Beltone AP-50: Last of the 60Hz Hum

[garytoosweet]

So you have a Cathodyne/split-load/Concertina phase inverter (V2) followed by separate gain stages (V3a/b) for inverted and non-inverted signals.
As V3 is not wired as differential amp (no tail resistor), your amp differs from the Danelectro circuit.

Thank you I think I've got my head around it now. I made an error due to not being familiar with Concertina PI and was unknowingly thrown off by the odd layout of the gain stage post PI pre Power. Didn't expect to learn so much with this old Teisco.

I am back looking at the hum which now ranges from about 10mV-100mV (volume control 0-Max).

When I pull V1 it drops down to a 10mV not effected by the volume control.

It seems like 10mV is the baseline 'hum' and the rest is being picked up by a sensitive stage/tube in V1.

I moved the amp off the bench and into another room and plugged connected it to the stock speaker cabinet. I found that now with the amp operating at full power the signal to noise ratio was quite acceptable, and the hum wasn't really noticeable in normal playing (i.e. not on the bench looking at everything under a microscope).

When I get more 6AU6, I will try rolling some tubes in V1 to see if I can find a particularly quiet one, but I am happy with where the amp is at.

[garytoosweet]

ADMIN/MOD: Can someone with permission please delete the schematic in the first post? It has an error and would be better off not floating around the net. I didn't realize there was a time limit on editing posts. I tried to find an admin to PM but wasn't able to.

Thank you!!!

[g1]

ADMIN/MOD: Can someone with permission please delete the schematic in the first post? It has an error and would be better off not floating around the net. I didn't realize there was a time limit on editing posts. I tried to find an admin to PM but wasn't able to.

Thank you!!!

That will kind of make a lot of the thread confusing. Can you at least tack on a corrected version at the end? Maybe an admin could add an edit to the first post to the effect of 'see post # xxx for corrected schematic'.

[garytoosweet]

That will kind of make a lot of the thread confusing. Can you at least tack on a corrected version at the end? Maybe an admin could add an edit to the first post to the effect of 'see post # xxx for corrected schematic'.

Yes the update schematic is attached here.