The AM Forum

There is a nice project in this month's QST for a real balanced tuner. A low power copy of the Johnson MatchBox.
And great pictures how to improvise making coil tap points. I wished I wudda seen that when I was building mine.

I think someone copied K1JJ's tuner.......just kidding..........design has been around for a while.

Well I don't have a prescription to QST, but what I built was a copy of the Palstar BT1500. That's a nice design and seems to work well.

I admitted to Tom K1JJ, that I bought and returned a Palstar BT1500A.
I did not open it, but saw internet pics of the interior. Beautiful, well made tuner.
The dual roller inductors were impressive. Expensive as all get out BUT it would not tune the present dipole for 160M. It tried, almost at 2.7mhz, but not 1.880mhz.
I was not going to go through hoops and tricks or adding or subtracting OWL to get it to work.
Paul was not very nice to deal with........."Nothing is ever wrong with my tuners, it's your stuff" I was tempted to keep it, as it did nicely tune 80-10 with no problem.
Maybe show us some pictures.
Fred

Who is Paul?

That tuner is something Id expect of folks who still use PP triodes and OWL ::)
Right out of The Waltons and their Zenith era

Palstar President and CEO, Paul Hrivnak, N8PH

Go easy here, some of us just don't like anything that requires more than one grid or fans blowing thru fins.... :P

73DG

ps..I never watched the Waltons, so there!

I saw that article today in QST.  The particle board construction kinda had me... But hey, work with what you have.   I see the added cap on the input coil.  Standard stuff from handbooks of many many years back.  I dont gear for the solder taps like that.  Looks busy and antennas change.  Better to have some kind of clamp or edge wound job.  Still, I was suprised to see the article. 

C

Thanks Pete...
Reading reviews on eHam and other sites about Palstar led me to the BT1500A. Many had praises for Palstar and the CEO, and how he always comes through.
Looking at the pictures, gave me second thoughts about the ability to continually deal with a 100% duty cycle carrier and antenna conditions changing. The roller inductors were an inch or so in dia.
Here's an inside look:::

http://www.ebay.com/itm/Palstar-BT1500A-Balanced-Antenna-Tuner-Double-L-/140654433026

The relays were well designed to switch the cap for series or parallel tuning. Pretty neat tuner......$$$
Fred

Funny. Yep mine does not have the nice roller inductors and is build on a piece of wood and I use jumper clips to change bands. I have up a 160m horizontal loop and a 40m vertical delta loop and this setup works fine for me. I only run <1kW so no worries. I'll attach a photo to give you a good laugh. I plan to put it in a nice chassis one of these days...

Interesting you call it a "low power copy" (even though the variable caps are from the KW Johnson Matchbox).  In the article, he states "The LCT design is also not limited to high power".  It's all relative.  ;)

It first glance I kind of sneered when I first saw the article, but after reading it, I was more impressed. This is not a step-by-step cookbook type of construction article.  Anyone who desires to reproduce the tuner would have to first learn a little about tuners and then use some of their own ingenuity to build it. For example, he shows a photo of the original prototype, which is substantially different from the final product. The capacitances of the split stator variables is not given; he merely lists them as Johnson Matchbox tune and load capacitors.  A potential builder not familiar with the Matchbox would have to do a  little research to figure out the capacitances and how to reproduce the Matchbox differential variable.  While listing the exact dimensions of his coils, he also includes a chart of inductances and capacitances for the various bands, along with plenty of references to articles in 1960s through 1980s era publications, web site articles and other sources, including has own website. He goes on to suggest other possible variations of tuners, such as using plug-in coils and eliminating the differential capacitor sections, and gives references where one might learn more about this type of circuit before attempting to build one's own.

Although I probably wouldn't build an exact copy of that tuner, which still has some of the same shortcomings as the Matchbox, overall that article was very good, and QST needs to publish more technical articles of that genre, as opposed to yet another station control console, LED "ON THE AIR" sign and novelty QRP CW transmitter built in a cat-food tin.

Of course, QST, ER and other magazines can't publish articles if no-one writes them.

I have not seen the article yet (is it in Feb. QST?) but am looking forward to seeing it.   My current only concern is that it will lead to the destruction of perfectly good Matchboxes.

Fred, this Paul guy at Palstar sounds like a clown.  If he gave me that line about his tuners I'd ask him if his balanced tuner can handle a 15 minute 350 watt AM transmission into a 6 ohm impedance.  I bet those dinky wire inductors would melt down.  I can't tell what they are wound on but it probably doesn't matter.  However, by today's hammy tuner standards, the price ~ $600, isn't a full ripoff but if you put it next to a KW Matchbox or BC939 you see the modern manufacturing deficiencies. 

my fugly cost me about $100. 1500 watts 24/7

I don't know why any one would destroy a perfectly good Johnson Matchbox to then build the same circuit breadboard style.

Wood or particle board is FB for tuners. I don't know where people got the idea a tuner needs to be in a metal box.

Building a tuner is probably one of the best ways to get someone into the homebrew scene. The cost is relatively low, construction is pretty simple and the utility of the end product is great.

Building a tuna in a metal box probably isn't a great idea anyway, considering the possibility for the input link to couple to the cabinet as one shorted turn.  I've read of cases where some hammy built a tuna and couldn't figure out why the cabinet was getting hot.

Considering that Cardwell, Ameritron/MFJ, and OEP are the only variable cap $$ sources remaining and you almost never see anything good at hamfests. That article is going to frustrate lots of beginners and many will wind up getting nasty RF burns using that layout.

