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GK-500 B problem




 
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Author Topic: GK-500 B problem  (Read 8377 times)
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WD4TC
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« on: October 28, 2009, 05:57:09 AM »

 Hello to the Group. I just got back on the 500B and got the Modulation deck completed and Next step RF deck. When I tune it up I can get the proper 15 mils of grid No problem on all bands. I can get the 300 to 330 mils of plate current on all bands but the catch is only 100 to 120 watts of carrier ? I have replaced the 4-125 with a known good 4-400 and the results are the same. I checked the Coupling caps all mica caps,Plate voltage is about 1900 Volts, I usually don't have any problem getting them up and going but this time I'm lost for answers . What am I missing ?...Tim...WD4TC..
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Tim...WD4TC 
If it not Glowing it,It's not much for Showing
Jim, W5JO
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« Reply #1 on: October 28, 2009, 08:06:17 AM »

Not much to go on here, but be sure the output circuit is wired correctly, especially the coarse load switch and all the caps attached to it.  If you have a cap checker check all those mica caps.  Are all the components on the deck original?  Is the realy working correctly?  What about the coax, wattmeter and dummy load?
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WQ9E
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« Reply #2 on: October 28, 2009, 11:52:40 AM »

Tim,

Possibly an inaccurate meter reading (shunt)?

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Rodger WQ9E
N3DRB The Derb
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« Reply #3 on: October 28, 2009, 01:54:49 PM »

4-125?? didnt that rig have a 4-250 as the stock final?

Does it have the stock fil transformer?
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WD4TC
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« Reply #4 on: October 28, 2009, 02:42:41 PM »

U right Derb.4-250 .it was way too early for me this morning..and I had 125 on my mind for some reason..Anyway I am still looking for the problem and have not come up with anything that looks or checks out of wack But there is for sure something and now I got to drop what I'm doing and go to Baltimore MD for Thursday and over to Laurel De. For Friday and back to NC for the weekend..Thanks to All that have replied..Tim..WD4TC..gone trucking...
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Tim...WD4TC 
If it not Glowing it,It's not much for Showing
kg8lb
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« Reply #5 on: October 29, 2009, 06:27:03 AM »

 What is your screen voltage and current ?
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WD5JKO
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WD5JKO


« Reply #6 on: October 29, 2009, 07:37:39 AM »


Tim,

    After you come back from trucking, I have an idea on this 500B.

If the DC input is around 500 watts, and the output is 100-120 watts, then something MUST be getting VERY hot from a plate efficiency that is < 25%. If the tube isn't bright orange, and nothing else is getting abnormally hot, then either your DC input calculation, or RF output reading is incorrect.

One source of poor efficiency would be a continuous parasitic oscillation. A neon bulb attached to a wooden stick and positioned near the tube plate should glow 'orange'. If you see 'purple', then there is significant VHF energy present. If you have a parasitic, I'd expect the tuning (grid and pi-net) to be erratic as knobs are turned through resonance.

Jim
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ke7trp
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« Reply #7 on: October 29, 2009, 11:57:15 AM »

Its very possible that you are just mistuning the King.  Do you have a Scope attached?  Its imparative that you run a scope with this Transmitter.  Since people remove knobs and you might not have any idea what is what, You might need to experiment. There are several Dip or peak positions throughout the tuning controls. 

I used a Spec AN and a Scope to get my final tuning chart built. 

If you need to check the tank circiut, you can use an MFJ 259B if you have one.  Just run it into the RF deck, Push the relay closed, Use a 6000 ohm resistor from plate cap to ground on the final.  Then tune for best match on each band.

Things that where bad in my RF deck:

I had TWO Cracked Door knobs.  The white ones under the deck. This might be your trouble.


Bad Grid coupling caps and a hose of out of spec resistors.   

Good luck!

Clark


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Jim, W5JO
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« Reply #8 on: October 29, 2009, 12:59:53 PM »

 

If you need to check the tank circiut, you can use an MFJ 259B if you have one.  Just run it into the RF deck, Push the relay closed, Use a 6000 ohm resistor from plate cap to ground on the final.  Then tune for best match on each band.

Isn't 6 K a bit high?
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ke7trp
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« Reply #9 on: October 29, 2009, 01:20:44 PM »

I guess that depends..   He can figure it out for his rig on plate voltage and current.  Thats what I learned here Smiley


c
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Steve - WB3HUZ
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« Reply #10 on: October 29, 2009, 04:46:55 PM »

What's the plate voltage, something around 2500? Plate current around 200 mA? If so, sounds like 6 k to me. Or is the plate voltage lower?
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ke7trp
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« Reply #11 on: October 29, 2009, 04:56:34 PM »

stock ones are 1800.  300 to 330 ma. 


