Johnson Viking Valiant modulation problem.

[W1OAT]

Hello everyone,
I?ve been working on getting a Viking Valiant on air for a while and a couple of days ago I sent out my first transmissions. The feedback I got was the my carrier level was good but my modulation was low. After tweaking the mic level and clipping I still had problems, so I went back to the manual and went through the setup again. In section C3 of the manual it says ? voltage read at modulator grids should be -55 volts.?  The original two tap variable resistor has been replaced with two potentiometers. They are of the correct value, however I cannot adjust the modulator grid to give me -55volts. The best I can get is -45volts. When I first bought this rig I noticed the 22ohm plate resistor on one of the 6146 modulator tubes was fried so I replaced them. I suspect that the blown resistor has something to do with the low grid voltage, but I?m unclear as to how. Does someone have some insight as to what is going on here?

[Dave K6XYZ]

Hello everyone,
I?ve been working on getting a Viking Valiant on air for a while and a couple of days ago I sent out my first transmissions. The feedback I got was the my carrier level was good but my modulation was low. After tweaking the mic level and clipping I still had problems, so I went back to the manual and went through the setup again. In section C3 of the manual it says ? voltage read at modulator grids should be -55 volts.?  The original two tap variable resistor has been replaced with two potentiometers. They are of the correct value, however I cannot adjust the modulator grid to give me -55volts. The best I can get is -45volts. When I first bought this rig I noticed the 22ohm plate resistor on one of the 6146 modulator tubes was fried so I replaced them. I suspect that the blown resistor has something to do with the low grid voltage, but I?m unclear as to how. Does someone have some insight as to what is going on here?

Hi Dan.....
Just yesterday I did routine maintenance on both of my Valiant 1's.
Both of them are factory assembled 60'/61 models.
Both have the side mounted pots for PA bias and modulator current.
I would first ensure that these pots are set correctly.

Set clipping fully CW...and leave it there.
You don't ever want any clipping..this control works backwards....see manual.

The manual is a bit confusing on how to set the PA bias...so to set it correctly...
Set the Oscillator to an unused xtal position.
Set the mode to CW. (remove CW key from rear jack)
Tip chassis onto it's side (don't put chassis upside down, this can cause VFO damage)
Connect meter to junction of L7 and 6146 pin 3.
Turn on filaments.
Do not operate plate switch or PTT....leave off.
Adjust lower pot for -52v.
Remove meter.
Set chassis upright.
Set Osc to VFO.
Set Mode to AM.
Tune up transmitter to 330ma into 50~ dummy load on 80M.
Put meter sw on Modulator.
While still transmitting...adjust upper pot for 40ma (modulator) on meter.

This will get you to where if it is still not working correctly, you can start troubleshooting from a known point.
I would not be too concerned about voltages unless the unit is not operating correctly after the above setup.

[DMOD]

Hello everyone,
I?ve been working on getting a Viking Valiant on air for a while and a couple of days ago I sent out my first transmissions. The feedback I got was the my carrier level was good but my modulation was low. After tweaking the mic level and clipping I still had problems, so I went back to the manual and went through the setup again. In section C3 of the manual it says ? voltage read at modulator grids should be -55 volts.?  The original two tap variable resistor has been replaced with two potentiometers. They are of the correct value, however I cannot adjust the modulator grid to give me -55volts. The best I can get is -45volts. When I first bought this rig I noticed the 22ohm plate resistor on one of the 6146 modulator tubes was fried so I replaced them. I suspect that the blown resistor has something to do with the low grid voltage, but I?m unclear as to how. Does someone have some insight as to what is going on here?

 -46V is the nominal grid bias voltage for the grids of the modulator tubes, so -45V is very close.

Those 5k WW pots are usually dirty so they may need cleaning before adjusting, but it doesn't look like R61 needs adjusting.


I would first measure the bias voltage to the left of R50, a 1k resistor, before making any adjustments to R61. Voltage at this point should be at least -235 volts. J9 Pin 5 also has this same voltage on it. It appears the 6BY5 may be ok.

Also adjust R13, the clamper control, for Final screen voltages of 175V at any pin 3 into a dummy load in CW mode at 40m after dip and load.

[W1OAT]

K6XYZ, I cannot adjust the bias to -52v. I max out at -42v.
DMOD, the reading I get on the left side R50 is only -220v (I?m assuming that by left side you mean the T4 transformer side?) on the right side I get -257v.

[DMOD]

K6XYZ, I cannot adjust the bias to -52v. I max out at -42v.
DMOD, the reading I get on the left side R50 is only -220v (I?m assuming that by left side you mean the T4 transformer side?) on the right side I get -257v.

I was referring to the schematic when speaking to left or right.


If your input AC voltage is around 120-124 volts, those voltages are a bit low, so try a different 6BY5 rectifier and possibly replace C93A,B with newer caps.

Here are some upgrades I did for my friend's Valiant.

[W1OAT]

I will have to order that rectifier tube and all I have is 10uf and 20uf caps. By the way the 1k resistor reads 1100 ohms. A little high perhaps?

[KB5MD]

I had the same problem with the 22 ohm resistor frying.  I changed out the adjoining 6146b and the problem went away.

[W1OAT]

After further investigation, I discovered the pot was reading low. I disconnected it from everything and measured again and got a max reading of 3750 ohms. I ordered a new one.