1951 Zenith Porthole Question
 

I've been working on a 1951 Zenith Porthole combo set for some time now and have finally progressed to the point of reassembly. When I picked up the set the original 12" speaker was missing, but I have an EV dual cone replacement I was planning on using.

The AM/FM radio/phono amp is a "free standing" unit containing it's own amp, power supply, AM/FM Tuner, etc. The TV power supply chassis has it's own self contained amp dedicated to the TV. The potential problem...or question is this: with two independant amps, and a single speaker, how would both outputs be attached to it? Was the original speaker a dual voice coil unit? Or was there some sort of a switch somewhere? I don't see any provisions for external switching... unless it's missing?

Any information would be appreciated.
Thanks.
Bob.

Hi Bob!
I'm not too familiar with that set but I'll take a shot in the dark. Is there a n extra switch hooked to the power switch on the tv section of the unit? One of my Zeniths uses a setup like that, when you turn on the tv it switches the speaker lead to the tv and back to the stereo when the tv is off. But that is a '65 color roundie, yours could be much different. I haven't had the pleasure of working on a Zenith porthole from that era so this is just a guess. Were there speaker wires in there before you took it apart or was it missing them? I'll do some research on it for you. John Marinello may be able to help you as well, Zenith Portholes are his forte.
Mark

Hi Mark;

The switch I found in this TV set was a SPST type switch used to turn the AC on/off to the TV. The switch in the set was bad and had been bypassed with a rear mounted toggle type. I was able to find a replacement switch and it has a DPST type switch.

My suspicion is that there's something missing or I'm just not seeing it. The wires coming from both the TV amp and the Tuner amp have factory installed male pins on them as if they were supposed to slip into a mating connector or socket somewhere??

If I recall correctly...the wires from the amps were just sort of dangling in the area where the original speaker had been, leading me to think it may have used a dual voice coil speaker?

Thanks for the information.
Bob

I think the best way to go on something like this is to find the Zenith service manual or a sams. Dual voice coil is definitely a possibility. BTW, I love that Zenith roundie you have in your garage! {and the 9 too!:D}

Mark....I do have the Sams and the Zenith Service manual, although the Zenith manual only covers the TV chassis, so it isn't any real use here. The Sams on the other hand does cover the combo unit, but to me is very unclear about the two audio output connnections.

On the TV chassis is says that it attaches to "SP 1", and on the Tuner output it indicates .."To SP 1 voice coil on TV chassis. From that description is sounds like they are both attached to the same speaker at the same time. I don't think that's very likely. It's a puzzlement.......
Thanks again.
Bob

PS ( I wish I had a place big enough to bring that beautiful Zenith Roundie in from my garage and run it. But....I'm working on that too. A big move may be coming along soon and then I'll have lots a space.)

I'm going to do some more research on this, now it has me confused. You'd think the dumb manuals would be clearer, but it don't surprise me. I'm not giving up yet!!

Dual voice coil on that one.

Thanks for the information John, although I guess that sort of leaves me high and dry. I'd imagine 12" dual voice coil full range speakers are not all that easy to come by.

I'll have to come up with some sort of a switch using a relay and the on/off switch of the TV. I'd imagine that the TV audio output should have override preference to the AM/FM.

Thanks again for all the help.
Bob.

I gave you bum info, sorry about that!

The speaker has a single voice coil. The leads are paralleled right at the speaker terminal.

Hi John;
Thanks for the updated information. I appreciate the effort. Looking at the schematic I would not have guessed that to be the case (using a single voice coil speaker that is....).

On the tuner amp one side of the output transformer is grounded to chassis. On the TV amp both sides of the output are floating. I did try hooking them both up to the speaker voice coil at the same time and didn't notice any ill effects, although the high end of the TV output seemed to drop off a little. But aside from that small change, everything else seemed to work fine.

Thanks again.
Bob.