Pro reverb tremolo problem

[Underwood]

I have a '66 Pro reverb and it works and sounds great. The only thing is when the vibrato(tremolo) is on when you hit a hard note or chord there is a static or distorted sound. Not so much if you play real soft. Any idea what it could be? Should I just change the caps in the vibrato section and whatever resistors that are out of spec? The whole amp is stock, it has all its blue molded caps still.Bias circuit cap has been upgraded but that is it.I replaced the vibrato tube and same problem. Maybe I will try another just in case I have two bad tubes.

[Underwood]

Tried more tubes and still same pr.oblem

[eleventeen]

Before changing out parts, I would be sure that you have no microphonic a: tubes and b: caps. Start with, and note that for tubes, a tube itself can be microphonic and the contacts in the socket can get corroded so they make only intermittent contact. Many times you can pull out, push in, pull out, then push back in the tubes in an effort to clean the socket contacts. If you have some Deoxit, a SMALL amount can help.

Flick the tubes with your finger and see if any are sensitive to vibration.

Are you really, really sure the problem only arises with trem on?

Often, with amps of this age, one or more contacts on a tube socket or two can get oxidized and the vibration of the amp being driven on the loud side can create some static.

Sometimes, pot shafts can get loose...and, if the knobs are snug against the front panel, they might not feel loose.

Finally, chopstick around on the parts board, looking for possibly microphoinc caps. This stuff can certainly happen in a 45+ year old amp! 

Good contacts on the reverb cables?

Just some ideas.

[Underwood]

Yeah i've tested it a million times and it only happens when the tremolo is on. I have changed out three different tubes that I kmnow are good and same thing happens. I haven't even opened it up yet, so when I do I will check the caps and clean it up a little.  Thanks!

[Raybob]

Yeah i've tested it a million times and it only happens when the tremolo is on. I have changed out three different tubes that I kmnow are good and same thing happens. I haven't even opened it up yet, so when I do I will check the caps and clean it up a little.  Thanks!

If it's only when trem is on, what about when it's switched on with foot switch but intensity is at zero?  Any problems then?

[Underwood]

good question. I will try that and let you know tomorrow.

[Underwood]

It only happens with the intensity on. With vibrato switched on, intensity all the way down it does not happen.

[punkykatt]

Try chopsticking the resistors , caps, wires, tube pins, roach in that circuit to try to make that sound and maybe pin point the cause if the unwanted sound?.