The AM Forum

Greeting from Old Shincracker,

Does anyone know a suitable substitute for the above audio transformers? A new ham, anxious to get his HT-37 on the air, stopped by to see if I could get it to fire up and check it out. Upon opening it up for general inspection, we were horrified to see that a rodent had eaten through both primaries and secondaries of both transformers. They are both way beyond repair. Short of buying another parts rig,(he can't afford it) does anyone know the impedance ratios or specs of these two parts etc? The HT-37 manual is silent about its specs? Maybe an interstage transformer? The rig does fire up and put out RF.

Rodents that do this kind of stuff should be tried for treason and executed!

Thanks for your consideration,

Peter N2IDU
Old Shincracker, Vt. 

I don't know the answer Peter but after repair your friend should read The Spotlight on the air to keep the rodents from appearing again.

Try Gary http://tubes_tubes_tubes.tripod.com/id4.html
He has tons of part rigs.

Peter,

The first phasing type SSB rig I restored was a CE-20A.  While going through it I found one of the two "modulation" transformers had an open winding.  These are 10 to 1 ratio transformers and I decided to try a pair of Radio Shack 12.6 volt transformers as a substitute while trying to find an actual replacement.  The replacements worked fine and they are still in place 12 years later.  I think most of these phasing rigs trace their ancestry back to an early QST design and it is likely the HT-37 uses the same 10 to 1 "modulation" transformers so you could try a pair of small 12 volt (120 volt primary) transformers to see if they also work OK in the HT-37.

The power transformer in the HT-37 is a known high failure item and changing to SS rectifiers (along with voltage dropping resistor plus transformer inrush current limiting) allows you to then disconnect the 5V windings removing this source of transformer failure.  This also applies to the HT-32 series and although I am not sure about the HT-30 I will also do the same for it when I restore it later this year.

Thank You Dave- W2VW I'll pass this info to my friend, and also thanks to Pete-WA2CWA and WQ9E for the leads. Pete, I have a phone call to Gary to see if he has any spares......WQ9E, your information was extremely helpful indeed.

Thanks,

Pete
N2IDU

Peter,
I got rid of my last HT-37 but I still have several parts rigs.  If I have the parts he needs I would gladly help out.  I don't even have a manual for the 37 since they went with the rigs.  What two transformers is he exactly looking for?  A picture would help.  The parts rigs do not have power transformers since they were known to go unless you do the mod that Rodger was referring to.  
Joe, GMS
    

SEE attached PDF; T102 and T103 on left side.

Hi Joe,

That would be just terrific! The two transformers needed are: T102 and T103. They are audio transformers/phasing types. They are exactly the same electrically but the Hallicrafters part numbers are as follows: T102.......... 055-300398         and T103...............055-300399.

Pete Wa2CWA posted a top view drawing from the Hallicrafters manual showing them on the left side of the image. His post is right after yours.

Thanks very much for contacting me.
Regards,

Peter N2IDU
Old Shincracker, Vt.

http://amfone.net/Amforum/index.php?action=dlattach;topic=36077.0;attach=42203

I will check out in the parts building and let you know if I have them.  I am pretty sure I do.  If I do have them, where do I ship them to?

73,
Joe, GMS

Hi Joe,

Wonderful!

Please let me know any cost involved and I will be happy to send you a reimbursement. My address is:

Peter T. Corrigan
568 Baltimore Rd.
Baltimore, Vt. 05143
N2IDU

If you need to communicate further with me via email. I am good in QRZ.

Thanks,
Pete

Consider it a gift.  I will pull the transformers and get them mailed out by tomorrow. 

73,
Joe, GMS

True spirit of Ham Radio.

Fred

You've got that correct Fred. It is the true spirit of ham radio. My ham radio friend is thrilled the HT-37 can now be repaired, thanks to the generosity of Joe W3GMS.

Peter

I pulled the two transformers off the parts rig.  I get continuity between the green and black wires but the other two wires appear to be open.  Tried to buzz them out to the other winding but still can not find continuity.  At first I thought this transformer is bad but the other transformer is acting exactly the same.  Its hard for me to believe I have two bad ones.

I no longer have a manual so I can visually see what the transformer looks like from a schematic perspective.

