Fender Blues Jr Weak Reverb

[misterc57]

The installed tank is an Accutronics 8EB2C1B

I have a FBJ tweed, whose reverb does not kick in until the pot is past 7. I tried a couple of different tanks I had (none were for a FBJ) and they all behaved like the installed tank.

I tried a FBJ at a local store and it's reverb behaves as desired across the range of the pot. That tank is a Belton BS3EB2C1B.

I am reading that these two different models are both used in FBJ but the Belton's perform better than the Accutronics.

I cannot find specs or anyone selling the Belton BS3EB2C1B.

Also I know that the comparison amp at the store is not exactly the same amp. The one I am looking at has a fat switch and mini pot for the fat switch, the one at the store has no mini pot.

I am also reading that there have been mods to address FBJ reverb issues such as a pot taper change.

Too much to consume and make sense of. What are your thoughts?

Thank you, Mark

[Mars Amp Repair]

It may be silly & obvious, but be certain you have the input & output cables connected properly . So unless it's really true these amps have weak reverb which I tend to doubt, I guess it's time to look into the reverb drive/regeneration circuit. It might be a good idea for starters to just replace the TL072. You could measure voltages on the IC to look for approx 0V on pins 4-7 and 1-3. If there is any appreciable offset from 0V, that could prove the IC is bad. Also, be certain there is supply voltage of +15V on pin8 and -15V on pin4.
From that point you'd be looking at signal path issues, eg: weak electrolytic coupling caps, etc. Though it does seem unlikely.
Glrn

[g1]

The installed tank is an Accutronics 8EB2C1B
mini pot for the fat switch, the one at the store has no mini pot.

A mod? If so, chances are there may be other mods or some mod that is affecting the reverb circuit.

[mozz]

If you swapped tanks and it's still the same, a swap to a Belton is not going to solve your problem. Since it is a blues jr, there are many mods to this and your problem lies with that mostly done incorrectly. See if that pot is jumpered underneath, then it would be a hacked mod. I am guess the tl072 also as was said.

[misterc57]

Turns out it was modded. That mini pot below the FAT switch is part of a "presence" mod and a lot of parts on the board looked replaced. I also did not see any op-amps on the board.

Should have taken a photo to post here but given all the mods, the owner took it back without further investigation.

Swapping the pan cables in/out helped to slightly improve the reverb depth. But still far from how it should be.

Thank you all!

[Jazz P Bass]

Here is a 'snip' of the reverb circuit with test voltages.