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Valiant VFO - C18

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Author Topic: Valiant VFO - C18  (Read 343 times)
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Posts: 11

« on: November 27, 2018, 06:11:03 PM »

Here's my Valiant VFO sitting naked on the bench. C18 the tubular 43pf NPO 500V capacitor is shorted. I understand that it is an ultrastable temperature compensating capactior used for VFO frequency stability. But it also seems to be the coupling capacitor between the actual oscillator circuit and the VFO tube, not a frequency determining capacitor. Is it critical to replace it with another NPO type capacitor? If so, are there special NPO type silver mica caps or will this one be a suitable replacement?

Mark - WA2FXM

* VFO C18.jpg (1223.82 KB, 1836x3264 - viewed 80 times.)
AC0OB - A Place where Thermionic Emitters Rule!
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« Reply #1 on: November 27, 2018, 06:23:04 PM »

C18's basic function is as a feedback capacitor to sustain oscillation and is a 43 pF 2.5% ceramic capacitor.

I would use a 39 pF 5% 500V mica.

Phil - AC0OB

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
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