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Author Topic: johnson viking valiant  (Read 700 times)
N8KTF
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Posts: 3




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« on: March 27, 2010, 08:35:26 PM »

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?
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VE3CUI
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« Reply #1 on: March 28, 2010, 07:09:43 AM »

Hi Mike,

From your brief description, it sounds to me like the Valiant is "taking-off" on you, i.e. some stage(s) after the VFO are oscillating, & that's why you're still getting RF output even with the VFO tube pulled.

You say you're getting a reading of 27-MHz, or so: what does this signal actually sound like...? Is it raspy, & unstable...? If so, your rig is acting like one big oscillator.

Those Johnson VFOs often need TLC in & of themselves: there's an "under-engineered" screen dropping (I believe) resistor in then that's prone to over-heat & fail...and the seams in the VFO enclosure must all be tight & secure, for even the slightest "crack" will allow the VFO & final amplifier stages to react to one another ("feedback"), which leads to no end of instability & raspiness on those bands where the rig operates "straight through" in terms of frequency, from VFO to final PA...

~73~ de Eddy VE3CUI - VE3XZ
gswynar@durham.net
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WB2WIK
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« Reply #2 on: March 28, 2010, 01:37:07 PM »

Is the frequency "stable," like 27.10500 MHz or something?

If so, I suspect you have a crystal installed and the VFO switch is turned to the XTAL position.

If the frequency is drifting around a lot, then you may indeed have an unintended oscillator!
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W8JI
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« Reply #3 on: March 29, 2010, 03:56:51 AM »

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.

73 Tom

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