Harmony H306a low output volume

[davohilts]

Plenty of output tube gain and voltage. You said you checked with different speakers. Have you checked speaker wiring/cable? Not shown in the schematic, but does this amp have external and internal speaker jacks and maybe you're plugged into the wrong one? It seems to me the problem is right there at the output- maybe a bad OT.

I will verify that the wires coming off the OT are properly connected and soldered, there are no jacks, just the 8 ohm load wiring to the speaker. My fear was a bad OT but maybe it is a bad ground or wire connection.
I will check out and report back.
Thanks for your advice!
Dave

[The Dude]

Apologies! Just looked at your numbers again. I was looking at the amount of gain produced by the output tubes and missed that the input on the grids is pretty low level. The numbers you posted actually look pretty reasonable with that in mind. Is there a setting on your phone that will get you more output?

[davohilts]

Apologies! Just looked at your numbers again. I was looking at the amount of gain produced by the output tubes and missed that the input on the grids is pretty low level. The numbers you posted actually look pretty reasonable with that in mind. Is there a setting on your phone that will get you more output?

yes, I can set the output of the phone to be a max of .244 VAC
the numbers change then.
voltage across the dummy load is now 8.1 VAC
Grid V3 = 1.44 Plate V3= 174
Grid V4 = 1.86 Plate V4= 173

[The Dude]

IMO, with 174VAC on the plates, the OT secondary should be substantially higher. I would turn off the amp, discharge caps, and meter the OT primary for resistance. Center tap to either side should be approximately the same.

[davohilts]

IMO, with 174VAC on the plates, the OT secondary should be substantially higher. I would turn off the amp, discharge caps, and meter the OT primary for resistance. Center tap to either side should be approximately the same.

the OT seems good to me but I could be wrong.
putting an ohm meter from center tap of primary to one side gives me 214 ohms, 228 on the other side and 2.6 ohms across the secondary

I must be missing something, maybe have something wired wrong. I'm gonna carefully go back over the circuit and verify that I followed the schematic

sigh....

[g1]

What I said about the OT wiring was my mistake, it is shown wired correctly.

[52 Bill]

Do you have another output transformer to swap in as a test?

[pdf64]

'voltage across the dummy load is now 8.1 VAC'
Can you take a feed to a speaker to check when it begins to get overdriven?
Via a 1k resistor to keep the volume reasonable.

[g1]

I'm a little surprised to see the screen voltage so low compared to the plate. Is R26 checking out as 10K ?
schematic with parts list here: HARMONY H306A SCH Service Manual free download, schematics, eeprom, repair info for electronics

[Randall]

"I'm not sure what the heck they are showing on the schematic but I grounded the high voltage B+ center tap to the same lug I grounded the 3 wire power cord."

I wish we could get this B+ understanding ironed out. Connections A and B are a convention that is not uncommon in schematics. Referring to connection B as B+ is a potentially dangerous affair. Obviously, you cannot ground your B+ high voltage without fireworks.