38-690 RF Chassis Removal - Printable Version
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38-690 RF Chassis Removal - orangestorm87 - 09-16-2025
I recently inherited a Philco 38-690-125 Run 4, and I am hoping to get it working again. I have gotten the power chassis re-capped as well as changed out some resistors that were out of spec. That was all fairly straight forward. Now I am onto the tuner chassis, which seems to be a bit more involved. Right now I have it on my bench and from what I have read in other 690 threads it looks like the middle part where the variable capacitor is located can be removed. There appears to be some capacitors that will be pretty impossible to get to unless I do this. I am confident in my electrical troubleshooting but am hoping to not disturb the "mechanics", or at least as little as possible.
My question is what does it take to remove this section? Do I need to completely disassemble the front dial to remove the shaft going through this section? Basically what is the minimum I need to take off / decouple before the middle section will be able to be removed?
RE: 38-690 RF Chassis Removal - radiorich - 09-17-2025
Hello orangestorm87,
Welcome to the Philco Phorum and I have not worked on that model before .
I sure someone here has and telly you exactly what it takes to remove it.
Sincerely Richard
RE: 38-690 RF Chassis Removal - RGK20m3 - 09-17-2025
I redid mine maybe 5 years ago; I recall that there were12 or 13 wires to disconnect, and the dial assembly was completely disassembled ( which was needed anyway as the coupler was rock hard and distorted from years of shaft misalignment due to the sub chassis mounting bushings having perished) and the dial was broken . I don’t recall any specific problems taking it apart.
Renovated Radios sells the sub chassis mounting bushings; I disassembled the coupler and replaced the rubber pieces with new cut from reinforced neoprene sheet.
Dial alignment is finicky and isn’t stated in the literature, use the procedure for the 38-116 if you want it to track correctly. The photo attached is of a similar shaft coupling that I just redid on a 38-7
Search “38-690” and read all the threads…..
RE: 38-690 RF Chassis Removal - RGK20m3 - 09-17-2025
Another couple of common problem areas are:
Power chassis, candohm resistors frequently are off value, which can affect bias at various points throughout. Also the interstage transformers primary sometimes go open; there are work arounds besides having the transformer rewound.
Tuner chassis, open antenna and tuning coils are a possibility. Band switch carries B+, which can cause carbon tracking- there is a tread on the forum about this.
RE: 38-690 RF Chassis Removal - morzh - 09-17-2025
I, as well as many people, including Ron Ramirez, have threads on 38-690.
Ron, I believe, replaced the middle section of the tuner with the one extracted from 38-116 (they are the same).
I was able to recap the middle section without having to remove it. It takes some persistence and some tools.
The only thing that is not quite possible to do without fully removing it is the full cleaning and contacts mending of the band switch, as the bottom contacts are too close to the chassis and the access angle is way too inconvenient. If you do not need it, the removal is not necessary.
However, if you have enough patience and marking tape, the removal is a good idea and will make the recap and cleaning that much easier.
RE: 38-690 RF Chassis Removal - orangestorm87 - 09-17-2025
Well thanks for the suggestions, and ya I have all the 38-690 threads on my reading list and have gone through a few so far.
The B+ on the band switch does sound like a pretty horrible problem. I guess that is more reason to get this thing totally disassembled. What exactly am I looking at to know if its a problem, or is it always a problem and I need to modify the wiring in some way?
So far everything has been pretty much original other than a few tubes that got swapped for metal ones. The chassis is very heavily coated in cadmium yellowish corrosion, so I am also taking my time and using GOOP on Q-Tips and slowly cleaning everything. Its a slog but hopefully won't have to worry about it all coming off the first time I crank up the BASS