Clark
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Jim, W5JO
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« Reply #12 on: October 29, 2009, 07:14:49 PM »

Typically these things are near 3500 ohms.
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Steve - WB3HUZ
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« Reply #13 on: October 29, 2009, 07:23:15 PM »

Yea, that's 3k.


stock ones are 1800.  300 to 330 ma. 


Clark
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ke7trp
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« Reply #14 on: October 29, 2009, 11:54:57 PM »

Yeah.. Jim was correct.. I was wrong. I looked over my notes. It was 3000 to 3200 for mine.  I have been working on the big Transmitter and had 6000 in my head.

Clark
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WD4TC
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« Reply #15 on: November 07, 2009, 07:02:26 PM »

Back on the GK-500 and here are the facts..
  Plate voltage =1900 Volts
  grid current 15 MA
  screen voltage +400V
  -125 bias
  280 MA=120 watts out
  screen 40 ma
  To add to the equation I can put about 3300 0hms across the tube to ground and the tuning circuit loads great 1to 1 swr 45 ohms res.
   Nothing getting hot in the tank circuit  all door knobs OK ? Its got me beat...
 
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Tim...WD4TC 
If it not Glowing it,It's not much for Showing
WQ9E
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« Reply #16 on: November 07, 2009, 07:33:10 PM »

Tim,

Have you verified the plate current with another meter?  If your input and output measurements are correct then that 4-400 should have a very orange anode.

Rodger WQ9E
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Rodger WQ9E
WD4TC
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« Reply #17 on: November 07, 2009, 08:04:30 PM »

That's what I thinking Roger.this thing is Acting Plun Stupid and can't find a thing ? I even pulled my A model deck for compairison and the are the same. I'm going back to the screen and bias again, It's got to be there somewhere..Thanks for the suggestions . I have checked them All OK..  Tim..WD4TC..
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Tim...WD4TC 
If it not Glowing it,It's not much for Showing
WD4TC
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« Reply #18 on: November 07, 2009, 08:26:05 PM »

  Well I went back and All Voltage Are where the are support to be -125 and +400  and Plate 1800V 310MA plate current 45MA Final Screen 15MA grid current, No color what so ever in the final Plates all this equal 125 watts output ! Ant that a Bit@#...Tim..WD4TC
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Tim...WD4TC 
If it not Glowing it,It's not much for Showing
N3DRB The Derb
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« Reply #19 on: November 07, 2009, 08:35:36 PM »

I'd have to start wondering about the tube itself. check your fil voltage? Did you use the same tube when you subbed the decks?

datasheet for the tube says more like 60 ma screen current instead of 45. Check your screen bypass cap?
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W2VW
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« Reply #20 on: November 07, 2009, 08:56:16 PM »

Is there a way to accidentally drive the final at 1/2 frequency?

The final could be doubling.
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Jim, W5JO
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« Reply #21 on: November 07, 2009, 09:34:56 PM »

This is sounding like a mis-tune in the exciter stage.  Are the knobs for the oscillator and buffer on correctly and do they match the chart in the book when they are peaked?  What about the VFO, is it giving you the right frequency?  What about the setting of the coarse load switch, what number is it on?
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WD5JKO
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WD5JKO


« Reply #22 on: November 08, 2009, 09:08:41 AM »


Tim,

I was going to say, check the 4-400 filament voltage, then I re-read your post:

   You said, " I even pulled my A model deck for compairison and the are the same."

Whoo-Nelly!  Doesn't this rule out the RF deck?

So what is left that is not in the RF deck?

Watt meter
coax
6146 driver power supply
VFO

If your are running 500 watts DC input, nothing gets hot, tube is not orange, then the RF output must be higher than 125 watts!!

Question, is the 4-400 tuning of grid and plate smooth, or do the meters jump suddenly as you tune through resonance? If it jumps, think parasitic.

Question, Can you try the 500B RF deck with a crystal instead of the VFO?

Question, is the GK 500A set up and operational? If yes, Can you stick the 500B RF deck in there to see how it behaves?

Question, do you have another watt meter?

Question, on the back of the RF deck is a switch for class C, or linear usage. Is the switch in the correct position?

I think you are close to figuring this out,
Jim
WD5JKO
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ke7trp
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« Reply #23 on: November 10, 2009, 11:23:41 AM »

I would be shocked if you are not mistuning this thing.   You can tune it out of resonance very easy and get the same results.

Clark
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WD8BIL
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« Reply #24 on: November 10, 2009, 01:06:24 PM »


Quote
Is there a way to accidentally drive the final at 1/2 frequency?

Get a frequency counter on it. Make sure your input and output frequencies are the same.
Or use the scope. Trigger on the drive signal.
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