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HK Deuce PT tranny potting questions

audiodon

audiodon

Addicted Member
Hi,
I've got a Citation II that had a mechanically buzzing power transformer that drives me to distraction.

There's not a lot of information I could find about unpotting and potting transformers, but I did find posts from chinacave, Dan055 and Battradio that helped.

So, I followed Dan055's advice and boiled up some water with the potted transformer in there, pulled off the bottom cover and, after a lot of noodling, finally got the transformer out. Then I boiled it some to get some of the potting goo out, and then put it in a dedicated toaster oven I have to dry out. But there's still a lot of this graphite-like potting material on the tranny, even after I've slit and pulled the paper covering the windings.

My plan is to give it a shellac bath and repot. That plan is subject to change though. I am concerned that the graphite potting goo will obstruct the shellac from getting in there and doing it's soaking magic. I like to soak it for a day while the shellac is warmed up to get everything nice and sticky and then dry, drain, and bake.

Here are some thoughts and questions.
1. I'm mulling over whether to just try and fix it or to do something else. These are supposed to be legendary transformers after all.
Does it make sense to send this to somewhere like Heyboer and get it mapped or is that already done? It's not broken, just has a mechanical buzz. There's always the possibility that I'll get something not as good back.

2. The potting stuff wasn't tar. It was much more like graphite. I couldn't seem to get it to liquid temperature, and extracting the transformer wasn't easy. Finally I got it softened enough to pull some out with a putty knife, allowing me to pulll out the transformer. The rest of it was scraped out and put in a bucket.
Any recommendations for replacement potting stuff and where to get it?

3. Any other suggestions or experiences that can shed some light here?

Don
 
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hey-Hey!!!,
Power iron is quite simple, and what you get back from Heyboer will be at least as good as what you send. I've sent them complex Altec output Iron, like S265Q and S271S and found their stuff matched the original down to resonant frequency of winding capacitance and leakage inductance. The Cit. II stuff isn't light weight, so don't expect the price to match lightweight Hammond 2-series power Iron.

Seems you didn't get the tar hot enough, if 100C boiling water softened it, 200C hot air would have liquified it.

Just how did you get the cover off the bottom?
cheers,
Douglas
 
It was a compression fit with a soldered foil all the way around. I cut through the foil with a putty knife and a hammer. Then I used a thin bladed screwdriver and a vise grip pulling a nut on one of the four threaded shafts a d wedged a corner up.
 
hey-Hey!!!,
I figured I'd have to put some heat to the solder; I don't like the idea of using a hammer. Probably take a pair of MAPP gas torches to the edge and spin the case around.
cheers,
Douglas
 
That'd work. The solder layer is quite thin. No thicker than aluminum foil.
I was just stumbling into the pot after reaching the limits of what research would tell me.
It's my first attempt and a trial by boiling water.
 
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You could take it to an electric motor shop and have it baked out, dipped, and re-baked. Or, you could probably do it yourself when your wife is away. Are there any fasteners to tighten on the core?
 
If it hummed when potted, it must REALLY hum now... have you applied AC to it after de-potting??
 
audiodon said:
The potting stuff wasn't tar. It was much more like graphite.
Click to expand...

It's unlikely to be graphite, because graphite is electrically conductive, but potting compounds are often filled with powdered minerals to improve thermal conductivity. Marble dust is commonly used in epoxy mixtures, for instance.
 
The potting material is pencil lead gray - making me think of graphite, and it stinks. My wife's complaining that it stunk up the garage and the garage isn't even connected to the house. It really stinks a lot. It makes the smell of tung oil seem pleasant by comparison.
 
My 2 cts worth....

Considerations for sending it off:

- Wire enamel technology has come a long way in the past 50 years. New wire will have far better breakdown characteristics than wire of old.
- Ditto on wire gauge tolerances. This would affect how well the windings are packed together and how well they interact.
- Hi Potting: Folks like Heyboer have the tools to test for proper breakdown voltages and cross-winding breakdowns, too.
- Re-potting in the case: The stinky stuff gets dealt with away from your residence and WAF issues.
- You _know_ it will be in good shape for the next 40 years.
- They have the forumlas for rewinding.
- They have the jigs to lay the wires properly in the coils.

Downsides:

- Is not inexpensive.
- Standard risks for shipping - both going and coming.

If you've gotten this far, I'd suggest serious rebuild. The buzzing sounds like a loose lamination. I've gotten rig of some by using a dead-blow mallet and gently tapping the core laminations - not guaranteed to work, though.

What you don't want to happen is to get the buzz to stop, repot and reinstall the transformer only to find that it starts again.....

Cheers,

David
 
Hi Don -

Sorry to hear of your transformer woes. They are like teeth - you never notice them when they are working correctly, but when something goes south, it jumps the line to the very top of the to-do list.

I would go with Dave's advice - to send it for professional re-build at one of the well-known sources fro that -

If it were a transformer you could more readily get a hold of, I would say have at it in your garage or the local motor re-winding shop (Good idea - for OTHER transformers..), but the time and cost to get another HK one might well far exceed having a pro repair yours right, painful though that might be.

I am in the same boat, although suitable PT's for the Heathkit W4 are WAY more plentiful that the HK PT......


-Ian
 
It's going to be redone.
I just have to make the connections and send it out.
Pesky holiday hoo haa is taking up that extra time right now.
 
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