The AM Forum

Hi All,

I think this was raised before , but I don't recall seeing an answer to it . I am looking for info on a UTC 'Special Series' transformer with a "CM" prefix - in particular CM-15 . I have looked at all the on-line info and catalogues I can find on UTC , but no mention of the "CM" range . It looks like a 30 watt package , and has tags  1 thru 13 on the base .

Many thanks , 

Are you sure it's a UTC Special Series, or is it a xfmr that looks like a UTC Special Series??

Is there a metal tag on the xfmr that reads UTC Special Series??  If so, is the CM-15 stamped into the metal tag or is it marked elsewhere on the xfmr??

There were other xfmr makers that used the same case style as the UTC Special series.

It could be a xfmr that UTC made special for an equipment manfacturer to use in their product.

Fred

Hi,

According to a fragment of an old UTC catalog that I have (no date I can find), CM-15 is a transformer designed for cathode modulation.  Rated at "15 watts audio with tapped secondary for 300 - 2000 ohms".

No connection diagram in what I have.

73,
Dean

Attached is a page from an old catalog.

It shows the CM-15 used in a circuit.

You can probably figure out the pins from that.

Dave

Thanks guys , this was most helpful ,

Much appreciated,

Carvel

Nice! it has a grid modulation winding to go with that.

Dave, would you care to scan that catalog and send me a CD, or loan it for scanning? I don't have any with the CM series on my website (bunkerofdoom.com) and it would be nice to make it available.

Patrick

Hi Patrick,

I got it off the web in PDF format. It's actually a hodge podge of a bunch of different UTC catalogs and app notes.

Someone did a lousy job of scanning it, but it has some data, including connection data for a bunch of UTC transformers I haven't seen elsewhere.

It looks like the site I got it from is no longer up, so it would be great if you could host it.

I'll email it to you if you send me your email. It's too big to attach.

Mine is dave@folger.com

Dave

That's a rare item, a modulation transformer for REAL cathode modulation, which is actually combined plate and control grid modulation, with a carrier efficiency intermediately between the two, depending on the ratio of grid to plate modulation. It was a promising configuration in the early 50s, but for some reason, fell by the wayside and was never widely used.

If it's a good transformer, and you don't plan to actually use it in a cathode modulated transmitter, I'd bet it would fetch a good price, even with shipping costs from SA, since those transformers are now 99% unobtanium.

Hi Patrick ,

If convenient could you drop a note on this thread maybe when you have loaded the UTC stuff - would like to add it to my old iron database .

No intention of parting with it at this stage , but will certainly trundle it around here if and before I do .

Best Regards,

Carvel