Mechanically isolate power transformer?

[Leo_Gnardo]

Some years back a customer brought two MusicMan 130 heads in for servicing. One had a PT that rattled the chassis with buzz. I checked the idea of filling the end bells. But pressing on the bells by hand had no effect, so much for that. What did work, is I mounted the four transformer bolts through silastic washers after opening up the mounting holes a fraction. The washers were leftovers from reverb tanks I had installed in other repairs. "Never throw anything away" worked for me here. A pair of flat washers, one on each side of the silastic helped keep it from squeezing out of its intended position. Mechanical hum transferred to the chassis from the PT went from obvious & annoying to "I can't hear it at all." The silastic material is excellent for minimizing vibration transfer, very tough, and showed no sign of distress after letting the amp heat up over the course of many hours. The customer was elated, and I hope he gets a lot of mileage out of his prize MusicMen.

Granted this may not be the ideal solution to every problem of this sort.

If you do swap PT's, you might consider swapping the old end bells onto the new PT. That way nobody but you, or maybe a scanny eyed tech, would be able to easily detect it's not the factory original.

[Paul G.]

If anybody is interested, the new Hammond transformer came today. I looks identical to the Schumacher, at least as much iron, and perfect drop in.

Installed it, brought up the voltage gradually on a Variac and current limiter while measuring B+ and bias voltages -- all ok, no smoke. Plugged directly into the wall, biased the output tubes, and turned it up.

Amp is now quiet, no hum at all. If there's a difference in tone between the old and new transformers, I can't hear it.

The only bad news is while jiggling things removing the old transformer, I bumped and broke one of my brand-new TAD 6L6GCs. I'm running an old set of 7581a I had sitting around. Oh well.

[Phil_S]

I am wondering a few things.
1) With the new PT, do you like it better, worse, or just different?
2) Is there a meaningful difference in VDC in various parts of the circuit?
3) Probably no answer for this one, but I wonder if the differences are just an artifact of replacing a tired old transformer. It isn't possible to use the Wayback machine to listen to the amp when it first came off the production line. Maybe it was meant to sound like this, with the replacement PT.

[Paul G.]

1. I can hear no difference between the old and new PT.
2. Voltages appear identical everywhere. Any differences are insignificant enough to be attributed to how the measurement is taken and possible voltage changes from the electric company.

I did take the amp out this weekend, and it is loud, clean and toneful. I wasn't able to get it above 2-1/2 on the volume knob, but it still sounded unbelievably juicy, chewy and delicious.