OK, I think it's finally fixed and ready for service.
Here's a 1965 Magnavox "Astro-Sonic" solid state console stereo, using the R204 series chassis. In previous videos; we performed routine repair work on the chassis and the record changer. However, we had an issue with poor FM performance. I thought I had the problem fixed; until I reassembled the stereo, was listening to a station, and it suddenly faded to near nothing. One thing is for sure, if something is going to mess up, it's going to wait until you have it all put back together to misbehave.
So, in this video, I took the chassis back out of the cabinet and found that the FM RF amp transistor, a germanium device, was intermittent. At first, It checked open. Then, I physically stimulated the transistor and got a reading. Then, one of the leads pulled out of the bottom of the transistor; so, that pretty much sealed the deal with that transistor being bad.
Early solid state equipment used germanium transistors and it wasn't until the later part of the '60's that silicon transistors became popular. Unfortunately, germanium transistors are not aging well and new production germanium transistors are getting hard to find and expensive. In fact, the NTE126 that's listed as a substitute for the original transistor in this stereo is almost $10 + shipping, while silicon transistors that serve in the same application are normally not over a dollar.
One might ask, why not simply replace a defective germanium transistor with a silicon device? In some cases, that will work; but, in other cases, the difference in bias voltage will not allow a silicon device to work in place of a germanium device. In some cases, it's possible to redesign the circuit to accept a silicon device. A germanium transistor conducts at around .2-.3 volts, while a silicon device conducts at .6-.7 volts. That may not seem like much of a difference; but, it's a big enough difference that it can cause a silicon transistor not to work in a circuit that was originally designed for a germanium transistor.
Digging through my junk stash, I found a '70's (or earlier) Archer-brand (Radio Shack) universal PNP silicon transistor. I installed this silicon device directly in place of the germanium device; and, fortunately, there wasn't any organ rejection and the chassis seems to be happy with the silicon transistor. Actually, the FM performance is now better than it ever was during my ownership of this unit.
This stereo also has an aux. input; but, the jacks are on the chassis. I don't know why they didn't place the jacks on the rear of the unit; but, since they didn't, I ran an RCA cable from the inside jacks out the back cover of the stereo. Now, this stereo can be used with modern playback devices.
The only thing left to do is clean/polish the cabinet and find an automatic 45 rpm adapter, so that I don't have to use the little yellow and red snap-in adapters.