Valiant trouble. Phase 2....

[ke7trp]

Thanks to all of you for your help with my quest to get the valiant up and running.  After finding the Screen resistor that someone added, and replacing the back section of the band switch, I now have full power.

I spent an hour at least on 160 meter tonight. 150 watts out easy. Great reports. The O scope showes nice clean picture and modulation.

Then I spent several hours on 75 tonight with conditions into CA with mixed reports.

The KW matchbox is hard to tune on 75 meters with this valiant.  With the globe Champ, I can get 0 to 1 watt reflected on my Zep antenna on any band. The antenna tuner is easy to tune and predictable by my chart.

The valiant will tune flat as a pancake on 160 and the scope is clean.

On 75, its nearly impossible to tune the KW matchbox to flat. I have some reactance that I cant tune out. About 5 to 10 watts reflected. The Scope looks dirty. The only way I can describe it is that two or three carriers are showing on the scope. As I tune the plate, the lines can intercept but never show clean.  On air reports are ok. But I can see reflected power on the bird. No matter the combination of tuning and matching on the KW gets me flat on 75.

Looks like I have some work left on this thing...  I hooked up the dummy load and took the KW and antenna out of line. Its cleaner on the scope but not perfect. I saw no reflected into the dummy load though. But def NOT CLEAN on the scope. You can see "hairs" on the peaks and several horizontal lines on the output.

I can only guess that this thing is DIRTY on 75. I dont have a spectrum to test the output. Any ideas why 160 tunes clean and flat on 160 but 75 wont?  Its obvious to me that its very harmonic... But why?

THanks again for all the help guys!

Clark
ke7trp

[WA1GFZ]

Clark,
Tune up the rig into the dummy load so you know it is set for 50 ohm load. Then put it to the match box and try to tune it flat. I would change the antenna or feed line length if it won't go flat. Another trick is change the antenna to a fan antenna and set the lengths slightly different to reduce the Q of the antenna. You can sometimes just hang a length of feeder off the tuner output to change the system length. Be careful with that as there may be some high voltage RF on the stub. The length of your ground lead may also be an issue.

[w3jn]

It almost sounds like you're tuning the matchbox to a harmonic.  The loading and plate tuning of the Valiant will affect the adjustments on the Matchbox, because the output of the Valiant may differ from 50 ohms.

Frank's advice is spot-on.  Tune the Valiant into a dummy load.  Then we know it's set for 50 ohms.  Then connect to the matchbox, and tune the matchbox ONLY.  Do NOT re-adjust the tune/load in the Valiant.

I have to do this with my GPT-750; otherwise, there are too many interacting adjustments and I can never get ANYTHING adjusted right.

[WQ9E]

Sounds like the issue I had with one of my Valiants on 160.  I noticed that when I used my Yaesu FT-1000MP to set up the tuner on 160 and then later used my Valiant there was a slight increase in SWR.  I put the Valiant on my spectrum analyzer and found it was putting out a nice little spur (around 5 watts) at around 140 Khz.  As best I could diagnose it there was some form of tuned plate tuned grid oscillator formed by the combination of the the grid and plate chokes in that particular Valiant.  The grid choke looked fine but when I replaced it with another from my parts Valiant the oscillation disappeared.

Rodger WQ9E

[W4EWH]

On 75, its nearly impossible to tune the KW matchbox to flat. I have some reactance that I cant tune out. About 5 to 10 watts reflected. The Scope looks dirty. The only way I can describe it is that two or three carriers are showing on the scope. As I tune the plate, the lines can intercept but never show clean.  On air reports are ok. But I can see reflected power on the bird. No matter the combination of tuning and matching on the KW gets me flat on 75.

Looks like I have some work left on this thing...  I hooked up the dummy load and took the KW and antenna out of line. Its cleaner on the scope but not perfect. I saw no reflected into the dummy load though. But def NOT CLEAN on the scope. You can see "hairs" on the peaks and several horizontal lines on the output.

If the dummy load looks dirty, check grounds and shields:

• Are you working with the shields off? If so, reattach them and retest.
• Is the tuner on the same ground strap as the Valiant? You can't have too big a ground.
• Try the spectrum analyzer, as was suggested. Spurs? RF Feedback?

HTH.

73,

Bill W1AC

[K1JJ]

The Scope looks dirty. The only way I can describe it is that two or three carriers are showing on the scope. As I tune the plate, the lines can intercept but never show clean. 
Looks like I have some work left on this thing...  I hooked up the dummy load and took the KW and antenna out of line. Its cleaner on the scope but not perfect. I saw no reflected into the dummy load though. But def NOT CLEAN on the scope. You can see "hairs" on the peaks and several horizontal lines on the output.

Clark
ke7trp

Clark,

From your description above, there is a chance you have a poor pickup into your scope. When I used to use a coil sampling loop for pickup, the scope display would change markedly from band to band, often getting lines thru the AM carrier, etc, like you described.

He's an easy scope pick up to try for all bands:
http://amfone.net/ECSound/K1JJ8.htm

For now, make a simple resistive divider and pick off the RF with your probe directly and see if the display gets any better. If it does, consider building up the simple capacitive divider sampler as described in the link above.


There may be more wrong with the rig, but at least you will know what you are seeing is real before continuing.

T

[ke7trp]

The way I was instructed was to tune the transmitter up into a Dummy load. Then tune the matchbox for no reflected power. The current should be back at the same point when the matchbox is tuned.

Its funny that the valiant needs different settings then the Globe hooked to the same coax.

Maybe my neutralization is off?   I set it by the book while watching the grid. However. The cap is not at the same position that the manual says. Its about half meshed and not a 1/4.

It sure works well on 160! Talking on 1885 right now at 160 watts out.




Clark

[ke7trp]

RESOLVED.

Ran a ground braid from the back of the valiant to the KW matchbox. THis cleaned up the scope and now it works on every band.

Thanks

Clark

[N3DRB The Derb]

yep. always hook yer tuna o yer rig and lin yar....and then ground em.....

[ke7trp]

Yep. Just forgot to hook up the Ground braid I had back there.   Its clean and loads up nice on all bands now.

Clark

[WA1GFZ]

You might want to tie your scope to the same ground

[ke7trp]

Oh sorry...I am not using the KW on 160..  I use the KW with an extended ZEP antenna fed with 450 ohm ladder line. I use it for 10 through 80.  On 160, I have an inverted L that is coax fed using a Palstar tuner. This tuner sits on top of the KW matchbox. For some reason the ground was not required when using the palstar on 160. maybe the big huge balun inside? 

I wish I could use the KW on 160 with my extended Zep.  I never got around to reviewing how to add 160 to it.

CLark

[k3zrf]

Glad you got that baby running. I've used a couple valiants over the last gazillion years and have had years and years of fun. Now that you have gone thru all the troubleshooting you should know your rig pretty well. Next crap out you will be able to pin down the problem quickly.

[ke7trp]

The learning curve was alot of fun with all the help I got! 

Clark

[Steve - WB3HUZ]

Lots of info here.

http://amfone.net/Amforum/index.php?topic=16984.40