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Bassman Master Volume Mod

5/30/2000 4:54 AM
Bassman Master Volume Mod
I have a silverface Bassman 135 with the master volume. For a clean sound it's as good as most of my blackface amps. I'd like to push it to see if it overdrives nicely but when you turn it up past 4 you run the risk of taking out the neighborhood. This is a really LOUD amp!  
The master volume looks like a great idea on paper but the problem is it doesn't seem to do anything. At least not at the volumes I've tried it at.  
Has anyone performed any mods on this type of master volume? Does anyone know the theory behind it's operation? I'd like to see if I can get it to actually work and avoid the overdrive pedals.  
5/30/2000 6:30 AM
Steve Ahola

    That Bassman 135 would be a very good platform for a 100W D'Clone, but I digress... ;)  
    I believe that a post-PI MV would work great in your amp. (Although the drawing shows four 0.1uF coupling caps, you might want to use four 0.047uF's instead.)  
    I assume that you are using this amp for guitar and it has been recommended that you change these values to their BF equivalent:  
PI grid-to-cathode resistors: 1M instead of 330k  
PI resistors: 82k/100k instead of 47k a "normal" bias supply  
    I like the 0.022uF mid cap used in the BFSR and a few other BF amps (instead of the more common 0.047uF).  
Steve Ahola  
P.S. Do you like the ultralinear OT? If not you could rewire it as regular OT with a choke or 1k resistor in the PS between the plates and the screens. (I'm not sure what wattage you would need to use for a 100W amp.)
5/30/2000 10:05 PM

Thanks for the info. I'm gonna tinker around with it a bit. I finished converting my AB165 Bassman to AA864 specs about a week ago. It sounds amazing. I haven't plugged into anything else since. Guess I've got the bug now.  
Ultralinear who? *laughs* Sorry, I don't know that much about these things. All I can say is that it sounds good. I just want to make the master volume work. :)

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