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Hi Jim, I agree with all you wrote, but apparently, Don doubted that the DVM connection to the LO of this S-20R could “kill” the oscillator.

I experienced that before: and this is why a 1Meg resistor was added in the Heathkit VTVM probes.

But there is more the probe shielded cable capacitance which can make trouble when the RF circuits were DC probed without that “isolating” resistor.

An similar kind of trick I use with my bench DMM is a probe with a 10Meg 1% resistor inserted within.

The displayed DC voltage is then half of the true value, but the very high impedance circuits such probed are -almost- not harmed.

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For the S-20R problem now: it was not a probing “incident” as all the DC values around the 6K8 triode section are off.

The oscillator is obviously not working, because when it does, the grid voltage have to be negative, as it operates in class C.

As I previously mentioned, something in the coupling capacitors is open, or as suggested by Richard, short in the variable capacitor LO section.

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