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TESTING the ART-13 Mod Iron




 
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Author Topic: TESTING the ART-13 Mod Iron  (Read 2517 times)
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WU2D
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« on: January 07, 2010, 09:30:25 PM »

I had a nice eyeball with Bill K1BF yesterday. He had an ART-13 Modulation Transformer for me in his trunk. I have been off the air with the ART-13 since the modulation transformer seems to have broken down internally and it has been singing for about a month. Time to change it out.

Take a look - you could eat off it. I buzzed it out and all windings showed normal DC ohms. There was nothing from any terminal to ground or between windings on the 20M scale.

Anyway, the device has three windings as you guys probably know:

Connections:

Terminals 1-3: 15000 Ohms, 4250v test voltage, current 150 mA balanced, (This is the Primary).

Terminal 2: Center Tap of the Primary.

Terminals 4-5: 7300 Ohms, 4250v test voltage, current 1-150 mA unbalanced, (This is the Secondary.

Terminals 6-7: 970 Ohms, 2500 test voltage, current 2-10 mA unbalanced, (Used to modulate the SCREEN of the 813 final).

I put 120 VAC 60 Hz from a variac across the primary and got 83 VAC on the secondary and 32 VAC on the screen. This agrees with the ratios on the transformer plate.

Can I assume that it is good? What else can I do to test it before shoving it into the ART-13? I do not have a Megger but I have a HV transformer and a variac.

Mike WU2D


* ART13_XFMR.jpg (1072.84 KB, 3252x2551 - viewed 345 times.)
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N2DTS
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« Reply #1 on: January 08, 2010, 08:58:20 AM »

Not sure about your original mod trans, maybe the bolts are just loose?
When they go bad, they usualy just short out.
Many mod trans can make noise, the bc610 trans did, I had three cvm-5's and two were loud, the other was silent, they all worked....

The load on the mod iron can also make them talk....

I think the only good way to test a mod trans is to put it in and strap it.
If you blow a breaker, its likely bad.

Brett
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WU2D
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« Reply #2 on: January 08, 2010, 09:25:23 AM »

Bret - you are right they all sing. No it sang a bit of course as normal - I am talking about zorch overs on voice peaks and lots of distortion. I changed out the valves, removed the feedback - no help.

Hey I will take the old one out and plop the new one in and lets see what happens!

Mike WU2D
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« Reply #3 on: January 08, 2010, 09:41:53 AM »

Sounds like the old one is bad.
Any way to insulate it from ground?

Is it oil filled?
It looks quality...

Brett
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WU2D
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« Reply #4 on: January 08, 2010, 10:27:36 AM »

They are quite an interesting transformer and many folks have these sitting on the shelf having accumulated them from various ART-13's of old. They were made by Chicago Transformer Company to Collins specs for use in the radio which could be at 10 thousand feet or more in an unpressurized situation. They had to be small light and survive temperature extremes. The unit is marked 50 watts but I have heard of hams putting 4-5 times that through them, thus the unit got the nickname - "the magic transformer". The separate screen winding is interesting and that is actually where I pick off my feedback.

Mike WU2D
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« Reply #5 on: January 08, 2010, 11:34:50 PM »

Maiden voyage tomorrow AM on the OMRN Net.

Mike WU2D
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WU2D
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« Reply #6 on: January 09, 2010, 07:58:23 AM »

YES!

First of all I lied a little bit about the transformer that Bill gave me. I did test it for DC resistance. BUT It was actually dirty beat up cut out beast with lots of rust and cut off leads. Bill did not want me to even take it because he thought it was likely bad. What you see in the picture is the AFTER. I sanded down the rust, removed the nuts, gave it a bath and a scrub, cooked it for an hour at 220F and then hit all of the ports with polyurethane and finally repainted it. It came out looking pretty nice.

The ART-13 is back on the air after a month of troubles. The transformer singing and distortion and general zorching on the audio is gone. This is a great transformer. I checked into the net this morning.

But the transformer turned out NOT to be the cause of the problem. The cause was a broken Jones plug on the audio module. This must have occurred when the unit was pulled in and out over the years. As you know mine is heavily modified - see schematic. The brown phenolic of the Jones plug captive in the module which is the male side was shattered and the entire group of pins was backed out so only a few had a good connection. This caused many issues.

The transformer that is in there now is quiet as a mouse with singing occurring only when the carrier is down and you speak into the mic - essentially an unloaded transformer situation. But even then there are no issues.

Let's see if she hold up. If so I will give the "bad" transformer the treatment.

Mike WU2D



* ART13Audio_New_WU2D.jpg (604 KB, 2274x1706 - viewed 363 times.)
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