Zenith Porthole G2952 part 2
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- Опубліковано 26 вер 2024
- Let's pull the chassis and see what we have to work with. Also, maybe that 16EP4 isn't so bad after all!
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Amazing beauty to see such a work of art. Such a joy to see this set and especially see the restoration coming up. Bob you're really an awesome person to be so kind in sharing this. Learned so much on my FAVORITE channel. Really bless me with being able to part of it even if just watching YOUR Fantastic. thanks a Trillion Mike
Zenith portholes are beautiful sets, but the scarcity of good CRT's is what keeps me from considering one for restoration for our collection. Looking forward to seeing this set in operation.
The first ones with the 28T926 chassis, 10" models, are easy to get a CRT for. 10BP4. Bob's chassis is nearly identical to the 28T chassis. So much so I'm having flashbacks from restoring one forty years ago.
(@7:57) Wow! Those wires are almost blinding. Usually the color of the insulation is so faded from heat, and so baked with dirt or cigarette haze that you can’t make out what color they are. At least you can follow the wire a lot easier! 😊
A trick i've used to remove stuck knobs is to insert shims made of OHP transparency sheets between the cabnet and knob slowly wedging it away ~0.1mm at a time, i've successfully used this against a knob that was glued on with silicone!
Woo Hoo! Congrats on the CRT. I know all about faulty analytical equipment taking one down blind alleys. That must have been a very pleasant surprise.
Oh Boy,..a deep dive !!
Looks like a neat old set! That's great that the CRT appears to be good too!
Appreciate the broad stroke breakdown of the topology on the set sir, Thanks! Also interesting to see the tube wake up under different test conditions. Looking forward to the dive,-jrh
At 1.30 switch is to disconnect outside antenna for lightning protection.
Thanks Bob for another interesting video. I'm glad you discovered the CRT tester problem before you went through all the trouble of modifying the CRT mounting to accomodate the all-glass CRT. That metal CRT should be fine with the emission it is showing. In actual use after the set is restored, the set won't likely get used that much, like it would in 1951, so the remaining life should be sufficient, assuming picture quality is good.
It is interesting that Zenith had quite a different take on their designs compared to other TV set manufacturers, who probably patterned their designs after RCA sets (more or less). Examples being the huge tuner mounted at the back of the chassis, the metal CRT, and separate filament and B+ power transformers to name a few. I was kind of surprised Zenith went with magnetic deflection on this model since the deflection angle was so low, probably because the limitations of electrostatic deflection would have lengthened the neck another few inches.
Zenith brought back that zoom feature in 1975 for their top of the sets, I remember seeing that as a TV Tech at the time. I can see why didn't catch on, as it reduced the resolution down to 250 (or so) lines.
You have a lot of components to replace on this restoration. I don't miss those old sand resistors, along with the corroded leads, they tend to cook other components nearby.
It's not that low. Typical earlier CRTs were 54 degrees like the 16AP4. What was odd is going 60 rather than jumping to 70. It was impractical to make electrostatic bigger than 8 inches.
@@bandersentv I think about 30 degrees deflection was the practical limit for electrostatic deflection. A screen larger than 8" would need to have the distance between the screen and deflection plates increased, which gets impractical quickly with the larger CRTs. I'm not sure but, think the 12" CRT RCA was using in 1939 was electrostatic but, the CRT length was about 3 feet.
Electrostatic deflection is the way to go for oscilloscopes, since high frequency sweep speeds are much more easily achieved versus magnetic deflection. Since TVs use a fixed low frequency deflection, magnetic deflection is the best overall compromise.
@@billharris6886 12AP4 magnetic deflection. There was the 10HP4 electrostatic CRT but only one obscure model used it. Deflection angle was around 40-50 degrees I'd estimate. I have a couple gigantic 12FP7 electrostic radar crts. I hooked one up to a little Motorola VT71 in a video years ago. I think it was called fun with CRTs
@@bandersentv Interesting! Thanks for correcting the errors in my poor memory.
It would be interesting to see a video of you repairing the wonky CRT tester. I know when shopping for these old units one worries about condition. Be good to know we can fix these.
I'll post a video tomorrow. Not quite what I expected.
Push pull flyback makes me excitement
I haven't looked at the circuit yet but, suspect the horizonal outputs were wired in parallel. Push-pull works great for RF power amps but, for a sweep circuit, it would be much harder, circuit wise, to generate a linear sawtooth wave. At any rate, the dual power pentode horizontal output is an indicator of robust circuit design, probably more than doubling the life of the horizontal output tube.
Yes, they are in parallel. That crazy Dumont Clifton of mine uses 807s in push pull mode to drive the horizontal but it's not a flyback. HV is generated separately. Same with that Westy I did last year with PP 7A5s driving the horizontal. Both sets use an RF HV supply.
@@bandersentv Thanks Bob for confirming the parallel operation. I find the pre-1950's sets the most interesting, with the non-TV specific tubes and non-streamlined TV designs that reduced tube and circuitry count.
I am very familiar with the 807; basically a 6L6 with a plate cap, very popular in HF transmitter circuits in the 1930's and 1940's. The push-pull high frequency power amps and power supplies are a nice configuration, they have low odd order harmonic output and the maximum plate voltage peaks can only rise to 2X the B+.
It's a shame that companies like Zenith didn't better document the development of TVs like this one. I can imagine how the prototype was set up on some kind of bench to work the bugs out. It would have been interesting to see how it was perfected.
They did in their multi-volume factory service manuals. The one scanned volume I found online does not cover this chassis. A viewer has already offered to lend me the volume that does.
Would taking a look at the other CRT tester make a good video when the projects die down or is it not worth the effort to fix?
Yes, I will be and sooner than later.