Johnson Viking Valiant (HELP)

[k5kab]

Tune process with the problem...........

3. Turn drive control to 3.
4. Turn meter switch to “grid”, Tune Exciter Dial to Maximum Grid Current.
Adjust grid current to 8 ma. By turning drive control.
(with drive controlled rotated to 5-10 I can not get any grid current ). By continuing with the tune process, the unit will pull 300+ ma. and give 115-120 watts of carrier. Playing with the final knob I can manipulate grid on the meter but any adjustments of the final grid goes back to 0.   

(40m VFO or 80m crystal into a dummy load results are the same)

[ke7trp]

Drive pot toast?  Is it adjusting at all?  Its normal for Grid to change when tuning the final.

C

[k5kab]

The drive pot is adjustable, once I’m past the maximize the exciter portion, of the process  I can vary grid on manipulation with the drive pot. Also with the final knob, grid is either on or at zero with just a touch of the final knob.

[k5kab]

The Valiant exciter section consist of a 6AU6 (V1) variable frequency oscillator. a 6CL6 (V3) crystal oscillator/buffer and a 5763 (V4) frequency multiplier/driver.

Two separate voltage regulation circuits are incorporated in the Valiant. One circuit, an OA2 (V2) regulates the screen voltage of the VFO (V1) for max frequency stability.
The second regulator circuit using two OC3/VR-105 tubes (V9, V10) holds the screen voltage of the final amplifier to close limits when operating the amplifier as a SSB linear amplifier. When the valiant is operated in the AM mode, the pair of VR-105 regulates the screen voltage of the 6146 modulators (V16, V17).

SW5 Position    Current Stage         Scale        Tubes          

GRID      GRID      Final Amp   0-25   V5, 6, 7


Exciter- - C74, tunes the place circuit of the multiplier, V4.


Just what does the OC3 do and could they prevent gride current when trying to max out the exciter? Again no exciter when im trying to tune up

[WQ9E]

After doing the exciter tune up on 80 meters (with the plate switch off), how far do you have to advance the drive control to get 8 mils of grid current?  

Is your final grid bias set properly (-70 using R22 on the earlier Valiant, -69 using R62 on later Valiants or those modified for use with the 6N2 transmitter).   Excessive bias will keep you from achieving proper grid drive.  

If bias is correct, I would substitute for the 6CL6 osci/buffer tube and 5763 multiplier/driver if you have subs available.  Otherwise, check resistance and voltage for these tubes.

[k5kab]

After doing the exciter tune up on 80 meters (with the plate switch off), how far do you have to advance the drive control to get 8 mils of grid current?  Drive set to 10 no grid...
Is your final grid bias set properly (-70 using R22 on the earlier Valiant, -69 using R62 on later Valiants or those modified for use with the 6N2 transmitter).   Excessive bias will keep you from achieving proper grid drive.  bias is good
If bias is correct, I would substitute for the 6CL6 osci/buffer tube and 5763 multiplier/driver if you have subs available.  Otherwise, check resistance and voltage for these tubes.    Will try changing the 6CL6 and the 5763.  Thanks  What does the OC3 control exactly? I have no way of testing these tubes but one seems to have a short ?

[WQ9E]

The 0C3 VR tubes regulate either the modulator screen grids (AM mode) or final screen grids (SSB mode) and will have no impact on your present issue.

Does the grid meter move at all with the excitation control?  You are getting some grid excitation to the final or it would not be producing output.  You may have a problem in the grid metering circuit itself, either the shunt, switch, or connections.

Go through the tune up procedure set for VFO control on 80 and set the drive control at 4.  Dip the final and then increase the loading slightly and see if you can increase the output.  Try varying the drive control and see if the output varies.

If you grid metering is not working, be careful as the 6146 finals really do not like high control grid current and are easily damaged with excessive grid current.

[Ed/KB1HYS]

This sounds like you might have a neutralization issue. (been there, done that).

from the Valiant manual:

Note: improper neutralization is very likely to become evident when loading the amplifier and adjusting grid current. Bringing the grid current up to the normal 8mA will cause the amplifier plate current to rise beyond the normal value. reducing the amplifier loading will then cause the grid current to fall off.  The net result of improper neutralization is to make it almost impossible to load the amplifier to the proper 330  or 450 ma while maintainting recommended 8 ma grid current.

Easy enough thing to check anyway as it requires no special equipment or disassembly.

maybe you have 6146B's or Jan tubes in there?  Sometimes they can be tricky to neutralize in a rig originally designe around the earlier version. (this shouldn't be but bumble bee shouldn't fly either).

Just a thought, and I finally had a chance to look at the manual.

[Ed/KB1HYS]

Could be, the meter/shunt(s) in the Valiant are unreliable.  I just found that section in the manual when i was looking for something else and the light when on.

[k5kab]

This sounds like you might have a neutralization issue. (been there, done that).

from the Valiant manual:

Note: improper neutralization is very likely to become evident when loading the amplifier and adjusting grid current. Bringing the grid current up to the normal 8mA will cause the amplifier plate current to rise beyond the normal value. reducing the amplifier loading will then cause the grid current to fall off.  The net result of improper neutralization is to make it almost impossible to load the amplifier to the proper 330  or 450 ma while maintainting recommended 8 ma grid current.

Ed:  You are the man.  I had two different tube manufactures installed and it was a neutralization problem. Installed the best suitable tubes and PRESTO,  7 ma of grid 330 ma of plate for 150 watts of carrier, make for great AM modulation . Thanks guys for all of the info !!! 

[k5kab]

Brian thanks for all of the info, you have an interesting web site great info there also. 73's

[Ed/KB1HYS]

Glad it worked out! 

Hope to work you on the air, Valiant to Valiant QSO...