I've been having a good time using my new-to-my-shack Heathkit SB-1400. I was — until Sunday night.
We have a 10-meter net on Sunday nights, and I was ready to debut the new rig. But when I keyed the mic and spoke, the rig transmitted just the first half-syllable and then the power out meter maxed out, and you could hear the rumble of some sort of hash-type crap.
Evidently, on 10 meters, the transmitter finals were going into oscillation. I thought maybe it was something related to RF floating around in the shack. The rig has a plastic case that's known to be a little quirky about RF. But this problem wasn't RF on the audio, it was no audio and something else going on.
The transmitted signal was outside HF apparently. It stopped the scanner a time or two on the other side of the room. I never did try to identify the oscillating frequency, but it sure did draw down on the power supply.
Charlie took the net for me while I fiddled with the rig.
If I tuned the antenna tuner (manual one) to create a big mismatch, the rig would transmit, albeit at a reduced power. Really strange.
I started to do a little research on the Web to look for RF-related complaints on this or the FT-747GX rig that this one is based upon. Nothing really out there.
I did download the schematic and looked it over. I figured there was some sort of oscillation at the final output stage. The rig switches in the appropriate set of drivers and the right signal from the right band when you change bands to transmit.
According to the schematic, the driver section that handles 10 meters also handles 12 meters. If there's a problem there, then the oscillation should be present on 12 meters too. I had not yet checked that. If that was ok, it would mean some sort of problem further back on the oscillator or it might truly be an RF problem.
I tuned the rig to 12 meters, and bingo! Sure enough, the oscillation is present there too. At least I've narrowed the problem down to that signal path on transmit.
At first I suspected maybe the rig was suffering from 11-meter mods, but this evidently isn't so. The rig doesn't transmit on 11 meters (unless they repaired the all-band-transmit jumper). It appears this rig has not been “opened up” to transmit on all frequencies,
Servicing it isn't a problem. But do I send it out for service or use it as is? It's going in the library soon anyway. Do I spend more money on it?
I would like to have it fixed eventually, just so I could use it on all bands, and say honestly it works on all bands. It would make a great field day rig.
I've got a Yaesu FT-757GX coming, and I'm tempted to wait and see how that rig plays before I send anything off for repairs.
Actually, I've got an Alinco DX-70T that's been boxed up for about a year. It has sticky T/R relays that need to be replaced. I'm about to send that thing off for repairs. The Alinco isn't really useful without the repairs; the SB-1400 can actually do what I've planned for it without repairs, so I'll hold off on that I guess.
EBAY ACQUISITIONS. The Uniden BC-350A scanner I won last week arrived this morning in the mail. Haven't hooked it up yet, but I will tomorrow.
I won an auction for a hand mic, a Yaesu mic to go with the SB-1400. My cobbled-up homebrew “Heil” style adapter is working fine though. I'm right proud of it, and it was much cheaper than Bob's version. Anyway, I've got my work cut out for me. It still bugs me about the TX bug on the SB-1400. i want it fixed.
In other eBay goodies I'm waiting for, the list includes an Ameco HF receiver, a Tempo 2020 VFO, a busted Vibroplex Champion key, and yet another Cedar Rapids bug. I've got to quit buying these things, I've got something like 5 of them already!
I'm out of here for now … 73 es CUL … de KY4Z dit …. dit ….