- 2025
- Apr
- 28
A PACO G-30 RF Signal Generator - Part 6: Troubleshooting
I’ve discovered the audio side of this unit doesn’t work. When you get a device like this, you can assume one of three things (and this applies to the state this device was in when received.)
1: There’s something wrong, i.e. something is broken.
2: You put a part in wrong, or made a mistake in replacing parts.
3: The previous owner did something wrong, and you followed in his (incorrect) footsteps.
I started this by checking the plate and grid voltages.
A word about this device: I can’t seem to figure out where they measured from here - Chassis is ground, but the device also is raised about 8V above ground to provide a negative voltage. Some measurements seem to be from chassis, some from raised ground (return). I wasn’t able to get some of the marked voltages, so…who knows. Bob from Accounting probably drew the schematic for this at lunch so it’s possible something isn’t exactly right.
Regardless, B+ was correct on the 6C4 audio oscillator. Grid was not, so ah-ha, there’s my problem. Well..not necessarily in this case because you could go to return and get a different voltage for each measurement. But in this case, it was the problem.
I discovered this because I looked at each part I took out and did a like-for-like comparison with what I put in. Everything matched. The problem became apparent once I really started looking at the schematic.
So, you’ll notice there’s a 15KΩ resistor coming from Pin 6 of the 6C4. That’s what the previous owner had in there.
The schematic, however, states that we need a 100kΩ resistor:
That’s probably the problem. I had some 100kΩ left from one of the previous rebuilds, where I wisely just bought a bunch. One of those goes in:
And, there’s our audio.
It’s 500Hz instead of 400Hz, but who cares. It’s still going to be heard just fine.
Since the device is now working, it’s time to button up for the wrapup post. Stay tuned!
Next part of this series: Coming soon.
Previous part of this series: https://wereboar.com … or-part-5-resistors/