The AM Forum

Went to VT and picked up the 4D32 HB xmtr I have been talking about on 75 and mentioned here on AMFONE.  I thought it was link coupled output but on closer look it's PI net.  Good.  So that makes things a little easier

So what I have so far is it's SG modulated and given Bob's penchant for HIFi and the XLR mic input, I'm guessing at the moment that's it's probably got good audio.

• TODO:  Trace out the circuit and generate a schematic.  Want to talk to one of my local friends to see about enclosing it -- although I have been known to gin up my own enclosures.
• HAVE: I have a lot of the PS components 1) 1500 v CT 300 ma PS.  2) 2 X 6 mfd 1000 vdc oil caps. 3) 300 ma swinging choke.
• NEED: 300 ma smoothing choke.  If I decide to go plate mod -- I'll need a CVM3 or equivalent mod iron.  The list may increase as time goes on.

Bob has (had?) been a friend of mine for over 57 years.  I think I want to put this back on the air as a payback for his great influence on my life.

Alan

Very cool. Have fun with it.

I like that! so well done and a a real tough mounting for the handles unlike most equipment where they are for looks..

The output coil - I notice is is quite a distance from the tank. I always thought they should be closer but i guess it works like it is supposed to.

They look pretty close to me.  I don't think the coil and capacitor could be much closer without mounting one directly on the other.

OTOH, I have seen commercially built AM broadcast transmitters with tank circuit  components mounted a couple of feet or more apart, and long stretches of wire strung between them.

No I'm sorry I mean the big coil and the little coil. Usually I see them closer on the same form.

If you look closely, it appears that small green winding is not attached to anything.

Remember, it was stated it is a PI network so I would suspect that small winding was placed there for scope attachment and since it also appears the thing was mounted in a rack setup of some sort, the scope could have been "clip leaded"...

Then again, that "RF OUTPUT" meter is not an RF Amp meter but a volt meter so it could use that winding and the wiring is not visible. I used to do a similar thing in my old rigs as a tuning aid. Not all amplifiers produce maximum output at minimum current!

That XLR mike input goes directly to a big multi tap input transformer: low impedance of course...

What I thought was a link coupling doesn't go anywhere.  It's PI net.  Nice BIG plate tuning cap.  The loading cap is the one on the underside.  Forgot to mention -- I think I still have a Triad M12-AL mod iron -- still looking in the garage for that.  That will take care of the mod...  Who knows?   A pair of 4d32's modulating a 4d32?

Thanks for comments, Al

Go classic, AL.

807s or 811As.

I'm inclined toward 807's or (my junkbox of) 1625's.  I already have the speech amp vector board built for that.

Al

Need info on this transformer.  It's the mic input

Al

Looks like it might have XLR balanced input, (definitely 3 pins in low contrast pix) but the back panel shot shows ground to one side, not the bottom lug which seems to be bent over and not connected ?   Interesting.  Might be 600 ohm to grids.  An ohms reading of quite low reading primary to much higher secondary might help verify that guess.  You can always put a very low voltage AC signal on the primary, say, less than a volt, peak and see what comes out the secondary.  Be careful 'cause it may be a pretty high step-up and short the secondary.  Might be safer to put, say 10 volts on the secondary (grid side) and see what shows on the primary and then do the ol' sq.rt. turns ratio trick, etc.

transformer catalog sheet w/ Z and freq response is here. In the bunker of doom, the home of doomed technology.

http://www.bunkerofdoom.com/xfm/UTC_1955_WEB/027.jpg

Couldn't access it from work.  However, I had a '63 catalogue that had this.  Now, where do I get the pin connections?  I'd like to document the beastie.  It looks like a FB mic xfmr.  Thanks guys for all of your comments.  Boy!  Youse AMers are a great bunch of people -- to quote Bill IFR ;D

Al

PS:  Loaded up ok at home.  So thanks an now I'm looking for the pin outs

Never found a pinout for that. A test with an ohm meter and then an oscillator+scope would probably do it.

OK

Here's another question.  Does anyone know what the specs are on this National choke?  I'm thinking the choke in the 4D32 plate circuit is a little light and this might do better.  The other one looks like a 2.5 mH choke

Al

PS: Steve (HUZ) Any time you think this subject should go to the Technical section, say the word and I'll stop here

Al,

As I remember the choke in the 4D32 rig is a 300ma  unit...  Think I had one in a single screen modded 813 I built back in 1950.

 

I'll just move it, and you can carry on at will. Wouldn't want to stop the discussing on such a cool rig!

The choke in there looks like a National R-300U 1mh @ 300ma and should be fine on 75.

The other one is similar to the 160-80M  4mh R-152 which handles up to 600ma but it may have resonances above 80M.

Carl
KM1H