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Shellac my tube amp transformers?

dBfreak,
You inspired me. So I tried it myself. I bought a gallon of Zinzsser clear shellac, warmed it up on the stove, poured off enough to accept the volume of the transformer, hung the transformer on a dowel, put down something to protect a shower stall floor, put an electric heater in the shower stall, and set it to soak for 24 hours.

After 36 hours, I pulled the transformer, drained it off, baked it in my new CL toaster oven for four hours.
After it sat a couple days, I performed the following steps:
1. Bought some wood shims and hammered the tips of four shims into each end where the windings come near the end of the laminations. Dipped them in shellac, tapped them in with a rubber mallet, snapped off what wood was inside.
2. Then I cut some gasket paper to size, soaked it in shellac and shellacked it to the exposed windings.
3. Next I shellacked the inside of the copper retainer, slid it down over the gasket paper and windings and shellacked it all again.
4. Baked it for four hours again.
5. Then I sanded the laminations and replaced the bolts with brass bolts.
6. Next I sanded the inside of the end bells and connected the bells back onto the laminations, tightening the bell ends like a four lug tire being put back on a car.
7. I got my trusty Rustoleum medium gloss black spray paint and painted the transformer. Unbolted the two output transformers, masked off the unit chassis and painted them too. Left overnight.
8. Reassembled power supply transformer and resoldered according to my drawing.
9. Fired up the unit on a variac until I hit full voltage.

Did all that work fix the buzz?
Nah. It might be diminished somewhat, but it's still present. Big disappointment.
See the pictures for corroboration.
 

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That blows! I wonder if it is coming from something else on the amp. Most transformers hum a bit and if there is something loose nearby it may be the noise. Another step could be isolation mounts of some sort. They use them on the engine mounts to keep the airframe from shaking to bits. If you have a good RC hobby shop nearby you might take a look. They will raise the TX up off the chassis about 1/4 inch or more, but might be worth a shot. Otherwise I have made my own using silicone fuel tubing (also RC hobby shop) Enlarge the holes in the chassis enough to take the tubing with the screw in it. Sand and de burr the holes. Then put a half inch on each bolt after it goes through the TX. When you tighten the bolts the tubing will compress and you can get it to float nicely. John
 
audiodon said:
dBfreak,
You inspired me. So I tried it myself. I bought a gallon of Zinzsser clear shellac, warmed it up on the stove, poured off enough to accept the volume of the transformer, hung the transformer on a dowel, put down something to protect a shower stall floor, put an electric heater in the shower stall, and set it to soak for 24 hours.

After 36 hours, I pulled the transformer, drained it off, baked it in my new CL toaster oven for four hours.
After it sat a couple days, I performed the following steps:
1. Bought some wood shims and hammered the tips of four shims into each end where the windings come near the end of the laminations. Dipped them in shellac, tapped them in with a rubber mallet, snapped off what wood was inside.
2. Then I cut some gasket paper to size, soaked it in shellac and shellacked it to the exposed windings.
3. Next I shellacked the inside of the copper retainer, slid it down over the gasket paper and windings and shellacked it all again.
4. Baked it for four hours again.
5. Then I sanded the laminations and replaced the bolts with brass bolts.
6. Next I sanded the inside of the end bells and connected the bells back onto the laminations, tightening the bell ends like a four lug tire being put back on a car.
7. I got my trusty Rustoleum medium gloss black spray paint and painted the transformer. Unbolted the two output transformers, masked off the unit chassis and painted them too. Left overnight.
8. Reassembled power supply transformer and resoldered according to my drawing.
9. Fired up the unit on a variac until I hit full voltage.

Did all that work fix the buzz?
Nah. It might be diminished somewhat, but it's still present. Big disappointment.
See the pictures for corroboration.
Click to expand...

Sorry to hear that. I didn't mean to inspire anybody. I still don't know how mine sound because I'm waiting on a quad of 6L6's.
 
audiodon said:
dBfreak,
You inspired me. So I tried it myself. I bought a gallon of Zinzsser clear shellac, warmed it up on the stove, poured off enough to accept the volume of the transformer, hung the transformer on a dowel, put down something to protect a shower stall floor, put an electric heater in the shower stall, and set it to soak for 24 hours.

After 36 hours, I pulled the transformer, drained it off, baked it in my new CL toaster oven for four hours.
After it sat a couple days, I performed the following steps:
1. Bought some wood shims and hammered the tips of four shims into each end where the windings come near the end of the laminations. Dipped them in shellac, tapped them in with a rubber mallet, snapped off what wood was inside.
2. Then I cut some gasket paper to size, soaked it in shellac and shellacked it to the exposed windings.
3. Next I shellacked the inside of the copper retainer, slid it down over the gasket paper and windings and shellacked it all again.
4. Baked it for four hours again.
5. Then I sanded the laminations and replaced the bolts with brass bolts.
6. Next I sanded the inside of the end bells and connected the bells back onto the laminations, tightening the bell ends like a four lug tire being put back on a car.
7. I got my trusty Rustoleum medium gloss black spray paint and painted the transformer. Unbolted the two output transformers, masked off the unit chassis and painted them too. Left overnight.
8. Reassembled power supply transformer and resoldered according to my drawing.
9. Fired up the unit on a variac until I hit full voltage.

