ART 13 Mod Transformer

[W4RFM]

Tell me some great stories about how much power has been run using one of these please.  I have heard rumors of 100 watts of audio and more.  Is that true?
Thanks
Bob

[k4kyv]

They should be capable of at least 100 watts of audio, since they were designed to match a pair of 811's to an 813.

I recall an article in a 1956 Radio & Television News magazine, describing using one as a replacement for a blown modulation transformer in a 1 kw rig, by mounting it on standoffs and using a blocking capacitor with a 10H power supply filter choke as a modulation reactor.

No doubt it had the Space Shuttle Sound, but those were the days before there was a space shuttle, and of course, everyone knew that the audio from a ham rig was supposed to sound crappy.  Only lids ran good sounding audio.  Broadcast quality wasn't in the spirit of good amateur practice.

[WQ9E]

Funny you mention this Don, I just came across that article last night.  At the time of the writing the author had run several weekend contests with the rig and stated that he had picked up a spare mod transformer but it looked like the spare was going to remain in its box.  The rig was a 500 watt unit using a pair of 813's in push pull modulated by a pair of 805's.  The 10H mod reactor probably did result in some pretty thin audio.

Rodger WQ9E

[W9GT]

I believe the ART-13 mod transformer is nominally rated at 100 watts of audio.  Assuming a reasonable safety factor for military use, they probably can be safely used at at least 150 watts.  I think they were pretty high quality, well-insulated units.  If you remove the DC from the secondary using a blocking / coupling cap and a reactor, then 200 watts shouldn't be a big deal.  I think it also has a screen winding, if I remember correctly.

As for running one on a KW input xmtr, that would be asking quite a bit out of it...on the order of 500 watts of audio.  Probably could not be expected to last forever at 5 times its intended ratings!!  On the other hand, if the rig was actually 500 Watts RF input, then 250 watts of audio is within the range of possible reasonable abuse without leading to the early demise of the transformer.

73,  Jack, W9GT

[k4kyv]

Funny you mention this Don, I just came across that article last night.  At the time of the writing the author had run several weekend contests with the rig and stated that he had picked up a spare mod transformer but it looked like the spare was going to remain in its box.  The rig was a 500 watt unit using a pair of 813's in push pull modulated by a pair of 805's.  The 10H mod reactor probably did result in some pretty thin audio.

I suppose my memory failed me after 53 years!    I remember reading the article when I was a little JN, after buying the magazine at the newsstand.

That was the first time I had ever heard of anyone using a modulation reactor and blocking capacitor, and that article was what introduced the concept to me.  I remember that the author mentioned the circuit being standard for plate modulated commercial broadcast transmitters.

[W4RFM]

Well, mine came today, and after the initial shock of thinking one side of the primary was open, (yeah I didn't notice the numbering, or read the Forum about these things) I started surfing to find out all the info I can about them.
My plan again is to run two 811's at about 135 watts to modulate a 4-125 for about 250 watts of carrier.
I would love to do the reactor thing that Don/KYV mentioned like the broadcast rigs did, IF I could find the iron!
Thanks Bob

[W9GT]

Well, mine came today, and after the initial shock of thinking one side of the primary was open, (yeah I didn't notice the numbering, or read the Forum about these things) I started surfing to find out all the info I can about them.
My plan again is to run two 811's at about 135 watts to modulate a 4-125 for about 250 watts of carrier.
I would love to do the reactor thing that Don/KYV mentioned like the broadcast rigs did, IF I could find the iron!
Thanks Bob

Just string three or four (10H or more each) filter chokes in series and use them for a mod reactor.  Should work fine.  Maybe not as good as a "real" mod reactor, but acceptable.  Then use a 2 to 4MFD oil cap @ 5 KV or more for the blocking cap.

73,  Jack, W9GT

[WQ9E]

I suppose my memory failed me after 53 years!    I remember reading the article when I was a little JN, after buying the magazine at the newsstand.

That was the first time I had ever heard of anyone using a modulation reactor and blocking capacitor, and that article was what introduced the concept to me.  I remember that the author mentioned the circuit being standard for plate modulated commercial broadcast transmitters.

Don,

Retaining that clear a memory after 53 years is pretty (expletive deleted) incredible!  My father had subscribed to Radio and Television News for a number of years and I found a stack of them in the attic when I was getting interested in ham radio in 1974.  The issues were no longer in order but I still remember the first one I looked through had a full page ad introducing the new Johnson Valiant and that was my Christmas present in December of 1974, I spent a lot of time tuning it into a light bulb dummy load while waiting for my novice ticket to arrive which took about 14 weeks during those days of the CB boom overloading the FCC.  The next issue I looked in had the double page ad introducing the Hallicrafters SX-88 and the third issue I looked in had a full page ad introducing the Johnson Viking 500.  I didn't get those for Christmas  however I did find a Viking 500 in 2007 and the SX-88 last year so better late than never.  I think finding those old Radio and Television News magazines had a major impact on my radio operating future and over the summer I managed to acquire about 150 more issues to build my collection.  They really did have some excellent radio construction articles.

Don, Let me know if you would like a scan of this article for old times sakes.

Rodger WQ9E

[k4kyv]

Don, Let me know if you would like a scan of this article for old times sakes.

Yes, please do that.  I think most of my old Radio & Television News mags got scattered far and wide years ago, before I started to put together a radio library.

Better still, why not post the scanned article as an attachment in a reply to this  thread, so others would have access to it (assuming the file size doesn't exceed the limit allowed for attachments on this message board)?  It would be enlightening for some readers who might not be familiar what we're talking about when we discuss modulation reactors and shunt feeding with modulation transformers.  If the file is too large for here, I'm sure Steve would be glad to put it on the AM Window website.

