Compared my amp to a Fuchs bassman mod today

[Bob-I]

where does the 0.0022 go?

Tommy

The OD exit. It's the coupler between OD1 and OD2

[Tdale]

Hmm, I don't have a 0.0022 there. I have a 0.01 there, as shown in the hybrid-a schem.

Should I change it, or are we talking about a different amp here?

Tommy

[Tdale]

Also.. I see there are two bias pots on the schematic. I've been thinking about that too, but haven't decided yet.

Is one pot usually enough, or are tubes so different that two pots is better?

Tommy

[dogears]

Different amp.... The HRM amps use a .0022

Hmm, I don't have a 0.0022 there. I have a 0.01 there, as shown in the hybrid-a schem.

Should I change it, or are we talking about a different amp here?

Tommy

[HiGain]

Bob, Your preamp filter caps are on the big side.

If you can depart in the PI, reduce the 24K resistor to 10K or 12K.

Jake

[tonelab2]

Bob, Your preamp filter caps are on the big side.

If you can depart in the PI, reduce the 24K resistor to 10K or 12K.

Jake

Well spotted, I'd swap out the 47uf's and the 33uf before anything else.

[dogears]

While you are at it, run the Dumble string in parallel, from the screen cap. Not in series as you have it. Move the reverb cap to a parallel screen feed as well, with a big dropping resistor to isolate it.

[Bob-I]

Well damn... what was I thinking when I put them big mothers in there.... I haven't even opened up the cap pan.

Ok, I know.. I had them laying around. Thx guys for spotting this. The changes will have to wait though, I'm at the airport heading to Japan until Friday. Maybe I can get by the Akihabra Electric town in Tokyo and pick up some caps cheep. Anyone need anything while I'm there?

[tonelab2]

Restored a '63 concert once that had been converted to a pro reverb.
Rebuilt the main board back to stock with NOS original parts. The amp sound shocking, too much bottom end. Couldn't use bass control at all , ran the treble dimed but still too much bass. Tried changing the 6k8 resistor
on the bass pot to a much lower value to shift the knee toward the mids ect. Couldn't fix it until I changed the filter supply back to stock values.
sounded great then.

[Bob-I]

Restored a '63 concert once that had been converted to a pro reverb.
Rebuilt the main board back to stock with NOS original parts. The amp sound shocking, too much bottom end. Couldn't use bass control at all , ran the treble dimed but still too much bass. Tried changing the 6k8 resistor
on the bass pot to a much lower value to shift the knee toward the mids ect. Couldn't fix it until I changed the filter supply back to stock values.
sounded great then.

Excellent, I'm confident that this is the issue. I completley forgot that I used filters that were laying around. I told myself at the time if it doesn't sound right that's the first thing I'd change. I can't remember... what was I talking about?

[swt]

Hey Bob...Can you tell me the difference in tone between the clean fender and the dumble?. thanks

[Bob-I]

Hey Bob...Can you tell me the difference in tone between the clean fender and the dumble?. thanks

The Fender clean is more scooped in the mids, the Dumble is fatter and more midrangy.

[skyboltone]

Excellent, I'm confident that this is the issue. I completley forgot that I used filters that were laying around. I told myself at the time if it doesn't sound right that's the first thing I'd change. I can't remember... what was I talking about?

Hey Bob, if you haven't ripped them out already, just for giggles try the hi-fi trick and bypass them. Just lay a much smaller level parallel to the oversized ones and see what it does to the tone.

I've never done it but have read it's a common trick amongst the golden ear crowd.

dan

[HiGain]

Hey Bob, if you haven't ripped them out already, just for giggles try the hi-fi trick and bypass them. Just lay a much smaller level parallel to the oversized ones and see what it does to the tone.

Do you mean a small uF film cap in parallel with the big electros? I've done this a little- used some 1uf solen fast caps in parallel with PS caps. It didn't reduce bass. I was hoping it would clear things up a little... but I didn't hear a difference in that case...

Jake

[skyboltone]

That's what I meant. I haven't tried it personally but have heard rumors to the effect that it would clean up flabby bass. It's good to clear that one up. Thanks

Dan