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Author Topic: Finishing up on my Valiant showing the heating reducing approach and tweaks  (Read 359 times)

N4MQ

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The VFO has the OA2 and 18k resistor removed from the cabinet and placed under the chassis and a zener in place of the vr tube.  My drift is reduced to a third by these methods, and you can see the temp probe on the VFO top lid.  ENJOY and Merry christmas and happy new year, W  :)  ;) D Y


 https://youtu.be/z3FRLLt25Jk
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W3SLK

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Woody, I question the reason for the placement of the, as WA1HLR says, "Chernobyl resistor." I know this thing becomes quite toasty but could it have been designed that way in an effort to stabilize the VFO?
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N4MQ

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I dont think the hot resistor 'heater' lends itself to that purpose. Going from ambient to a stabilized operating point, is a complex process, and i have tried to reduce the upper temp 'range' for that reason. AM is more forgiving due to its width and detection process.

My johnson 2000 had factory heater resistors attached to the vfo cover to apply a STANDBY level of heat.   That was still not sufficient for SSB operation and I added a HUFF N PUFF circuit to lock my vfo on freq. a bit better. As the warmer components change size and characteristics their tuned freq. changes ,we call that drift. Hallicrafter receivers had a clock timer to turn them on before your typical operating time, aiding in prewarming. - predrifting.

Almost HO HO HO TIME.Woody
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N2DTS

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Maybe to keep moisture out of the vfo components?
You would think they had a reason, even if it was a bad one, for putting hot parts inside the vfo....
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W9IQ

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Maybe to keep moisture out of the vfo components?
You would think they had a reason, even if it was a bad one, for putting hot parts inside the vfo....

It was primarily to have a constant (high) temperature so that components wouldn't drift with ambient temperature and operating variations. Not unlike the concept behind a temperature controlled crystal oven.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W3SLK

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W9IQ said:
Quote
It was primarily to have a constant (high) temperature so that components wouldn't drift with ambient temperature and operating variations. Not unlike the concept behind a temperature controlled crystal oven.

- Glenn W9IQ
Thats what I was thinking. I know the Heathkit TX-1 Apache keeps the 6AU6 lit in the VFO assembly so long as the rig is plugged in to the outlet, regardless of whether the transmitter is turned off.
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KE0ZU

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I agree with the "Hi-temp" proponents.   

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Regards, Mike
https://mikeharrison.smugmug.com/
Pics and bold print are usually links.

N4MQ

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My intent in the vfo heat reduction changes was to reduce the drift due to vfo case warming.  A oven approach would be useful however there is no heat source in the Valiant when the rig is off.  Limiting the amount of temperature rise reduces the amount of drift as I now see an excursion of only 2 kc from cold to stabilized, previously it was about 6 kc.

I had used a temperature contoller on my restored Invader 2000 to control the factory vfo case heaters, to allow a more constant heat source when the rig was off.  That worked well but I did not wish to add that extra bit to the Valiant.

Happy New year, 73 Woody
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