ART-13 modulation transformer problem

[wa2dtw]

Just obtained an ART13 modulation transformer from the "e" place, and wanted to use it to plate modulate an ARC5.
There is continuity between one end of the primary and the center tap, but the opposite end of the primary has no continuity with the center tap or the other end.
The transformer seems completely sealed, and I can't get inside.

Is there a possibility that this can be fixed, or is it now just a door stop?
The secondaries seem OK.

Thanks and 73
Steve WA2DTW

[W1RKW]

Steve,
If you have the transformer with the 3 terminals at the top facing you, you may find that the center and left terminals will have continuity but no continuity to the right terminal. The right terminal connects to the top 2 terminals on the opposite side of the transformer.  The bottom 2 terminals on the opposite side of the transformer are independant of all other terminals and have continuity between each other.  Hope this helps.

[wa2dtw]

Bob
Many thanks.  That is exactly how it is.
Now- to figure out why- 
I thought that the 3 terminals facing me were the 2 ends of the primary with the center tap in the middle, and the opposite terminals were the secondary for the plate and the screen of the final.
Obviously, that is not how it is set up.

In any case, I'm very glad that the transformer is good.

73
Steve WA2DTW

[KE6DF]

Here is the pin-out of the ART-13 modulation transformer:

Power: 50 watts audio max. (Note: Hams have successfully used this transformer at power levels far exceeding (2-5 times) this rating.)

Audio Response:-2 dB @ 300 Hz, 0 dB @ 1000Hz, -2 dB @ 4000Hz

Connections:

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

Terminal 2: Center Tap.

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).

Of course this doesn't help much if the terminals on the unit you have are not numbered. I looked at the one in my ART-13 and didn't see the numbers on it.

[W2JBL]

     i have that same transformer and just recently used it with a pair of 807's to modulate 160 and 75 meter ARC-5's with absolutely stellar results. good luck with your project. as i found out it was a perfect choice of mod iron. thanks to WA1HLR for the advice he gave me on this, in particular using that iron. by the way- the srceen winding will not work if you try to hit the ARC-5 screens with it. too much audio. i feed the 1625 screens with a 37.5K screen resistor off the modulated B+ and put the screen winding to work with a 15K 2W load resistor across it and then to a voltage divider providing inverse feedback to the first section of the 12BH7 phase inverter. the ARC-5 sounds real good, and i have witnesses to prove it. don't forget to install proper bypass caps on the ARC-5 1625 cathodes, screens, and grid leak (do that one where the lead comes out of the oscillator coil can) and as close to the tubes as possible- that's the only real flaw in the design.

[WU2D]

That ART-13 transformer is a great one when it comes to what power you can get through it for such a small package. And it takes abuse in all forms.

Timtron has always regarded the ART-13 transformer as a Magic device.

Mike WU2D

[wa2dtw]

To W1RKW, WB6IYH, W2JBL and WU2D
Many thanks.  This is tremendously helpful.

73
Steve WA2DTW

[Tim WA1HnyLR]

Yep, The fART 13 mod transformer is definitly a magic device. I have pushed as much as 300 watts through one with the DC current removed by a 20 Hy reactor. A single 4-400 modulated by a pair of 572-B tubes @ 2500 VDC. The audio responce was  was good down to 300 Hz . Below 300 the audio distortion went through the roof.l Not enough core material for the power level. The high end was good to 6Khz before rolloff . At lower power levels the fART 13 mod transformer is pretty decent. When installed in a Ranger transmitter the audio was good down to about 50Hz The high end was good to 10Khz . The impedance match allowed for 125% positive peak capability. The tertiary screen winding could serve as a negative feedback winding. The transformer is good for up to 150Ma of unbalanced DC in secondary. Used as designed  an 813 modulated by a pair of 811 s with 1Kv on the plate the audio responce  is very respectable . Have fun,
Tim WA1HnyLR