Potato Cakes
Well-known member
Hello, everyone,
A friend of mine has a silverface Bassman amp that he has used for a number of years but it goes to insane breakup past 3 on the volume dial of the normal channel. I was told that in years past you could turn up the volume quite a bit before it would start to distort, but after another friend borrowed it and then had it the tubes changed before returning it, that's apparently when the current situation came to be. It had been recently serviced by some other tech and he found bad power caps and output tubes but that did not fix it. I replaced the tubes in the normal section (the only part actually being used) with per schematic lower gain 12AX7's (7025) and a 12AT7 for the phase inverter and it still had the same issue. I did mess around with other tube combinations to get a little more headroom but the output was affected and my friend uses the amp volume to be heard in a live four piece rock band setting. For context, the other guitar player uses a Vox AC30 and doesn't not have this issue.
My first observation is that there seems to be too much low end as is one of the causes of the early break up. I plan on changing out the cathode bypass cap from the standard 1k5/25uF to 2k2-3k3/1uF on V1 and then go from there. I haven't opened it up yet. I am just planning this out to make sure I have the parts before surgery.
I would like to hear from anyone who has worked on a silverface Bassman amps and was able to achieve high headroom/output and what other values I should consider changing to get a louder, cleaner signal, at least to maybe 5 or 6 instead of under 3 on the volume dial.
Thanks!
Paul
A friend of mine has a silverface Bassman amp that he has used for a number of years but it goes to insane breakup past 3 on the volume dial of the normal channel. I was told that in years past you could turn up the volume quite a bit before it would start to distort, but after another friend borrowed it and then had it the tubes changed before returning it, that's apparently when the current situation came to be. It had been recently serviced by some other tech and he found bad power caps and output tubes but that did not fix it. I replaced the tubes in the normal section (the only part actually being used) with per schematic lower gain 12AX7's (7025) and a 12AT7 for the phase inverter and it still had the same issue. I did mess around with other tube combinations to get a little more headroom but the output was affected and my friend uses the amp volume to be heard in a live four piece rock band setting. For context, the other guitar player uses a Vox AC30 and doesn't not have this issue.
My first observation is that there seems to be too much low end as is one of the causes of the early break up. I plan on changing out the cathode bypass cap from the standard 1k5/25uF to 2k2-3k3/1uF on V1 and then go from there. I haven't opened it up yet. I am just planning this out to make sure I have the parts before surgery.
I would like to hear from anyone who has worked on a silverface Bassman amps and was able to achieve high headroom/output and what other values I should consider changing to get a louder, cleaner signal, at least to maybe 5 or 6 instead of under 3 on the volume dial.
Thanks!
Paul
