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Author Topic: True balanced line kW tuners for 160-10?  (Read 62808 times)
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K5UJ
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« Reply #50 on: July 10, 2011, 04:30:15 PM »

I in no way said or implied that there was any equivalence between the KW Matchbox and the TAC-1.

Below is my post (emphasis added):

<<Right--it was made in the heyday of TMC and AM and the "1 KW" probably referred to 1 KW input AM just like the KW Matchbox is by modern standards a ~ 2.5 KW tuner but the TAC-1 is probably still conservatively rated even by those standards.>>

The TAC-1 is clearly a better constructed product, but in fairness to Johnson, the KW Matchbox was not built for military service, but rather for hams, and by modern standards is a vastly superior tuner compared to what is available new today.   I am pleased and content to run mine but of course I would not turn down an opportunity to purchase a TAC-1 if I could afford it.

Don, I saw your post on the AMradio reflector and wondered if my comment precipitated it.  Kindly notice the qualifier "modern standards" in my post.   I freely admit to being an appliance operator by the standards of most AMers and absolutely make no pretense of being anything else.  I am working hard to learn and improve my ability as an amateur radio operator, however I fully realize that at this point in my life I may never live long enough to attain the level of ability and knowledge some of you have, who have been building and learning from an early age.   I find your comment surprisingly excessive and out of character.   Perhaps it was in humor and I misinterpreted it.

73

Rob
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« Reply #51 on: July 11, 2011, 12:54:46 AM »

I in no way said or implied that there was any equivalence between the KW Matchbox and the TAC-1.

Below is my post (emphasis added):

<<Right--it was made in the heyday of TMC and AM and the "1 KW" probably referred to 1 KW input AM just like the KW Matchbox is by modern standards a ~ 2.5 KW tuner but the TAC-1 is probably still conservatively rated even by those standards.>> ...

I've been thinking about this all evening. I've come to the conclusion that Don said what he did from an AM perspective.

Can it really handle 2.5 kW on AM? I can't say, but my guess is that the answer is no.

I've read dozens of different posts that claimed that the KW matchbox is good for far more than 1 KW. But I think that they were referring to CW and slopbucket operation. :-)

I have a lot of respect for Don and his technical expertise, but even the best of us get moody sometimes. How about if we all forgive and forget, and move past this as mature men?
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« Reply #52 on: July 11, 2011, 01:42:16 AM »

Dealing with big BC rigs for years shows one that in any L/C net (which an antenna tuner is), the contact surface comes into play for the I carried, the insulation for the E.

Figure a bit under 4.5 A @ 220 V @ 50 Ohms = about 1kW RF wise.  That ought to be where your highest I is, on the 50-Ohm input circuit.

On the balanced wire line output, say 600Z for instance, the E is over 750 with the I down to just over 1.25, and that is without modulation.  It gets pretty tingly approaching 100% mod....

Insulators and caps need good insulation, rollers & switch contacts need low resistance in terms of square mm to handle being adjusted while in operation and not burning up or arcing over. 

Seldom does a small diameter wire crap out, even with lots of RF on it.  Where it connects to something, on purpose or by accident, is where the grief comes from.

Run the numbers and take a look at the guts of whatever unit you want to use, see if you think it will hold up.

73DG
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k4kyv
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« Reply #53 on: July 11, 2011, 11:01:06 AM »

Don, I saw your post on the AMradio reflector and wondered if my comment precipitated it.  Kindly notice the qualifier "modern standards" in my post.   I freely admit to being an appliance operator by the standards of most AMers and absolutely make no pretense of being anything else...  I find your comment surprisingly excessive and out of character.   Perhaps it was in humor and I misinterpreted it.

I think you did. I also posted a similar one on QRZ.com too, and a few people got bent out of shape, but most thought it was funny. Think of it as in the combined spirit of W2OY and George Carlin. Or maybe Burt.

BTW, here is another one to add to the list:

   You refer to output transistors as "Pills"  Grin
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Don, K4KYV                                       AMI#5
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Steve - K4HX
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« Reply #54 on: July 11, 2011, 11:15:56 AM »

The answer to that depends on the load. But more than 2.5 kW has been run through a Matchbox.


Quote
Can it really handle 2.5 kW on AM? I can't say, but my guess is that the answer is no.
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k4kyv
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« Reply #55 on: July 11, 2011, 01:18:45 PM »

But more than 2.5 kW has been run through a Matchbox.

Was that 2.5 KW of AM?

I doubt an EFJ matchbox would withstand a fully modulated 2.5 KW carrier for very long before things started heating up.  And it would probably flash over on modulation peaks before you got anywhere near 100%.

Maybe, if the load were just exactly right.  But IMO you would have at best a very narrow range between excessive heating, and tuning capacitor (and maybe switch) flash-overs.
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Don, K4KYV                                       AMI#5
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« Reply #56 on: July 11, 2011, 05:29:00 PM »

"Pills."  Yeah, I forgot about that one.  I should go look at QRZ and see what was posted. 

