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Plate chokes. Who you gonna call?

linearone

King of NY
Apr 2, 2005
902
264
73
Rotten Apple Trees
www.acboxes.com
I had always wanted to order a peter dahl plate choke but when they sold to harbach that ended. Jeff has no intentions right now to start making plate chokes. Who would you call tomorrow if you wanted a plate choke custom made in the 4 amp range? Obviously I want a reputable company that can test it for any self resonances in the "hf" bands.
 

For legal limit amateur band amps I would get one from Ameritron but for what you want you are pretty much SOL I think. Time to start thinking about winding and testing your own.
 
Yeah, I just hate the idea of using the MFJ as a grid dip meter. Perhaps I will buy a dedicated unit.

Anyone ever use ferrite loaded chokes? They seem to have a mixed review online with some folks saying they heat up. Its my opinion they aren't properly securing the ferrite in the telfon with an epoxy or something letting it vibrate.
 
I've been wondering about this, are you talking about the plate choke found on the plate cap of an amplifier/transmitting tube? Typically a higher wattage low value resistor wound loosely with wire, that one?
Or, the one that typically stands up in the amplifier, usually of very small wire, maybe with more than one 'coil' that the above thingy attaches to?
- 'Doc

(the smaller thingy usually called a parasitic suppressor)
 
I've been wondering about this, are you talking about the plate choke found on the plate cap of an amplifier/transmitting tube? Typically a higher wattage low value resistor wound loosely with wire, that one?
Or, the one that typically stands up in the amplifier, usually of very small wire, maybe with more than one 'coil' that the above thingy attaches to?
- 'Doc

(the smaller thingy usually called a parasitic suppressor)

yes, not a parrasitic.

I just spoke to a hamster buddy of mine and he is going to lend me his very old dipper. He says he has all the coils for it so we shall see. I will probably groove a Teflon rod approx 1" diameter, bore a hole in it, load it with russkie ferrite and wind it up with 18awg 200c wire and see what happens.

I expect 300uh+. You can sneak by when playing with low power but at 4 amps any deficiencies will be readily apparent!
 
Update. I got around to this this weekend. I took the same teflon form and turned it on the lathe to make a little recess for the coil to lay in. Thought it would hold the windings better. I bored a length wise hole about 3/16 or 1/4" in diameter a few inches long down the center.
Wound it with high temp 18 awg 200c magnet wire. got 56uh. I shoved a russian ferrite rod in there of unknown permeability (think I was told 61 mix but cannot be sure). 5 minute epoxied it all in and closed the top . It now is double the inductance, roughly 116uh. Stuck it in box, secured it with nylon 1/4-20 screws and keyed it up. No issues thus far.
forgot to use the boonton gdo on it though... oh well.

linearone-albums-linearone-s-cb-pictures-base-mobile-picture2172-plate-choke.jpg


I make a nice choke.
 
If you are simply dealing with a monoband amp then making a plate choke isn't all that bad especially for 10/11m. It's quite easy to get enough inductance on those freqs. and you don't have to worry nearly as much about resonances as they are usually much lower.
 
what would you have reccomended?


Actually in my post above I forgot to commend you on the choke you made. It looks great and I would have done the same thing. (y) If I had a lathe I mean.:D

BTW, the first amp I ever built was for 11m and consisted of a pair of 6KD6's. The plate choke was the barrel of a Bic pen close wound with vinyl covered 24 ga. wire and the pen barrel was filled with ferrite beads.I could watch the power output increase each time I dropped another bead into the choke core. :laugh: Your choke looks a lot better than my first one. Plate voltage was 800 volts BTW on that little crappy insulated wire. :laugh:
 
Actually in my post above I forgot to commend you on the choke you made. It looks great and I would have done the same thing. (y) If I had a lathe I mean.:D

BTW, the first amp I ever built was for 11m and consisted of a pair of 6KD6's. The plate choke was the barrel of a Bic pen close wound with vinyl covered 24 ga. wire and the pen barrel was filled with ferrite beads.I could watch the power output increase each time I dropped another bead into the choke core. :laugh: Your choke looks a lot better than my first one. Plate voltage was 800 volts BTW on that little crappy insulated wire. :laugh:


lol.. sometimes the small stuff is more fun! big parts are easier for me to get my hands on now...lol
 
Nice looking choke.

If you are building a multi-band amp you can always use another choke installed at a 90 degree angle like the old 4-1000 amps use to get the extra inductance you are looking for.

Monobander that looks like it should work fine.
 
Judging from the corrugated transmission line (and 4 amps), I'm guessing there is reasonable power here. I question if the core material will stay cool under full power. Considering the full RF voltage on the high impedance side will be dropped across this choke, I would expect extreme core heating and possible damage to the core permeability. If the bottom of the core is close to ground there is also the chance RF could arc through the Teflon to the core looking for ground. If it works, great. If you have problems with heating and don't run under 15 MHz, that choke should work fine without the core. If it gives you any problems under full power you can probably just press out the core since nothing sticks to Teflon well. I also have to add that you do nice work with attention to detail.
 
Judging from the corrugated transmission line (and 4 amps), I'm guessing there is reasonable power here. I question if the core material will stay cool under full power. Considering the full RF voltage on the high impedance side will be dropped across this choke, I would expect extreme core heating and possible damage to the core permeability. If the bottom of the core is close to ground there is also the chance RF could arc through the Teflon to the core looking for ground. If it works, great. If you have problems with heating and don't run under 15 MHz, that choke should work fine without the core. If it gives you any problems under full power you can probably just press out the core since nothing sticks to Teflon well. I also have to add that you do nice work with attention to detail.

Thanks shockwave. Currently I have passed 2 amps through it without issue BUT I havent been on the key for a long period or time yet. When the skip rolls we shall see how its long term durability holds up. I stated 4 amps because there is an extra hole in the deck I'd like to fill some time soon.
I only placed the ferrite in from the top and its only about a 3 1/2" long section. Its WAY far away from the bottom and if you notice I didnt try to place any conductors on the top of the form for support. I just ran the lead out and away. I too am worried about the idea of the ferrite heating etc but only time will tell.

I seem to remember a chart somewhere on the interweb that showed inductances and their (generally) resonances. I remember that 60uh was supposed to be resonant on 26mhz or something. Any clue if this sounds familiar? Maybe it was in a handbook or something.

on another note the choke this one replaced was working. It was fugly and made with teflon wire and was only 29uh.
 

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