Another Project?
 

One of my coworkers told me on Friday that he was going over to pick up a free old tv this weekend. He said it was in large cabinet with double doors, and that it was a radio phono combo, but the phono (and the drawer it came in) had been removed. Ideally, he wants to put his flat panel on top of this set, and have me get the TV/Radio working again. He would put his home theater gear in the gap where the phono had been. He also said the radio had a round dial, instead of the slide rule type typical of these sets.

Well, he emailed me some pictures this evening. Looks like fun. It is a GE model 802. Here are the pictures he sent me:

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Nice set, somewhat scarce too.
One just sold on eBay last week: http://cgi.ebay.com/1947-GE-model-80...d=p3286.c0.m14

I have the tabletop version without the phono, model 803, not my favorite set to work on.

Bah, I just got to work on this set, and it looks like the transformer is toast. I had pulled the rectifier and powered it up to see if the filament string was still good, and just as quickly powered it down when I didn't see any filament glow. A dim bulb test revealed a shorted transformer. Ohming it out, it looks like the filament string secondary is the problem.

Let this be a lesson in plugging in a questionable set! As found, the 5Y3 was burned up, and the power resistors coupled to the electrolytics were blackened, one had even blown apart! My guess is that someone in the past powered it up, and left it powered up, as smoked rolled out of the chassis, waiting for a picture to come up.

It's a shame, too. This had a very nice replacement crt, with a date code of 1952. It tests practically new.

Sounds like the packard bell in my avatar:

I guess it originaly had a fryed flyback,, When i bought it, someone had allready pluged it in and smoked the transformer and the 5U4. To make matters worse, the 17RP4 was weak. A nos fly and transformer and a crt later i got it running great.. :D

Steve

Well, I've talked to the set's owner, and between the option of getting his money back, or pressing on, he chose the latter. He really wants to see it working!

I have a few spare good transformers, but nothing that quite matches GE's design. The 802 uses two rectifiers, a 5U4 to put out something like 250 volts at 160ma, and a 5Y3 "boost" that puts out 425 volts at 85ma. If this were any other type of tv, I would probably have a match.

I'll dig into the original transformer first, and try to determine what is really going on with this thing. If I've only lost one of the secondaries, maybe I could patch in something else.

What are the chances on getting it rewound?

We've contacted a couple of rewinding services, and minimum cost for that would be around $250. That's a bit out of our budget, to say the least.

There's plenty of room to install a sub-chassis that would hold replacement power transformers below deck in that cabinet. Just be careful with the high voltage, hopefully you can get a transformer that supplies the high voltage that can fit on the TV chassis, and have the sub-chassis feed the tube heaters. This assumes nothing unobtanium is also bad...

Filament secondaries will measure near 0 ohms when good, so be sure that you aren't being fooled by that. Remove all tubes and try the dim bulb test.

If it is just a filament winding I would say that wouldn't be so bad. Should be space for a beefy filament transformer somewhere in there, and I don't guess they cost too much.

If it really is a shorted filament secondary, then a separate filament transformer won't help much since the short will still overload the transformer.

I agree with wa2ise though that ohming the secondary isn't a reliable test.

John

Well, this thing failed the dimbulb test days ago, I just forgot to mention that. I'd say it is pretty dead, since even with all of the tubes pulled, the simple act of powering it on with "no load" is enough to overload the transformer, as it rapidly heats up and makes a fairly audible hum to boot.

I hope to get into this a little more tonight-disconnect the tf leads and really see what is happening here, before going through transformer replacement hell.

I removed the transformer tonight and pried the bells off to see if I got lucky and it was just shorting out a bit inside the case. What a mess! The transformer is charred, with bits of ash raining out of the case. Whoever last powered this up must have left it on for quite a while before giving up, and I'll bet their house smelled great when it was over. Now that it is isolated, I can ohm it out much better, and it appears the failure is on the center tapped 5y3 secondary, but there is a lot more damage here than that.

On removing it, I found another item-a mystery winding that goes to the radio section. Looks like the transformers for the 801 (which I have the service info for) and the 802 are different. Guess I'll have to finally track down the SAMS for that. GE really loved packing in a lot of stuff in this transformer, I see that they used some shims to give the end bells the clearance they need.

My strategy now would be to make a power chassis, which would slip in where the record player used to be. I will probably have to buy two transformers, something like a 350-0-350 and a 450-0-450 and run them up to the main chassis through an umbilical cable. I can't be sure until I get the SAMS.

Sent you a P.M. concerning the schematic. :yes:

Be sure to check for what might have killed that transformer, like a shorted filter cap or such. It's possible the transformer killed itself, but you want to be sure there isn't a problem that would ruin a replacement transformer.