Let's see....As I recall the KW MB caps are pretty widely spaced.  Not sure where the flashing takes place.     The bandswitch and link/inductor and taps all seem to be capable of handling a fairly decent amount of current.  I think all of the leads to the inductor are silver plated strap.  Unless I am mistaken it was built to handle the Desk KW.  Around 600 watts. 

speaking of power, I finally have a 3 A thermocouple meter in line with a decent 50 ohm load.  I am looking forward to seeing how 2 or 3 A of RF squares with these watt meters I have.
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« Reply #57 on: July 11, 2011, 05:34:36 PM »

Have you ever tried it?


But more than 2.5 kW has been run through a Matchbox.

Was that 2.5 KW of AM?

I doubt an EFJ matchbox would withstand a fully modulated 2.5 KW carrier for very long before things started heating up.  And it would probably flash over on modulation peaks before you got anywhere near 100%.

Maybe, if the load were just exactly right.  But IMO you would have at best a very narrow range between excessive heating, and tuning capacitor (and maybe switch) flash-overs.
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« Reply #58 on: July 11, 2011, 08:30:10 PM »

2.5 KW PEP no problem, 2.5 KW carrier rots of ruck.
The SO239 connected to the output will be your first failure
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« Reply #59 on: July 11, 2011, 08:56:45 PM »

The SO239 connected to the output will be your first failure

With AM carrier power levels between 1 & 5kW and if your tuner is in a box, time to go to type LC, 7/8" EIA, or better yet 1-5/8" EIA.  Even 7/16 DIN is OK.

If an open breadboard job, think at least of using 7/8" heliax for the 50-Ohm TX-to-tuner link. 

Also, stand clear.

I once walked past an open & operating 50kW ATU on a wall and my hair stood up (what was left of it and by itself!) when I neared the output end, as it was a short daytime stick with really high -J.

73DG
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Steve - K4HX
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« Reply #60 on: July 11, 2011, 08:58:54 PM »

Have you tried it?

2.5 KW PEP no problem, 2.5 KW carrier rots of ruck.
The SO239 connected to the output will be your first failure
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« Reply #61 on: July 11, 2011, 09:39:42 PM »

into a dummy load of course but I flashed over the SO239 on the output side.
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« Reply #62 on: July 11, 2011, 09:50:47 PM »

into a dummy load of course but I flashed over the SO239 on the output side.

I love this website.   Grin
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Steve - K4HX
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« Reply #63 on: July 11, 2011, 09:52:07 PM »

Try it into open-wire line and get back to me.


into a dummy load of course but I flashed over the SO239 on the output side.
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k4kyv
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« Reply #64 on: July 11, 2011, 10:13:44 PM »

I once tried a homebrew link coupled balanced tuner feeding my 80m dipole on 160 as a quarter-wave dipole.  The tuning cap was a BC-610 plate tuning cap, 150/150 pf @ 7 KV.  I think the EFJ KW Matchbox tuning cap has the same spacing or slightly smaller. The the tuner end of the OWL was exactly midway between a high current point and a high voltage point, so it presented a highly reactive load to the tuner. I was able to tap down on the coil with the OWL and get a good match to the coax line from the transmitter.  But running 100 watts, I could not modulate 100% without flashing over the tuning cap.  I added another 60 ft. of OWL, bringing the tuner end of the OWL to a high voltage point, and I  parallel fed it directly off the tuner without tapping down. I could then 100% modulate as much carrier as I had the capability of generating without flashing anything over.  As expected, the tuning is very sharp, and I cannot QSY more than about 5 kc/s with that set-up without re-adjusting the tuner, but I worked all over N. America with that antenna before I got my ground radials laid to allow me to use the tower as a quarter-wave vertical..
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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« Reply #65 on: July 11, 2011, 10:15:22 PM »

2.5 KW PEP no problem, 2.5 KW carrier rots of ruck.
The SO239 connected to the output will be your first failure

Maybe. But I've seen 5 and 10 kW run through RG-8 and multiple UHF connectors on continuous-duty medium-wave transmitters.

It got warm, but it was not hot by any means.

I'm not recommending that anyone do that, but I know what I saw.
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« Reply #66 on: July 12, 2011, 08:12:36 AM »

2.5 KW PEP no problem, 2.5 KW carrier rots of ruck.
The SO239 connected to the output will be your first failure

Frank is definately right!!

As you all know, I run a short antenna, so this definately raises some tuner / feedline issues. Especially at high power.

I dont have any problems on 80 and up, but I do on 160. I have a short run of coass between the tuna and the balun. (yea, yea, I had to do it that way but it works)
At 700w or so of carrier on 160, I have to keep the modulation down to around 90% or a little less. If I crank on the audio, I will burn the PL-259s off of the coass and/or the SO-239s off of the tuna chassis!! Done it several times!!  Grin  Grin

The little skinny center pin of a type "N" connector wouldn even think of holding that much feedline current. (Remember that the coass isn't running at anywhere near 50 ohms)

If you have to sin with extreemly high swr on coass, it is always better to run the coass at a lower impedance where I-R losses are your only issue vs a high impedance where the capacitive reactance of the coass ends up absorbing all of your outpoot power.
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« Reply #67 on: July 12, 2011, 08:46:57 PM »

I removed the output UHF jack on mine.   After reading something Frank posted about it sometime last year I got rid of the stock UHF jacks with the phenolic and put in a new one with teflon on the input. 
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