[Mark Korda]

Hi Lennie,
   Somewhere on this forum a few months ago I was watching a video on the building of a McIntosh tube amp. Before the transformers were installed they were turned upside down and a black tar like goop was poured into the bottom of the bells which covered any plates or windings. If I'm correct it was to stop mechanical vibration within the transformer.
    I didn't even notice the output transformers in my Dynaco. If all totaled up there are 10 missing transformer lag bolts and lockwashers, rubber washers, washers,and nuts securing the outer bells. The Mark 3 transformers I just looked at are the same way, each one missing 4 bolts.
   As a project I am going to try to find those bolts, install them, and see if some hum goes away. It may be far from your problem but an easy project for me to try troubleshooting.
    Why would David Hafler, the founder of Dynaco who's forte was the Ultralinear transformer, skimp on a few bolts holding the bells secured on his trannys?.....take care and good luck fixing the hum what ever the problem is......Mark Korda.

[witchdoctor]

This video discusses the dynamo of "hum". please enjoy  :

https://www.youtube.com/watch?v=Ua_O8dWswMA

[john1970]

Hi Lennie,

It is not clear from your initial post which transformers are buzzing.  Is it all of them?  A couple of more ideas on how to check for the problem:

1) Once you identify the component(s) that has the issue can you take it to a hifi shop and test it on their AC power instead of the power in your apartment?  I once had an issue with an integrated amp, CD player and small bookshelf speakers and I ended up taking the entire system to a dealer to help troubleshoot. 

2) If the PS Audio P500 did resolve the problem, would it be worthwhile to try a product that uses an isolation transformer?  Definitely, borrow a unit from a dealer since you need to ensure it solves the problem before purchasing.  An isolation transformer if properly sized can easily handle 200 W. 

Good luck,

John