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An aside from ongoing topic S-20R mixer cct. … While trying to “see” how the LO circuit works things got me in a big knot. C38 seems to run from some osc tanks back to the mixer RF tank

Bob: good luck with the sx 100 you have the next to last run if i recall had so many that i collected over the years it is hard to recall hihi. but i can say this the sx 100 is a great receiver

Good early morning Jacques , yes … and the grid is very positive because there is no oscillation so something quite wrong in the feedback loop.. its hard to test a LO that wont fire-up

TomDepending on your model of GDO you can either use it to generate a signal and look for a dip in "grid" voltage at resonance as power is absorbed by the LO tank circuit or you can use it as a

Hi Don. Any tube having a “floating” control grid, a heated cathode and a positive plate voltage cannot pass any current, because the electron flow will charge the grid highly negative and this

Tony, thanks for the reply, will remove all of them also. Bob w8exv

Hi Jacques Your words seem good to me until “IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all”… I don’t understand that. “could

This might help. 1-4-5-1, RF BLOCKING PROBE The inexpensive DVM’s and VOM’s work fine unless you are trying to measure a dc voltage with RF present, like the plate, grid or cathode of an

Hi Don, simple: the 6K8 is made as a triode + hexode, sharing the same cathode, so the cathode bias resistor (R8) voltage depends on both the triode and hexode sections. So even if the triode section

Jacques +++ Yes that’s what I tried to say a bit too generally. It is probably only the grid[S] that cant reliably take the capacitance of a “wire probe” or whatever the term is, and mostly

I mentioned in a previous post that I sniffed the LO with a GDO. The LO is not working. Tom

Jacques & TomNot mentioned so far was the use of another working radio to see if the oscillator is alive.? The oscillator frequency should be either above or below the received frequency spaced by

NO do NOT leave them in the radio they like to go off like an M80 73 Tony WA4JQS -- This email has been checked for viruses by AVG antivirus software. www.avg.com

Tom, I guess that this “big old mica capacitor” is C7, which decouple the 6K8 cathode to GND, in parallel with C8 (0.05?F, 200V). IF it is a REAL mica cap (not the “postage stamp” PIO ones),

Thank you, Jim and Jacques. Frankly, I'm not concerned about DMM inaccuracies and their probable or possible causes. The voltage readings I reported are proof enough that something is wrong,

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

TomJacques is right on the money, with a positive triode grid voltage on pin 5 of the 6K8, just about all of the other voltage readings will be off except for perhaps the heater voltage.? It is worth

My sx-100mk2a has several black cat caps, woud it be ok to leave these in or replace them also. thanks in advance Bob w8exv

My 410B has a built in 22 megohm isolation resistor built into the DC probe. My GR VTVM does not but I put a one meg resistor in series with it. It has a 10 meg input resistance so the extra

Richard do your DVM’s have an isolation probe for capacitance decoupling back to the DOT? Resistance of DVMs can be very high, but test wires have capacitance that will mess with tuned