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  #1  
Old 09-03-2016, 01:41 AM
Phil Nelson's Avatar
Phil Nelson Phil Nelson is offline
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WTB: Miller 4526 HV coil for DuMont RA-102

I need a high-voltage transformer for a Dumont RA-102 television.

The Dumont part number is either 21B-12446 (parts list) or 21B-14213 (what appears on my transformer).

This is a tall hollow-core coil with several "pancakes" stacked vertically. Here's a pic of the transformer in situ:



I have been told that a Miller 4526 might work. I contacted Moyer Electronics and they're still looking. Meanwhile, if you have one, I'd love to buy it.

You can email me by going to http://antiqueradio.org/contact.htm .

Thanks!

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Last edited by Phil Nelson; 12-05-2016 at 09:33 PM.
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  #2  
Old 09-03-2016, 01:55 AM
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Eric H Eric H is offline
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Phil, did yours go open or just quit working because of an internal short?

I fixed one in my Raytheon Porthole that was shorted internally by washing it (in soap and water!) then spraying it with high dielectric epoxy paint.
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Old 09-03-2016, 03:18 AM
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Phil Nelson Phil Nelson is offline
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I have never seen it working. After doing basic rehab (recap, replace bad resistors, etc.), I did initial power-up and the transformer started arcing around the edge of the top pancake. The HV output was at most 2.5KV before I shut it down, which is about 1/4 of what you need for the 10" CRT, and that was with the HV control cranked up all the way.

There's no visible damage in the area where I saw arcing, but there's a hair-thin wire stub hanging loose on the opposite side of that pancake, and no obvious place where you might reconnect it.

There has been some monkey business in this HV section. Someone had removed the doorknob filter cap and very crudely hotwired things to work (??) without it. Not sure why you would want to run it without the doorknob filter cap, unless you substituted a CRT with aquadag where the original had none. Or maybe someone was just robbing parts.

The tapped connection on this transformer had also been ripped loose and then crudely refastened with a clod of electrical tape and little or no solder.

When you say washing with soap and water, do you mean you removed the coil and gave it a bath? Or just cleaned it up in place?

If the arcing that I saw was surface corona, I can imagine how cleaning & recoating the transformer might cure that. I'm not sure how that could fix internal shorts. Wouldn't the shorts still do their thing under the new insulation?

Phil Nelson
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Old 09-05-2016, 02:32 PM
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Kevin Kuehn Kevin Kuehn is offline
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For what it's worth my Thordarson cross ref says a HVO 51 subs for a Miller 4526. Although subbing a sub sometimes gets iffy.
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Old 09-05-2016, 02:40 PM
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Eric H Eric H is offline
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If it's got a wire hanging loose then coating it might not help.

For the HV coil on my Raytheon, which was physically intact, but abruptly quit working in the middle of a recap, I took it out,washed it in hot water and some purple cleaner to get all the dust and dirt out of it, then baked it at about 170 for a half hour or so and then after it sat overnight I sprayed it with some Dielectric Epoxy, and by sprayed I mean drenched it, let it soak into the coils, it worked great, HV was strong after that.
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Old 09-05-2016, 04:21 PM
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Phil Nelson Phil Nelson is offline
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Quote:
Originally Posted by Phil Nelson View Post
The tapped connection on this transformer had also been ripped loose and then crudely refastened with a clod of electrical tape and little or no solder.
This photo shows the transformer when I got the set:

http://antiqueradio.org/art/DuMontRA...lCondition.jpg

I repaired and resoldered that connection as neatly as I could, but who knows if the set ever worked in this condition. It looks like some layers from the surface were just torn loose and wrapped back together. This connection leads to the grid cap of the 807 tube.

I haven't found a source for a new coil. Meanwhile, I tried the set again and saw no arcing on the top, but there was some arcing near the place where these wires exit the pancake. I cleaned the area with rubbing alcohol, let it bake under a lamp, and then applied some thin corona dope. I'll retry the set this evening.

