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Author Topic: KW Flashbox. Here is the damage  (Read 40191 times)
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N0WEK
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« Reply #25 on: September 18, 2010, 04:58:39 PM »

Steve,  Let us know the aparatus you use to see through the metal case or where you born with xray vision?


C

Don't need to see inside if the knobs are set correctly!  Grin
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Todd, KA1KAQ
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« Reply #26 on: September 18, 2010, 05:47:55 PM »

    Steve,

    Your KISS advice does not work with the differential capacitor on the flash
    boxes!      Works fine on the left TUNE knob...

Think about this for a second, Ralphie: When you set it at 50, the plates are half-meshed, perpendicular to the lower and upper plates. Unless you align on the wrong side of the shaft, it will be fully meshed in the lower plates at 100 on the dial. This means if you set it fully meshed on the lower plates as you would with any standard air variable and set the dial for 100, it will automatically be at 50 when half meshed in the upper and lower sections.

The numbers on the skirt keep you from setting it wrong, but yes - if someone has messed with the knobs at some point, you have no choice but to pull the cover to get inside for a visual alignment.

Which gets back to what I said early on in the thread which apparently required verification by Clarky:
Quote
As far as knob calibration, highest number on the skirt (100 on the Flashbox IIRC) should equal fully meshed. 50, half meshed, 0 fully open.

Same, basic truth applies, regardless of brand. The description pasted by Clark isn't from the Johnson manual, it was someone's (Bob Sullivan?) observation that they came up with since it isn't covered in the manual. It's not inaccurate, just makes it sound more complicated than it needs to be. Grin

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ke7trp
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« Reply #27 on: September 18, 2010, 06:20:43 PM »

Steve, Your nuts. Roll Eyes  The entire post is about the knob postion on the shaft.  After 50 years of servicing, the knobs on these things are never set right.

You must look inside and set the knobs.  Once set, You should be ok. But also, look inside and use the setting that has the most mesh.


C
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Steve - WB3HUZ
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« Reply #28 on: September 18, 2010, 06:35:37 PM »

I may be nuts, but you're the one burning up your Matchbox. Pot to kettle, over?
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ke7trp
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« Reply #29 on: September 18, 2010, 07:09:06 PM »

LOL! You crack me up man


The flashbox failed because the landscapers piled up my ladder line in a pile on the concrete Shocked Shocked

The second time around the knobs where set wrong.  Check your matchbox guys :


 

C
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Steve - WB3HUZ
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« Reply #30 on: September 18, 2010, 07:55:55 PM »

I'd have a word with those landscapers. When I blow up my tuner, I want it to be ALL my fault!   Wink

The knobs on my Matchbox were messed up too, mostly because the set screws didn't hold very well. If I ever get another MB, I'll probably put verniers on it. But unless I get one really cheap, building one is the better route - better design and less expensive.
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Todd, KA1KAQ
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« Reply #31 on: September 18, 2010, 07:59:03 PM »

Building is a FAR better option, as 'JJ and others have shown. The Flashboxes are nice enough, within their limitations. Getting into them is far more hassle than the utility they provide, IMO.
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Steve - WB3HUZ
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« Reply #32 on: September 18, 2010, 08:18:15 PM »

I would not pay more than about $75 for one.
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ke7trp
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« Reply #33 on: September 18, 2010, 08:56:02 PM »

As far as tuners go, Its def in the top 5 tuners ever made.  The TMC being the top.

The trouble with the JJ is that its not badswitched.  Its a real pain for someone like me that changes bands allot. I thought about bandswitching one with vac relays and a small Power supply.  I am going to wait to see what robert comes up with. For now the KW is working great on low power.

C
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K1JJ
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« Reply #34 on: September 18, 2010, 10:13:45 PM »



The trouble with the JJ is that its not badswitched.  



It could be.  First find the optimum taps for all bands.

Then get a big two-pole bandswitch and wire it up. To make it really versatile, use two bandswitches - one used to select the two antenna openwire taps on the coil and the second to select the two capacitor taps on the coil.

Though, most guys find pre-marked coil labels using clips to be quite quick. If you're worried about the tuner being exposed, make a Plexiglas cover with hinges to access it easily.

T
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« Reply #35 on: September 18, 2010, 11:59:52 PM »

Mine is going in a big hallicrafters HT32 case with a hinged top to access. 


Question for you tom.  Have you tried to use the tuner on higher bands?  10,15 and 20? 

