questions on a big 10-160 plate choke 3CX3000 style

[Opcom]

The 3CX3000A7 amp I was given is missing the plate RF choke. I'd like to find one that will take 5KV DC and 2.5A, since those are the tube ratings. Bands to be covered as the amp is are 10-160. (maybe 6 could be added.. that would be cool) I'd like to avoid self resonances and other evils at this power level due to what can happen.

I've seen chokes that started at the top with a few turns, then more turns, then a lot of turns, ostensibly to reduce capacitance at high frequencies, reduce resonances, and cover the entire spectrum. The amp's pi-net will literally cover 1.5 to 32 MHz, so an approriate choke would be void of resonances in this region as well as having a high enough Z at the low end. No sense making limits on performance. What do you guys think of this?

I am wary of old used chokes again due to the quite high power and I am not confident at this time to wind one properly, as this amp kind of would be costly if it blows up. Would it make sense to use two somewhat different chokes in series?

Isn't there someone, a ham, who makes really good and modern indestruct-o RF chokes to order? If I have this remaining part, I can just about test the thing. Really close. Appreciate any leads.

[nq5t]

Maybe check out the notion of using ferrite in the choke.  See    http://www.kk5dr.com/chokes.htm

[Tom W2ILA]

I used this from RF-parts in the T368 but its not up to your ratings.  K1JJ had done a writeup on winding your own hi-power chokes using PVC forms.  None of my searches turned up the archives though.

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.

[KM1H]

A Google will turn up several choices if you search for "3CX-3000A7 amplifier", or YC-156, 3CX-10000, etc.

Just stick to 160-10.

Carl
KM1H

[K4TLJ]

I found this of interest.
http://www.kk5dr.com/chokes.htm
http://www.kk5dr.com/TestAchoke.htm

[flintstone mop]

OK OPCOM
We know what's going to happen next!!!!

http://www.youtube.com/watch?v=I_QGa4oSMMQ&NR=1

Big Stuff


Fred

[Opcom]

Interesting page there. I do have a large high current large pi-would choke with progressively larger windings as they get to the bottom. It is too tall to fit. Old, bakelite or fiber tube form, with cloth covered wire in the PI sections. I could swep it, but I'm just not sure it would tke the voltage due to the many layers of wire in some sections. It was made for a strapping rig, but not over 2KV I would guess. WWII kind.

Ok, the tools are here - grid dip meter, L/C meter. glue. Need to find a form. I have ferrite from loopsticks. I am willing to give it a try!  KK5DR  - what a real ham. He has done real experimetns and advanced the science. Even if this has been done before, I certainly have not seen it for sale on a shelf.

I need to find the K1JJ article. That seems the most straightforward, PVC is cheap.. and I could slip some ferrite in.

That video made me remember I have no 5 or 10KW slug for the Bird.

Nor dummy load anywhere large enough
I could pulse the RF using a bird 600W load on a 5% duty cycle. maybe. Do the measurement by taking the RF voltage off a divider.

10KW to 50 Ohms is 707V RMS. My amp will not do anywhere near that. Maybe half, in PEP, but the 2.5KVA power supply XFMR is too small to keep it up. This amp will be for legal limit AM only. No CB-blasting and no pissing off the FCC!! I do not wish to be permanently relegated to 4 watts and a CB radio.

How does that Wizard guy stay out of trouble building them CB linears? Does he pay off the FCC inspector or what?

[flintstone mop]

I agree. Where is the FCC during those "key down" contests they have.

Fred

[Detroit47]

I agree. Where is the FCC during those "key down" contests they have.

Fred

I asked our local FCC field man that question at a swap, and he said " we don't have any money so if my phone don't ring I don't care what they do"

n8qpc

[Opcom]

wow. I wonder if there are any job openings.

[KD6VXI]

I agree. Where is the FCC during those "key down" contests they have.

Fred

When I 'consulted' for people operating those amplifiers, I had 3 customers that worked for the F.C.C.

One in San Diego (now retired), and two in the Los Angeles office.

The people who work for the FCC are no less corrupt than any other branch of government.  I know of a handful of 'large scale' amateur operators, a QSL bureau manager, contesters, etc. that all operate on the 27.025 mhz superbowl.

