Anyone know where this mod tranny is from?

[ka2pbo]

Hi All,
 Found this mod iron in the garage. Im almost positive its military. It even has a red Eagle and a black star stamped on the bottom.

It reads :

A.J.F. Industries
Stock # 2Z9633.8
TF 1A12YY

LEVEL  100 WATT
Frequency response @ 3db  100 - 5000 cps
WV  1400V DC

Primary  2500 ohms
Secondary  7500 ohms

July, 1953

also has what i assume to be a screen winding

Its 6" x 7" x 5" and it weighs 20lb

Maybe someone can I.D. it for me. Im curious about the 2500 ohm primary and what mod tube would have liked that.

Heres a few not so good pics:

Thanks
 
Rick  
KA2PBO  

[KA2DZT]

Push-pull parallel 6L6s would work with the xfmr.  Probably 6550s, may be others.

Fred

[Opcom]

Might be from a ground-based UHF AM set for aviation. Those sometimes ran tubes at low-ish voltages and made a 100W carrier or so, and had a nice wide frequency response like that. The best way to find the number is "TF1A12YY" with no space.

A similar 125W one here from the AN/GRT-3 has an 8K CT primary for two 811A's, and a 2300 ohm sec. for two 4X150's. All ran at 900VDC. -what I mean by low. They sometimes had spark gaps attached.

[N2DTS]

I have a 120 watt (good for more then that) 8000 to 2800 ohm, has screen taps, and 200-20,000 Hz response, +0, -1 db. 20,000 Hz???

Something like TF1rx14yy, got it from fair radio 30 years ago.

The screen taps likely were for 4x150 screens.

[Opcom]

I think that is the one I was referencing and I was wrong about the secondary Z and exact watts.
The secondary with the CT is low power for the limiter plates.
The screen was modulated by a cathode follower off the modulated B+.

The file "AN_GRT3_T282.pdf" linked on this page "http://bunkerofdoom.com/lit/mil_uhf_01/index.html" gives the original application (If I am correct).
850V B+ 811 modulators, two 4x150's on the RF side at 850V
The transformer is huge for 125W. Is that the one?

Rick's transformer with a 2500 Ohm CT winding might also be good for driving high current modulator grids like 3-500Z's. well maybe, with some kind of huge class A tube running 1KV and driving the 7.5K winding with 30-40W.
Any spec on the secondary current for the final on the TF1A12YY?

At some point there ought be a military parts book showing what it is from.

someone has a few?
http://www.chipfind.net/search/index.htm?part=TF1A1

[N2DTS]

The one I have is rated for 300 ma I think.
And yes, that low power winding says something like 1 ma I think, so no good for screens.

Might make a nice feedback source or modulation indicator though.

[KL7OF]

Low power winding for modulating the audio driver tube(s)??

[ka2pbo]

I cant read anything else on the transformer; its all scratched up so I dont know the secondary current.

I really like the UHF Transmitter you posted. Especially the screen modulator tube set-up ! Thats worthy of further study !

Thanks for the replies Gentlemen !

Hopefully I make use of this thing. Push -pull 6l6s sounds cool. Maybe modulating an 813 ? 1200v @ 160ma =192 watts and 7500 ohms !

Im gonna go search the military parts list for a while.

Thanks

Rick  "PBO"

[N2DTS]

My trans is good for 250 ma on the modulator side, and 300 ma on the rf side.
1750 working volts. 19 pounds exactly.

A pair of 6L6's modulating an 813 sounds a bit like a pair of 6AQ5's modulating a 4-1000..

[ka2pbo]

Push-Pull Parallel  6L6s is what " DZT" suggested . For a pair; Class AB2 can get ya 50 watts @ 3800 ohms. Sounds do-able

[W3RSW]

A reasonable way to determine secondary current rating is to simply measure the DC resistance and see how it compares to the primary.  You already know the transformer is good for 100 watts.  First assumption is that both primary and secondary are wound with same guage wire. 

Run a small voltage on primary, say from a 6.3 vac fil. Xformer and see what voltage is found on each secondary winding.  Possibly  the secondaries will be same since "Center Tap" is indicated on secondary side. If the voltages found match z/R expectations in approximately correct ratios then the wire guage and hence similar current ratings are verified. Even a first iteration will give you most of the info you need.  At 100 watts I anticipate that the secondary will reflect the primary's impedance current product or any similar primary impedance to current ratio.

Well you know what I mean.   

[ka2pbo]

Thanks Rick !

The only problem is I don't know what the Primary current is either. It says :  430 (smudge) DC  Term #2. That's  the primary C.T. . I don't know if it reads MA or V DC. I cant make it out. I did take some readings before I realized I couldn't read it.

Primary resistance : 28ohms  Secondary 50 ohms each winding. I put 2.5 volts on the primary and read 2.1 and 2.15? . When I series up the secondaries  I measured 5.25 . ? But; I guess I cant do much with it if I don't know at least the primary current.

