What about QRO Plate Chokes??

[WBear2GCR]

Ok, so what about QRO plate chokes?

Simply "solenoid" - straight winding - wound on a ceramic form, all you need??

If so, why buy one if you have wire, varnish, a ceramic form and some time??

What's the sophisticated RF savvy ham's inside info??
What's the considerations to check for or design to prevent resonances in band, or in general??


          _-_-WBear2GCR

[K1JJ]

A strapping and cheap way to go is to cut off a 1" diameter, 14" long piece of PVC and wind #20 - #22 insulated wire on. Put three 'L' brackets on the bottom.

As far as resonances, it should be checked in circuit becuz of additional tube and component influences. ie, At higher freqs, you may see a good choke, series resonant out of the ham bands, on the bench... but in circuit, it could be pulled into trouble areas.

I just wind it and then test it on all bands in a hot rig. Out of about 25 chokes I've made, I can remember maybe two that blew up cuz of resonances right off the bat.

My point is it's actually difficult to wind a choke that happens to fall into the ham bands simply cuz the bands are such a small spot in the spectrum. You'd have to be unlucky to do it.  But if it blows up, just rewind it a little differently next time.  Quickest way.

Here's the plate choke I wound for the new 4-1000a X 833A's.  I tested it on 160-20M and runs FB at maximum power out. Like the pretty stripped blue color?

http://home.comcast.net/~k1jj/wsb/html/view.cgi-photo.html--SiteID-3018584.html

Same with the 813 rig - this choke is black cuz I taped it over:
http://home.comcast.net/~k1jj/wsb/html/view.cgi-photo.html--SiteID-3018598.html

73,
T

[WA1GFZ]

B&W 800 I've tested at 5 KW peak designed for 1 KW AM 80 through 10 meters. it does have a bad spot around 25 MHz. The B&W801 works good on 160.

[n2bc]

I've used RFParts RFC-3 ($25ish) on 160 thru 10 with good results.  It's relatively small (1" x 6") if space is an issue.

Bill N2BC

http://www.rfparts.com/choke.html

[WBear2GCR]

GFZ,

can you post a pix of that B&W choke?

Tom,

14" long!! Dats a big un!

          _-_-bear

[K6IC]

The RF Parts and the Ameritron Plate RFC's look the same to me,  and not too expensive,  as noted ... ceramic form,  tapped at the base and has lugs for wire -- covers 160 - 10 M.  Ameritron runs about 3650 VDC on plates of largest amps,  but for Plate Modulated rigs,  the V rating of this item may not be enuf ... prob OK,  but U never know.

VU san  has wound many more RFC's than I,  so would use him as a reference.

Richie Measures has some strong beliefs about plate RFC's.  Some feel that he issa bit too compulsive,  but he has some good reading in his articles ... somewhere in there is one about Plate RFC's ...             

 http://www.somis.org/

Good AM  Vic  K6IC

[KL7OF]

I made the plate choke for the Collins BC transmitter by close winding #24 enameled on a 3/4 inch PVC pipe form.  There are 6 inches of winding.  The choke showed no resonances on 40 75 or 160 with the dip meter and has worked in the circuit on 75 without heating or any other problems for 3 years...wrap it tight and use several coats of cheap fingernail polish on the end windings to hold everything together. Good for full scrote .......

[K1JJ]

..wrap it tight and use several coats of cheap fingernail polish on the end windings to hold everything together. Good for full scrote .......

Yep, Art Collins would be proud...    EZ enuff to wind them.

BTW, To hold the end wires, I drill a tiny hole through the PVC on both ends and slip the wire through.

T

[W1ATR]

I read somewhere about a guy that drills out the center of a 1" teflon form and stuffs a ferrite rod down in there, then seals it back up with hot glue, of something. I guess it's supposed to make a short coil think it's a big one. (eg 90uH will act like a 1000uH.)

I'll see if I can find the article and send it up here.

SK

[K1JJ]

I read somewhere about a guy that drills out the center of a 1" teflon form and stuffs a ferrite rod down in there, then seals it back up with hot glue, of something. I guess it's supposed to make a short coil think it's a big one. (eg 90uH will act like a 1000uH.)

