Valiant Restoration K3MSB

[N1BCG]

^^ Agreed. The key is to not have significantly higher voltages than what you find in the manual.

As for the drift, do you have another 6AU6 to try as V1? I've noticed differences in characteristics between brands, and in this critical application, it could solve the issue. Also, have you checked R18 that it is actually 18k? A lower resistance will cause excessive current in V2, the OA2 regulator, which is another tube to check.

[k3msb]

Dave and Clark

Thanks for your comments.

I will check what the filament voltage is for 115VAC in.

R18 being 18K?    R18 is supposed to be 20K.   Do you mean R3?    I replaced that with a 10W 20K resistor under the chassis.

[N1BCG]

Do you mean R3?    I replaced that with a 10W 20K resistor under the chassis.

Ah! Touche!  Yes, R3...

[Dave K6XYZ]

Dave and Clark

Thanks for your comments.

I will check what the filament voltage is for 115VAC in.

R18 being 18K?    R18 is supposed to be 20K.   Do you mean R3?    I replaced that with a 10W 20K resistor under the chassis.

I always replace R3 with the correct value as well as locating the resistor in the original location.
A contributing factor with the drifting may be that the VFO compartment never comes up to the temperature that the ckt was designed and compensated for.
With R3 outside the compartment....might be too cool in there...so it takes much longer to settle down if ever.
I know that guys install R3 below the chassis but.......
Probably have to test it to see if there is an impact on the drift.
Also as someone else said....replace the 6CL6 and the VR tube inside.
If your VFO box is missing the vertical phenolic bandspread  variable extensions (5) you can get 5/16" plastic caps and snap into the holes to keep the heat in.
I always remove those damn things because the clip thing that fits onto the variable falls off.
To adjust the band spread I remove one cap at a time and stick a RF sniffer in the hole and get the freq right on.
This saves taking that VFO apart to try to get those clips back on....that's a real hassle.

[k3msb]

I did some measurements with the line voltage at 115 and 120 VAC.   I used the voltages in Table 1, with the Valiant configured accordingly, as reference.

Executive Summary:   The Valiant likes 120V better than 115 V.

Details:

Notation:    100/80 means 100V HV OFF and 80V HV ON......

Measurements made using a Fluke DVM  (which is probably not 20K ohms/V......)

Bias Reference:  -265V

115V AC:   -226/-202
120V AC:   -251/-228

Modulator Resting Current:

115V AC:  75 mA Min
120V AC:  50 mA Min

Low Voltage Reference: 300 VDC (Measured at J8-4):

115V AC:   348/289      120V AC:   381/320

Power Output:

115V AC:  140W        120V AC:  170W

VFO Heater Voltages:

TB6-2 Reference 5.8 VAC

115V AC:  5.6/5.3  VAC     120V AC:  6.1/5.9 VAC

TB6-5 Reference 5.8 VAC

115V AC:  5.4/5.0  VAC     120V AC:  5.9/5.7 VAC

TB6-6 Reference 340 VDC

115V AC:  348/293        120V AC:  379/324

I will lug the beastie to the operating position and redo my drift tests.......   Standby.....

[k3msb]

Stability over 120 seconds was better running the radio on 120 VAC instead of 115 VAC.

40M CW: (330 mA Ip)
+30 Sec:     +80 Hz
+60 Sec:     +90 Hz
+90 Sec:     +90 Hz
+120 Sec:    +80 Hz
Total of 90 Hz over 2 minutes.

40M AM:   (330 mA Ip,  60 mA Im)
+30 Sec:     +20 Hz
+60 Sec:     +30 Hz
+90 Sec:     +40 Hz
+120 Sec:   +40 Hz
Total of 40 Hz over 2 minutes.

I'm going to put the Valiant back in the case and put in on-line.

[N1BCG]

Great news! Seems like the bias supply issue is resolved as well.

[Dave K6XYZ]

Good news....glad to have helped out a bit with the drifting.