[Milsurplus] PP-109, RT-68/GRC update

[Falls, Jim]

Hello All - I opened the can of the suspect vib using a small pair of flush cutoff wire cutters (grab the lip and roll it over) and found a lot of carbon residue on the reed above the contacts (Normal?). They were not welded as expected, but I sanded them carefully anyway, cleaned and reloaded the unit.

Here's a kink: When I originally swapped the vibs around, I took the one from the front and put it in the rear (defective unit) position. Everything ran cool including the big electrolytics, fuses OK. That's why I assumed it was a bad vib unit causing the trouble.

I put the "repaired" vib back in the front socket where I had stored it, figuring the vibs were interchangeable, hooked the '69 up and got deafening silence from the radio. 90V check got zero, all others OK except #1 RF setting.

 Did a variety of tests and ended putting the repaired vib unit back in its original socket. All three were in their original positions now. Powered up the '68 and it received fine, but still very low/no transmit output (I could pick it up in the shack w/a 2nd receiver, but no one else could hear me (I don't have an RF wattmeter for 6M). 

On the front panel, RF test switch position #1 still read zero (not even a twitch when keying up), all others (2-6) read OK, all filament tests, including 90V, OK on the meter.

I opened the '68 and found a marginal 2E24 and 2 other dead tubes behind the 2E24 in the transmitter train. When keyed up, the 2E24 gave off a faint blue glow on the right side (viewed from the front of the radio) for about 1.5 seconds, then looked normal. If it is gassy, why does the glow go away? I have ordered replacements and will check things when they arrive. Hopefully, the PSU problem didn't fry them.

In the interim, I will check output voltages and resistance tests per the PSU manual and take the transceiver back to my pal who has a mains powered PSU (PP-1175?) just to see if the radio works when I have the replacement tubes.

PS1: I have the schematic for the PSU, but the manual doesn't have any parts list to ID any of the components ("buffer capacitor", for example) or give their ratings. The plug-in electrolytic ratings I got off the cans.

PS2: A 2-section plug-in electrolytic question: these have 4 pins (1 each for the 2 sections, 2 other pins are common ground). I get a low resistance between the two + pins on one of them (C-25a/b, beyond the vib unit in the 85V circuit). I would expect that for each of the two sections (testing from + to -, resistance increasing over time as the cap charges), but the + pins are supposed to be separate from one another, correct?

PS3: "Buffer capacitors" filter the RF hash generated by the vib contacts arcing, correct?

Yet another "Learning Experience"

Thanks for all the help so far.

Jim Falls
KG6FWT
Eureka, CA