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Author Topic: Power out increases until the load cap is 100 % meshed  (Read 13666 times)
KM4AH
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Posts: 963




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« on: February 01, 2018, 06:28:07 PM »

What is that telling me ?  One would think it has to be under coupled. But, the power out continues to increase.

Pair of 3-500Z's on 40 meters.  75 meters tunes as usual. Haven't tried other bands.
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W8JX
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« Reply #1 on: February 01, 2018, 06:35:00 PM »

Check capacitor on 40m band-switch position. If not bad, increase value.   
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Ham since 1969....  Old School 20wpm REAL Extra Class..
AF6LJ
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« Reply #2 on: February 01, 2018, 06:52:18 PM »

Also check your input VSWR on forty meters, bad match = low drive = not enough loading cap.
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W1BR
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« Reply #3 on: February 01, 2018, 07:01:50 PM »

What model amp?
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KM4AH
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Posts: 963




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« Reply #4 on: February 01, 2018, 11:57:39 PM »

What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .
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W8JX
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« Reply #5 on: February 02, 2018, 03:07:02 AM »

What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KM4AH
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Posts: 963




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« Reply #6 on: February 02, 2018, 04:40:31 AM »

What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.

It is a 500 PF door knob. When you go to 75 meters it adds another 750 PF door knob. And, when you go to 160 there are two large red wafer caps in parallel that are added.

The only door knob I have here that will fit in that space is a 1000 PF 5 KV.

So, that is too much I assume. Would another 750 PF door knob work and not get everything else below 40 out of whack ?

I am a hell of a parts replacer. Since I am going to have to order one anyway what value would you use ?
« Last Edit: February 02, 2018, 04:45:13 AM by KM4AH » Logged
W1QJ
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Posts: 2983




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« Reply #7 on: February 02, 2018, 04:54:13 AM »

If your problem is on 40 meters there should be no padding needed on 40 if the right tune cab was installed.  That amp was a fabrication remember.
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W8JX
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Posts: 13268




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« Reply #8 on: February 02, 2018, 04:57:35 AM »

What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.


It is a 500 PF door knob. When you go to 75 meters it adds another 750 PF door knob. And, when you go to 160 there are two large red wafer caps in parallel that are added.

The only door knob I have here that will fit in that space is a 1000 PF 5 KV.

So, that is too much I assume. Would another 750 PF door knob work and not get everything else below 40 out of whack ?

I am a hell of a parts replacer. Since I am going to have to order one anyway what value would you use ?

You could try swapping 750 door knob used on 80 with 500 used on 40 to see what it does for 40m to give you a idea of value you might need. As far as effect on lower bands, a small change should have minimal impact
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Ham since 1969....  Old School 20wpm REAL Extra Class..
N8CBX
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Posts: 565




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« Reply #9 on: February 02, 2018, 06:09:46 AM »

HV door knob caps are unnecessary for C2, only necessary for C1. Silver mica 1kv caps can easily be use for your padder C2 caps.
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
W1QJ
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Posts: 2983




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« Reply #10 on: February 02, 2018, 06:34:18 AM »

No padding of load or tube is required if the right caps were used in the conversion.  I’d install the correct stuff.
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G3RZP
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Posts: 1319




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« Reply #11 on: February 02, 2018, 06:58:42 AM »

A 750pF capacitor on 7 MHz is about -j30. 1500 watts in 50 ohms is 274 volts rms on a carrier. The capacitor in that condition would have about 9 amps flowing through it, so would need to be rated for the current. 
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KM4AH
Member

Posts: 963




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« Reply #12 on: February 02, 2018, 07:45:36 AM »

What model amp?

It is an Amp Supply LK500NTB  No Tune that has been converted to a standard tune.  The workmanship is beautiful, but something is a little off on 40 .

Increase value of capacitor in 40m circuit 20% or so.


It is a 500 PF door knob. When you go to 75 meters it adds another 750 PF door knob. And, when you go to 160 there are two large red wafer caps in parallel that are added.

The only door knob I have here that will fit in that space is a 1000 PF 5 KV.

So, that is too much I assume. Would another 750 PF door knob work and not get everything else below 40 out of whack ?

I am a hell of a parts replacer. Since I am going to have to order one anyway what value would you use ?

You could try swapping 750 door knob used on 80 with 500 used on 40 to see what it does for 40m to give you a idea of value you might need. As far as effect on lower bands, a small change should have minimal impact

That will be the simplest thing to try. The tuning is such that the Load Cap on 75 has little dramatic effect. I mean you can find a peak output, but 1/4 turn in either direction won't make 50 watts out difference. Matter of fact on 40 you can unmesh the cap from 0 up to 20 on the dial and won't lose 50 watts. Running about 75 watts drive and 1200 or so out.


BTW, the owner said it was blowing a fuse on 40 meters. I have not had that problem. But, when tweaking the tune and load for max out using a pulser it starts to make a clicking  noise when C2 is finally fully meshed and power out is still increasing. Doesn't sound like an arc, could be the T/R relay. But, something going on that I don't much like.
« Last Edit: February 02, 2018, 07:51:29 AM by KM4AH » Logged
N3QE
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Posts: 5593




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« Reply #13 on: February 02, 2018, 07:49:42 AM »

It means you aren't driving the amp hard enough when tuning.

If you start actually driving the amp into it's "sweet spot" for power delivery, you will find you have to advance the load control.

If you are tuning up with voice modulation it is likely it is not possible to hit the proper tune up based on average-reading meters. Solid carrier or at least a pulser at PEP power is the way to tune.
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W8JX
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Posts: 13268




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« Reply #14 on: February 02, 2018, 07:51:38 AM »

That will be the simplest thing to try. The tuning is such that the Load Cap on 75 has little dramatic effect. I mean you can find a peak output, but 1/4 turn in either direction won't make 50 watts out difference. Matter of fact on 40 you can unmesh the cap from 0 up to 20 on the dial and won't lose 50 watts. Running about 75 watts drive and 1200 or so out.

Try swapping both, placing 80m 750 pf on 40m and 40m 500 pf cap on 80.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
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