[Steve - WB3HUZ]

Indeed. Good stuff. It would complement the info on the ART-13 mod tranny already on the site.

http://www.amwindow.org/tech/htm/modtran/misc/art13.htm

Don, Let me know if you would like a scan of this article for old times sakes.

Yes, please do that.  I think most of my old Radio & Television News mags got scattered far and wide years ago, before I started to put together a radio library.

Better still, why not post the scanned article as an attachment in a reply to this  thread, so others would have access to it (assuming the file size doesn't exceed the limit allowed for attachments on this message board)?  It would be enlightening for some readers who might not be familiar what we're talking about when we discuss modulation reactors and shunt feeding with modulation transformers.  If the file is too large for here, I'm sure Steve would be glad to put it on the AM Window website.

[WQ9E]

Shunt fed article from August '58 Radio and Television News.  Steve, please feel free to move the attachments to the tech area if you wish.

Rodger WQ9E

[Steve - WB3HUZ]

Thanks very much.

[WQ9E]

You are very welcome, thanks for maintaining the site!

Rodger

[W4RFM]

Thank all you folks, this is great stuff.
BM

[W7XXX]

Anyone seen a later version of the Art-13 mod xfmr? I have one that is unused and it looks like the original except the insulators are bigger around and shorter. The ratio on the secondary plate winding test the same as the original, but the screen has a higher ratio 1:.1. That would mean at 1kv on plate, the screen would have 100 volts. That doesn't seem right. The original screen ratio was 1:.26 if I remember right or 1kv on the plate and 260 on the screen.

The guy I got it from said the others he took from the original packing also tested the same, so it can't be a defective winding, unless the whole bunch were rejects.

I have seen homebrew rigs with this little xfmr mounted on insulators with 3kv on the plate loaded to 150ma.,that worked great. I have heard stories of heavier loading, but wasn't an eye witness. I have heard some nice audio from homebrew rigs using this xfmr, both from rigs running the B+ straight thru the secondary and also isolating it using a reactor and blocking capacitor.

[W4RFM]

Rodger, thanks for posting the article, I saved it to My Docs and cleaned it a little in Photo Shop, printed it out, and now it is in my collection with other valuable stuff.
BM

[w1vtp]

I think this makes for better viewing. 

BTW - at the end of the article it shows the chuck key attached to the handle of a power drill using a rubber band.  My version is to use electrical tape to attach the chuck key near the end of the power cord. This forces the user to unplug the drill while using the key -- in important safety feature.  I've heard more than one user of my drill grumble about that feature until I pointed out that he did have to unplug the power to the drill before inserting the key.

Al

[W4RFM]

So now I have to ask this question: would / should a Kenyon/Stancor/UTC rated 40-50-60 watts with the same choke and cap hook up sound as good or better than the ART-13?  If so I could make the Collins iron available to someone who needs it for a ART-13 restoration, cause it dont matter to me. I just want my A M to sound REALLY good, hopefully flat response from 100 hertz to about 3500 or so.

Opinions please....

Bob

[KE6DF]

I will totally defer to the more knowledgable members, but I'm rather skeptical of the
notion that one can use a 50 watt mod transformer and a couple power supply chokes
as modified heising reactor and end up fully modulating a 500 watt transmitter
with good quality audio.

I suspect the standards of what consitutes good quality have changed a lot since
Genaille wrote that article as Don said.

Plus, the mil spec ART-13 transformer was probably grossly over designed for it's
50 watt rating.

Sure taking the DC off the secondary helps with core saturation, but then running
the transformer way above it's ratings -- even with the DC rerouted through the
heising reactor -- still seems like it would subject you to flattened peaks.

[K1JJ]

Hi Bob,

I have some real-whirl info for you.

About fifteen years ago I was running a pair of 813's X triode-connected 813's. The rig used a 500W broadcash iron mod xfmr.

Someone who was looking to build one too axed me how an ART-13 mod xfmr would work for the rig.  I disconnected the broadcash iron and clip leaded in an ART-13 mod xfmr on the spot. I didn't expect much, being it is so small.   I was using a Heising choke, which kept the DC off the xfmr - good idea.  I loaded the rig up to about 500 watts.


I was told that the highs were still reasonably decent, but the low end was down with not much below 120 hz or so. In the off-air monitor, I was impressed and thought it sounded pretty decent. However, there was no way to ram any boosted deep low end thru it - it just didn't have the iron mass to handle it without distortion. Bottom line is the xfmr is a sleeper and a great unit to use as a spare or something to use until you find some bigger iron.

They did a great job designing it for durability, compactness and reasonable audio quality-  a little better than communications quality, but not broadcash quality, in my opinion.  It was the perfect WWII xfmr for the job at hand years ago.

Good luck -

Tom, K1JJ

[W4RFM]

I only plan to push about 135 watts thru it, so I guess I will play the hand I have been dealt - Collins it is. Thanks folks. 

[Steve - WB3HUZ]

Rodger provided me with some higher resolution scans of the article from Radio  & TV News. I've cleaned them up a little and put them  up on The AM Window Web Site.  These should be suitable screen display or printing. Enjoy.

http://www.amwindow.org/tech/htm/shuntfedmod.htm

[Steve - WB3HUZ]

Another good article on the subject by Don, K4KYV.

http://www.amwindow.org/tech/htm/modheising.htm

[Steve - WB3HUZ]

And yet another one.

http://www.amwindow.org/tech/htm/heisingorwhat.htm