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Author Topic: VIKING2 OSCILLATOR WONT SHUT OFF..HELP..  (Read 5055 times)
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ve6pg
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« on: January 24, 2010, 02:32:16 PM »

... i know i have asked this before, but the problem still exists...
..ok...when i turn-off the plate switch, the oscillator is still running, and if i talk, you can hear my audio thru the receiver...if i switch the 122 vfo to the next higher band,and back, the carrier is gone. i can do the same thing by switching the xtal switch to "1", then back to 0. again, the carrier is gone. so viker gurus, what are your thoughts as to why the oscillator keeps running, after i turn-off the plate switch?..

..tnx...tim..

..sk..
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N2DTS
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« Reply #1 on: January 24, 2010, 04:22:46 PM »

Some rigs use bias to stop the osc from running, maybe its too low, or something is oscilating when it should not be, should be VERY easy to find the problem with a meter and/or a scope.

The viking 2 does not have a built in vfo, so how is the vfo being keyed?
Looks like pin 8 on the accessory socket goes to the VFO?
V6 is enabled by the cw key jack and the switch 2 and switch 3c phone/cw switch.

Brett
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WQ9E
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« Reply #2 on: January 24, 2010, 04:42:42 PM »

Tim,

Johnson published a differential keyer modification to add the same circuit used in the Valiant and later versions of the Ranger.  Does your Viking2 have this installed?  It sounds like it probably does (you will see some added components in the transmitter cabinet including a 12AU7 and a pot to control the keyer setting).

If it is in yours, locate the keyer adjust pot and turn it a little past the point that makes it cut the VFO off when you kill the plate switch.
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Rodger WQ9E
ve6pg
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« Reply #3 on: January 24, 2010, 04:44:31 PM »

..brett...it does the same thing, with a crystal...i'm thinking, the 6au6 is not shutting off..

..?..


 ..sk..
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ve6pg
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« Reply #4 on: January 24, 2010, 04:46:50 PM »

...no...there is no mod. understand, this problem has been "creeping-up" for years, and now it is full scale carrier...

..tim..

..sk..
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WQ9E
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« Reply #5 on: January 24, 2010, 04:57:49 PM »

Try it with your VFO unplugged so you can localize the problem to the VFO or transmitter (since the transmitter stays keyed in the crystal position you can still test it with the VFO removed).

If it still does it with the VFO disconnected, very leaky C-15, very leaky C50,  extreme heater to cathode leakage in V6, SW-2 section contaminated and leaky.

If it only does it with VFO-122 connected, then leaky C69 or bad oscillator tube (heater cathode leakage/short).

But your symptoms perfectly mimic a poorly adjusted differential keyer so make sure someone didn't add the circuit before you got the rig.
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Rodger WQ9E
ve6pg
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« Reply #6 on: January 24, 2010, 06:28:46 PM »

..ok..i'll go thru the caps again...i've owned this rig rig fer 30 yrs., and there have been no keyer mods...originally there was a very weak carrier...not enough to bother anyone. but now, it is full strap...vfo, or no vfo..no difference...

..tim..

..sk..
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N2DTS
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« Reply #7 on: January 24, 2010, 09:04:46 PM »

You unplug the vfo (not just turn the switch) and you still have carrier?
I find that very hard to buy, as the first stage on the Viking 2 is not a vfo and has no way to generate any sort of stable signal.
A heater to cathode short in V6 might turn the tube on, since one side of the filament is grounded, but it should not oscilate by itself.

The only things that can turn V6 on in AM are the switch (2) and pin 8 of the accessory plug on the back...as long as V6 does not have a filiment to cathode short.

Brett
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KB3DKS
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« Reply #8 on: January 25, 2010, 03:09:25 AM »

  The plate switch is a DPST. Half switches the plate transformer primary and the other half turns on the oscillator tube. That section has probably been contaminated by the plate section contact arcs.
 Plug in a key or open dummy plug into the key jack in CW mode and see if that stops the osc.
Also check the ACCY plug for leakage or a shorted bypass cap on pin 8. Seems to me there is also a key jack on the 122 VFO. Check the Octal plug for shorts ground to pin 8 as well. Also... that keying line goes thru the meter switch. Any shorts or leakage around there would keep the osc. on.

My 2C

Bill,
KB3DKS in 1 Land
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ve6pg
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« Reply #9 on: January 25, 2010, 06:38:18 AM »

..the manual says sw2 is a DPDT..i'll look at it..

..tim..

..sk..
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WD8BIL
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« Reply #10 on: January 25, 2010, 07:35:50 AM »

Tim,
Stick a crystal in one of the sockets and see ifn it still does it.
It sounds like the bias on the buffer stage is missing causing it to oscillate.
Check ALL the reisistors in the bias voltage divider string. Make sure your
bias voltages are correct.
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W1AEX
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« Reply #11 on: January 25, 2010, 10:44:34 AM »

Tim,

My modified Viking One with the three 6146B finals could be tuned in such a way that the oscillator would take off without keying it while in the AM mode. There were a combination of things that would cause this:

Incorrect meter shunts that did not tell me my grid current was actually sitting at around 15 ma. This of course was bad for the tubes and my three 6146B's are much healthier with about 6 ma total (2 ma on each). The heavy drive setting was causing a nasty self-oscillation problem in a lower stage. Fixing the meter shunts and running at 6 ma of grid drive helped stop the run-away oscillator problem.

The above issue helped to illustrate that my finals were very poorly neutralized and required the installation of a neutralizing bridge circuit. People could hear the oscillator running and radiating right through the tank circuit to the antenna, either on frequency or whooshing up the band when I un-keyed. Since I added the neutralizing components, it doesn't exhibit this behavior with normal settings, however, if I run the grid drive up, it can still be encouraged to take off.

I don't think it's a stretch to imagine that a Viking 2 with a pair of 6146's might exhibit the same issue under the right conditions. You might want to check your meter shunt resistor values and make sure they aren't deceiving you.

73,

Rob
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ve6pg
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« Reply #12 on: January 25, 2010, 07:26:16 PM »

..bud...it does it with a crystal as well...with the vfo disconnected...i see the buffer current is up now, as well..

..sk..
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ve6pg
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« Reply #13 on: January 27, 2010, 07:03:02 AM »

i should clarify this....the carrier is there, either with a crystal, or the vfo. so, the vfo is not in question...as i mentioned previously, the buffer current is now high. i will look into this, when i have more time...

..tim..

..sk..
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