568 chassis. You could replace those 150Ω cathode resistors with 1Ω resistors and see how much the current increases. But if the amp is loud enough for the kid I'd just leave it as is.

[PRR]

Raising the idle will not raise the maximum power.

A too-low idle may sound hoarse at very soft output. But the kid isn't lugging a friggin Twin to play soft. And the low-level gain loss does help take the edge off the system hiss between sets.

[jim]

True that.  There is very little noise at all.  It does sounds a tiny bit cold but its better for modern rock/metal.   Besides,  if you "goose the juice" weak stuff will show up.  I'll just write another estimate....Jim