I'll see if I can find the article and send it up here.

SK

I once had a big rig that wud not quite cover 160M, just 75M cuz the plate choke did not have enuff inductance. So I tried adding a short stick of ferrite rod down the center of the choke.   On 160M the ferrite got so hot it snapped into two pieces. I burned my fingers taking it out.

Probably not a good idea doing it with high permability ferrite... :-)   (But it works really FB for low impedance fil bifilar chokes)

I have seen this done for tank coils in the Alpha linears... they will use a donut core for 160M if I remember right...  Probably low perm material. Used to save space in the rig vs: a big coil.

T

[WBear2GCR]

Yah mon!

Kewl beans!

I shall wind me own, matey!

(found the B&W pix on the web... no prob)

Have some delrin on hand... PVC probably, and the guts of a commercial Wilcox "exciter deck" to check to see if there is one already made in it... ceramic would be nice ( it does have a big arse neutralizing cap fwiw...) .

Will check Rich Measure's site... may use his nichrome parasitic concept... seems to make sense.

Also take a look at both of my copies of Orr's hdbk...

Anyone ever put two in series where the realestate is at a premium?? 

           _-_-WBear2GCR

[KL7OF]

..wrap it tight and use several coats of cheap fingernail polish on the end windings to hold everything together. Good for full scrote .......

Yep, Art Collins would be proud...    EZ enuff to wind them.

BTW, To hold the end wires, I drill a tiny hole through the PVC on both ends and slip the wire through.

Tom .....I drill some small holes for the wires in the ends  and drilled additional holes to mount two small copper tabs that the wires are soldered to.....The stock collins mounting hardware  fits on the end of the copper tabs..The fingernail polish (I use green) holds the end wraps until they are soldered and looks cool as well... I tested the particular PVC pipe I used by taking it for a ride in the microwave oven....It didn't heat up.....Good for RF

[K1JJ]

[... I tested the particular PVC pipe I used by taking it for a ride in the microwave oven....It didn't heat up.....Good for RF

Yes, agreed Steve. I tried it myself and found the same. In addition, I've put some serious power through various linears on many HF bands and then felt the PVC choke form to be sure. Except for some radiant heat from the tube, they run cold on HF. (as you'd expect)

If the choke heats up, it's probably a series resonace. As you know, there are "degrees" of series resonance... it can be right in the band of close by...

BTW, for the archives,  I've found if an amplifer tunes real broad and sloppy, especially on 160M, there is a good chance that the plate choke needs more inductance. By JSing in another choke in series as a test usually cures it. The original choke may even show some heat if too small. This can confuse someone thinking it might be a series resonance instead. It's always amazed me how much choke inductance is needed for 160M. That's why you see 14" long, 1" diameter chokes in my 160M rigs... overkill. (using #24 insulated wire can require them bigger than normal)

73,
T

[n2bc]

Quick note regarding the RFParts choke.

I've used 3 of them:

1)  2x4-1000 amp, 4KV on the anodes, class C and AB1
2)  2x4-400 AM rig, modulated by 2x4-400s (rebuild of an RCA BTA-1R1)  3.2KV on the anodes in 'illegal mode'
3)  5CX1500 AB1 linear /w 4.8KV on the anode

1 & 2 are 160 thru 10 w/o WARC, 3 is 160 thru 10 including WARC.  The chokes have worked fine.

While a near operating freq resonance will kill a plate choke in short order, equally important to the choke doing it's job is the use of a good quality, high current rated bypass cap. 

[pwfallon]

Regarding the RF Parts RF plate choke, any idea as to the max plate voltage rating?

Joe (aka PW Fallon)

[k4kyv]

That's one of the things I  like about series-fed link-coupled tank circuits.  The rf choke is at a low rf-voltage point in the tank circuit, the midpoint of a balanced tank, and the bottom end of  at unbalanced tank.  The rf choke is less critical.  Almost any rf choke will do, if it has enough current carrying capacity.  Choke resonance is not a factor.

