FDP Forum / Low output on Fender '71 Bandmaster (barely any volume until 4)/ 9 messages in thread.
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| jazzgeetar Metrowest Boston, MA |
I have a 1971 Fender Bandmaster and it's not sounding like it's putting out the output it should. Specifically, I'm not getting much (if any) volume until I get to close to 4 on the volume knob. Is this normal? I'm assuming it's not normal but am trying to make sure. Maybe I should get it checked out by a tech as maybe its the power tubes or a transformer... |
| Mudcloth Elgin, Tx. USA |
Do you get the normal amount of volume from 4-10?<br /> You might trying spraying the pot with deoxit or a similar cleaner first. Swapping out the pot would be the next step, for me. Sometimes the pot goes bad and needs to be replaced. |
| amphead4 Cincinnati, USA |
If max volume is low so it's obvious that it's not a pot taper symptom, troubleshooting steps can start with tube substitution followed by pulling the chassis and comparing all the DC voltages to the schematic. <br /> <br /> Are both channels low? Then concentrate on the phase inverter on towards the speaker. <br /> <br /> I wouldn't suspect a transformer right away. Start with the low cost and easy to replace items first. <br /> <br /> How long since the last cap job? Low output can be caused by weak tubes, low voltages, drifted resistors, dirty tube sockets and on and on. |
| jazzgeetar Metrowest Boston, MA |
Thanks guys. Both channels are low like this. Maybe I'll check the PI tube and bring it in to a tech. The power tubes look to be very old, they're Fender labeled. I bought this amp not too long ago, so I don't know all its history but I believe it has been recapped...but I think I'll just bring it in to a tech because at the very least I think it could use new power tubes and make sure they're biased right. |
| Peegoo Contributing Member ********** ********** That chicken is WRONG, baby. |
Good call! |
| picturevalve Wales. U.K. |
Check the cathode bypass caps on the first and second stages. |
| L.H.B. Contributing Member *** the joisey flats welcome to the zoo... |
are the bass and mid controls turned down? |
| jazzgeetar Metrowest Boston, MA |
Just updating this thread...<br /> <br /> I took the amp to a tech. What he found was the wrong screen resistors installed and replaced both of those resistors. He replaced leaky caps in the vibrato circuit. Checked the tubes (which seem good) and adjusted the bias.<br /> <br /> As far as the volume knob thing, he didn't find anything wrong with the circuit or the output (once it was properly biased) and said the no volume until 3 on the volume knob is probably a result of the taper of the original volume pots. He found it to output close to 40 watts and said some of these old pots varied.<br /> <br /> So, I'm going to live with the current taper of the volume knobs rather than replace them. I guess it was more of a mental thing because output seems to be ok. |
| Hammond101 Contributing Member * So. Cal. USA |
Jazz,<br /> <br /> I've had several Bandmasters over the years. I found the normal, non-vibrato channel to be much gainier and sound better with six string guitar.<br /> <br /> That vibrato circuit kills a little sizzle in that channel. Sucks if you like to use the vib. but ya just turn the volume knob a bit more.<br /> <br /> If I remember the BF AB763 Bandmasters had audio taper pots and the later versions linier.<br /> <br /> |
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