Thanks
Rick

[KA2DZT]

The xfmr is easy to figure.

It's mark 100W.  Ask yourself what tubes will give me 100 watts of audio with a 2500 imp.  Most likely 4 6L6s, 4 807s, 4 1625s.  Probably 2 6550s will also work.  Now ask yourself what 200 watt PA will work within a 1400 WV.   One 813 is a good guess.  It's not 6146s or the WV probably would be less.

When a xfmr is marked with WV it means you can put 1400 volts DC on it.  You can also assume both sides are rated at 1400 volts.  Of course the smaller modulators will only run at a maximum of about 700 VDC.

You can figure the turns ratio very easily by putting an AC voltage on the primary (across the whole winding), now measure the voltage on the secondary.  The impedance of the secondary is the square of the turns ratio.  With this transformer I will guess it's a step-up ratio, primary to secondary. If it's not a step-up, the xfmr is of little value using a 813.

Guessing at the current rating for the secondary, it has to be at least 200-300 ma.  You would need at least that current to come close to 200 watts at 1400 volts.  But the ratio needs to be a step-up.  So, first find what the ratio is and let us know.

Another thing, only one of the secondary windings is for the PA,  the other one is either for screen modulation or maybe feed back or don't use it at all.

You'll have to figure which secondary winding is for the PA.  Start by measuring all the DC resistances,  let us know that.  Note, there should be a slight difference in DC resistance between the two halves of the primary, let us know that.

Wait to hear from you.

Fred

[Opcom]

Thanks Rick !

The only problem is I don't know what the Primary current is either. It says :  430 (smudge) DC  Term #2. That's  the primary C.T. . I don't know if it reads MA or V DC. I cant make it out. I did take some readings before I realized I couldn't read it.

Primary resistance : 28ohms  Secondary 50 ohms each winding. I put 2.5 volts on the primary and read 2.1 and 2.15? . When I series up the secondaries  I measured 5.25 . ? But; I guess I cant do much with it if I don't know at least the primary current.

Thanks
Rick

I searched that part number a lot and some posts or offers show that it is 7K CT or that the windings are equal.
430mA or Volts might be right for the 2500 CT winding at 100W for a quad of 6L6's or similar tubes.

Try the military parts/collectors/radios lists and others like greenkeys, etc. you never know who might have used something like that, or replaced one and recalls it dimly, til your post there jogs their memory.

[KA2DZT]

I re-read your last post.  I see that both secondaries measure the same.  You also measured the same voltage output.  Interesting, measure the resistance of the windings again with a digital ohmmeter, just to be sure.

If the secondary windings measure everything equally then both windings are for the PA.  If so, put both in series and hope you have a step-up ratio .  Make accurate voltage measurements.  Also note, there may be a very slight difference in DC resistance on the two secondaries.

The slight difference in DC resistance comes from fact that the windings are on top of each other.  The greater diameter of the windings requires more wire which results in a slightly greater resistance.  This is true for the primary and secondary.

If the windings measure exactly the same DC resistance, then the xfmr has side-by-side windings.

Fred  

[KA2DZT]

Taking a closer look at the pic, I see what looks to be a 7K impedance on the secondary.  Judging from the way the drawing is shown, one sec winding having more turns than the other, it seems that the two secondary windings are not the same.

Hard to say what the 430 is, voltage or current.  My guess, current.  The voltage rating is already shown as 1400 volts.  If the 1400 volts only referred to one side, it would have been shown on one side or the other, not down at the bottom where other ratings are shown.

Fred

[KA2DZT]

Went back and looked at your first post.  I see that you already show the secondary impedance as 7500 ohms.  That's good, xfmr has a 1.7 turns ratio step-up.  You could get 100% modulation on a 813 easily with only 500-600 volts on the modulators while running 1200-1400 volts on the PA.

Fred

[ka2pbo]

Thanks Fred !

I have 813  and sockets and filament xfrmrs so that would be the way to go. Now I just have to decide on what mod tubes to use.The push/pull parallel 6L6 sound cool.Guess I have some homework to do.

Opcom ;

I will definitely start posting on the other sites and see what comes back. Your website is awesome! I downloaded the Collins 242 F-2 manual ; only because its such a neat radio AND i really like that screen mod tube circuit!

Thanks Again All ! If I come up with the specs and origin of this transformer  I will  share it of course .

Rick

KA2PBO

[Opcom]

Thank you for the compliment! Please do share what you find. There are probably more of them out there.

The screen mod tube circuit you refer to is from the T-282, right?

from the manuals on hand, it's not from the 242F-2, T-217, T-282, TV-15.. There is a 242F-5 but I have no book on that.

[ka2pbo]

Sorry,

What I should have said was "I downloaded the Collins 242 F2 manual only because its a really neat radio and I really like the screen modulator tube circuit from the MD 141 .

Thanks Again

Rick