F-2B Muddy Channel

[rv_bass]

I was hoping some of the more tech savvy people here might have some thoughts.  Channel A on my F-2B sounds muddy compared to channel B (channel B is clean sounding).  Does anyone know what might cause this to happen?  I was thinking it might need a tube replacement.  I have a spare F-2B and both channels sound clean on that one.  Both F-2Bs are older blue versions with red knobs.  Thanks in advance!

[StephenR]

Have you tried swapping tubes from one of the channels that sounds clean? Probably a good place to start your troubleshooting.

[lbpesq]

I'd start by swapping the tube from channel A to B and vice versa, and see it the problem follows the tube.

Bill, tgo

[rv_bass]

Thanks, I’m a knucklehead and missed the obvious, I’ll try that tonight and report back.

[rv_bass]

Well, I switched the tubes between Channels A and B and Channel A was still muddy, and Channel B was clean with the tube from Channel A.  I also put the tubes from the first F-2B (the one with the muddy Channel A) into a second F-2b and switched the tubes between Channels A & B in the second F-2B, and both channels were clean regardless of tube used.   So, looks like I have a muddy Channel A in one of my F-2Bs.  I might bring it down to have an amp tech look at it and see if there is a way to get the channel sounding clean.

[David Houck]

For what it's worth, as my memory is somewhat less than reliable, I once had a similar problem.  One of the channels was sounding muddy, so I switched the tubes.  After the switch, the same channel was muddy; so I took it to a local tech.  He put new tubes in, and it was fine.

That was some time ago, and my memory is less than reliable.

[rv_bass]

Thanks, David.  I’ll brimg it down to a tech tomorrow and see how it goes. 

[lbpesq]

Let you tech know the F-2B schematic is readily available with a google search.

Bill, tgo

[mica]

The schematics are usually much closer than that - it's also pasted under the lid.

[rv_bass]

Thanks, Mica, I was just signing in to say the same thing

[lbpesq]

Oh, you guys are good!

Bill, tgo

[gtrguy]

For starters:
Exercise the pots. If the F2-B has contact switches inside the case on the jacks (either the F2-B or the F1-X does, I don't remember which) clean them by carefully inserting a fine sandpaper strip cut and folded over, between the points and pulling it through them a few times.  Run a 9mm pistol cleaning brass brush into the input/output jacks to clean them.