The massive 1975 Zenith combo has arrived...

[DaveWM]

how have the slide controls held up? I often find them loosey goosey or not very smooth.

[drh4683]

thanks all,

The slide pots seem OK for the most part, not too loose. Slide controls were always gimicky in my book and never practical and always subject to intermittents and breaks in the carbon trace. They are simply eye candy in this case with the colors around them that light up. Since I have no control over the treble, I did test the pot and it was working. However, all of the 1uF@50v lytics were shot. ESR off the charts. The caps are cheap, made in Taiwan with the brand name of "Richey". The nichicons are all pretty decent yet but I've got about 10 of these Richey lytics to replace. That should bring my treble back and quite possibly even my lack of stereo balance/output on the left channel. I could clearly tell these richey caps were being used in a left channel and right channel circuits within the receiver as I was seeing two identical circuits with the way the components were configured. Like I said before, the left channel works, but the output is much weaker than the right. I did test the TO-3's on the amp chassis. I did detect much higher leakage in one driver vs the other, not sure which channel was which. Im kind of doing this troubleshooting blindly as I don't have a schematic for this particular receiver and amp. Im hoping to just stumble across a bad transistor and/or cap simply by basic test methods using my sencore super cricket for the transistors (out of circuit), and the dicksmith ESR for the lytics. So far, the gain on all the transistors have been excellent but like I said, I noticed much higher leakage on one of the TO-3 drivers. The one transistor (121-793) measured about 20uA leakage and the transistor of the other channel was almost 100uA. Quite a difference. Lytics and resistors in the amp seemed good when doing mirror image comparisons between the channels. These TO-3's are germanium too, didn't know that junk was still being used in the mid 70's. Not a fan of germanium transistors

[Findm-Keepm]

Doug, are the outputs germanium too? I can see the Motorola drivers would be, but those outputs were made by Delco, who had graduated to all-silicon by 1970. Some of the later high-power Zenith Allegro units used a similar amp, with Delco outputs. DTS-701's, IIRC, and Zenith's replacements were all Delco straight up, with no 121- markings. Those little IEC-branded black caps were called firecrackers back in the day - the mantra was "replace all of the Callins and Firecrackers....and it'll be fixed."

I'll do some digging tomorrow - I may have the Zenith lit for your unit. My stuff runs through 1972, and gets spotty after that, with the exception of clock radios and record changers. I'll also check my deep storage for the Zenith drivers - you can always replace them with ECG/NTE 121's. We used a stash of 2N1558's we had - good Motorola PNP Germaniums made for military aircraft inverters. They were surplused by the thousands when Vietnam wound down.

Lemme get to checking for you - Cheers,

[Jeffhs]

Glad to know that your Zenith console made it from Oregon to Chicago unscathed. It was a good thing the trailer the set was in was covered, if you say it was raining cats and dogs the day it arrived at your house.

I am nothing short of amazed that Zenith had built the stereo section of your TV on a PC board, with the television set itself being hand wired. If they hand-wired the TV, I would have expected the stereo to have had point-to-point wiring as well. I could never understand why they went back to PC board construction for their radios even as far back as the Royal 500 series of the 1950s. I have a Zenith R-70 AM/FM portable radio, made in 1980, with the entire set, except the speaker and controls, on a PC board; however, my 1958 Zenith Royal 1000 Transoceanic portable is hand-wired, with a metal chassis and plug-in transistors, and it is heavy as the dickens even without batteries. Strange that Zenith would abandon point-to-point hand-wiring after all their years in radio and TV in favor of PC board construction; with the reputation for quality their hand-wired sets had earned over that time, their reversion to PC boards seems to me like a step backwards.

Does your set have the original CRT? If so, it must have been one of Zenith's best. Until now, I had never heard of or seen any TV set with a 36-year-old CRT that still works as well as yours seems to. The screen shot of the weather forecast (looks like it's from The Weather Channel) on your set looks great, almost like new. That's why I doubt that the TV has the original CRT. If it is in fact the original tube, the set's former owners must not have used the television much, except perhaps for the evening news. It is also possible that they gave up on the set when DTV arrived in June 2009, before ATSC->NTSC converter boxes were available.

BTW, I wouldn't change anything in the stereo tuner/amplifier if it is working well (unless, of course, you are troubleshooting the problems with the one weak stereo channel and the inoperative tone control, as I'm sure you are or soon will be). Speaking from experience, modifying or trying to improve a radio, TV or anything else that is operating perfectly well can, and often does, lead to big problems, with the unit operating worse (if it works at all) after the modifications than it was working before you started.

[DaveWM]

if its like other zenith combos the TV does NOT use the tuner amp, but rather has a cut out switch the disconnects the speakers from the amp and switches to the TV based audio (and may or may not kill power the the stereo tuner/amp). On mine I made up a a new wire harness that bypassed that and just drove a small interanl speaker (there was a place for on) from the TV audio and left the main spearker connected to the amp. this way I could power up the amp and drive the L and R directly from my video source. it REALLY makes for a nice setup with that powerfull amp in true TV stereo sound. I would just use the tape inputs. I left the small speaker hooked up so you would just leave the TV volume turned down. I did not want to have the audio stage unloaded. The entire process was just done by the new wire harness, I even left the old one in place so it would be easy to return to the orig setup, if for some reason that would ever by desired.

[Carmine]

I would be interested in how to do that conversion too, because I think all of my germanium transistors are shorted in my Emperor.