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1.0 mh Choke

Crusher

Well-Known Member
May 12, 2007
838
369
73
Looking for a 1.0mH-2.5mH rated at about 1amp. For a project I am working on. Anyone know were I may be able to locate one? Using it as a safety choke so that if blocking caps would go, it would short out HV supply so that I don't have HV going to antenna.

Any help would be great.
 

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
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Nova Scotia,Canada
If that's all you need it for then almost any value will do. Heck,grab a piece of ferrite rod from an old AM radio and wind it with 22-26 gauge wire and your done. The only requirement for value in such an application is that it have enough inductance to block the lowest frequency you will be using. Even if you operated on 160m the ferrite rod idea will work.
 

Crusher

Well-Known Member
May 12, 2007
838
369
73
OK, Well I have plenty of 6" in length ferrite rods that are 1/4" in diameter. The permeability is 400. I wound one with some 16 Gauge enameled wire and it gave me an inductance reading of 320uH. Will try using something like 22-24 gauge maybe doing a multilayer and try and get it up some. Thank you. On a side not, I am using this for 2 gs-35B's. Would this also work for a single 3cx3000a7 or would I have to use a slightly larger gauge for current capability. Haven't used these before and just wanted to make sure I am on right track. thanks again for responses.
 

Crusher

Well-Known Member
May 12, 2007
838
369
73
I should have mentioned earlier, it is for 27-28Mhz circuit. I just did 2 layers on ferrite rod, using 16 gauge enameled wire (it's what I had laying around) and it gave me a measurement of 1.19mH. Thanks again for the advice. As a side not, I just bought 500 feet of 22 gauge enameled wire like suggested off Ebay for future projects.
 

paws264

Active Member
Apr 6, 2005
647
5
28
OK, Well I have plenty of 6" in length ferrite rods that are 1/4" in diameter. The permeability is 400. I wound one with some 16 Gauge enameled wire and it gave me an inductance reading of 320uH. Will try using something like 22-24 gauge maybe doing a multilayer and try and get it up some. Thank you. On a side not, I am using this for 2 gs-35B's. Would this also work for a single 3cx3000a7 or would I have to use a slightly larger gauge for current capability. Haven't used these before and just wanted to make sure I am on right track. thanks again for responses.

Got any pictures of yours?

amp-2.jpg


:)

october011.jpg


.

.
 

paws264

Active Member
Apr 6, 2005
647
5
28
I never have seen one of those choke ever have to come into use but, you put it in just in case.

My plate blocking is 2 X 465pf @40 Kv in parallel which represents about 3 ohms at frequency.

.
 

Crusher

Well-Known Member
May 12, 2007
838
369
73
Looks really good paws. Mine is not completely finished. I still have to install plate and grid current meters. Also have bias circuit done, but waiting till I get meters so that I can get everything spaced right. I had a 2200pf 12kv installed but I am switching out to a pair of 680pf @20kv just so that I don't have to worry excessive current. Otherwise, I might really need choke. I like the KP1-4. I have one of those sitting in a box. Heck of a deal on Ebay. I like the parasitic chokes as well. Especially on these tubes as they can operate at such a high frequency they are necessary. You can't see it in picture, but I have a vacuum relay on the output.
 

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Slam Dunk

Member
Jul 11, 2006
79
0
16
Looks really good paws. Mine is not completely finished. I still have to install plate and grid current meters. Also have bias circuit done, but waiting till I get meters so that I can get everything spaced right. I had a 2200pf 12kv installed but I am switching out to a pair of 680pf @20kv just so that I don't have to worry excessive current. Otherwise, I might really need choke. I like the KP1-4. I have one of those sitting in a box. Heck of a deal on Ebay. I like the parasitic chokes as well. Especially on these tubes as they can operate at such a high frequency they are necessary. You can't see it in picture, but I have a vacuum relay on the output.

I like the way yours looks, well thought out and everything is neatly mounted. What solution did you come up with for the tube sockets, did you make your own or did you buy "production" models?

What about your filaments and bias circuit; when I first started, I paralleled both tubes on the same filament supply but, Tony King (W4ZT-sk) convinced me to go with separate filament supplies, tri-filar cathode chokes, bias circuits and, metering. I ripped the whole bottom out and started over.

dualtubebiasandfil.jpg


I tied fifty 1-watt 33 volt zeners in parallel to come up with the equivalent 33 volt @ 50 watt bias supply. Each tube has it own 33 volt bias circuit which comes out to 100 of the 33 volt, 1 watt zeners.

.
 

Crusher

Well-Known Member
May 12, 2007
838
369
73
For the filaments, I am running regulated DC. For the bias circuit, I am using a 33V 1W zener to drive a 2n3055. That way The npn does all the work. I will have some more pics up when I get it how I want. Both tubes are paralleled. they are fed off the same circuit. Will have to see if one is a power hog over the other. Also have to move my input relay closer to my output relay. The wire is too long and have a high SWR if I try to feed thru the circuit/relays. The case is probably overkill, but tons of room. First AC amp I have built and am using this as my experiment to get things figured out.
 

Crusher

Well-Known Member
May 12, 2007
838
369
73
While we are getting into a little indepth, when winding a choke like this or anything similar, what is safe or should I worry about a choke resonating? Somebody mentioned this to me and was wondering if anyone had input on this. What is safe, not safe, if overkill on the windings is good? just wondering what evrones thoughts were on this?
 

Slam Dunk

Member
Jul 11, 2006
79
0
16
While we are getting into a little indepth, when winding a choke like this or anything similar, what is safe or should I worry about a choke resonating? Somebody mentioned this to me and was wondering if anyone had input on this. What is safe, not safe, if overkill on the windings is good? just wondering what evrones thoughts were on this?

Speaking specifically about the plate choke if, you are building a single band amp especially for thr higher frequencies then resonance is not an issue, the more turns the better.

Same deal on the bi-filar / tri-filar input chokes on directly heated Cathode tubes.

My way for GS-35b input chokes, that's #15 Enameled Magnet wire:

DCP00330.jpg


.
 

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