hi my name is mike, n8ktf. i have a valiant that powers up, has modulation and rf power out , but the vfo does not seem to work. even with the 6au6 vfo, 6cl6 osc/buff, 5763 multiplier tubes pulled out, it will still tune up and display a 27 mhz frequency on my freq. counter when in the 20/15 meter band . rf out is terminated into a 50 ohm oil filled load. even with said tubes installed, the internal vfo will not change the frequency no matter what band i select. i can tune 80 thru 10 meters up on the amplifier but the vfo seems inoprable. what gives?
If you pulled the the 5763 and 6CL6 out there is only one possible reason the transmitter is putting out power....the PA stage is oscillating.
The PA is neutralized with an air variable capacitor on the center shield panel. There is several hundred volts of dc on that capacitor, and the metal shaft is at 100 volts or so. If you do not KNOW what you are doing, get help from someone who does.
The Valiant will oscillate with the neutralization wrong, and it can oscillate for other reasons also like bad parasitic suppressor resistors or bad bypass capacitors on the screen grids.