Amp hum increases and decreases

[rlw3]

Ron, you are right about the difficulty of opening the amp up. The hum was extremely low yesterday when it was very cool. Today was warmer and had a little encrease in hum. Thinking all of my problem might be air conditioners. I live very close to a military base so I wonder what it contributes. Read Briz's thread, the problem of hum was helped by loosing the trannies and giving them shock obsorbers. Sounds great but very hard to do

[ronenash]

If you want to go in to this you can take the cover bottom cover off. You will find the screws that hold the tranny cover underneath. I would put a piece of rubber or something between the tranny and the cover. I would definitely not loose the screws. Remember, these transformers weigh a lot and if they are not well attached they can deform the chassis when you move the amp.
A more sensible solution in my opinion would be to get a good power conditioner such as the Torus.

[microstrip]

IMHO, putting rubber between the transformers and and the cage will only make it worst, as it will thermally insulate the power transformer, increasing its temperature. As I do not have children or pets around, my amplifiers are now operating without the transformer covers. BTW, releasing the transformer mounts a few turns is not dangerous, as the nuts are self locking and will stay attached.

As I suspect that the mechanical hum is caused by the increase of the temperature that dilates the iron blades, every thing you can do to circulate the air in the vicinity of the transformer will reduce hum. I have also tried decreasing the tube bias by 30% and the transformer immediately became silent - but sound decreased quality.

But my greatest hope is still on putting new silent blocks for the transformer and for the cage mount that will rise height about half inch.

[rlw3]

Why does releasing/loosening the transformer mounts work?
Please describe the silent blocks you write about?
Would placing small wood blocks like ayre myrtlewood blocks under the tranny cage be good?
How do you remove the tranny cage safely?

[microstrip]

Originally Posted by rlw3

Why does releasing/loosening the transformer mounts work?
Please describe the silent blocks you write about?
Would placing small wood blocks like ayre myrtlewood blocks under the tranny cage be good?
How do you remove the tranny cage safely?

Releasing/loosening the transformer mounts can help to decoupling the transformer from the chassis, avoiding communicating the vibration to the whole structure. The silent blocks I consider are small soft rubber cylinders with decoupled metal inserts or screws. Wood blocks will not decouple the transformer from the chassis as they are not isolators between 50/60 and 300 Hz.

The transformer cage is easily taken out after the four screws holding it are taken. You have to take out the bottom plate to have access to them. In my case it lead to the the most significant improvement.

BTW, as the amplifier is very heavy I always manipulate it on a large two inch thick foam plate on the floor.

[erfurt]

I'd had some issues with my plasma tv injecting dc into the ac line which unfortunately is common with the stereo gear. The transformers in my mono amps would hum in a cyclical type pattern about every 20 seconds.
Gilbert at Blue Circle Audio devised this hum killer device with built in 1/2 BC6000 conditioning and a bypass switch to bypass quiet device when tv is off.
Hooked both amps to this unit and plugged it into wall - superb results.
Very cool and works like a charm.
Added a couple of 6x filters into thr spare outlets for good measure.