Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => AmpTools/Tech Tips => Topic started by: kagliostro on October 09, 2011, 04:19:47 am

Title: Humming PT - There is a way to block that vibration ?
Post by: kagliostro on October 09, 2011, 04:19:47 am

I've an old RCA PA amp and I want to reuse the transformers

the PT is audibly humming

there is a way to eliminate that vibration ?

Thanks

Kagliostro

Title: Re: Humming PT - There is a way to block that vibration ?
Post by: overtone on October 09, 2011, 02:13:49 pm

I would check that the laminations are still bolted tightly together,
best, tony

Title: Re: Humming PT - There is a way to block that vibration ?
Post by: jjasilli on October 10, 2011, 12:10:58 pm

Maybe mount the PT on rubber grommets or a flat piece of surgical rubber.  That won't eliminate the hum at its source, but may dampen it and cut down on chassis vibration.  If you do separate the PT from the chassis, then it would probably be best to reground the body of the PT.

Title: Re: Humming PT - There is a way to block that vibration ?
Post by: kagliostro on October 10, 2011, 01:38:02 pm

Thanks

I'll look to the screw that keep together laminations and I'll see if is possible to do something that way

I was thinking if there is a way to submerge the PT in something that can fix the lamination each other ??  :w2:

Kagliostro

Title: Re: Humming PT - There is a way to block that vibration ?
Post by: jjasilli on October 10, 2011, 05:44:09 pm

Checkout this:  http://www.chimeralabs.com/transrebuild.html (http://www.chimeralabs.com/transrebuild.html)

Title: Re: Humming PT - There is a way to block that vibration ?
Post by: stingray_65 on October 10, 2011, 11:15:31 pm

It is not enough to simply isolate the tranny from the chassis with rubber mounts.

While this will stop unwanted vibrations from shaking your tubes and solder connections, it will do nothing to prolong the life of the transformer.

When a transformer hums, it is being very inefficient. the magnetic field is being used to vibrate the laminations, this wasted energy is placing a greater load on the windings, resulting in more wasted heat.

increased heat leads to a faster breakdown of the enamel insulation on the wire. once broke down a short will occur.

The link Jjasilli has good info, But I have my doubts as to how effective it would be. I would think that once a tranny starts to hum and vibrate nothing short of vacuum potting would be effective.

good news is building a vacuum chamber is simple.

I've used old refrigerator cooling pumps with great results for a while.  They will fail after some use.

the chamber must be rather small, or the outside atmosphere will crush it.

You need not draw a hard vacuum either. 5-8 inches of Mercury will do fine.

your potting liquid should be very thin, and cure catalyticly, if it dries   by out gassing you may trap solvents inside the transformer.


Ray

Title: Re: Humming PT - There is a way to block that vibration ?
Post by: kagliostro on October 11, 2011, 01:33:26 pm

Many thanks Jjasilli & Stingray_65

I'll read the link content with attention and try to do something

Thanks again

Kagliostro

Title: Re: Humming PT - There is a way to block that vibration ?
Post by: stingray_65 on October 11, 2011, 08:43:08 pm

K,

I got to thinking a bit, maybe a dip in some shellac just might do as JJ's link suggested.

After all it seems to work for the author of that how to.

I tend to over think and over build  things.


Good luck

Ray