C
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K1JJ
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« Reply #36 on: September 19, 2010, 12:12:59 AM »

Question for you tom.  Have you tried to use the tuner on higher bands?  10,15 and 20?  
C


Yes, Clark -   I once built one for 20M as a mono-bander tuner. It tuned a 36 el wire Sterba curtain array out in the field.  I ran hardline to the tuner, open wire to the Sterba itself. Worked very well.  The coil had to be very large and I used a vac var cap. If the coil is wide spaced and large diameter to fit the band, there's no reason why it won't work up on 10M.  It's all about layout, of course.

Stray C can be a problem, especially with a metal enclosure surrounding it, but shud still be fine.  The taps will be critical on 10M, sometimes making something as small as 1/2 turn on the coil important to get 1:1.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
ke7trp
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« Reply #37 on: September 19, 2010, 09:51:22 AM »

Have you tried the standard design tuner with a OWL doublet for all bands? As I see it, I am going to loose the higher bands with that design.

C
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ke7trp
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« Reply #38 on: September 19, 2010, 11:24:26 AM »

I am starting to think something else is going on here.  This morning on 3855 AM group, I started to have arcing again.  This time, I was at low power and less then legal limit on peaks.

I stopped and put the rig into a dummy and the rig is fine, Its the KW arcing again. 

Here is what troubles me.  I can put the T368 on at full power fully modulated which is about the same power I am running with the new rig, No arcs.  I can talk for hours. 

I can also put the Icom and three tube 800 amp on and run RTTY double the legal limit with no arcs.

The output of the transmitter seems clean on the scopes.  Its a bit wide right now since my filter is not in line, However, The most RF output is under 10KC.   Any ideas here?  I just cant understand why the T3 can run full out and the new Rig cant run the same power level without arcing.

Any suggestions?  Its going to be a while before the new tuner is done.  I was really looking forward to running the contest today.  Maybe I can hook up the King500 and at least try to enjoy myself on the bands today.

C
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Todd, KA1KAQ
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« Reply #39 on: September 19, 2010, 12:12:00 PM »

Complete shot in the dark: higher voice peaks and associated voltages on the GK 500 than the T-368. Makes no sense if both are equal in output otherwise. That's the only thing I can think of that could vary enough to make a difference, unless there's a serious impedance issue somewhere.

Frank, forgot to mention before, but the KW Flashbox was not in line with the big rig when Steve and I tested it. Ant is cut for, and resonant at 3800, works GREAT down as low as 3705, tunes up fine on 3870 and above but arcs as soon as you hit the audio. My guess is it's related somehow to the inductance vs capacitance differences for the high or low end, despite checking nearly identically on Steve's MFJ analyzer for SWR, impedance, etc on both ends of the band.

As Steve said, it might be one of those mysteries that never gets solved, but it sure is a puzzler.
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« Reply #40 on: September 19, 2010, 01:20:02 PM »

I think a spectrum analyzer might tell the tale here Clark.  If it handles the power from one transmitter but not the other it sounds like your GK is intermittently going into parasitic oscillation and the off frequency output is causing the flashover.

Several years ago I was using a Valiant on the local 160 meter AM net on 1815.  It was the one I had in the barn and I was setting the tuner up with my 1000MP and then switching over to the Valiant.  When I had a 1 to 1 SWR with the MP it was slightly higher with the Valiant and the SWR increased as the Valiant power was reduced.  I looked at it on my spectrum analyzer and found nothing until I looked below the fundamental.  There was a ragged oscillation at around 190 Khz. that was producing a couple of watts output.  I think it came from some sort of TPTG oscillation in the final and I slightly rearranged some of the lead dress around the final sockets and it went away; changing finals didn't help. 
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ke7trp
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« Reply #41 on: September 19, 2010, 01:42:11 PM »

The GK500 and the T368 do not arc the tuner out at 100%+ mod.  The New transmitter does.  Even when I hold it using a peak limiter down at 85 to 90% mod. The power output peak is less then the T3. Yet it still arcs the tuner.  I am running a test right now using a bird dummy load and the Icom band scope. I am going to tune around each band to see if I can spot some pips.  My Spec an is not available right now so this is all I can do.  Something must be going on that I cant see on the O-scope. It really does have a wonderfull and linear pattern.

C
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ke7trp
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« Reply #42 on: September 19, 2010, 02:02:23 PM »

Transmitter tuned on low power to 3870 into a bird dummy load.  Using the icom 756 pro:

3870,  Calibrated at exactly 40 DB on the scope.
7.740 calibrated at exactly 12 DB on the scope.
11.610 calibrated at 5 DB.
15.480 s8 signal.

