The AM Forum

I think my Viker II is ready to give a try and is transmitting fine into a dummy load.  Its time to give it a try on the air but my wimpy little MFJ tuna will have issues I think and I want a new reason to do some homebrewing 8)

I want to throw together a K1JJ tuna.  It looks easy to build and will probably handle anything I could throw at it.  The only problem I am having is sourcing the parts.  An air variable or vacuum variable seems to cost a lot more than my currently unemployed arse can spend so I was wondering if anyone had any inpoot on finding these gems.  eBay is out of the question for me...i got burned a few times and through in the towel on that headache. 

Thanks for any tips or suggestions to help me get this project going.

Chris.

I was just at Murphy Surplus this past Saturday. He had some bread slicers.
you can wind your own coils.

I too am working on my Viker, and am also thinking about building the same tuner. I was planning on using a Vac Variable, just so I could use it with the 813 rig I'll be building sometime in the future. ;D

I checked the Max-Gain systems site, and they seem to have decent prices. I sent them an email to see if they have any scratch 'n dent or out of spec caps, but I never got a reply ???

But, they seem to have a good selection.

Here's a link:
http://www.mgs4u.com/index.html

Call Alan Bond on the phone. He'll work with you. Max Gain is a good show.

Hi Chris,

Yes, Huzman made a good suggestion abbout calling Alan Bond at Max Gain.  We have both done a lot of biz with him and he's the best. Always really good prices and he's a trusting soul. He will always let you return stuff that isn't right.


A vac cap is best, but a breadslicer is OK too. If the breadslicer arcs over under extreme QRO, then you can usually find a lower impedance set of tap combos that will reduce the voltage.

That tuner is an education in itself about matching the line to the rig. Be sure to use preset tabs for all bands once you settle into the best 1:1 matches. In becomes a no-brainer to change bands.

Post a few pics when you get it running!

T




Just so others know what we are talking about:

http://amfone.net/Amforum/index.php?topic=18054.0


There's also a ton of threads about the tuner with a search, "K1JJ Tuner" on this website. Make sure you are on the AMfone "home" page when searching.

Steve and Tom, thanks for the info!!! I (and I suspect the OP) will give him a call tomorrow. :D

eBay has numerous good Russki VC variables at reasonable prices,  I've bought aplenty and always gotten my moneys' worth.  Make sure to get the drive mechanisms if you can as well....The shipping is easy from the Ukraine & the like.
73DG

Thanks everyone for the replies.  It looks like there is no way around getting this built cheap so I will have to put the project on hold for now.  Maybe at a future ham fest or something I can stumble on cheap parts for this.  After checking out the $$ for these at the links provided I guess you could say I am suffering from sticker shock :o

Oh well, back to pumpin out a wopping 20 watts on my FT-101E

Tom, when I do get this underway i will post pictures.  thanks
Chris.

What do you want for the "big" capacitor?
500pf?   3, 5, 7kv?

I've got some boxes out in the shop...

Might have something..
( I know I have one brandy new 550pf , 5.5kv slicer out there, but that's made of gold...)

How much power are you going to run?


You may not need to go all-out with huge coil and wicked big vac-variable.
Especially where there's a budget involved...

I would NEVER spend $200-300 on a capacitor.. !!
Especially if it's just to make the tuna look cool..

Too bad you won't do ebay, I've bought a bunch of vac-variables on there for under $100.

Bread-slicers too...


I was using a 3kv slicer with my E-rig (300 watts carrier) on arced over a couple times..
But I guess that's going to depend on the bands you operate, and the antenna.. etc.

Chris...Put up a resonant wire ....No tuna needed

Yep, cut a dipole for 3.885 or wherever you want to operate and that way you can at least get it on the air while you scrounge up for the Tuna...

That's what I did, actually have a parallel dipole with a 75 meter cut for the ghetto and a 40 meter under it cut for about 7.220, that gets me up on 7.290 and down to 7.160 "and all points inbetween" (gotta sing that like ZZ Top) without the tuner.

Cost? I had a roll if 14g solid insulated copper, feedline and a W2DU choke... so it only cost me an afternoon of trimming. 

John KX5JT

YEP! :)

There are any number of ways to make your own HV variable caps.  A couple pieces of sheet copper and a piece of glass to separate them, and an arrangement so one sheet of copper can slide so as to adjust the capacitance and you're done.  The guys that build mag loops have some stuff up on the net on how to do this.  Here's one on how to build a differential capacitor, but you could simplify it considerably since you just need a single variable:  http://www.standpipe.com/w2bri/article1.htm

No reason you shouldn't be able to build this for under $30 or so, even if you buy all new copper.

