Fender Blues Deluxe (again)

[Fred G.]

Greetings all,

I'm checking out a Fender Blues Deluxe for a friend - this is the second time I've taken this beast on for him.

The original complaint (this time) was that it has a very subtle "distortion/buzz" on the "finish" of certain notes. Very subtle, but irritating, if you listen for it.

However, as I began troubleshooting it, I noticed that the amp was kind of making an odd intermittent hum/noise. I thought it might be a microphonic tube, and when I began tapping on V2 it sent the entire amp into a solid oscillation that sounds a lot like, well, a sine wave test signal. Swapping out tubes has no effect, nor does turning the volumes up or down. I can feel the vibration in the power tubes as well as through the top of the cabinet. I can somewhat stop the oscillation by tapping on the cabinet top or by exerting pressure on it.

Suggestions?

Thanks in advance,

Fred G.

[Mick Bailey]

A frequent condition of these amps is cracking around the tube base pins. I always inspect and re-solder these. Grey Illinois filter caps are also susceptible to failure. Take a close look around the positive ends to look for oozed and dried out crud.

[g1]

And when you said swapping out tubes, that includes power tubes? I only ask because sometimes people will exclude power tubes when dealing with microphonics.

[Enzo]

it has a very subtle "distortion/buzz" on the "finish" of certain notes.

Classic description of a rubbing speaker voice coil, so check for that by substitution.

[Fred G.]

Enzo,

I've tried it with 3 other cabinets, the problem is still there regardless of cabinet.

I've only had snatches of time to mess with this amp, but I did open it up and start chop-sticking and poking around. One thing I've found to be very peculiar - the power transformer vibrates constantly, so does the main PCB on the edge near the power xformer. This is without an instrument being played through it. The vibrations can also be felt through the top of the cabinet. It doesn't vibrate much on the opposite edge of the PCB.

Any observations on this?

Thanks,

Fred G.

[Enzo]

Some transformers sing. I don't worry about it until it sounds like the poor thing is loaded tons.

If the speakers are not at fault, fair enough. It is just the first thing to eliminate.

[Fred G.]

Right.

I'm going after the easy stuff first - tubes, speakers. The noise sounds a heck of a lot like a mechanical rattle, but, as I said, I tried three different cabinets...a Bad Cat 1-12, a home build 1-12 with a Weber silver bell, and a 2-12 home build with old Oxfords in it. Same noise, slightly different "ambience", lol.

So that kind of power tranny vibration isn't uncommon, then? I don't do this frequently enough to speak from loads of varied experience. It struck me as unusual.

[Mick Bailey]

Power transformer vibration is common - I have a Pro Reverb on the bench right now that rattles all my tools. No fault but that's the way it is. Are the B+ and heater voltages OK and does the transformer stay warm but not hot? A transformer will buzz under excessive load but usually something will be getting hot or blowing.

Check as well that it's tightened down securely.

[SoulFetish]

In this case, its not the PT rattling.
In these series of amps, the ceramic snubber caps cause mechanical/acoustic buzzing which is audible. It's nothing to worry about, but it is annoying.
One way to tell the difference is whether the noise is gone when the amp is in standby. The ceramic caps buzz is occurs only when the amp is switched out of standby, if memory serves.

[drewl]

Have one with a similar complaint.

Couldn't get it to crap out until I cranked it all the way up and pounded some chords for about five minutes.

It then started this incredibly horrid shrieking and howling on it's own, which turned out to be the phase inverter