I'm not as brave as Pete (N6QW) - if I assume that he restored his R-4B all at once. Chances are, he didn't, but he did give me a darn good road-map. My first goals for this evening were to check to see if Radio Shack really did sell long-shafted 10k pots anymore - they do (!) and so I parted with about 3 bucks and change and brought it home.
The pot will be to replace the RF GAIN control - which the PO had ditched in favour of rigging up some sort of alternative RF Gain/AGC circuit. This is the source of that extra knob on the front. This rework will, however, continue tomorrow night. Tonight, my actual goals in working on the receiver were to undo the audio mods, thereby unleashing the 6EH5 again. For some reason, the PO shorted the grid to the cathode and ran a piece of RG-174 from this to the INJ jack. He moved the INJ over to the SPARE location and installed another RCA jack there. Why? Darned if I know. It seems he didn't need the high-level audio, probably because he was using an external audio amp. I have no idea why he'd want to move (and cut!) the INJ shielded line. Anyway, as luck would have it, after removing that piece of RG-174, I determined that it was the perfect length to go from the correct jack back over to T4. So, I removed the old shielded cable from T4 to the SPARE jack and installed the free end of the piece of RG-174 over to its correct location on T4. It's very tight in there around the bandswitch! I removed what I thought was an extra capacitor on the board nearest the AF GAIN control. When I turned the rig on, I was greeted with nothing! At least there was no smoke... I found a couple of problems. That "extra" cap was moved over to the foil side of the board to make room for a big electrolytic that's paralleled across one of the terminals on the can cap (a bad idea that will be addressed later - maybe) I had removed a .47 that was substituted for the original .01 that couples the audio output to the speaker! No wonder there was no audio! Put a new .01 on the foil side and voila! Now I can keep the AF GAIN barely cracked open and get plenty of audio - just like it was designed to do! A more troubling matter reared its head - the INJ didn't seem to be working properly. Strangely enough, if I switched to the transmitter, I was getting signals as tuned by BOTH PTO's. Obviously, the negative bias wasn't working for some reason. After metering and sniffing around, I found a wire attached to the resistor board directly beneath the PTO that wasn't soldered! I'm amazed this receiver had worked for as long as it did - this was the wire from T4 to the resistor board. I re-soldered this wire and everything's working as it should (except the RF Gain, of course). I'm done for this evening. I sliced open the tip of my left index finger whilst trimming the RG-174 with my nice-n-sharp Swiss Army Knife. It's now starting to hurt. Tomorrow, I begin the process of unraveling the RF GAIN and AGC mods. This one's going to be a lot more work. Once those changes are done, I'll put two - count 'em - headphone jacks in: one mono jack where it's supposed to be (on the side) and one to plug the hole in the front panel, which I'll rig as a L-R-shorted stereo jack so that one can use stereo phones without an adaptor. I figure that if the damn hole is going to be there anyway, it might as well do something useful! Pete, again, thanks for being the pioneer. With a stone-stock, working R-4B that I can use - plus Garey's CD - I'm having an easier time than you probably did. Getting to that 150-ohm resistor is going to be a challenge. Enjoy Those Drakes... Steve Wedge, W1ES/4 To be is to do - Socrates To do is to be - Plato Do be do be do. - Sinatra All my computers have my signature with various pearls of wisdom appended thereto.
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