Phil Nelson

Last edited by Phil Nelson; 09-05-2016 at 05:52 PM.
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  #7  
Old 09-06-2016, 02:19 PM
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Phil Nelson Phil Nelson is offline
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Well, applying corona dope eliminated the arcing -- and also eliminated all HV output. Perhaps the transformer was only making a "connection" through sparks before, not through the ragged connection that I tried to fix.

Meanwhile, I have been told that I could also try a Merit TV-231. So here's the current search list:

Miller 4526
Merit TV-231
Thordarson HVO-51

Regards,

Phil Nelson
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  #8  
Old 09-06-2016, 02:40 PM
broadcaster broadcaster is offline
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Phil, I have a Westinghouse HV supply from a 12 inch Westinghouse TV set that uses that same HV RF coil. The whole supply is $50, plus $10 shipping. Checks good. Charles Harper, Email brdcster@gmail.com
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  #9  
Old 09-06-2016, 03:03 PM
walterbeers walterbeers is offline
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It's strange that in all my years of working on old TVs, I have never seen an RF coil like that used as a flyback (high voltage) transformer. Probably was quite reliable in it's day.
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  #10  
Old 09-06-2016, 03:40 PM
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The HV supply is not a flyback type. I believe it's an RF-type supply similar to what was used in 7-inch sets like the Motorola VT-71, only beefier because the 10-inch CRT requires higher high voltage. I think these xfmrs don't fail often, but this set was subject to some crude "repairs" in the past -- or maybe some kid was experimenting or cannibalizing parts.

Broadcaster, I tried to send you a couple of emails about your Westinghouse HV supply. Maybe they were bounced by your email system, or something. Anyway, get me a message and we can make a deal.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Last edited by Phil Nelson; 09-06-2016 at 09:04 PM.
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  #11  
Old 09-21-2016, 02:53 PM
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Phil Nelson Phil Nelson is offline
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Does anyone happen to have a data sheet for the Thordarson HVO-51 transformer? I found a source who has it, but I don't want to buy blindly.

Meanwhile, from Broadcaster I got an HV supply from a Westinghouse TV that I have hotwired to produce 10KV and thus a raster. Seeing a picture is helpful in finishing the restoration, but long-term I would greatly prefer to repair the native HV supply, rather than have an outboard supply hanging from a hook in the cabinet.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html
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  #12  
Old 09-21-2016, 11:55 PM
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Kevin Kuehn Kevin Kuehn is offline
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Here's what's listed in the catalog, but I think the actual parts would include a more detailed spec sheet.



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  #13  
Old 09-22-2016, 01:06 AM
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Phil Nelson Phil Nelson is offline
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Thanks. Every bit of info helps!

Actually, I wonder if the HVO-50 would also work -- or maybe even be more appropriate -- since it supplies 10KV. Typical second anode voltage for the 12JP4 CRT in my set is 10KV, and I'm getting plenty of brightness & contrast with about 8KV from the outboard Westinghouse supply.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html
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  #14  
Old 09-22-2016, 02:17 PM
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Phil Nelson Phil Nelson is offline
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OK, it looks like the HVO-51 is a flyback type transformer, not suitable for this TV:



The Thordarson HVO-50 does look like the right RF type:





And a Merit catalog shows a TV-231 that appears to be the same deal:



In sum, I guess I'm looking for one of the following:

Miller 4526
Thordarson HVO-50
Merit TV-231

A NOS part would be ideal, but if someone can salvage one of these without breaking the little wires, I'd go for that, too.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html
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  #15  
Old 09-22-2016, 03:23 PM
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Kevin Kuehn Kevin Kuehn is offline
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Phil,

That HVO-51 you posted is a Merit part, not the same as a Thordarson HVO-51. But I agree the Thordarson HVO-50 is also a good candidate, although the mounting spacing is different than the 51.
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