Viking Valiant tune-up question (160 and 80 meters)

[n2awa]

Just finished re-capping, etc. a new (to me) Viking Valiant. This is my first introduction into AM transmitters. I know very little about them compared to most of you!

Tune-up question:

On 160 and 80 meters:
I was finally able to see grid current by increasing the DRIVE control past "3" (owner's manual says to set drive to "3").

For 160 meters, the DRIVE control had to be set at "5".

For 80 meters, the DRIVE control had to be set close to full "10".

Then, when I monitored the plate, I backed off on the DRIVE (a bit) to get 330mA (for phone operation).

Is this normal or does it indicate something is wrong?

[WA1GFZ]

You should not reduce drive to reduce plate current. This could mean you don't have a 50 ohm load. The best way is to increase load C. Valients have a common problem of blowing the fixed load caps. An open cap would show up as high plate current and shallow plate dip. Also check your bias voltage on the final grids.
You may be tuned up on a harmonic on 80 meters to require so much drive. Start with the low level stages having the tuning caps at maximum c and tune for the first dip.

[n2awa]

Let me back up a step (hopefully for clarity). The first place I see a "problem" when tuning on 80 meters (or 160 meters) is where the manual says:

Turn DRIVE control to 3.

Turn METER switch to "grid", tune EXCITER dial for maximum grid current.

Note that with the DRIVE set to 3, no grid current is seen for any EXCITER dial setting.

Adjust grid current to 8 mA by turning DRIVE control.

Even with the drive set to maximum (10), I cannot attain 8mA grid current.

[WBear2GCR]

I have a Valiant II.

Place the thing in VFO position, then over to "ZERO".

First step is to listen for your signal on an 80m receiver - also check 40 and 160.
On my unit, someone had misaligned the "kicker" that switches the VFO off the bandswitch that is found under the unit. It wasn't on 80m when it said it was.

Assumin it is on 80m.

Switch the meter switch to BUFF, and look for a  dip when you move the exciter control. Assuming you see current and a dip, then go to the GRID position you ought to see ample swing.

IF the rig then does not show grid current on 80m, try 40m - that doesn't use the kicker switch! If that works, realign the kicker so that the VFO is on 80m in the 80m bandswitch position... the thing works funny, I had to dork and switch it manually a few times to figure it out.

If that does not work, then see if the rig will load up properly, keep the drive control set to the nominal "3" or "4" position... if the rig loads up properly, then the problem is likely in the metering circuit. If the rig does not load up properly then it's time to scope the drive path...

Hopefully you have a scope to look at what is going on...
A receiver set to the frequency will give you an aural indication of the function of the controls...

               _-_-bear

[n2awa]

I can not beat (is that what you mean by "hear"?) any signal on 80 or 160. I guess this makes sense if there is no grid current, then there is no output. But when I go from VFO to ZERO (OSCILLATOR KNOB), the BUFF current does rise a bit.

All of the other bands seemed to tune up into a 50 ohm dummy load (Heathkit "Cantenna") well.

The "kicker" (cam block) may certainly be mis-aligned, as I had to remove it to free up the frozen shaft. I thought I played with enough to get it back on correctly, but who knows.  I can check this again.

Again, when I go from VFO to ZERO, I am seeing NO grid current at any EXCITER knob setting (on 160 and 80 meters).

[WBear2GCR]

The cam block is misaligned, probably.

Put the rig up on its back or side, get the receiver on.
Put the rig on 40m, set the switch for ZERO.
Put the receiver on 40m, BFO or SSB mode, find the VFO's carrier.
You may need a local wire near the rig from the receiver, or not.
Then manually move the cam block - with the reciever on 80m... tune for the
signal.

Once you find the signal, note where the bandswitch (you did not move the bandswitch
yet) has to be so that when you move it to 80m it puts the cam block into the position
you just noted.

Then loosen the setscrew and reset the cam block, test.

It does not work quite the way it looks like it should!!

Things should work if the rig works on 40m then it ought to work on 80m...

             _-_-bear

[n2awa]

Thanks for the suggestions. I will try them, and report back. Might not get to it in the next day or so though. I hope that is all it is.

[Ed/KB1HYS]

I've got a valiant too.  Been up to my elbows in it lately. 

If you want to compare notes, that would be a FB thing I think.

By stock in 6146 tubes...
 

[kc2ifr]

Check the screen dropping resistor on the driver and check the plate swamping resistor on the same toob.....
Bill

[n2awa]

Hi Bill,

>Check the screen dropping resistor on the driver and
>check the plate swamping resistor on the same toob.....

Do you mean the Type 5763 (V4) RF Multiplier/Driver tube? 

[n2awa]

Also, I checked the cam block position, and it was fine. Compared mine to another Valiant. Also listened on my Kenwood TS-530S (poor man's digital frequency counter?) and heard the zero beat on all bands except 80 and 160. Might be a loose or broken connection in the VFO box. Will investigate.

[n2awa]

Finally got the Valiant going on 80 and 160 tonight. I wish I could point to something specific, but when I re-opened the VFO box, I did a number of things like move wires that were close, put some De-Oxit on the VFO tube sockets, etc. No major problems were found. But whatever it was, it's gone. 

[WA1GFZ]

hope you checked the screen dropping resistor

[n2awa]

Still waiting for clarification as to which one that is. Schematic is shown above. I checked the 2.2 ohm resistor (looks like R56) near the Type 5763 (V4) RF Multiplier/Driver tube and it was fine. Is that the one?

[WA1GFZ]

Screen dropping resistor in the VFO in my case. My 122 was at 40K when I checked it...and it still made an output. Very common failure

[Ed/KB1HYS]

R 3 on the schematic is The "Chernobyl Resistor"  an 18k 2 watter inside the VFO Cabinet.  It is under rated and prone to failure.  You'll have to open the side of the VFO enclosure to get at it. Snip out the old one and run two wires down and out of the cabinet to a 20K 5 watter and install outside the VFO under the chassis.  Use a thicker rigid wire for the lead in/out (I use bell wire I get from HD solid and 18 or 20 Gauge) and secure the replacement to the chassis well to prevent problems.  I used a small cable clamp to secure mine to a convienient screw/standoff directly under the opening for the VFO.

Working inside the VFO enclosure is a sure 'nuff pain but moving the resistor beats repairing the VFO after a Volcanic Failure.

This is one of the Must Do mods for the Valiant (and other Johnson rigs) to keep it running right.
That and a correctly fused 3 wire cord are probably mandatory.

Lot's of people like to tear into Valiants to "Improve" the audio.  Stock audio is like a bad phone, but you can bypass the clipper circuit with a cap, and bypass the LP Filter in the audio chain and you get decent (My Opinion) audio at 100% modulation.  This is the minimalist approach, easy to return the unit to stock condition if desired, and I'm sure others on the board will argue that there's a lot more that can be done, but that's a matter of choice.
You can also feed equalized processed audio into the phone patch RCA plug once you've bypassed the clipper & Filter.

I've also done the Mods from K6HLO, they are relatively straight forward, being mostly cap replacements, a negative peak clipper, and adding a choke for screen modulation of the finals. If you want I can forward a copy to you.

[n2awa]

I made the R3 Chernobyl resistor modification. Used a 5 watt, 18k wire-wound. As far as audio mods, I'm going to wait until I get some more feedback from other stations before I make a decision. Now that it is up and running, it may be "only the beginning" and more work may be needed to fine-tune it.