*WARNING*
THERE ARE HIGH VOLTAGES PRESENT IN THESE DEVICES THAT CAN KILL YOU
USE CAUTION!
This amplifier was extremely well reviewed in 1985 by Stereophile . However, they are all typically plagued with mechanical hum from the transformer and also from the large Magnecraft open relay. I suppose that some rooms/installations would cause it to be more or less noticeable, but I found it very noticeable in my listening room in between quiet passages and while listening at quite levels - Bah!
Now PS Audio makes this device called the "Humbuster". How it basically works, is that it removes any possible DC component from the AC line. This DC component often, but not always, may cause some toroidal transformers to hum. I tried this product, and I actually own one now, but I can tell you it won't do much of anything for this amp. However it worked absolutely awesome on a back-up amp, a Fosgate-Audionics 4100, nearly eliminating any of its audible hum.
After much searching around, I decided to have the transformer serviced and vacuum-dipped. I won't even get into how much of a bitch it was removing and re-installing this almost 30lb hunk of metal. But I will tell you that the service I got from Transformer Rewinding Service was excellent. Unfortunately this did not solve the hum issue...hmm.
As it turned out, the biggest problem was the relay coil and replacing it with a brand new one (almost 25 yrs newer?) didn't change a thing. These coils that run on 120v AC, are humming along at 60hz, wanting to open and close along with the frequency itself, 60 times a second. With some help from "Mooly" at diyAudio, I was able to construct a DC supply and feed the coil with DC instead of AC. And what do you know, it works!
Edit: Connecting to mains without a transformer is dangerous and not recommended
