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Author Topic: Drying out power transformer and misc. audio transformers on HT-37 ?  (Read 6880 times)
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N2IDU
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« on: March 22, 2014, 09:40:40 AM »

It is my understanding that the power transformers are the weak link in the Ht-37's due to shorting of the filament voltage to the high voltage winding. I will be solid stating it in the near future to avoid this. So far it works!

I would like to heat the transformer up to drive out any moisture and then dip it in (polyurethane?) to seal it up to avoid future water migration. Who knows what kind of environment this transmitter was stored in. I would like to pull a vacuum on the transformer while it is being dipped but have no way, at present, to do this. Any DIY methods would be appreciated!
 
I've  never tried this before, so I am looking for instructions on the proper way it should be handled. I would need to know specifics on, how high the heat should be?, how long it should be warmed?, how long it should stay in the solution,? how long it should be re-heated after dipping and temperature, when its safe to use it and any dangers associated with this?, the pros and cons   etc. etc. 

Also, I am really concerned about the two audio/phasing transformers. Can these also be treated in this fashion as they are also prone to opening up due to moisture and acid paper? They are very fragile. ( see my prior post about these audio transformers) If not, are there any other methods to fortify them or rejuvenate them?

Would appreciate hearing from anybody who has done this and their comments.

Thanks,

Peter
N2IDU
Old Shincracker, Vt.

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wb3eii
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« Reply #1 on: March 22, 2014, 01:53:36 PM »

My experience with drying:
 I found a plate transformer from the 1940's that had been sitting on a concrete floor in  an unheated garage for 20-25 years.
 As this was too big to put in an oven (over 150 pounds), I dried  it using internal resistance.
  Secondary  winding was shorted to itself, primary was supplied  with reduced voltage  via a large  stepdown transformer and a variac.
 Variac was adjusted to higher voltages  in steps as the plate  transformer slowly  heated.
 Over the period of a week, heat on the plate  transformer was  raised to the  point where a hand was uncomfortably warm after 3 to 5 seconds.
 I held this temperature a  day  longer.
 This transformer has been in use  since  and has performed  as designed.
  no experience in dipping or varnishing
 73, Ed
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KA0HCP
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« Reply #2 on: March 22, 2014, 02:19:07 PM »

The navy procedure for salvage and recovery is to use a 120F oven for as long as needed to dry equipment.

When I clean radios I leave them in until they are hot to the touch and the air from the oven feels dry to my face.  Most ovens have poor temp control down low, so it pays to use a thermometer with a remote probe to keep track.  Preheat the oven before putting your parts in, so they avoid the hot elements.
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KE6DF
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« Reply #3 on: March 26, 2014, 06:59:25 PM »

I put transformers in my garden shed for the months of June - August. Several weeks of over 100 degree (in the shade) dries them well -- it gets to 120 - 140 inside the shed.

That works in the dry California central valley and deserts and places like Arizona. Probably wouldn't work in humid areas.

Also, like 'eii said run a current through them to heat them up internally.
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w1vtp
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« Reply #4 on: March 26, 2014, 09:32:28 PM »

I think Timmy, HLR uses his "NOVAAAAH" as a drying out oven during the summer.  So that would be about, what, 120 - 130 degrees?

Timmy is a good source of info on reclaiming old transformers that have been in moist environments

Al
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W3GMS
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« Reply #5 on: March 26, 2014, 10:06:30 PM »

Peter,
On the HT-37 audio transformers, I would be very hesitant to get them hot by shorting a winding and apply voltage to the other winding.  The hi impedance nature of this transformer is wound with such fine gauge wire that I think you would run the risk of opening the winding up if you forced enough current in it to cause it to heat up.  Dry heat would be the safest in my opinion on that transformer.  If your talking about a power transformer, then that's a different situation.

Joe, GMS
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AB3L
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« Reply #6 on: March 27, 2014, 07:12:02 AM »

I used a steam pipe to heat up a choke and get the potting to flow. It sat there under aluminum foil for about two weeks.
I was lucky enough to have this I know, so if you have this available at work or know someone who does this is a nice source of hot dry air and the smell wasn't in the kitchen.
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N2IDU
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« Reply #7 on: March 28, 2014, 08:27:42 AM »

Hi Joe,

Perish the thought of shorting out any windings on those transformers. I was able to pull apart one of the original damaged ones and measure both the high and low impedance windings with a micrometer. The high impedance winding was AWG 38/39 and the low impedance winding was AWG 32/33. I would be hesitant to attempt that method even with a power transformer!  It would be just my luck the thing would catch fire and I would be tried for treason and executed!

Peter
N2IDU
Old Shincracker, Vt.
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KB2WIG
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« Reply #8 on: March 28, 2014, 11:34:57 AM »


" I would be tried for treason and executed! " *

That only happens with Collins equiptments. With Hallies, they make you wear tight boxers and give you a weggie.


klc

* That's quite a message.


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flintstone mop
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« Reply #9 on: March 28, 2014, 07:25:58 PM »

lowest setting of your wife's oven and throw the suckers in there for about 4 hours.
not gonna hurt a thing
Fred
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« Reply #10 on: March 28, 2014, 07:59:24 PM »

how about putting the thing in a presure cooker and heating it, and using a vacuum pump to evacuate the space?
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Radio Candelstein
w1vtp
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« Reply #11 on: March 28, 2014, 10:08:59 PM »

how about putting the thing in a presure cooker and heating it, and using a vacuum pump to evacuate the space?

I believe that's what Tim, HLR does when he does his thing with transformers.  He has the process down pat

a
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N2IDU
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« Reply #12 on: March 30, 2014, 02:36:55 PM »

Thanks to all who gave me plenty of ideas to consider on this project. I'll report back when I have completed the task. We did manage to borrow a vacuum pump and my friend retrofitted a pressure cooker to pull a vacuum and seal them up. The HT-37 power transformer is being warmed up at a constant 140 degrees for a day or so. Then we will dip it in polyurethane and pull a vacuum on it. Next will be the audio transformers which will go through the same steps.

Thanks for everyonesr input.

Peter

N2IDU
Old Shincracker, Vt.
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N0WEK
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« Reply #13 on: March 30, 2014, 07:41:52 PM »

Thanks to all who gave me plenty of ideas to consider on this project. I'll report back when I have completed the task. We did manage to borrow a vacuum pump and my friend retrofitted a pressure cooker to pull a vacuum and seal them up. The HT-37 power transformer is being warmed up at a constant 140 degrees for a day or so. Then we will dip it in polyurethane and pull a vacuum on it. Next will be the audio transformers which will go through the same steps.

Thanks for everyonesr input.

Peter

N2IDU
Old Shincracker, Vt.

A friend's chamber and potting motors...

https://www.youtube.com/watch?v=zmWYGb0EB-8&list=UUj_XaV1ss-qdD-lPUtTEcXw
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