Figuring out the taps and cap settings is a LOT easier if you have a MFJ SWR analazyer, or even better, a network analyzer.  A HP3577A, if you have one lying around, makes short work of this  ;D

Thanks for the great ideas guys.  Now were talking down round my bud git ;D  I really like the idea of rolling my own variable...thanks for the link.  It sounds like a couple resonant dipoles will have to do for now.

OK guys, found something I might be able to use.  It is a very large 1000 pf dual section variable with ceramic insulators.  I think it would be easy to remove every other plate and get the capacity and voltage rating I am looking for.  What do  you guys think?


(http://img692.imageshack.us/img692/92/caps005.jpg) (http://img692.imageshack.us/i/caps005.jpg/)

That will work out just fine with every other plate removed. 500 pf will be enuff. Be sure to mount it insulated above ground as per the schematic.

T

Don't trash it, trade it for someting better. Try to use it as it is. I use a pair of 300 pf 10,000 volt caps in the fugly tuner. 2000 pf makes a good loading cap

hey Chris,
You're on a good track with the cap. Take it slow. The next will be the coil. Everyone has their favorite flavor on how to do it. I think I made my coil from 50 foot 1/8? dia? copper tubing from any home  improvement store.
Beings that you're still low power, use what you have now. And just take easy steps. Sept is the start of lower noise from MaNature, so you got a while.
The JJ tuner is easy and goodness and will handle legal limit......no sweat.

The bands are really noisy here!!! ( The Phils) S-9 40M,20M.....15 and up less noise.

Fred

Chris,

Is that cap 1000 pf PER section  (2000pf total) ?  or 500pf per section?   If 2,000 pf total, 1000 pf is a bit much if you remove every other plate cuz the voltage rating will still be low.  In that case I wud take Frank's advice and trade it for a 500 pf at 6KV or more.  Those 2000 pf loading caps are rare and I'm sure someone here wud love to swap it with you for a BC-610 style plate tuning cap or similar type that wud be perfect for your tuner use at 1 KW +.

T

I have an extra BC-610 plate cap (dual 150 pf/section @ 3/16" or 7 KV spacing) that I would be willing to trade for it.  It would be a shame to trash that cap by removing attempting to remove every other plate.  Besides, it  looks like a Cardwell cap, and those are harder impossible to modify like you can the ones made by EF Johnson.  The rotor plates can be disassembled, but the stator plates are press fitted together, and possibly brazed. About the only way you could remove them would be to chop them out, but then the spacing of the capacitor wouldn't come out right, since removing every other rotor plate reduces the spacing of the remaining ones by the thickness of a plate, while chopping out stator plates leaves the spacing of the remaining ones unaltered.

Let me know if you are interested in a trade.

Tom and Don,
The cap ended up being 1000pf per section and I really didnt want to hack that one up anyway...it was too purdy :-*  I didnt have the cap but was working out a deal for it and ended up passing.

I was offered this one by the same fellow though yet it is only 260 pf.  It is also a cardwell though and has higher spacing/rating although I am not sure what the rating is.  What do you think?  He is also throwing in a 100pf and 200pf door knob caps.  Could this be an option?
(http://img143.imageshack.us/img143/7443/capps001.jpg) (http://img143.imageshack.us/i/capps001.jpg/)

Chris.

Measure the spacing between stator and rotor plates.  Some of the common spacings that I recall are: 0.175" = 7 kv.  0.25" = 9 kv  0.125 = 4500v.  You can find a chart of all the common spacings in most any radio handbook, at least in the older ones printed in the days when hams actually built rigs.

If you need a split stator cap, it is easy to convert a single section one, even a Cardwell.  Disassemble the capacitor and carefully remove  the middle plate or two plates (depending on whether it has an  odd or even number of plates) from the stator.  Now (in the case of the Cardwell) cut the stator frame exactly in the middle, again extremely carefully and leave a gap that is at least twice the width of the plate spacing.  File it off smooth so there are no jagged edges and reassemble the capacitor.  Since you have the 1000 pf/section split stator one, study exactly how it is constructed and reproduce that physical construction for the other one.

Because of the removed plate(s), the total capacitance of the converted capacitor will be slightly less than it was as the original single section one.

That 260 PF cap ought to do the trick, looks like the spacing is wide enough for a hunnert watt carrier rig.  Remember on voice peaks the voltage will be quite a bit more. 

How much voltage is at the cap depends on where you are on the node of your feedline.  If the voltage is way high, add a bit more feedline or cut a bit out.

There can be truly amazing amounts of circulating current in these tunas, so the door knobs may or may not work.  Worth a try though.

i agree with JN; the spacing in the 260 pF cap looks okay.  I use these 250 pF CRL hamfest doorknobs in a tuner on 160 here running about 250 watts.  They get a teeny bit warm to the touch on a long transmission.

Great thread.

