This must be one rare set to have. The 40BC50 is definitly a chassis for the US market. Zenith service manual CM-118 includes the 4B25C19 chassis which is the first generation 4 tube hybrid chassis. There appears to be no supplements or addendums to CM-118 that include anything about the 40BC50.
This must have been a very short lived chassis. I have many zenith tech topics issues, which is basically a mailed out list to TV shops by zenith to aid the techs in quickly repairing sets as it was a trouble and cause list for various TV chassis, and those TV shops that discovered and repaired the symptoms got the credit with their name and the TV shop they worked for. Very helpful information to have for those techs that perhaps found a similiar symptom, they could identfy the problem then go ahead and replace C243 for example. Problem solved.
Well, I have issue 85 which is a list of ALL US marketed zenith color TV chassis from 1968 (when zenith introduced "tech topics") up to the "F" line of 1975. It was simply an index, you find the chassis and then it indicates what issues had that chassis listed with symptoms. Just about all the chassis had "X" mark for january-december of all of the years as various techs across the country would find something wrong and report it.
What is interesting to note is that the 40BC50 was empty boxes for all the months indicating that nothing was discussed in any of the issues. this issue 85 is from 1975, which is more than enough time for a trouble to show up considering how many of these sets would have been in service at the time. For the sake of the argument, the 25CC55 had numerous reports. I only say this because the chassis is apparently very similar. Either the chassis was extremely reliable, or hardly any were sold and or produced. Im going to assume it was a very short lived version that was replaced quickly by the 25CC55.
Chad, these are the oldest varactor tuning sets I have, both are from 1973. Like I say, 71 and 72 models would have used this more mechanically involved varactor tuning system. You can see the one of the '73 sets at this thread which I show a close up of the tuner controls:
http://audiokarma.org/forums/showthr...ghlight=25DC56
And you can see the other one at the "estate sale finds in 2006" thread tward the end as I found another one in December.
vintagecollect, these sets would have used the 25VAMP22 crt.
The other photos are from CM-118. The other photo is a 1971 model B4774W, which you can also see listed in CM-118 as having the 40BC50 chassis. The other models Ive listed before are also on this list and as you can see are the only three models produced with this chassis. The B4774W set is extremely similar to the one I just found with the tube type 12B14C50 chassis. what makes it different is the that the top of the TV overhangs the cabinet and the legs are slightly different configuration, but uses the exact same front eschuteon and control panels.