Is there any way to use a YO-100 as a scope for circuit testing, even in a limited way?
The manual kinda alludes to that but no details.
Any input will be appreciated.
Ed WA4NJY
Bradenton, Fl
The YO-100 has a convenient audio input RCA jack on the back and a 200mV p-p per cm sensitivity 10Hz-40KHz. Why can't this be used for audio?
If more gain is needed, make a super simple outboard amp in a little box, with a gain of 10 or so using half a 12AX7, then duplicate with the other half, so you now have x10 and x100, and capacitor couple the in and out to BNC jacks on the front of your box. Now have added 20mV and 2mV per cm with an outboard preamp. Why not? Very simple stuff.
Here, I drew up the schematic for a preamp like this with response of about 10Hz to >100KHz, and it includes reference to the circuit in the RC-25 book. The resistance coupled amplifier circuits are from the RCA engineers and will work fine. I think it is a worthwhile thing to try out for the audio tracing. Plus, it can protect the front end of the scope, although it has a tube there too so no worries.
If you think a 47K input Z is too low for your troubleshooting, you can put a 470K or 1M resistor in for R8 and change C4 to 0.1uF. If you rate C8 at 1KV, then you can measure signals in plate circuits having up to 500-600V on them.
No matter what, the output of the preamp can't spike over 90V because that's its B+, and the YO-100's C1 audio input capacitor to its 12BY7 grid should be able to handle that (check and see).
Th RC-25 tube manual is online many places including here:
http://www.bunkerofdoom.com/tube/man/index.htmlSo I hope you can have some fun, use that scope, and not have to spend a bunch of $ on an expensive scope unless you want to. Buy the cat or dog some treats with the money you save.
One note the caps should be non-electrolytic, that is important. Inexpensive kinds are perfectly OK, the typical junkbox orange drop or little rectangular plastic ones etc. are OK for this. Not critical. An exception might be the C1, C5 50uF cathode decoupling caps, and even C6 the 10uF unit, but the idea is to improve stability by avoiding leakage.