I have returned from the 2026 ETF convention with a wealth of knowledge and experience. Not only was I able to pull the chassis out of the museum's set, we actually got it working!
It had been restored some 25 years ago, but it had never been properly reassembled or powered up at the museum.
We spent some time pulling and studying the chassis - especially the tuner. Note this set seems to have an FM descriminator circuit added by RCA.
Here's the main coil with windings for the antenna, LO and mixer.
We discovered that the 878 tube had been replaced with an 879 and the focus wire cut. Seems someone was a bit lazy when the chassis were pulled to ship the set to the museum and cut it instead of properly disconnecting it from the screw terminal.
The rest looked OK so we proceeded with a power up in stages.
First, with all the rectifier tubes pulled. All the tube lit up so we proceeded with the HV rectifier tubes then the 5U4s.
Here it is with an 8013A in place of the 878
All was going fine but no raster on the CRT. Eventually someone noticed there was a splotch as it powered down. The led us to discover a bad contrast control. Further, we needed to bypass a resistor to get the brightness control into the proper bias range for the CRT.
OK, raster but no image. We tried direct video injection in the grid of the video amp but that didn't go well. So back to the tuner. The original A305A mixed tube grid cap had broken loose. We subbed a 6D6 and after some more control manipulation we finally had a stable image!
Note this set has some sort of CV326 or some such British military CRT installed in it hence the odd phosphor color.
The thin rubber CRT mask shifted out of place while we worked on the set.
Next time we visit, we'll repair the A305A grid cap, replace the bad contrast control and reseat the CRT mask.
Another curious thing is the mirror in the lid.
This set has a polished piece of (stainless steel) metal and a lightweight lid. You can see some corrosion has started on the right side.
Mine and others have a heavy front surface mirror piece of glass in the lid.