The Johnson KW had poor matching range on 80M plus loss on 20-10M and other designs are far superior. A truly balanced tuner would make more sense IMO. Two tapped coils and as many caps and banana plugs/jacks as needed to load into anything would be the way to go.

Many years ago, I purchased an AT1500BAL tuner from Palstar.  It's basically the Rick Measures design which uses an balun on the input driving two synchronized rotary inductors.  The capacitor either bridges across the output or input of each rotary inductor pair depending on if the impedance is greater than or less than 50 ohms.  

Prior to buying the tuner, I had many excellent talks with Paul at Palstar.  He was not nasty or at least bit cocky on the phone.  He knew Fred Hammond real well and shared some neat stories about him.   Maybe the years of dealing with Ham's have got to him!  

The tuner that I purchased was very well built and handles high power very well.  Extremely large edge wound rotary inductors and nice turns counters with excellent construction inside.  A small timing belt is used to keep the rotary inductors in sync.  No complaints at all and with over 10 years of service it has not skipped a beat and I run QRO!  

I love to homebrew, but at the time I was very busy with my career and had no time to build anything.  Previously I used a Johnson KW matchbox but it would not match the impedance of the new open wire line length out to the family room, especially on 160M.  For 160M I had a vacuum condenser in parallel with the coil and with some feedline lengths it worked good, but that was not the case with the family room station.  I did not want to hack up a mint Johnson Matchbox, so I went with the balanced tuner from Palstar.  

Today being retired, I would simply build a link coupled tuner with a single capacitor resonating the coil and taps in to find the resonant points along with the proper impedance point based on the reflected impedance of the open wire line.  Simple and cheap!    

Joe, W3GMS        

I picked up an early MFJ (before called MFJ) low power, portable tuner at a local flea market.   It did not work worth a damn.   I opened it up, it actually used a vertically mounted coil inductor, the top was very close to the metal cabinet cover.    I removed the metal cover and it worked fine.    I made a plastic cover to use in place of the metal one.   Makes a good portable tuner now.

I agree with your comments, except for this. I could have bought nearly a truck load of air variable and vac caps over the past 2-3 years at only a handful of fests. I did by several very nice vac caps for around $50 from a guy at NearFest. He had a bunch more. I should have snagged all of them!



I also don't know why they would get nasty RF burns. Don't touch any metal when RF is present and all is good.  :)

I had a similar problem with a $500 Palastar tuner. I bought it from The Ham Station. When I got it  - it was intermittent as if the SO239 connector had a loose connection. It also had a hard "bump" when tuning the roller inductor.

I called and talked to "Paul" and he told me that the loose connection must have happened after it left the factory - that it could not have left the factory in that condition. I was told to return it at my cost and that I should have NOT purchased it at The Ham Station. I started to get a bit warm and told him I was going to open it up and see what was going on. He did not like it but finally agreed. I opened it up and found a real sloppy problem - the wire running through the toroid for sampling RF was NEVER soldered and was intermittent. The roller inductor had a big blob of solder on it that caused the hard bump. I fixed it and called Paul back. He got angry and told me that could not be the case and essentially called me a liar. He did not even want to see a before and after photo of the problems. I then asked about the solder blob and he told me that the solder blob was normal and that he had another call and had to go.

I still have the tuner - but never will I buy anything from Palastar again.

Pat

Hey "BBQ",
Don't change the layout of your tuner....You and Frank GFZd and few others here use the same open design. Keep your children and pets away when doing an ole buzzard.

Well it'll be a while if I do. That thing has been sitting there for about three years now and no (little) kids and no pets here, so no worries.

1 good RF burn is usually enough to learn ya.

It goes right to the bone!! :o

 ;D  ;D  ;)
been there, done that!! My big HB "hole in the wall" tuna did that on 160. Fine on all other bands. A little re-arranging of the physical positions of a few of the internals took care of the problem.

When running high power AM, (and short antennas) you have to be ready to expect the unexpected. getting all of the bugs worked out is the challenge and half of the fun...........

Reportedly, Blown-Away Bob, K1AJL (SK) used RF from a DX-100 to burn away a recurring cancerous tumour on his leg. Unlike with his initial "proper" treatment at a medical facility, the cancer appeared not to return. He died, likely by accidentally drowning, several years later while swimming alone in a stone quarry.

I worked for a Mexican radio network back in the 70s, and had to rebuild a vertical antenna matching unit in Oxaca. 

If I remember, it operated around 800 kHz and the tower was only some 80' high, pushed by a 5kW transmitter.  A real 'shorty', close to the flight path at the local airport.

The whole damn thing glowed blue at night & pulsed with modulation, too cool.

It was the only time I had to use the 'extended range' on my operating impedance bridge to do a base measurement.  It read some ridiculously low resistance, and the -J was in the thousands of ohms.

Not efficient, but it was the best they could do on the dirt available.

The ATU had been whacked by lightning, and was a total loss.

73DG

Probably on par with those 43' 160m verticals that Hammy Hambone was led to believe were at the ideal height. It might have even worked a little better, because it most likely had a half-decent radial ground system.

Did it have any kind of top loading?  Sounds like a good candidate for a multi-wire flat-top vertical tee, or better still, a bunch of horizontal top loading wires extending out like spokes on a wheel.

There is no such thing as a good RF burn but I get your drift! The smell from a RF burn is not unlike day old dead fish worms frying in a skillet on a camping trip, when the fish are not biting and your forgot to bring your food along  :D :D :D

great tuner built in the true spirit of  Am HAM RADIO......  Thanks for the picture....

Sounds like that mex radio station could have used a closed loop......Not as much fun to look at under power, but probably work betttttter over that poor gnd........