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Author Topic: Wanted: Plate Choke for Hallicrafters HT-40  (Read 2323 times)
W9XC
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Posts: 19




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« on: June 21, 2013, 09:04:38 PM »

I need a plate choke for a Hallicrafters HT-40 transmitter I'm restoring. The photo here: http://w9xc.net/projects/HT40Restoration/HT-40-plate-choke.jpg shows an example of one - I don't need the caps or parasitic suppressor but it's not a problem if they're attached. Anybody got one? My email is on QRZ or reply here. Thanks - Les, W9XC
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N3DT
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Posts: 667




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« Reply #1 on: June 23, 2013, 06:02:21 AM »

hammondmfg.com sells new chokes if you know what size you need.  Reasonable prices too, better than buying some overpriced piece of crap from ebay.
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KE3WD
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Posts: 5689




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« Reply #2 on: June 23, 2013, 07:49:07 AM »

Chokes and Coils are the one component that we do not have to purchase ready built. 

It is rather astonishing to see the number of hams on internet sites and forums looking to find coils or chokes like this one. 

Coil winding is a relatively easy thing to accomplish, the amount of math behind it is negligible, plus the fact that the Internet is chock full of automated calculators for these purposes. 

And, if you have the original choke or coil, but it is suffering from burned wiring or insulation, often is the case that you don't even have to know the henry value at all.  Just carefully disassemble the old wiring, counting turns and making a note of such, use the dial caliper to ascertain the gauge of the wire, obtain same, rewind to match what was there. 

If the choke or coil is missing entirely, it is still possible to roll your own, the investigation just has to go a bit deeper as to the parameters, henry value, current handling, etc. -- and come up with a coil form of the right type and size to handle the job. 


73
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W9XC
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Posts: 19




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« Reply #3 on: June 23, 2013, 10:40:11 AM »

David (N3DT), thanks for your suggestion. The part I needed is an RF plate choke, rather than a power supply choke of the kind Hammond offers - I've used their transformers and chokes in tube guitar amp projects, they're good.

Clark (KE3WD), thanks alot for the observations, well taken. In this case, the bottom of the ceramic form of the choke had cracked and broken off where it's attached to the chassis with a bolt. (This may be a semi-generic problem - while looking around a couple weeks ago I came across a closed Ebay auction for an HT-40 choke with exactly the same crack - though why anyone would have bought it in that condition was beyond me.)

I thought about rebuilding the base, say with JB-weld or something, or just rolling my own - the schematic helpfully does list the actual inductance so it's eminently possible. But in this case I wanted the original part if I could get it reasonably.

As it's turned out, another restorer offered to send me an actual HT-40 RF plate choke for the price of postage, so it's all working out.

Thanks again for taking the time to give your thoughts, and to everyone else who took a look at this. It seems now resolved, and I do appreciate your thoughts.

73,

- Les, W9XC
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KB4QAA
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Posts: 2488




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« Reply #4 on: June 23, 2013, 12:37:33 PM »

Hammond DOES sell RF chokes of all varieties.  153x series.   Radiodaze carries the full Hammond line.  Page 49 of Hammond Transformer & Inductor catalog.  http://www.hammondmfg.com/cats.htm

RFparts also carries a wide variety.
« Last Edit: June 23, 2013, 12:43:47 PM by KB4QAA » Logged
KE3WD
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Posts: 5689




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« Reply #5 on: June 23, 2013, 01:12:10 PM »

Solid Potato Salad on the replacement then. 


When having to deal with a cracked ceramic form, I've had great results rolling my own using fiberglass extrusion/pultrusion stock.  McMaster Carr may still sell some, there are other sources. 

Cuts with fine bladed saw or dremel, is drillable for mounting purposes, seems to be about as resistant to heat as the old ceramic - and does not split or crack as the ceramics often do. 


EnJOY,


73
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W9XC
Member

Posts: 19




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« Reply #6 on: June 23, 2013, 02:11:33 PM »

KB4QAA, (and N3DT) right you are!  My bad on the Hammond RF chokes, there they are on pg 49. I'll remember that for next time I need one.

Thanks for the followup and correction,

- Les, W9XC
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