Valiant Trouble. This one has me stumped. Low output.

[ke7trp]

I had a nice running Valiant.  I took it out of line and used my Globe Chump for 6 months.  Hooked the valiant up and had some trouble.

In short.. The back part of the band switch was arcing.  I was greatfull when Robert Sent me one! The old one had a carbon track on it.

With the bandswitch installed. No more arcing.

Transmitter tunes up and loads to 300 MA MAX into a Dummy load (wont load higher).  Problem is I get only 90 watts out. Grid checks out perfect. Freq stable.  PEP is about 300 watts out.

Checked all the tubes with the TV7.  Found all where good.

Checked each 6146 in the final one at a time and then checked each socket.  I got about 50 watts per socket.
Found one 20 watt tube.. Replaced it.. All 5 tubes now make 50 watts each.

Put two in the modulator section.

Put three in the output.

Tuned it up.. 90 watts out.. Hmmm.  All tubes are good. All socket positions are good.

Run one tube.. 50 watts.
Run two tubes. 90 watts.
Run three tubes 90 watts.


Checked HV.  760 volts. 866s are out and diodes are in.  700 solid under load. Adjusted Bias and clamper tube.

Any ideas guys?

Tubes are good.
Voltages are good.
Audio is clean on scope.
Sounds good on the air.
Output is low.

Clark
Ke7trp

[Jim, W5JO]

Are the tune and load knob setting the same as when it worked right?

[K1JJ]

Clark,

300 ma X 700V =210 w input.   90w output /210w input = 42% efficiency.  Should be closer to 75% or so.

Question is, where is the power going?  Are the finals showing serious plate color?   That's 40w of heat dissipating per tube when a 6146 is rated at only 25w. (35w with a 'B')   Are other components heating up?

Or maybe the finals aren't inputting 210w as you think - a clue.

Also, check that third  6146 socket and associated wiring/components  carefully since the addition of that final makes no difference. Does that tube show more color than the others?

Let us know.

T

[ke7trp]

Trying to run 160 AM right now is nearly impossible with the CW contest going on..   I am down on 1885 if anyone is up late and has the guns to get over the CW.

I left it keyed at 300MA and 90 watts output for 15 solid minutes into the dummy load. The power did not change one watt and the plates where not glowing red.

I should have been more clear... You can add the third tube in any of the sockets.  I can run two tubes in the back two.. 90 watts.   Add a third to the open socket. Nothing gained but a little peak power.  I can then take one of the back tubes out.. 90 watts..

It is not tube or socket dependant.

I dont see anything getting hot and I would think after 15 minutes something would be damn hot. The meter is a bird 43 that I use everyday. I even tried three slugs.. 100, 500 and 1000. All show a bit less then 100 watts carrier with about 250 to 300 PEP.

I also want to let you guys know that I checked Bias on modulator and final and set as per manual. I also changed and set the clamper tube and adjustment.

Thanks alot for helping me!

Clark

[KD6VXI]

Trying to run 160 AM right now is nearly impossible with the CW contest going on..   I am down on 1885 if anyone is up late and has the guns to get over the CW.

I left it keyed at 300MA and 90 watts output for 15 solid minutes into the dummy load. The power did not change one watt and the plates where not glowing red.

I should have been more clear... You can add the third tube in any of the sockets.  I can run two tubes in the back two.. 90 watts.   Add a third to the open socket. Nothing gained but a little peak power.  I can then take one of the back tubes out.. 90 watts..

It is not tube or socket dependant.

I dont see anything getting hot and I would think after 15 minutes something would be damn hot. The meter is a bird 43 that I use everyday. I even tried three slugs.. 100, 500 and 1000. All show a bit less then 100 watts carrier with about 250 to 300 PEP.

I also want to let you guys know that I checked Bias on modulator and final and set as per manual. I also changed and set the clamper tube and adjustment.

Thanks alot for helping me!

Clark

You and your boat anchors.

Good luck. 

