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

[ke7trp]

I am confident in my Meter and shunt working properly.

If I set the mod bias to the voltage specified, the meter reads the mod current specified in the manual.
If I set the final bias to the voltage specified, the mter reads the final resting current on SSB that is stated.

If I load past 350MA I do not get any more power. Just a bit more carrier. Loading higher is not really making any difference. Alot of people are suggesting I am loading it light because the meter is inacurate. I loaded it at 450 MA and had no real increase in power anyways. 

THats a good idea on the mouser caps for the shunt. I will save that information.

These caps where tested with a modern Tectronics meter. In and out of circiut with no voltage.  I dont have a leakage tester. I wish I did and I am looking for one now.

Clark

[ke7trp]

Ok.. I guess, I will make put some of the caps in that Robert Sent me. I should be able to get close.. these caps are 3500 working 7000 surge and 1000P. I also have some 39Ps.   

Thanks

Clark

[ke7trp]

Its not the caps.  I just put two 1000s to get 500 in the spot that needs 600pf. Close enough. No change. I then used a 1000 where it calls for the 900 section. No change in output. I then used a 1000 and a 100 to get 1100 for the 1200pf location. No change.. 90 to 100 watts.

I then inserted the meter to check the shunt. My meter is 20 MA low. Not bad.  I loaded it to 330ma of actual current at 700 volts. Output is 110 watts with 415 pep at 100%.  If I remove one tube and run two, I get the same exact output.  I removed each tube one at a time so I ran only two in every location. Same output. Add the third in and you dont get any increase in output. Filiment volts is 6.1 volts.

I guess I will run it like this. It makes 110 and its clean on the air. I wanted to get it up and running as a back up to my Globe. With your guys help, I have my back up transmitter. Its not full power but its working.  Nobody is going to tell I am missing 40 to 50 watts. If it ever fails completely we will know the problem.

I learned alot from you guys and if there is anything that I can do just ask.

Thanks to all of you for the help!!!!

Clark

[ke7trp]

Checks at 180 PF  Looks perfect.  Checked in and out of circiut.

The C39 network is supposed to be 330 but checks around 400PF.  Also looks perfect.

Clark

[WQ9E]

Clark,

Given the original size of your coupling cap your Valiant started life as an early unit and it may not have had all of the updates.  The way the metering was set up originally in the AM mode the final plate current (actually cathode current) reads 30 ma high because the current for the VR regulator tubes also passes through the meter shunt.  Later on the wiring was changed slightly so that the VR tube current no longer passed through the meter shunt.  Johnson's interim fix was to change the instructions to load to 360 mils instead of 330 on AM.

Since you get the same output with 2 tubes as you do with 3 it is also possible your grid excitation is a bit low; this might be one last thing to check with your meter.  You don't want to overdo it at the 6146 control grids aren't terribly rugged but if your actual excitation is significantly less than indicated your efficiency is really going to suffer.  To do a quick experiment, temporarily try a very short test with 12 mils of indicated grid drive and if your efficiency goes up significantly then check your grid metering circuit.

I believe the service bulletin is on BAMA but if not I will be happy to email it to you as an attachment.

Rodger WQ9E

[WA1GFZ]

How about the plate blocking cap. It could be open. Parallel it with 1000 pf and give it a try.

[ke7trp]

Plate door knob replaced. Was a 500 and now a 1000PF.

Ran grid up to 12 ma. Lost 5 watts doing that. Set it back at 7.5 ma.  Adding Grid is not increasing power so I guess thats not it.


The Neut cap is fine. I just checked it.

Grid:

Full load 350 MA on 80 meters is 118 volts.  Found that someone soldered in a resistor inline on the grid. I jumped it with a test lead. now 140 volts. No change in power output can be seen. Hooked test clip to terminal (bypassing both resistors) and put 150 volts of screen on. No real change in ouput. Right at 100 watts.

This valiant is a later one from what I can tell.  It did not have the small 500 PF cap for the door knob. It had a larger 500PF at 20KV.  I put in a 1000PF cap that is half the size but came out of another RF amp. Its working better with the 1000PF for sure. I can load to 100 watts on 160 now. Before 160 was way down.

Also want to mention. I loaded it on every band a few minutes ago. Output is about the same on every band 100 watts or so. No single band does significantly more or less then another.

Let me know what you guys think about the Screen volts.  I have no idea why anyone would drop the volts down with a resistor like that. Its def not supposed to be there. At any rate.. The added Screen did not increase the power


Clark

[ke7trp]

Check the cap. Its perfect. 1003PF Swapped it for another one. No change.

I ripped out two resistors that some previous owner had added to the Screen. Before was 118 volts. That resistor was a bit charred.  I ran solid copper wire to screen junction over to the terminal.  Now I have a solid 155volts on the screens.

I now get 130 watts key and 490 watts PEP.  If I load it to an indicated 390 which is really 360.  I can pin the 500 watt slug. I think this means its fixed unless someone has anything else to add here. It wont load to 150 ot 160 watts but its close and its making 500 watts peak out. I am at least in the ball park here..

I am going to recheck the bias, neutralization, and set the clamper one last time to 10 ma and put it back in service. Should be fun to talk on it tonight for the AMI net on 75.  Also going to talk down on 1885 wiht it to my friends.

Now I can focus my time on the Globe 300.

Are we all in agreement that this radio is about where it should be? 

Thanks again for all the help!!!!!!  I learned a hell of alot with all of your help!

