开云体育

Hi all,
Picked up a FRG-7 as part of an auction lot, and it's in need of a pretty heavy restoration - both cosmetically and circuit operation wise.
First up will be electrolytic cap replacement and a thorough check that all supply voltages are where they're supposed to be, and I'll go from there to see what other work needs doing.
But I also notice that the previous owner has pulled most of the components associated with the BFO, including Q408 & T406.

Looks like Q408, a 2SK19-GR, can be replaced with a common N-ch JFET like the MPF102 (being in Australia, NTE equivalents are not common here) - hope someone might be able to confirm the MPF102 is suitable?
And for T406 - guess I'll just try any donor variable inductor coil, especially if it comes from a 455kHz section of a suitable donor radio, perhaps may need to alter the value of C437 to bring it to proper resonance?? Unless someone has a suggestion for a specific, readily available equivalent?

Thanks in advance,
Jason

Hi Jason,
Lex - one of the group members is parting out an FRG-7. His website is https://www.ph2lb.nl/blog/index.php?page=for-sale-frg7-parts .

I see one eBay seller in Hong Kong has sold 50 sets of 3 2SK19 for less than $10 and has good feedback.
eBay Item # 172163056900.

73
Roger VE7LB

Hi Roger,
Thanks for the speedy reply!
On closer examination, the original owner has done the ceramic resonator BFO mod and located the BFO on the underside chassis in it's own little shielded box, complete with feedthrough caps etc.? Really nice job, actually, though a lot of the original PCB trackwork around the BFO has been scratched off, which is a bit of a shame.
Had me wondering there for a minute!
Thanks,
Jason

Hi Jason,
That's good timing! I was just looking at that pdf (Files Folder #7 -? FRG-7 BFO Mod.pdf) and was about to suggest that was possibly what the previous owner was going to do.

There have been reports of the existing BFO circuit drifting. When you get your FRG-7 finished you possibly could report on how well the new ceramic resonator BFO mod circuit works.

73
Roger VE7LB

Well, this turned out to be quite a bigger job than anticipated.
Apart from the usual electrolytic capacitor replacements, I also found all the mylar / polyester capacitors had delaminated - possibly due to the extreme thermal cycling typical of a desert miner's shack where this FRG came from.? So all of those were replaced too.?
The first mixer pair Q102 & Q103 were found to be way down on conversion gain, so replaced those with MPF102s, and Q105 was a touch suspect so it too was similarly replaced.?
T102 primary was open circuit, and after removing and opening the can, the reason became clear - tiny enamelled wires had splattered like a fuse near the PCB pins.? Probably caused by a nearby lightning strike?? Didn't look like the result of? corrosion.? Anyway, very carefully managed to resolder some hair thin wire to the open circuit wires coming out of the transformer bobbin and on to the PCB legs, and band B is in business once again.
The incandescent bulbs were replaced with white LEDs, and the luminous output of each balanced to give an even backlighting effect.
Finally, a quick & dirty alignment was done... didn't do the 1st LO chain or the 2nd IF line up (I miss having access to a tracking generator...)

After all that, happy to report this FRG-7 is working beautifully again, excellent sensitivity, great dial tracking, sounds lovely.? And the BFO stability with a ceramic element source?? It is excellent!? I've had WWVH on zero beat for an hour, and drift was less than 30 Hz.? Of course, some of that could also be partly due to 3rd LO drift as well, so the real figure for the BFO alone could be less than that.

Just waiting for the local mechanic shop to sand blast the case back to bare metal for repainting, and I have to mix up some paint to touch up a few minor bits of wear on the front panel, and the job will be 100% done.
Thanks,
Jason (happy 1st time FRG-7 - now working! - owner)