--Shane

[KL7OF]

Check your wattmeter

[w3jn]

I moved this from the handbook section (which is for completed projects, papers, etc) so it would get more exposure.

I believe the key is in this statement

Transmitter tunes up and loads to 300 MA MAX into a Dummy load (wont load higher)

SHould be able to load it up to much more than that.  Check the B+ (both HV and medium V).   Check the screen voltage, and finally check the idling grid bias voltage.

Also the shunts on the meter are a known trouble spot and I woulnd't trust it.   Try giving it some more grid current, could be the grid current shunt is bad and causing the meter to read high.  When you adjusted the bias, if you did it using the internal meter, it could be wrong if the Valiant's meter is reading incorrectly.

[Jim, W5JO]

I am leaning toward one of the Tune  or Load caps being bad.

[WA1GFZ]

Why would leave it keyed 15 minutes. You may have damaged the tubes by beating the crap out of them.

[AB2EZ]

Clark

You provided a very comprehensive list of symptoms and data that rule out a lot of possible causes. The fact the the rig modulates properly, and that the B+ is ok with 3 tubes in place, says a lot. For example, when the modulator modulates the plate voltage, the rf output amplitude follows (modulates properly). Etc.

It's a long shot... but check the filament wiring. If there is a high resistance somewhere... perhaps the filament voltage on the 6146 rf tubes is dropping too much when 3 tubes are plugged in.

Stu

[K1JJ]

In short.. The back part of the band switch was arcing.  I was greatfull when Robert Sent me one! The old one had a carbon track on it.

With the bandswitch installed. No more arcing.

Check to see if you may have wired up the new band switch incorrectly. You might have the inductor taps connected to the wrong band for which you are on.

Good suggestion!

How many times has something run well, then we make a change and it craps out. We sometimes forget to back-track and undo or closely review our change first.

T

[AB2EZ]

Good point.

Even if its not a connection error... if the rf load impedance is too high, you will run out of plate voltage on rf peaks... and that will limit the current. However, the rig will still modulate.

Make sure that you have not used too much loading capacitance. As the loading capacitance is increased, the r.f. load impedance on the tube will increase.

Try reducing the loading capacitance (which most people would refer to "heavier loading"... which I always think is confusing).

Stu

[ke7trp]

Hi Shane.. Fix the 250s?

Switch wiring is correct. This problem existed before the switch replacement. The old switch has a carbon trace on it to a rivet that was causing it to arc. I have gone back and double checked it as per your suggested.

Plate volts are 700 under load with solid state rectifiers.
Screen volts is 230 under load with solid state rectifiers.

If this watt meter reads low, I have the worlds strongest Ranger....

I will check the fil volts on the rig today. Thanks for the tip.

Took all tubes out and swapped in tubes from a working spare valiant. Same power out. 90 watts.

You should be able to key this all night if needed at 300 ma.  10 min is typical on AM if I get long winded. Nothing is getting hot. I was using a heat gun to test.

From all the help here I am greatfull!

I think my next step is to hand check all the loading caps. Robert sent me some (what a nice guy).

The reason is that only loading 5, 6 and 7 work. The others pin the plate current. I thought this was because of the band I am on which is 80 or 160 but others have told me that the loading should not have high current on each band.

Thanks again to all of you that are helping me!   My Globe Champ after 54 years of use is losing its final tubes. I am trying to source another set and I want to get the valiant up and running as a backup.

Thanks

Clark
ke7trp

[k3zrf]

I have had a similar problem with my old beat valiant....pull the clamp tube out of the socket (6AQ5 or something like that) and load her up again measuring the outpoot.

[ke7trp]

Pulled the clamper out. Same 90 watts.  Thanks for the tip.

I am going to start testing the caps soon. My meter is dead and wont read them. Another ham is comming over with his meter in an hour. Hopefully its just a bad cap or two.

What value variable will work?  Any links or schematics? 