Clark

[K1JJ]

Hey, that's good news, Clark!

So it was the screen voltage loading down. That was a bear of a problem to find.  Bob/W1RKW had a similar problem with his 813 rig last week and squared it away too.

I must admit, I was baffled with the symptoms after a while.
Hindsight is 20-20, of course, but what can we learn from this for next time?

Perhaps one of most powerful troubleshooting techniques is to exhaustively measure voltages with the VOM and scope. Watch what they do under dynamic conditions on the scope and compare this with the specs, or a working unit... or our best estimate of what each measurment shud look like.

Quick story:  When I was a young tech, just out of school, I had trouble with a repair job. I went to the head engr and asked for advice. His first response was, "Have you measured all the voltages and compared them to the manual?"  I said no, I haven't gotten to that yet. He just shook his head... :-)

That lesson stuck with me and I keep learning it over and over in my own work.


Well, anyway, yours was a tough problem created by some hambone doing a bad modification to the rig - the worst kind of problems...and took a good effort to discover. 

Congrats to you and all the guys who helped here!

Tom, K1JJ

[WQ9E]

Clark,

Glad you found the problem! Congratulations!  There is nothing like a rig that has been modified (especially poorly) to generate hard to find problems. 

Enjoy your "new" Valiant, it is a fun rig to operate.  As a novice I used one at the 75 watt level and used the hum of the plate transformer as my keying monitor.  Those were the fun days.

73 Rodger WQ9E

[ke7trp]

I am talking on 1885 now with the valiant. Loaded at an indicated 360MA with 150 watts out! PEP is about 500.  Its talking around 450. 

Thanks to all of your for the help. I am greatfull for the learning experience.  I am going to use the valiant on 160 for a while and then off to 75 for the AMI net.  Hope to hear some of you guys on the air!


Clark
Ke7TRP

[ke7trp]

Can someone CONFIRM proper Screen Volts on the 6146s.  My manual clearly shows 152 volts on Pin three of the 6146. Tonight on a net, the guys are insisting this should be 200 or more volts. Can someone confirm this for us?

Clark

[K1JJ]

Can someone CONFIRM proper Screen Volts on the 6146s.  My manual clearly shows 152 volts on Pin three of the 6146. Tonight on a net, the guys are insisting this should be 200 or more volts. Can someone confirm this for us?

Clark

Clark,

My 1955 Handbook shows for telephony, one tube, 6146:

600 volts plate voltage  @ 85ma
150V screen voltage  @ 12 ma
-85v Bias  @ 3ma
52w output

OR

CW:
750v plate
160v screen

OR

CW:
400v plate
200v screen


It shows a max screen voltage of 250 V and 3w dissipation, so you have some wiggle room there.


73,
Tom, K1JJ

[ke7trp]

I have 153 volts of screen.  I get 155 watts on 160 and 135 on 80 meters.  I talked on it for an hour straight on 160 tonight with great reports. 3 hours on 75 meters at 135 watts. with good reports. Some of the guys said the screen is to low and that I have issues still.  The manual shows 152 volts on pin 3 screen.  I think this transmitter is working 100% with all the help I got. I really enjoyed the bands tonight with it. Some claimed the audio is thin.. But its a stock valiant.

Thanks again for all the help guys!!

Clark

[WA1GFZ]

I got better positive peak modulation when I dropped the screen voltage from 200 to 160 to 170. At 150 the output power drops off.

[KL7OF]

error

[KB2WIG]

 "" It you run the plate current and screen voltage higher your running the risk of blowing the modulation transformer, etc. "


Cowards die many times before their deaths. The valiant never taste of death but once.

W.S.

[N3DRB The Derb]

Some claimed the audio is thin.. But its a stock valiant.

congrats clark! observation is your most powerful tool to fix radios. 8 times out of 10 its previous "repairs" or mods from a former owner.
 

stock valiants need a fair amount of work before they swing the munky.

[Steve - WB3HUZ]

Yep. The difference in signal strength between 110-115 watts and 150 watts is not noticeable. The better quality audio at the lower power level will be noticed.

[ke7trp]

This radio is now 100% functional.  It makes full power on every band and is stable. I had some issues with the output wave form but when I ran a ground braid to the tuner this was resolved.

Thanks to all for the the help. I have been loading it at 330 actual and it seems happy. 

Clark

[WA1GFZ]

I have an ARC39 mod transformer that was the same line up as the valiant with 28 volt heaters in an aircraft rig. I think it would be a good spare for the V2 or Valiant. I think it came from Fair Radio. It is rated 50 watts RMS/ 100 watts peak. Nice sealed unit. It ran lower voltages but in a mil application. No idea how it sounds but looks nice.

[flintstone mop]

It seems like the output section is at fault. The arcing contacts on the old bandswitch was a component (loading cap?? / components) breaking down and turning into a high ohmage resistor.

Fred

[The Slab Bacon]

Yep. The difference in signal strength between 110-115 watts and 150 watts is not noticeable. The better quality audio at the lower power level will be noticed.

thank you Brutha!! ! ! ! ! ! ! ! !  At least I didnt have to say it this time! The weak link in a valiant is the undersized mod tranny. Reducing the current through the secondary will help the audio dramatically. Loading it lighter is the best "bang for the buck" audio mod you can do.
                                                            The Slab Bacon

[ke7trp]

Understood.  I will load it down to 110 watts or so and let it breath a bit.

Clark