Did all that work fix the buzz?
Nah. It might be diminished somewhat, but it's still present. Big disappointment.
See the pictures for corroboration.
Click to expand...

Use good rubber washers! That's what I did, I got the idea from reading about "Technical Brain" Power Amps, which cost $250K !!! It worked wonders!! Also I did Mass loading where I could, and finally used Brass Footer underneath.
 
What little I know about potting coils ... they are done under vacuum. I would expect the wire to be enameled, not shellac'd. Shellac remains soluble in alcohol indefinitely. If the wires were insulated with shellac, the new shellac would dissolve the old shellac, and the windings could touch. I would think this is not a good thing.

Possible you could immerse the transformer in some rather fluid potting compound, and place under vacuum. The air in the gaps would boil out, to be replaced by the potting material.

I realize that this is pretty drastic, and requires some special equipment. But I think that's what you'll need if you want to fill the voids in the coil.
 
Wow Don - that bites.

I like the rubber isolation idea - The only thing I might (have) suggested would be soaking the TX in the shellac under a vacuum, to reach the obviously stubborn culprit area.

Truly heroic DIY, though.

Edit:

I see someone had the same idea, while I was typing.

I had to make some specialized photo gear, back when I used film, Kodachrome at that, that involved potting the electronics in GE RTV under a hard vacuum for use in wet / underwater environments. Its a royal pain, but effective. I may still have access to the vacuum pump if you need it.
 
Last edited:
I'd like to learn more about using a vacuum pump.

Eventually that tranny did quiet down. I think it had to bake from the inside to finally take.

This thread is old. I've done at least six since then and the success rate after extending the bake time and the time in use before evaluating is very high. All power transformers for tube amps have been a success.
 
audiodon said:
I'd like to learn more about using a vacuum pump.



The process is called vacuum pressure impregnation. You can find many sites on the web detailing the process. Epoxy, polyester, and polyesterimide resins, are generally used, companies such as Von Roll, Dolph, and Epoxylite manufacture various types of VPI resins.
VPI is superior to solvent varnishes and the conventional “dip and bake” method. Solvent varnishes lose a significant portion of volume during baking, leaving voids in the windings. A weak porous structure results. VPI provides a solid mass structure that provides greater mechanical strength, superior heat dissipation, and a higher level of environmental protection.
Click to expand...
 
Last edited:
How are all the voltages? Is it possible that you are just over stressing the power transformer? Maybe reduce current through the output tubes and see if it helps?

Can you get it to reduce the buzz with lower voltage on the primary through a variac?

Maybe a nice new one custom from Hayboer or Edcor would be a good way to go. :)

I think you did a great job on your restoration of that transformer! I would not call that wasted time!!

Also, I use brass washers between the chassis and the transformers... maybe brass and rubber washers, or use those rubber washers mentioned in another thread?
 
Saratoga48 said:
audiodon said:
I'd like to learn more about using a vacuum pump.



The process is called vacuum pressure impregnation. You can find many sites on the web detailing the process. Epoxy, polyester, and polyesterimide resins, are generally used, companies such as Von Roll, Dolph, and Epoxylite manufacture various types of VPI resins.
VPI is superior to solvent varnishes and the conventional “dip and bake” method. Solvent varnishes lose a significant portion of volume during baking, leaving voids in the windings. A weak porous structure results. VPI provides a solid mass structure that provides greater mechanical strength, superior heat dissipation, and a higher level of environmental protection.
Click to expand...


Wow - Thanks for the info - sounds like you know a LOT about this process. More than my converted pressure-cooker and hardware store rig !
Click to expand...
 
chinacave said:
Saratoga48 said:
Wow - Thanks for the info - sounds like you know a LOT about this process. More than my converted pressure-cooker and hardware store rig !
Click to expand...

Your little "pressure cooker rig" will do just fine, with the right resins, as long as you can get a good bake cycle.

I worked in my early years for the Insulating materials department of General Electric as laboratory manager. In the early 70s many of the initial VPI processes and resins for motor and generator coils were developed by GE.
Von Roll now owns all of the insulating materials manufacturing that once was GE.
Click to expand...
 
That tranny is fine now.

This was all before I discovered putting a couple of thermisters on both sides of the primary to drop the voltage a bit. I typically use 47 ohm ones (CL-80 I think for receivers and integrateds). A bucking transformer would do the same thing.

I seem to keep getting amps with buzzing trannies. I've learned to live with it. I have to say that power tranny buzz has become one of my pet peeves. I am, however, not trying to be the cat lady of orphan buzzing transformers.
 
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