I've checked over the set's power supply, and I keep going back to the multisection filter caps. They all test bad, using my Heathkit cap checker. Certainly the e-cap section that was tied into the video IF bias supply was bad enough to cause a 2 watt power resistor to burn up into two pieces. The primary filter cap in the 5y3's filament string had also belched its guts out as well. So for now, I would just say that the transformer was killed recently by someone who powered it up with bad caps. After all, the set's owner was given this set for free, so it is possible the previous owner toasted it, knew it was badly damaged and gave up on it.

This leaves me with looking for a replacement power supply. Here is how the 802's tf broke down:

The plates of the 5u4 and 5y3 are shared on a single center-tapped to ground secondary.

The low voltage windings go to the 5u4's plates and put out 270 volts.
The higher voltage windings go to the 5y3's plates, supplying 440 volts.

There are two 5v windings for the rectifier filaments.

There is a center-tapped winding dedicated to the two filaments related to the phono preamp tubes.

There are two more pairs of filament secondarys, these are not center tapped:
The first filament secondary supplies 8 tube filaments and the dial lamps. This is all for the radio.

The second supplies 13 tube filaments for the television tubes.

So, I suppose to find the current handling of this transformer, I need to sit down with my tube manual and add up all of the filament currents in each string? Do the same for the plate/screen currents for the rectifier plate windings?

Wow, I knew that this thing would eat a lot of power, but this is pretty excessive:

The tv tube filaments alone add up to 9.4 amps!

The radio filament string will require 2.7a

The phono filaments, .6a.

The 5y3 plates will need to supply 440v @ 85ma, the 5u4, 270v @ 160ma.

So now, where to get something like this? Playthings of the Past has a nice list of spares here:

http://www.oldradioparts.com/2a23efl.txt

The closest thing that I own in my spares is a transformer to an rca T120 from the late '40s. It boasts a lot of tubes, but seems to fall short for my purposes:
700vct @.22adc, two filament strings: 1.2a and 9a

Still working away at this thing. The 802 has so many secondaries the best I could come up with for a replacement is to build a massive power chassis, which will require three transformers, and two large wirewound tapped power resistors to get the B+ in line. I plan to fit all of this into the space where the turntable once was. The two transformers that I need will ship tomorrow, and then I'll begin building the power supply, which has so many taps and such a high amperage rating that I'm sure it could be adapted to power any 1940's television.

Wow, you are definitely dedicated to reviving this set. Keep posting on the progress, it's very good reading.
Too bad there wasn't a spare chassis hanging around for you to steal the transformer but I guess that chassis from these consoles are pretty rare.
Rob

Will the tranny from an 801 work?
 

I happen to ahve a spare 801 chassis--with tranny, I think. I bought it off of the bay a coupe of years ago, when I got my 801 set. But my set has an OK tranny.

let me know--.. I know where the chassis is--and it is accseeible.

Will it work? Yes and no-it will certainly power 95% of the set, so you will definitely be getting a pm from me.

The 801 tranny lacks the secondary to power the filaments for the two tubes in the phono circuit. While this would be okay, as the phono is missing, on of those two tubes is an audio IF tube, which tells me the tv will be without sound. But still, wiring in a tiny filament transformer versus building that massive power supply would seem to be the way to go.

I also just realized that GE failed to put a fuse anywhere on this set-probably another reason for all of this heartache decades later. You can be sure this set will have at least one once I am finished.

Sounds like it has some sort of B+ voltage doubler, could you just sub in a B+ transformer that puts out the voltage you require? I can think of several tube amps off hand that would make around 450 VDC at that current output (or more) from only a single 5U4 rectifier. Just something to think about.

Well, my power transformers arrived-I highly recommend Playthings of the Past-he sent me a photocopy of the datasheet for the one tranny, and heavily labeled the other one to ensure proper installation.

Somehow, I made a mistake, and the one transformer produces a bit more voltage than I really need-350v instead of 240v. So, maybe someone can check my math:

The final B+ needs to be 240v @160ma. My calculations show I need a 687.5 ohm 17.6w resistor to drop those 110v, from a 350v supply voltage.

The B++ line needs to be 315v@85ma. I figured I need a 411 ohm 2.95w resistor to drop that from a 350v supply voltage. Do these figures seem to work?

Re: phono preamp: this must have been one of the sets where G.E. used their new (for the time) variable reluctance pickup rather than a crystal.

Finally! I think this is the first bit of good news I have had since I started this thing:

Over the past week I mounted my transformers to an upside-down 9x13 cakepan, and began to wire that up, as well as to rewire the tv chassis to accept a large terminal block to wire the power supply into. Well, tonight I finished all of that, and hooked up the filament string only. After a few tests, I was confident enough to place all of the tubes on the chassis, and I was greeted with their heavenly glow:

edit:
sorry no photo, but I am having some net issues.


I would like to continue to power this set up in this manner, a bit at a time, adding on one transformer secondary source after another.

Cool. Glad to hear that it's starting to come together.

