Zenith MJ1035--hot chassis with a filament transformer?

[Jeffhs]

I have a Zenith MJ-1035 AM/FM/stereo FM radio that supposedly has a hot chassis (there is a warning on the back cover stating that one side of the chassis is connected directly to the AC line). However, to my surprise, as I found out from the schematic (got the Sams for my set today) and after giving the chassis a good look, I found a small transformer in the lower left corner. The parts list shows this transformer to be a 110-to-12-volt stepdown unit used for the tube filaments only, so this is not a series string as I first thought. My question is this. Why did Zenith use a transformer in the MJ1035 to power the tube filaments, but not for B+? This was not a cheap radio when it was new (I read somewhere that it went for close to $200 when new in the early to mid sixties), and besides, Zenith (the original Zenith Radio Corporation of Chicago, Illinois) was not in the habit of cutting corners. The use of a transformer for filament power alone, and not B+, seems to me to have been well out of character for Zenith, even in the 1960s. I would have expected the MJ1035 to have been set up for full transformer power, rather than simply for the filaments. Why they designed this high-end (at the time) radio this way is beyond me. I will ask the same question Tom Bavis asked in a previous post to this thread: Would it have added that much more to the price to use a dual-voltage transformer with a B+ winding as well as the 6.3-volt filament supply winding?

[Chad Hauris]

I have an early 1950's Zenith console which has a variation on this setup...it uses an autotransformer to supply a higher voltage to the rectifier for higher plate supply voltage but has the filaments in a series string and a hot chassis.

I'm not sure why they would have used just a filament transformer on your set with a hot chassis? What is the tube line-up, are they all 6V or 12v filament tubes? I have seen setups like this on tube type color TV's with a hot chassis, but it is often an autotransformer with taps for the CRT filament and then other tube filament strings in series...this setup is because most color CRT filaments draw a different amount of current than the amplifier tubes in it but not sure why a radio would do it?

They probably looked at the cost of a full power transformer and decided it was too much but still it seems strange.

[Nolan Woodbury]

I'm curious Jeff, have you looked at the chassis of the 845 to see how (or if?) it differs? Next time I have the wrenches out, I may do the same.

I'm not really sure why Zenith would do this, but as we've discussed before; impressive as the MJ 1035 looks, it isn't as punchy or as reception friendly as the C/H 845s. I wonder if a comparison would yield an answer?

(or spur a modification.....)