Dobro amp 6107

[angelodp]

Max, on the position of the cap you mentioned, here is how I have it in the layout. Is that incorrect.

[maxkracht]

Sorta, but there probably isn't any harm to how it currently is, you are just adding more resistance to the field coil instead of adding more resistance to the choke. I would listen to the noise level as is, listen to the noise level with a jumper across the 1k resistor, and listen with the cap attached to the other side of the 1k resistor. Whatever sounds better is "correct".

The field coil is an electromagnet powering the speaker, but it is also acting as another choke, in case that makes it easier to understand. You can pretend like it's a power supply in an amp you are more familiar with, like your 5e3. It's exactly the same layout, but with a couple chokes instead of resistors. Put a resistor in series with the choke, you get more resistance and hopefully less hum, but also more voltage drop. So, tradeoffs.

[angelodp]

So I increased the cap at the juncture of choke output to the 1k R up to 22uf and now works with 5Z3 and hum reduced almost to nil. I am holding my breath. Could be that the 8uf that was there got damaged when the first choke blew. Back to normal on this amp is a relief.

[angelodp]

All done, back to the owner shortly, he is pleased.