All is not lost if these two are both bad since I have a second parts rig. 

Joe, W3GMS     

Joe,

I have not run into this in my own HT-37 or another I restored but I expect these are subject to the same problem that kills the Central Electronics transformers and the audio driver transformers in Johnson, Heathkit, and other rigs.  The high impedance winding uses very fine wire that is easily destroyed by the acidic insulating paper used in vintage transformers.  It probably happens more quickly in a more humid environment but it can hit any of these old transformers. We really cannot complain because they lasted a very long time but this isn't uncommon.  Vintage relays with high resistance coils are another example of this problem.

Hi Rodger,
I am sure your right. 

I have confirmed that both transformers from my 1st parts rigs have an open winding.  Its also the high impedance winding that has opened. 

Good news is that I retrieved my 2nd parts rig and just removed the first transformer and its good!  Now if the second one is good Peter's friend will be all set.

73,
Joe, GMS 

Joe,

In any case, if the second xformer's primary is open he could go to the alternative fix using a pr of 115 to 6v filament xformers as stated in earlier posts.   All is not lost.     The HT 37 is a great exciter...

In my HB SSB rig I built back in 1952 (I was the 3rd station on 75 SSB in DE back then, EX signal drifter ---> HB phasing ssb generator ---> GG 807) I used a pair of UTC special series potted audio xformers (they were on the shelf in the lab) in the phase modulator and that rig worked the last time I checked it a couple years back....

I had to build the audio phase shift unit as B&W hadn't built their plugin unit yet...Lots of fun with capacity bridge and scope...

It might be wise to measure impedance ratio between primary and secondary, resistance of the windings, etc. to keep on hand for future problems when an actual exact replacement is not at hand. There might be other transformers out there in the real world that can be used as a replacement. Hallicrafters, like a lot of other manufacturers, were not very detailed on specs for their transformers and other types of inductors.

Yes!

Second transformer from second parts rig is good as well!  So now the requirement of 2 good transformer is met!  

Hi Z winding = 1K DCR with 23H of inductance
Lo Z winding = 40 ohms with 950 mH of inductance

Voltage turns Ratio: 1:5

The frequency response is very good.  About a 1.5dB down at 100 Hz and flat well beyond 10Khz.  Those measurements were taken without any DC flowing through the transformer.     

Both transformers essentially read the same.  

Heading to the post office Peter so they will go out today.

Joe, W3GMS  
 

I did most of that Pete, but based on your suggestion will feed a small amount of AC into one winding to get the turns ratio. 

Joe, GMS

Ralph,
We always knew that you were ahead of your time OT'er!!  Hope all is well.
Joe, GMS

Joe,  I also run low on some letters and try to save some for more important words.  As luck would have it, I have some extra "Ks" that I'm not using.  So here's one for you, at no charge.  A bargain at twice the price.

"k"   ;D

Fred

People tell me I should proof read better and that is true Fred!  My mind goes very fast and my typing generally falls behind!  Its a problem I have always had so its not related to me getting older!  My English teachers in high school use to tell me that its good that I was going to be an engineer!!  Also you can tell I did not go to catholic school otherwise I would not have survived!! 

 

I just added in my former post the turns ratio information along with the other data I took on the two good transformers. 

Window at the post office closes at 4PM Peter, so this will now go out on Monday.

Blame it on Pete, CWA for wanting more DATA  ;)

Joe, GMS

If you lived in Jersey, post offices are open on Saturdays.

Those transformers don't look that big to have 23H of inductance on the primary but then again, I don't remember ever owning a HT-37 so can't picture the actual size.

Lots of very fine turns on the high impedance side of the transformer which also makes it vulnerable to opening as Rodger pointed out.  I was amazed that the first two on the first parts rig were bad.  Fortunately the second parts set had two good ones.  All the readings were taken on my HP-4261A LCR bridge.

Joe, GMS   

A thousand thanks Joe,

Sorry to hear that you had to go to so much trouble with the first Ht-37. I am delighted you were able to find two good ones.
I'll let you know when they arrive.

Thanks again.

Peter
N2IDU
Old Shincracker, Vt.

Peter,
 
My pleasure helping out on this project.

Joe, GMS