Thanks alot guys!  Sitting on 3870 with the Globe champ if anyone wants to chat.

Clark
ke7trp

[W7XXX]

Clark, With one tube at 50 watts out, what is input? If it is correct then it has to be the additional tubes with the increase of current in the pi network breaking down a loading cap. In this case testing the caps with a meter may not show anything. I would replace them all or as suggested put in a variable around 1500 mmf.

[WQ9E]

Well, in the minimum loading position there is a total of 3,000 pf of fixed capacitance in the Valiant as designed (all coarse loading cap sections in parallel).  If you want to retain all band coverage at minimum you are going to need around 2,400 pf of loading in addition to the variable loading cap already present and this will still require you to start out at fairly heavy loading (so tune quickly since the off resonance plate current is going to be pretty high).  It isn't that difficult to find standard fixed mica caps in the 1200, 900, 600, and 300 pf sizes and since you have already replaced the switch I would vote for keeping it stock.

 At least your Valiant must not have been in CB service because on 11 meters the higher capacity loading caps would not have seen any action!

Rodger WQ9E

[WA1GFZ]

a T tuner is a high pass while an L is low pass. You can make a T a low pass by using 2 inductors and 1 cap.


da wrong subject

[The Slab Bacon]

just FWIW my valiant makes around 100-105w out when only loaded for 275-290 ma of plate current. I never load it up to the max 360ma. It helps keep the undersized mod tranny from saturating. If your output is low, check to make sure you have wnough grid drive to the final, and that your tank coil taps are on the right turns. If the L/C ratio is wrong you wont get mush outpoot. Also check your neutralization cap. If your max output point is way off of the plate curent dip, suspect something in the neutralization circuit. Also like Dave said, give it a quick try with 6AQ5 clamp tube completely pulled out. Check your final bias as well as valiants used a combination of both fixed and grid leak bias on the finals. If the grid leak resistor is way out of tolerance the clamp tube will do strange things.

                                                                          The Slab Bacon

[k7yoo]

Before you go completely nuts place separate milliameter in series with the PA plate current. I went through the same deal on a Viking 500 and finally found that the meter shunt inside the plate current meter was broken off. What I thought was full current was actually much less. It may be either a bad meter shunt or the "gimmick" silver mica loading cap is toast. If you can't load any heavier and get more output it is the cap.
BTW what does the screen voltage measure?

Don't throw away the arced bandswitch wafer. I have fixed dozens of them by glass beading the carbon path off. If the contact is fried I replace them with spares from donor switches.

[WD5JKO]

  I know this is a long shot but isn't the final on a Valiant neutralized? If so the grid 1 current should be rather constant as the plate is tuned through resonance when the neutralization is correct. Maybe the neutralization circuit has shifted such that adding more tubes makes things worse because the drive is self limiting with increasing plate to grid capacitance.

   Also, you say the rig modulates upward just fine, but have you looked at this with a scope configured in X:Y mode so you can observe the trapezoid pattern? This will require adding a HV resistive divider to sample the modulated B+ for the X axis. The trapezoid pattern will show the Class C 6146 final RF linearity when modulating and poor linearity if present will be very apparent. Poor linearity can have all kinds of root causes. One of them is poor neutralization.

good luck,
Jim
WD5JKO

[w8khk]

Before you go completely nuts place separate milliameter in series with the PA plate current. I went through the same deal on a Viking 500 and finally found that the meter shunt inside the plate current meter was broken off. What I thought was full current was actually much less. It may be either a bad meter shunt or the "gimmick" silver mica loading cap is toast. If you can't load any heavier and get more output it is the cap.

While rebuilding my Valiant, I found the shunts for final plate current and modulator plate current to be way off calibration.  Rather than deal with trying to adjust such a small value of resistance wire, I replaced the shunts with 0.47 ohm 5 watt fixed resistors, then I added a resistor of about 500 ohms in series with the meter movement for those two measurements.  For the modulator plate current reading, the series resistor is between the shunt resistor and the meter switch + terminal.  For the final plate current reading, the series resistor is in the negative return, between the meter switch - terminal and ground (this switch terminal was previously connected to ground.)  I calibrated the series resistors out-of-circuit, using a small battery, a pot, and a calibrated milliameter, current verified by a Beckman DVM.  Now I can trust the readings. 

