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Old 6th January 2012, 01:57 AM   #21
dgta is offline dgta  United States
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Good discussion. Lots of folks very familiar with these machines. My original intent was not to make the 752 into a lab instrument, just to make it "par" after some repairs/rebuild. Thanks to all.

This unfortunately took a turn for the worse, as I discovered one transformer winding is open. Does anyone know where I can get a 752 transformer or one that is functionally equivalent?
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Old 6th January 2012, 03:19 AM   #22
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Quote:
Originally Posted by dgta View Post
This unfortunately took a turn for the worse, as I discovered one transformer winding is open. Does anyone know where I can get a 752 transformer or one that is functionally equivalent?
That sucks. Sorry to read this. I have a Hickok 580A that has an open screen supply winding. I've checked into replacements and there aren't any. I plan to use a small transformer like a Stancor P8181 (150V 25mA) half wave to serve as a stand-in. But it's become a back burner project since I have other testers. Hamond also makes a small 100-0-100 volt unit that might work. Mounting it is the biggest challenge, but it's doable.
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Old 6th January 2012, 04:49 AM   #23
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I believe the main problem with finding a replacement transformer for the Hickok 752 and the military models is that they combine all the supplies into one transformer, which makes it almost impossible to get a new transformer wound (and the cost would be very high). Alltubetesters does have some replacements transformers that he has custom wound, he does indicate that he has replacements for the Hickok 539 tube tester and I believe also the 580/A (I discussed it with him several years ago). The 539 uses two transformers; the 580/A has a separate filament, screen and plate transformer. The latter two transformers are wound with different voltages with multiple voltage taps (they are not the same). I have both of these testers, but with a number of mods to improve their accuracy/reliability. You might email a couple of the people who repair these testers to see if they have any options. Best of luck.
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Old 6th January 2012, 07:10 AM   #24
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I'm going to go out on a limb here and suggest a possible source for tube type equipment transformers. Deane Kidd, former Tektronics engineer of great note is apparently still kicking around as of Nov. 2011. He "HAD" a major stock of old tektronics parts and manuals. Don't know on what -if any- level he might still be active, but you might give him a shot at: Deane Kidd dektyr@teleport.com
I think it best not to list his phone and address here.

Anyway, it is just possible he has a stock of old tube type tek transformers. When I've dealt with him in the past on Tek parts he was more than reasonable about pricing.

Just a suggestion.
Doc
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Old 6th January 2012, 08:16 AM   #25
dgta is offline dgta  United States
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Agree with mksj100. It's not practical to have a transformer custom-wound. If I had the time I could un-wind the bad transformer, count the turns and re-wind it. But it's a bit of a job with the zillion windings and taps.

I'm hoping I can find someone parting out a tester.
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Old 6th January 2012, 08:55 AM   #26
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Not so much of a limb, it seems, as someone already had a full page about Tek scope transformers up, linked back to here.
Tek power transformers

Now question remains as to if Deane Kidd has any around.

Doc
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Old 6th January 2012, 11:10 AM   #27
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There is a possible last resort attempt at repairing the secondary 150v windings.
A retired tech gave me some advise for repairing open windings on field coil speakers. He said that he has used a high voltage transformer like the type used for the old neon lights. I have one that is 120v primary,12,000v secondary. With the coil disconnected and isolated, you can connect the 2 high voltage leads to the open coil and inergize if for about 3-5 seconds, then hit it again for about the same time. What this will sometimes do is weld the open wires back in place. I have actually used this method 2 times with success and, to my suprise, had the proper resistance back in the field coil.
The 2 field coils I applied this to were 8.2k and the speakers are still working fine after 2 years now.
The 150v windings would have fewer turns than what I used this method for, but with a variac you may be able to apply lower supply to lower the secondary voltages and acomplish the repair. If your transformer is going to be removed and trashed anyway, it may be worth a shot.
Anyone know what the actual resistance should be for the 150v winding?
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Old 6th January 2012, 12:59 PM   #28
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did I miss something here??? Which windings on the tranny? What are the letters on the tranny with the bad winding?

As mentioned, depending on which winding, a stand in sub could be a possibility for that bad winding.
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Old 6th January 2012, 04:08 PM   #29
dgta is offline dgta  United States
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The bad winding is U-VV-V, specifically the VV-V section of it.

This is one of the 2 matched plate voltage windings (labeled 170V on diagram). Each has a middle tap (roughly 47%) for "low plate" and the good winding also has a 20V tap for the diode test circuit. I can keep that 20V winding.

Any off the shelf xfmr that looks like that? Thanks.
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Old 6th January 2012, 06:10 PM   #30
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I am not sure I follow completely, these are two different windings. If the whole u-vv-v winding is shot that is one thing, if both have a problem that is another. Hammond may have something, email them if it is the u-vv-v winding. If just the u-vv-v winding is gone, having two trannies each with the right voltage and in series can cure the problem. If so, you may need to reverse the line in if the phase is out with respect to the original tranny.
I can look and see how many Hickoks used this tranny, it should be most. On occasion I see Hickok parts on eBay including trannies. You might also email Alan Douglas and see if he has any, I think he got many parts when Chris H. passed a few years ago. You might also email Kara Chaffee at Home Page she is a wizzard, I just love her, and one of the oldest in the business ( and won't screw you like some others who 'repair' testers) and could have spare transformers.
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