Signal Tracing Demo - Low & High Impedance Test Point Locations 

Thank you Gregg. Hope you’re doing well. Best, Don

Sorry for my belated response, I’m hopeful you’ll get it playing soon. The pre-selector is a band pass filter for the receiver, so by design it only passes signals along for the band of interest thus improving the receiver front-end performance. For my edification, have the old capacitors and out of tolerance resistors been replaced? Can you hear anything from the loudspeaker while adjusting the volume control? Best, Don

@@RestoreOldRadios Thanks for the response! My grandmother used to say, "A helping hand is a helping hand, regardless of when it's extended". I'm a firm believer in that, and I certainly appreciate ANY response. A quick note about how I acquired the radio: my neighbor is an older lady (I'm 52 years old, so that should provide some perspective on the term "older") who's had it for many years. It was played somewhat regularly, and she'd let me listen to it whenever I'd go over to fix her computer/printer/TV issues. After she told me that it had never broken down or repaired, I told her how surprised I was that the e-caps were still operational and that it hadn't gone out on her. Well, her grandson took it upon himself to proactively swap out the e-caps to forestall tube any damage from them giving out unexpectedly. He neglected to mention that he had removed the tuner when he brought me the original cans to re-stuff. I only found out two weeks later when I got the call from the lady, telling me that her grandson had botched the job. I was surprised to find the tuner completely removed but was confident that once it was reconnected that it would fire right up. After all, I had heard it playing only two or three weeks prior. While the tuner was removed, I ran it through my ultrasonic cleaner and afterward rinsed it thoroughly. I reattached it as described above and double-checked to make sure the e-caps were reconnected as shown in the schematic. I also found a stray wire that had broken loose - it appears to be the ground lead (black wire) for the 2nd IF coil - which I reattached to the volume control tap. Since I personally experienced that the set was operational before the tuner was removed, I didn't bother replacing any other components. I hooked it up to my Variac and slowly raised the voltage to make sure nothing ran afoul. I attached your handy-dandy signal tracer to the grid cap of the 6A8 expecting everything to work but found the strange results. I'm happy to swap out the caps and resistors since I'll eventually be doing that anyway; I just figured it would be a quick fix since it was working a few weeks back, and it might be trickier to track down issue(s) the further from original it got. :( I used your signal generator trick to verify that he primary and secondary windings of the audio transformer are good, and that the speaker is operational. It also attracts my small screwdriver, so we know it's magnetized. Since I first posted my question, I observed a few more things: The ONLY time I can get a signal AT ALL from the tuning cap is when there's an "antenna" (in my case, several test leads clipped together) connected to the lug on the back side of the chassis. I don't recall that being the case with other radios, but maybe I'm imagining it. I reconnected the "antenna" back to the lug so that I could get a signal from the tuner, and tuned in my strongest local station (KIXI 880 AM in Seattle) with the tracer on the pre-selector section of the tuning cap. I checked all the sections again and got the same results: No signal from the oscillator section, a clear signal from the preselector section, and a much weaker signal from the detector. Touching the 6A8 grid cap with a wetted finger did nothing at all. I pulled the leads off the lug and attached them directly to the 6A8 grid cap, also with no noticeable change. :( :( Another thing that I noticed was there are FOUR wires in total coming through the chassis from the bottom of the tuning cap and attaching to a ground. There's one black wire coming from the detector section frame, another black wire coming from the pre-selector frame, but TWO wires coming from the oscillator section of the tuner - one of them is the same black color as the grounds on the other sections, but the other appears to be green when viewed under a bright light. Perhaps this green wire isn't actually a ground, and should be connected elsewhere? I'm keen to take your advice on how to proceed next. As always, thanks in advance for your support!

It’s the same exact circuit built as the other in a single plastic enclosure (all in one) I mentioned. I use a momentary push button switch for turning on/off and a piece of copper foil tape on the side by the switch that ties to circuit ground that your finger rest on while using the unit. Hope this helps. Best, Don

Allan - two pieces of brass tubing with heat shrink separating the conductors. My as-built drawings are available at the URL in the video description (show more). Thanks for watching. Best, Don

@@RestoreOldRadios that's awesome, Don

Mark - sorry for my belated response. The 56pF capacitor I used is rated at 600V. Just use a voltage rating that is greater than the circuit under test. Hope this helps. Best, Don

Jim - ergonomically Probe 1, but portability and features since I built it to support my Bluetooth Tx makes it too close to call. Both perform equally well. I increased the LM386 gain in the all in one as well. The copper tape on the right side is attached to circuit ground beside the momentary on/off switch (which I really like) allows my finger to ground the circuit and mitigate 60 Hz noise. I thought that was pretty clever. Thanks for watching. Best, Don

I appreciate it Jack. Hope all is well with you. Best, Don

Dennis - to your point, one could compromise and probably find values for the capacitor and resistor combination that works satisfactory. My intention with the video was to demonstrate how the ST loading can compromise the usefulness of the tracer at times. Thanks for reaching out and watching. Best, Don

Thanks a bunch Bobby. Best, Don

Thanks Tim. Hope you’re doing well. All the best. Don

Thank you Josh. Take care my friend. Best, Don

Cass - it’s great to hear from you. It’s been muggy here with some low 90s over the past few weeks. Lots of rain for this time of year; 11.3” month to date and more in the forecast this week. Thanks for your kind words and I appreciate you watching and reaching out. Best, Don

Mark - thanks again for joining and I hope the build goes well. Should you have any questions, please let me know. All the best. Don

Kevin - they are easy to build and the plans are on the show more (description) of the video. Thanks again for watching. Best, Don