So..  Advice as to what to do here is this considered good for a typical AM transmitter?  I cant find any other spurs anywhere on the Icom from bottom to top.

realize that this Icoms AGC and other factors might be at play here and I dont have access to my Spec AN right now. So this is all I have guys. Its possible that the icom has tuned circiuts on the ham bands that make this test invalid. 

Retuning of the transmitter does not effect the levels much.  That is everything goes up or down. Extra load from 300 to 450 mills on the plate is not effecting the harmonics.

Clark
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ke7trp
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« Reply #43 on: September 19, 2010, 02:19:49 PM »

Ran the test on the T368:

3870 is 40 DB
7.740 is S6
Cant hear third and fourth harmonic. 


This is a 21 DB difference from primary to second harmonic from the T3 to this big rig.

C
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« Reply #44 on: September 19, 2010, 02:21:48 PM »

Clark,

I am not familiar with the 756 so I can't really comment on those results.

One of the key requirements with getting accurate results from a spectrum analyzer is the pickup feeding the analyzer must be flat across the frequency range of interest.  Without this,  you cannot accurately measure harmonic suppression or other such parameters.  But in this case measuring the exact attenuation of harmonics is probably not the issue, I have a feeling that you are getting instability at or near the modulation peaks and the frequency is probably in the VHF range.

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Rodger WQ9E
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« Reply #45 on: September 19, 2010, 02:27:26 PM »

Just for the heck of it Clark, pull out one of those low pass filters (TVI filters) you have and put it in line between the TX and tuner. If you might be producing VHF within the filter range it might help for now until you find a fix.

The other thing you might try is 6 coils at about 6" diameter coax balun between the rig and tuner.

I have seen both fixes tried with good results in the past.

Mike
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W3GMS
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« Reply #46 on: September 19, 2010, 02:52:49 PM »

Clark,
We all know that a 375 carrier modulated 100% is 1500 W of peak power.  It would be interesting to run 1500 W of carrier with no modulation and see if it arc's.  I bet it doesn't.  Then take the carrier up to 2KW with no modulation and see if it arc's.  It probably won't.  If you can run that amount of carrier power without it spitting over then it should easily handle your positive peak modulation when your running the legal amount of carrier, ie-375.  The Johnson KW matchbox is a very robust tuner from a pure power standpoint.  It biggest limintation is the impedance range that it covers when compared to other tuner topologies.  You could always build a bigger tuner but I think there is still something not quite right and it would be nice to solve that problem regardless if you build a bigger tuner or not.  I am assuming that your able to get a good match to your antenna when using the tuner.  I ran a Johnson KW matchbox for years at the legal limit with plenty of positive peak modulation without ever having an issue.  If you do have a triggered parasitic that certainly does not take things in the right direction!  Triggered parasitics do occur under modulation.  I am assuming you have all the normal parasitic plate and grid parasitic suppresors in place on your new rig.  If the transmitter is putting out energy under modulation, the match at that frequency will be poor and it could appear as a very big voltage note at the output of the tuner, hence the zorch!   
Just part of the shakedown with a new piece of gear...
Regards,
Joe, GMS         
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ke7trp
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« Reply #47 on: September 19, 2010, 03:08:53 PM »

My calculations where wrong:

T368 at 500 watts into Dummy load fully modulated is 49 DB down to the second harmonic.

The new Rig is only 21 DB down. 

TVI filter did nothing thats for the tip though.

I put a tuner between the exciter and the new rig.  Thinking, This would lower the second harmonic down to the 4-400s. This did nothing.  Its still 21 db down to the second harmonic.

Can someone confirm this is my problem?  To much energy on the second harmonic that the tuner cant pass?

C
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« Reply #48 on: September 19, 2010, 03:16:18 PM »

Clark,

Running 1500 watts peak output, 21 db down is a tad under 15 watts and I doubt that is making it arc on the second harmonic.  But there is an easy way to verify.  Set the tuner up for 3885 and then use another rig to run 15 to 20 watts on the upper end of 40 meters and see what happens.

The 2'nd harmonic is being generated in the 4-400 final so a tuner or low pass filter between it and the exciter won't help.
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ke7trp
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« Reply #49 on: September 19, 2010, 03:19:12 PM »

Ok Rodger. Thats not my problem then. 15 watts does not arc the tuner.  Thanks for all the help guys. I am really trying to understand this and learn here.  I cant wrap my head around the fact that identical outputs, One transmitter arcs. 

I am now thinking that the maybe the bandwidth is just to wide on the new rig???

C
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