The FCC doesn't care, as someone else pointed out, if their phone doesn't ring.  That, and more than a few of the guys on the FCC payroll are also 11 meter operators.  Publicly or not, is another question.

--Shane

[Bill, KD0HG]

Shane, my experience with the Denver FCC office has been completely different.

Hardworking professionals, every one of them.

And they *do* care. They've been overwhelmed with traveling around everywhere during the digital TV transition, handling tens of thousands of phone calls. Not to mention all of the (99.9% ridiculous) complaints about radio and TV programming, RFI, pirate broadcasters and internet issues. The last thing they have time to do is hang out and punk CB shootouts. If you want that level of enforcement, then ask your congressman to fund more field inspector positions. They had to close down many monitoring stations years ago for lack of funding.

"Corrupt" is a completely false and unfair allegation. I've worked with them for years on interference, broadcasting operations and inspections. Professional and helpful has been my own experience. They want to solve problems, not write up violation notices for the sake of doing so. They don't have a quota for speeding tickets and they likely have to put up with BS from upstairs like many other employed individuals do.

Don't tar everyone with the same brush.

[W7TFO]

I concur with Bill.  The FCC out of San Diego (where the Arizona stuff is handled) has always been cognizant and fair.  Lately they have been a bit more tempered, sorta' real world human feelings mixed with high tech.

It was obvious they didn't dispatch without a good reason.  Gone are the days when they 'trolled' for violations by just driving from town to town.

The new field vehicles (Chevy Tahoe's with custom systems installed) are impossible to hide from, be it pirate radio or just a intermod problem.  Reportedly they bought a whole fleet of them for use everywhere.

Interestingly, the agents I dealt with didn't do 'CB' or ham enforcement, said that was another team out of the same office that also did the part 90 stuff.

dg

[KM1H]

Gee, I hope they wont spot my 6AQ5 AM BCB broadcaster that covers most of my property playing 50-60's sounds

My dealings with the Boston office were always absolutely professional, especially when I first moved here and one neighbor was raising holy hell about the then 160' tower. He told me he was conned into coming out and I wouldnt be hearing from him again.

Carl
KM1H

[Opcom]

I don't think the FCC is corrupt, but they will take your fees and not help you, and just keep them. speaking of pirates, Halloween is always a big night. I'll try to listen for some. I might go out to the countryside with a plastic radio and throw out my spool of #14 between poles at a friend's farm. I have only ever heard one real pirate on the air and it was on halloween.

But wait, I only want to finish repairing that amp for legal AM use on the hammy bands. I don't intend to run over 1500W peaks. The bigness of the amp will make it last a long time and run cooler since AM is always hard on amplifiers. If I were to run 4KW peaks, then it would have the same issue as my NCL-2000 at 200W carrier/800W peaks - -overheating! And I think it will be cleaner too (I hope) since it will run at far less than its max, and has a pi-L as I have discovered. There is this weirdo dual-section bandswitching in the plate area, and I could not figure out why the extra coil with all the turns was there. Then the light went on, and I traced it out. huh.

somewhere, in another hoard yet undiscovered, lurks the parts to make another one of these. asked the gentleman about procuring them. What happeend according to him was the builder's friend wanted one too, and for whatever reason, perhaps cost, changed his mind after all the sheetmetal work was done and some parts obtained.

I have now noticed there is not much height room for the RF choke. It is supposed to sit on to of that black capacitor in the tube compartment. I think. I have never seen a stout choke, only tall and skinny.

what you guys think on that? I'm almost scared to fire this up. The choke is missing for a reason, but what? did it cook? was it needed elsewhere?

also look where the adjustments for the cathode tank are. Yikes!

[K5UJ]

I guess I'm missing something.   I was thinking if there is a cathode tank ckt. u must be talking about tuned input?  but in the photos i don't see one, or at least I don't see any adjustment controls.   

Generally I'd prefer to have a more space in the cabinet between components but I'm sure I'm stating the obvious to everyone here.

rob

[KB2WIG]

 " I have only ever heard one real pirate on the air and it was on halloween. "

The most memorable one I remember said the following

" WRNO is a Communist plot " zero beat with 'rno.

If we talk r/e pirates, did we hijack this thread??


klc