The AM Forum

I know it is a modulation transformer, but I lost the information about the specification. Hoping to use it with a pair of 813's.
                                                            Joe W4AAB

Looks like it's a Hallicrafters number.  It may be one from a BC-610 or other military xmtr made by Hallicrafters.  Stancor made many xfmrs for Hallicrafters.

I'm sure someone will know what this xfmr is.

Fred

Here is a post on this site about a transformer with the same number.

But the poster says it's a plate power transformer:

http://amfone.net/Amforum/index.php?topic=20296.msg145433#msg145433

Yep I have one of those here as well.

Not modulation, is plate supply of 2 or 2.5 kV from 115 Volt line.

73DG

I concur, had one like it. HV insulators on one side, lower voltage on the other.

I am using an identical transformer in my homebrew rig. Plate transformer 2000 or 2500 VDC output @ 500mA with single section choke input filter. From a BC-610 as mentioned. Only thing is, mine has a different number on the little placard:  52B046. Taps to vary the voltage are on the primary side.

Ron

Thanks so much!! It was given to me. That makes good sense.Now I need the info on the terminals as far as the primary side.
                                                  73 de Joe W4AAB

The primary is tapped, to allow selection of 2 or 2.5kV output.  Ohm it out, pretty simple.

73DG

I made a BIG mistake. It is #55B028, not C. The terminals on one side  have P above B in 2 rows(4 terminals) the other side, the two terminals on the other side say P and B. Looks like the 2 terminals are the output, and the 4 terminals are the push-pull terminals to the modulator tubes.
                                                           Joe W4AAB

OK, there is one other reference on the site to that part number:

http://amfone.net/Amforum/index.php?topic=4523.msg34282#msg34282

It's 30 lb mod transformer.

I'm betting it's the BC-610 modulation tranny. 100TH's x 250TL.

Put a little AC voltage into the primary and you can figure out the ratio.

Dave

I just sold a couple of BC-610 mod transormers, although a more modern version. They were 21000 ohm primary and 8000 ohm secondary.

Ron

I will wire it up and consult the tube specs that I have. I wanted to use push-pull 813's but have 4-125's and 100TH's.
                                               Joe W4AAB

I'd use the tubes it was designed for, 100th's.  Something that relatively small will not have the poop to fudge in the input department.

An 8K load is not that hard to emulate, but 250th's are not at all hard to obtain.

73DG

I got to finish the high voltage supply so I can check out the 100TH's. Thanks for all the help!!
                               Joe W4AAB

I have one of those BC-610 plate xfmrs on a dolly in my office,  gets in the way at times.  110Lbs,  the mod xfmr is much smaller.  Four terminals on one end and two on the other end is the mod tranny.  I thought the part number looked familiar but you said it was a mod xfmr so I didn't check my part number.

Fred

Regarding using the tubes matching the Transformer design, it's probably more a question of matching impedances.  This can be done with voltages and loading to a great extent as most of you know.

My pair of 813's at the "reduced" voltage of 1600 are happy with 811's or 572B,s as modulators. - plenty of audio for voice peaks, etc.  Phase reversal anywhere along the chain, lately at the plate caps of the modulator tubes really shows the difference between so-so modulation vs. what you can get with voice peaks well over 100 percent on a scope or mod monitor. 

By all means use a mod. Monitor scope. All kinds of thigs become revealed. - proper drive in RF chain, mod. AF gain, pos. peaks vs. negative crossings, proper phase in the chain, RF power vs. various tuning and loading settings, e. g., amp efficiency... You name it.

At any rate, don't be afraid to experiment; for this a scope is almost mandatory. Try various combos of tubes with your mod. Tranny, easiest with almost just socket changes provided filament voltages are already the same and with fairly equal fil. Currents etc.

I once built an adaptor box with a pair of 813's fitting over a 4-1000 socket with wires feeding down through the 4 x1 pin holes.  Sorry in some ways that I traded that amp off to w3hm as it had a beautiful 7.5 or 6.3 vac at 21 amps fil. Xfor.