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Post subject: '59 Bassman Reissue, Low Volume
Posted: Mon Aug 16, 2010 1:34 pm
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Hi,
I have a bassman reissue, and it is outputting only a tiny bit of volume. I found that there were two blown resistors for the power tubes, so i replaced them, and I even replaced those power tubes which were damaged after the resistors blew. I had the three pre-amp tubes checked, and they seemed to draw the right amount of power. Despite all this, I am still having incredibly low volume, even at the highest volume settings. Any suggestions, or ideas on this problem?
Thanks,
Saul


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Posted: Mon Aug 16, 2010 3:44 pm
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First of all the resistors probably did not cause the power tubes to go bad! It is usually the other way around! A bad power tube can blow fuses and frie other components! If you have some bad power tubes, it is likely time to change the preamp tubes also, especially the PI tube! As a good rule of thumb change the PI tube along with a power tube change!

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Posted: Mon Aug 16, 2010 8:12 pm
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Welcome to the forum, Saul ! Just wondering which resistors failed ? How is the idle bias on the new power tubes ? Apologize for all the questions, but can you do voltage tests or would you have take it to a tech for that ? Art

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Posted: Tue Aug 17, 2010 3:59 am
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A couple more Q's to ponder & get ulcers over, sorry :cry:

Which two resistors popped? See link. Was it the screen resistors (R32 & 33)? Or the grid stoppers (R44 & 45)? There's a chance that if one pair popped, the other pair may have popped or gone WAY out of tolerance. Both pairs of resistors are there to act as sort of "fuses" in case of a runaway power tube (screen resistors) and/or amp instabilities (like parasitic oscillations)---the grid stoppers.

Check both sets for resistance values are within tolerances. If these resistors are on circuit boards (I haven't worked on a RI Bassman), check the board for burnt tracings.

Also, if a resistor pops sometimes the power tube first arc across the pins. This can leave a carbon "tracing." The tracings are hard to see on black or brown sockets. But, unless they are cleaned and removed, you may never get the amp to work properly.

Last. Check the fuses on the circuit board (see layout diagram at bottom of link).

Anyhow, good luck on your amp.


http://support.fender.com/schematics/gu ... ematic.pdf


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