I'm gathering pieces parts also now for a K1JJ link coupled tuna also Chris.

I have a hunch but want to know, from them that know, what roll the doorknob caps play, when to use them and what values to look for.

Also, If using a Vac. variable, what value ranges (upper & lower) will put the K1JJ type tuna safely in the legal limit range.

                                                      Tanks, Happy Friday, DJ

You should avoid using the doorknobs...
IF your variable cap needs just a little more capacitance, you could try to add a doorknob in parallel with the cap (or each segment of the cap if it's split/ganged)

But the power you run and antenna load etc will determine how much circulating current and voltage, .... doorknobs may/may not handle the task.

7 to 10kv is a safe voltage range... but must be able to handle the current too.

I've used a 5kv... ok most of the time, but when you hit the right antenna+feedline/frequency combination, sparks can fly!

DJ,

The guys got it correct on the doorknobs.  They can be used as coupling caps in plate circuits and bypass caps at the bottom of a plate choke. However, resonant circuits, like tank circuits, have tremendous circulating current depending on their Q.

These old TV door knobs were designed to handle high voltage(30kv) but handle only low RF current, less than a few amps in some cases. So they will literally explode when used in a 1KW amplifer in the plate tank circuit as C1 or C2. I've seen a friend do it when using them as plate tuning caps with a switch on a 4-1000A linear. I warned him, but what a mess he had to clean up... :)


Yes, 260pf will be OK in the tuner. As I mentioned, if you run out of capacitance, there is usually another combination of taps where you can use more coil and less capacitance to find a good 1:1 swr match. There are usually at least two sets of combos. The Q will be different, that's all.

Worst case is look around for a suitable padder air variable. OR, find a small fixed vac cap. Some of those 100 -200pf fixed caps are cheap.  

Another solution is to use a high quality doorknob designed for current. . There are ones that are like, 100-200pf. They are designed for high current RF and good for 5-15KV or so. Some are beige with silver plated tabs. They are at flea mkts, usually <$10.

T

If doorknobs are a problem Fair Radio has 1 MHz tx micas for sale.

OK, I'm getting a better idea of the value ranges.
I'm trying to wrap my head around the theory, not just Lincoln log this together.

While putting together a grocery list for the meat and potatoes components I don't want to jump on marginal stuff if holding out yields a cleaner, more rugged, set up.  

As far as vac var. caps, are the Eastern Bloc variety OK from anyone's experience?
Some neat turn counters offered also but not much use w/o the housing and their not giving 'em away  :o . The shipping is also the devil in the details. I'll check out the domestics sources mentioned at the top of the thread also.
For reference, would 10-1200Pf / 4Kv be marginal?  

Chris, I don't mean to co-op the thread here.

                                               D.  

Just skimmed over the thread as I'm about to head out the door, but...

Has anyone logged any typical capacitance values for various frequencies using the K1JJ Tuna?  Yes, the antenna/feedline combination would be a huge variable and no two setups may show the same C value for a given frequency, but a ballpark figure would be nice.

I wonder if a homebrew cap made from two lengths of bare/plated copper tubing, one smaller in diameter than the other, telescoping together, separated by Teflon sheet/tubing, would work.  Thoughts?  ???

I believe 375 to 500 pf is needed to get down to 160 meters, with a 40uH coil.


A 1200pf 4kv cap would be marginal, mostly because I think they are usualll more expensive than a, say, 500pf at 5kv...

I suppose if you came across a real bargain the 1200 would work... probably..
Not sure if it is designed to handle the current.

OK, I have been able to scrounge a few parts for the tuner like this 220pf Cardwell, a few 100pf doorknobs, ceramic stand-offs, large insulated knob and this tapped tank coil which I dont think will have any use in the build.  It is only about 12 microhenries (18 turns, 3 inch diamater, 4.5 inches long) and besides it will be fun to build the large 3/8 copper coil with about 40 turns.  The coil will be cut in half and attached with jumpers for series or parallel hook-up.  I think this weekend I will start the build and go ahead and do it minus the input cap C2 until I can locate one.  Thanks for the input and help guys.
Chris.
(http://img84.imageshack.us/img84/5323/mailom.jpg) (http://img84.imageshack.us/i/mailom.jpg/)

Don't count that coil out.  It all depends on your feedline length etc - IE the total complex load the tuner sees at its terminals.

On 75 the output is tapped at +/- 3 turns on my coil; the capacitor is applied to about the +/- 15 uH points from the center of the coil.    Wind an input link and see what happens!

I find that the parasitic capacitance in my huge coil pretty much precludes its use above 20 meters, so don't go nutso with winding a huge one.

YUP..........JN.
That's what happened to mine.
I thought the total push for the K1JJ tuner was the lower bands to overcome the losses from the crappy expensive tuners.
Fred