After reading this thread, I am considering replacing the tuning and loading caps in my Valiant, and reducing dependence upon all the fixed caps.  Lots of good info in this thread, surely helpful points to consider while bringing my Valiant online!

[ke7trp]

Worked on the valiant tonight.

ALL the caps are good and test about what they should.  C38 and C39 (the two groups of four) measure a bit higher then stated.  one is 150 but measures 188.  The other is 330 total but measures 400.  I guess thats ok.

I then measured the loading cap and switch.  600,900,1200 is what its supposed to be. It tested at 600, 950 and 1400.  Close enough?

All postions of the course loading switch are working. Everytime I switch it up, I get more cap. The total is 3000 or so.

My valiant had a 500PF door knob.  I installed a new 1000PF cap and found I could get a bit more loading. I then tried 2000PF but saw no real difference in power. Just where it loaded. I left a single 1000PF in.

At 330 MA I get 100 watts with 400 pep. 
At 400 MA I get 110 watts with 420 pep.
At 450 MA I get 130 watts with 420 pep.

I also tried another watt meter just to make sure my Bird was correct. Both watt meters matched. 

I did not measure or test the shunt. I think its working ok. The bias voltages are exactly inline with the indicated current on the meter for the plate and modulators.

I asked all the guys on the air about power output. They tell me the same thing.. 150 to 160 watts with about 500 forward.

I guess mine is weak. Not much else I can test unless anyone has anymore ideas. Thanks to all of you for the help and parts!  I really learned alot and I had fun working on it.

I sure wish I knew where the power is going. The volts and the current are there. The output is not. Nothing is getting hot or glowing even after a 10 minute key up at 100 watts out.

Clark

[KD6VXI]

I sure wish I knew where the power is going. The volts and the current are there. The output is not. Nothing is getting hot or glowing even after a 10 minute key up at 100 watts out.

Clark

I'd guess metering, then.  If nothing is getting hot, then it isn't dissipating what you think it is.

I'll email you on the other. 

--Shane

[WQ9E]

As I recall the original shunts for the final and modulator meter circuits are supposed to be about 1/4" after tinning but since I don't have the manual handy lets say they are supposed to be 1/2" or .500 inch of actual resistance wire net of the amount tinned.  If the original constructor actually ended up with .600 after tinning (only a 1/10 of an inch error) then your meter is going to be reading significantly higher than actual.  Somehow the idea of precision shunt and having them cut and tinned by a kit builder doesn't seem to make sense.

In general, the tendency is for the shunts to be too long which is on the safe side.  It meant the owner never loaded the final to rated power and realistically the difference between 100 watts out and 150 is not significant at the receiving end.  However, if your final shunt is incorrect but your modulator shunt is correct then you will over modulate running the modulator at rated (which in this case would be actual) current.

I bought a bag full of little low value precision resistors from Mouser and it only takes a couple of minutes to replace the existing shunt with an accurate one.  Although you have a fair amount of leeway with the 3 finals an inaccurate shunt in the modulator will lead to either excessive distortion from too little resting current being set or excessive dissipation from too high an actual resting current.

I replaced mine in my original Valiant after using a precision Wheatstone bridge and measured the shunt as being 30% high.  If those shunts are accurate it is more due to luck than anything else.

You definitely have a Valiant that at least started out as an early model.  The 500 pf coupling cap wasn't big enough for proper tuning on 80 or 160.  If you plan to operate a lot on 160, depending upon the antenna you use you may want to go to the 2,000 pf value used in later models.  Your current coupling cap is fine for any antenna the Valiant will match on 80 meters and higher.

Rodger WQ9E