Sweet Linda came home today.

[Oldskoolfan]

Back to back in parallel, so anode to cathode on one end, anode to cathode on the other end.

Just to be clear, the diodes are paralleled across C6, cathode to anode?

 

[Gepetto]

Just to be clear, the diodes are paralleled across C6, cathode to anode?

Yes

 

[Oldskoolfan]

That 470uf, 100v cap seems...large as a replacement upgrade for C6, a 100uf, 6.3v cap.
What say ye? I have smaller.

Help!

 

[Gepetto]

I use 470uF/25V caps for that application

 

[Oldskoolfan]

these two caps are tied one to each rail and ground. They are not in any schematic and I'm wondering if a tech put these in to reduce/eliminate the "thump". They are .33uf, 100v caps. There is almost no thump on power on or off.

 

[Skratch]

Those are installed from the factory on later Series 1 400's

 

[Skratch]

Also they used ferrite beads

 

[Oldskoolfan]

Also they used ferrite beads

This one got the caps but no beads.

 

[Gepetto]

View attachment 86825 these two caps are tied one to each rail and ground. They are not in any schematic and I'm wondering if a tech put these in to reduce/eliminate the "thump". They are .33uf, 100v caps. There is almost no thump on power on or off.

They have zero to do with thump, they are decoupling to counteract the inductance of the power supply wires leading to these distant rail points.

 

[Gepetto]

This one got the caps but no beads.

Situational. Counteracts the paralleled base connection which can lead to high frequency oscillations. These aren't on earlier amps, suspect this was discovered and the practice started. It is not the best way to deal with it but this is easy.