[K6IC]

Using the link noted above for the RFParts choke :

"1.8-30 MHz Amateur Bands including WARC.

Ideal for amplifiers using 811A, 572B, 813, 833, 3-500Z, 8877, 3CX800A7, etc.

Used extensively in the Ameritron and similar Linear Amps.

1.5A, 225 uH, 4 KV max

Size: 5 5/8" L x 1" diameter Ceramic coil form

Part Number: RFC-3     •     $24.95 ea."   ...

I plan to try one in my 'ol  CCA BC rig ... 4-400's X 4-400's @ abt  3100 VDC Plate V.

Look to the west for the flash.

73  Thanks for all the info.   Vic   K6IC

[Opcom]

Talk about an old topic, but might as well resurrent that on that has the best title.

Of the choke materials, which do you prefer and which do you dislike and why?

ceramic

teflon

delrin (acetal resin)

PVC

I'm going to try winding my own. 4500V, 2.1A peak on a 3CX3000. I would not like it to melt or otherwise explode the first time. A 12" long 1" diameter teflon rod is $20. Not sure about ceramic except it is not easy to drill. I been warned about PVC burning at the higher end of HF.

[Detroit47]

Talk about an old topic, but might as well resurrent that on that has the best title.

Of the choke materials, which do you prefer and which do you dislike and why?

ceramic

teflon

delrin (acetal resin)

PVC

I use the microwave test if it gets hot in a microwave don't use it, so that leaves PVC out. I have also seen ceramic fail at high power due to impurities. Teflon is by far the best choice.
John N8QPC

[N8UH]

You can get Teflon round online for about $13:

http://www.onlinemetals.com/merchant.cfm?pid=6517&step=4&showunits=inches&id=214&top_cat=181

I order from them a lot 

I was also wondering about Delrin though. Machines very nice, and is a bit stiffer.

[The Slab Bacon]

But be careful with teflon as well. If you do do something that smokes it out
(arcing and burning) it puts out some seriously noxious and poisonus smoke.
It is not likely to happen easily, but it can happen. It takes a LOT of heat to do it.

[Bill, KD0HG]

I had the same experience as JJ using a ferrite bar inside a hollow plate choke. Got so hot it shattered pieces everywhere.

You can help inhibit resonances by close winding the choke for an inch or two, then leave 1/4" gaps between the succeeding close-wound sections.

If used, VHF parasitic suppressors should be air wound out of lossy wire like nichrome, which will also help stabilize an amp. I use pieces of #16 galvanized steel fence wire.

[KM1H]

Ameritron supplies the choke to RF Parts. And its more than ample for a pair of 8877's on CW/SSB. I use it in all my AM amps and the cost is so low its not worth the time and effort to wind one. Its high inductance and 160-80M reactance make it ideal for keeping RF out of the PS and not overheating the bypass cap as do some amps that actually use the choke as part of the tank circuit.

The 802 is the currently available 160-10M B&W choke and it includes the WARC bands where the 801 fried. Its a bolt in upgrade in many commercial amps going back to the 60's including the Alpha 77DX and SX.

The DC voltage is virtually the same at both ends of the choke and isnt an issue. However RF voltages from an improper HB version with in-band series resonances can get extremely high and destroy a choke in under a second. Large wire has no benefit and can create problems with distributed C forming extra resonances. For 1500W PEP AM #26 is sufficient if you dont use some easily melted form such as PVC.  Ceramic or hard Teflon are the choices commercially.

Carl

[KA8WTK]

Curiosity speaking here.....
How about a plate choke from an old broadcast transmitter? I have several of what appear to be old broadcast chokes, in that they are much larger than what you find in most amatuer equipment.

[The Slab Bacon]

Curiosity speaking here.....
How about a plate choke from an old broadcast transmitter? I have several of what appear to be old broadcast chokes, in that they are much larger than what you find in most amatuer equipment.

If they have enuff inductance to work down there, they should be OK-Fine up on the short wave bands. Just check em for series resonances.