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 Post subject: transformer buzzing, what do you recommend?
PostPosted: Feb Mon 29, 2016 2:35 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 672
Location: Fairfax, VA
got a pair of Eico HF-30s a while back, pretty sad shape, but I rebuilt these and they cleaned up nicely. In cleaning them up, I had to remove the covers to the power and output trannys, they were rust-bucket rusty! In taking the top shells off, the top lam pulled up a bit on one side. Painted and reinstalled, but now they are buzzing (mechanical), even the output tranny is buzzing a little, but the power tranny is way too loud. The first amp, I installed a wedge between the coil and lams, these trannies did not have one which surprised me, is that a good step? It did help the fist one considerably, but the second one, at least my first try, not so much, so I have taken the tranny off and installed a wood wedge both on the top and bottom, real tight! I also added glypt to the bottom of the lam that was loose on one side to hold it down, good idea? I am thinking of maybe using a cork surround between the top lam and the cover, is that OK to do, or not? Any suggestions are welcomed, thanks!


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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Feb Mon 29, 2016 2:49 am 
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Location: Charleston, W.Va.
Hi Randy,
I don't think there is anything necessarily wrong with what you have done, but apparently it has not fixed the problem.

My practice on loose noisy transformer laminations has always been to tighten them up as much as possible with their bolts, nuts and lockwashers, then coat the laminations & covers with oil-base varnish (conventional alkyd varnish, not polyurethane), allowing it to dry for at least 24 hours. After drying, if necessary I apply a second coat and likewise allow it to dry.

The same thing can also be done with black oil-based (alkyd) enamel, rather than varnish.

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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Feb Mon 29, 2016 3:01 am 
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I use a different procedure to quiet noisy transformers. I loosen the bolts, tap on the laminations to loosen them up, prepare a wedge for the bobbin. I also find or fabricate fiber washers for the through bolts and the through chassis stud ends. Then varnish the laminations while tapping on them, flowing as much varnish as I can while the bolts are loose. Then drive in the wedge, tighten the bolts and allow to dry. Then remount to chassis using fiber washers between the chassis and the studs of the transformer. Some vibration comes from magnetic induction. Breaking the path of the flux will reduce the hum and actually lighten the load on the transformer. On some transformers copper straps from the top cover to the bottom cover will reduce the hum the strap does NOT form a complete turn. It helps reduce the external field of the flux and induction into the chassis. I try to do this with the transformer wired in place.

GL

Chas

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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Feb Mon 29, 2016 6:05 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
Varnish is good. What is done with motors, is they are dipped, and baked in
an oven.

I even remember a story about the gent who built the first Phase Linear
amplifiers baking the special power transformers in his kitchen oven. Urban
legend?

Every wire in a motor or a transformer would move according to
ancient laws, every time you tried to use the magnetic field to
transform or do work.

So you glue them down.

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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Feb Mon 29, 2016 7:33 pm 
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Check the size of the first electrolytic capacitor in the power supply. I thought bigger MFD was better, but that caused 120 Hz current spikes and the transformer vibrated the entire radio. I went back to the size shown on the schematic. Then I used a bucking transformer to reduce the line voltage as well, and finally tamed the beast.


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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Feb Mon 29, 2016 7:54 pm 
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Chas wrote:
I use a different procedure to quiet noisy transformers. I loosen the bolts, tap on the laminations to loosen them up, prepare a wedge for the bobbin. I also find or fabricate fiber washers for the through bolts and the through chassis stud ends. Then varnish the laminations while tapping on them, flowing as much varnish as I can while the bolts are loose. Then drive in the wedge, tighten the bolts and allow to dry. Then remount to chassis using fiber washers between the chassis and the studs of the transformer. Some vibration comes from magnetic induction. Breaking the path of the flux will reduce the hum and actually lighten the load on the transformer. On some transformers copper straps from the top cover to the bottom cover will reduce the hum the strap does NOT form a complete turn. It helps reduce the external field of the flux and induction into the chassis. I try to do this with the transformer wired in place.

GL

Chas

My procedure is very similar:
--loosen the bolts
--use an old utility knife blade to open up the laminations whereever possible
-- douse with shellac--using the knife blade to help it flow into any openings
--tighten the bolts

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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Jul Sun 14, 2019 2:30 am 
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Location: Ferndale, Michigan
I'm glad I found this topic. I will try these techniques on a noisy RCA 9K I'm working on with a very buzzy transformer.


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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Jul Sun 14, 2019 8:54 am 
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When winding new coils I have begun vacuum impregnating them with varnish. I may try this with an entire transformer some time as an experiment.
The vacuum chamber that comes with a food saver system is a convenient size for this process.

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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Jul Sun 14, 2019 11:44 am 
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processhead wrote:
When winding new coils I have begun vacuum impregnating them with varnish. I may try this with an entire transformer some time as an experiment.
The vacuum chamber that comes with a food saver system is a convenient size for this process.


I saw your process with a field coil rewind. Really neat! Keeps the moisture out too.

I wonder if this would be of benefit to working oscillator coils. Clean them off, dry them out, and then seal. Might keep osc drifting down some. I know some of my radios have subtle changes in alignment in different seasons. Humidity in the house changes and has always been my suspect for this minor issue.

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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Jul Sun 14, 2019 12:11 pm 
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came across this video the other day for this issue;
https://www.youtube.com/watch?v=dtOwewfqucI

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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Jul Sun 14, 2019 8:02 pm 
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Location: Annapolis, MD
processhead wrote:
When winding new coils I have begun vacuum impregnating them with varnish. I may try this with an entire transformer some time as an experiment.
The vacuum chamber that comes with a food saver system is a convenient size for this process.

What varnish do you use? I have done various searches on this, and it seems that very few people sell electrical "baking varnish" to the public.

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"Voltage is fun to watch, but it's the CURRENT that does the work."


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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Jul Sun 14, 2019 10:11 pm 
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Joined: Jul Tue 15, 2008 6:13 pm
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Location: Gretna, Nebraska
I was told by another ARF member that plain polyurethane wood finish is ok to use and has the required insulation qualities to use as a electrical varnish.
The one I use takes a few days to dry at room temperature and I have not tried to dry it at elevated temperature to speed up the process.

Edit, I have been using a Minwax floor varnish. To reduce the volume of varnish required to completely immerse the coil, I just place the coil in a bag a fill it with enough varnish for coverage. Then place it in the vacuum chamber.

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Last edited by processhead on Jul Mon 15, 2019 6:16 am, edited 1 time in total.

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 Post subject: Re: transformer buzzing, what do you recommend?
PostPosted: Jul Mon 15, 2019 12:33 am 
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First problem is possibly loose windings plenty of advice there. However, transformers do growl if they are overloaded.


Overloading as suggested can be due to old & leaking capacitors of all types. Principally Waxed Paper, Electrolytic, Oil filled and the size of the first one in a "capacitor input" filter. Increasing the first filter cap will affect the voltage developed. Generalising the bigger it is the more voltage developed and of course: Up goes the current and the more likely, it will strip the rectifier cathode, should it be over that recommended by the tube manufacturer.

Do check that it is actually fitted with the same value parts as listed on its schematic.

Marc


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