Flabby Bruno

txbluesboy · Post by **txbluesboy** » Tue Jan 04, 2011 3:42 pm

A friend of mine brought me his Bruno "Tweedy Pie"
by for me to look at. It appears to be a Tweed Bassman
circuit with a footswitchable added gain stage. It has
a real flabby bass on the low E string. I thought maybe
it just needed a recap, did that, but no help. Anyone have
any experience with these amps?

Cliff Schecht · Post by **Cliff Schecht** » Tue Jan 04, 2011 4:19 pm

If it's really close to the Tweed Bassman than it might be too flabby. A lot of people add extra capacitance after the rectifier and on the screens to cut down on noise and tighten up the bass. I noticed my 5F6A clone gets flabby bass too at full-on distortion. This really depends on your EQ settings too but those only change up the sound so much.

txbluesboy · Post by **txbluesboy** » Tue Jan 04, 2011 4:23 pm

This is without even using the OD stage. You have to turn the bass pot all the way down,even then it seems flabby.

vibratoking · Post by **vibratoking** » Tue Jan 04, 2011 4:53 pm

Just a sanity check. Are you sure it's not the speaker? I have cured lot's of flabby bass by replacing poor speakers.

txbluesboy · Post by **txbluesboy** » Tue Jan 04, 2011 5:24 pm

vibratoking wrote:Just a sanity check. Are you sure it's not the speaker? I have cured lot's of flabby bass by replacing poor speakers.

Thanks, thats the first thing I ruled out before doing the recap however.

Super_Reverb · Post by **Super_Reverb** » Wed Jan 05, 2011 5:19 am

I'd suggest checking the B+ voltage to the output stage. Using Si rectifiers or a rectifier tube with lower series R will boost B+ and tighten up bass.

I had a similar issue in a vintage Fender when using large cathose bypass caps in preamp gain stages or coupling caps that are too large.

Reproducing bass frequencies requires a lot of energy from P/S and limiting bass response can tighten up bass.

rob

txbluesboy · Post by **txbluesboy** » Thu Jan 06, 2011 5:07 pm

OK, I just noticed the 5F6a circuit uses a12AY7 in V1. This amp has a 12AX7.
I don't have an AY but substituted an AT and that helped a lot. What do you
tweed Bassman guys usually run in V1?

FUCHSAUDIO · Post by **FUCHSAUDIO** » Fri Jan 07, 2011 12:30 am

You could cut back the cathode caps (if TB uses 22 like Fender, go to 10 or 4.7), which will clean things up a bunch too. Check the pi input and output caps, if he diddled with the values it can cause LF instability too and cause flab.

Tube Amp Archive

Flabby Bruno

Flabby Bruno

Re: Flabby Bruno

Re: Flabby Bruno

Re: Flabby Bruno

Re: Flabby Bruno

Re: Flabby Bruno

Re: Flabby Bruno

Re: Flabby Bruno