Fender Bassman help?

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babyhead

babyhead

Well-known member
Joined
Jun 12, 2004
Messages
476
Location
Loas Angeles
Hey All!

I have an old Bassman that I have had with me for years that I am finally getting around to working order. In this schematic:

http://www.ampwares.com/ffg/schem/bassman_aa864_schem.gif

the diode between the center tap of the power tranfs and the bias pot is very sensitive to any shock and needs to be replaced. What diode rating do I need for this???

Thanks!
 
Hi Babyhead,

It is very low voltage in this point, (around 50 volts) so you can use any 1N-400X diode, for example 1N-4002 are ok.

Replace also the 25uF 50 volt capacitor next to the diode. (you can use 50uF 100 volt, they are very small to day)

Watch up with the polarity, we have negative voltage in this point, so the diode "ring mark" to AC side and capacitor +/positive to ground.

--Bo
 
I've never seen a shock sensitive diode, so if the problem persits after replacement, the next place I would look would be the pot itself.
 
It turns out it was loose! I replaced it anyway considering its age and my abundance of diodes... also the cap was changed to an FC 47uf/63v. Finding more loose shite as I go. This thing does sound gooood.

Thanks again!
 
While you're in there, check the tube sockets. I've seen silverface Fenders in which some connections to the sockets were never soldered--no lie! QC slipped after CBS took them over.
 
One loose resistor on one of the power tube sockets... Now I'm good to go!

Very spongy, quiet, and super vint!

Thanks All!
 
> Fenders in which some connections to the sockets were never soldered--no lie!

Bogen had the same workers and inspectors on their last tube amps. In motor-driving duty, when the screen not-soldered joint finally let go, the output transformer caught fire and stank-up the whole floor.
 

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