BF Bassman Low Volume on Bass channel

[dpm309]

Have a Blackface Bassman (AB165) on the bench that needs a tune up and 3-prong plug. Customer was getting shocked from it. The bass channel is not as loud as the normal channel and is very muddy sounding. Replaced the power cord, checked the caps, tubes, and voltages. Voltages are in line so I replaced V1 and 2 with new JJs without any difference in volume or tone on the bass channel. The normal channel sounds great. Someone had replaced the caps in the tone stack of the bass channel (all 0.1uf) with 2 AEROVOX (0.1uf) and 1 orange cap 0.1uf (this one to the deep switch). Am reading about 0.18uf on the AEROVOX caps even though they are marked 0.1 so I don't know if this would cause the issue. The other mod made to this amp was the resistor across the hum balance pot with a 22k instead of a 15k. Going to replace both of the AEROVOX caps with orange drops along with the 250pf ceramic cap to see if that improves the tone and volume. Is there anything else I should be looking at? All of the components associated with the bass channel check out with no open resistors or caps. I have attached photos showing the past mods.

[shooter]

anything else I should be looking at?

the schematic I'm looking at has a .01 "smoothing" cap on the plate R for V1a of the bass channel.  makes sense for a bass channel, but could be muddying up the signal    easy enough to lift one side n see

[sluckey]

That amp is a bass amp. The bass channel will sound muddy if trying to play a guitar through it.

[dpm309]

Shooter, I will give that a try. Sluckey - my bass player had one of these way back and I used to play guitar through it at times. I remember the bass channel being darker but not muddy sounding and dull. I don't remember if it was a silver or black face.

[shooter]

https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_ab165.pdf
looking at the TS, the plate .01 looks like it wasn't meant for any screaming guitar, maybe swampy/bluesy 

[NewYorker]

I don't comment here often, but here goes ...

When you tested the AEROVOX cap's, did you disconnect them from the circuit?  I'm wondering if your cap-tester may be seeing them as if they are in parallel and therefore measuring something more like .2 mF.

Do the Bass and Treble controls on the Bass Channel have any effect?  Do they seem to do what they are supposed to do, muddy sound notwithstanding?

Also, given that the AEROVOX cap's are not original, I would make sure that they are fully and correctly connected, and that there aren't any stray leads touching something they shouldn't touch, like ground.

Ed

[dpm309]

Yes, I did disconnect the AEROVOX caps before measuring them and there are no stray leads. As far as the tone controls, the bass control does not seem to do much. The treble control works as it should. I am going to replace both AEROVOX caps with orange drops as long as I have the amp opened up. Might also try replacing the bass control.

[Willabe]

Customer was getting shocked from it. The bass channel is not as loud as the normal channel and is very muddy sounding.

 

The K bypass caps look to be original? Are the B+ filter caps original too?

They might be part of the problem?

[dpm309]

The filter caps are not the originals so they were replaced some time ago but look good with no bulges or leaks. The normal channel sounds great with virtually no noise. I will change out the K caps along with the tone caps for the bass channel to see if that helps.