I got the power resistors today, only there is a single problem: they don't do anything to the voltage. For example:

A few posts up, I figured to drop a 350 volt supply voltage to 240 volts, I would need 687.5 ohms to do the job. Well, putting a 700 ohm resistor on each secondary arm (leaving the center tap to go to ground) gives me about 330 volts (measuring AC from one secondary arm to ground, or the center tap). Removing those resistors, I still have 330 volts. Absolutely no change. Putting on several Kilohms of resistors doesn't change anything, either.

What do I need to do to drop the B+ here? These resistors were the very first thing the transformer secondaries met, before reaching the rectifier circuits or anything else on the tv chassis. I should think these resistors should be able to bake off at least a little voltage, even the electrical engineers at work were on board with my plan. It's all just a bit frustrating.

Do you have a load attached - how much current ? Your voltage drop will be R x I.

Oh yeah, the tv was hooked up to it. That should be enough load, I should say.

I found my resistor value by RXI:

for the 687.5, that was found by:

687.5 X .160= 110

the 110 volts is the voltage drop I need (350-240), the .160 is the 160ma that the tv runs under load at the rectifier, and the 687.5 would be the resistance needed. I hope that makes sense.

I even gave this problem to a guy at work, he just started an electrical internship, and is learning the basics of DC. I simply gave him the current and the voltage needed to be dropped, and he got the same answer. He was happy to be working with a "real" problem, rather than one on paper.

Sorry, I didn't remember your earlier post where you layed out your plan.

Sure, it makes sense. The math is sound so something's screwy here. Did you measure any voltage drop across the resistors? Did they get warm?

You could try adding a single dropping resistor after the rectifier instead.

I had a passing thought that my old '48 Admiral consolette uses a transformer similar to that. I don't remember the specs on it but it does have the dual hv windings. Seems like it has about 270v and 155v output at the currents you are looking for.
Terry

I found the problem-the choke after the rectifier is open. AAAAHHHH!!! Anyway, I have a few that will meet the current rating, but none that have as much resistance or inductance as the original (500 ohm, 7H). I think I'll have to make a run to storage and pull my T-120 chassis and see if that choke will be a good match.

I found that when I disconnected the bad choke, some voltages went down, while others went up. It must have been loading things down. I'll have a better idea once I get a new choke in.

A little light at the end of a very dark tunnel....B+ is a few volts low, B++ is dead on. The flyback (although this is an iron core transformer, so is this still a flyback?) is putting out just under 10kv, the schematic calls for 8.3kv. Vertical is shrunken, but the controls are very dirty...perhaps a deoxit will clear all of that up.


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Awesome :banana: It's great to see that CRT glowing!

I just can't seem to get anywhere with this set. The Phono section seems to be working (though I would need the proper phono cartridge to be sure). The AM radio performs superbly, but I cannot get anything on FM, or audio or video on any of the television settings.

All of the voltages are in line as they should be, but I just don't own any television alignment equipment except for a color bar generator. I can inject audio and video through all of the stages, but when I try to inject any rf into any stage, I barely get anything-probably just swamping the receiver, as I get this same weak signal on all channels.

I have added all new tubes into the rf/if sections, cleaned the tube sockets, cleaned all of the controls, and measured continuity across all coils. I just have no clue where to go from here-save for adding a/v jacks and bypassing the tuner entirely.

I'm curious. If the present owner of this TV already has a modern flat-panel set he wants to put on top of the cabinet, what would he need the original TV for? :scratch2: The only thing I can come up with is that he may want to feed the audio from his home theater setup through the original TV's sound channels, but that doesn't make much if any sense since all home theater receivers have outputs for multiple speakers (some as many as seven, counting subwoofers).

Also, there is the problem of power line isolation. I personally wouldn't try to use a 70-year-old TV with any audio system having solid-state components, unless I were sure beyond the shadow of even the most unreasonable doubt that the isolation capacitors were good--most such caps in unrestored sets of this age all but certainly failed years or decades ago, and cannot be trusted. Even if the original isolation networks were replaced with new components, I would still be leery of such things as ground loops or voltage on the chassis of the modern device.

Jeff,

The owner's ideal plan would be to use the set to watch B&W films on a few times a month. The flat panel would be the "daily driver" for all of his other programming.

They would be hooked up separately, sharing a cable box (a/v outputs going to the flat panel, coax out going to an rf modulator for the GE). If I did have to add a/v inputs, you can be sure that even though the coupling caps are all replaced, I would still add a cap to the inputs, to further isolate any solid state gear that could be feeding it.

A few neat items on circuit design in this set:

I found the plate voltages to be 50v too high on all of the video IFs. It turns out that the contrast control is actually a gain control. As you adjust the contrast, you can alter the plate voltage of all IF sections by about 60v or so.

The vertical and horizontal hold controls are in the rear of the set. The literature I have been reading on this set describes these controls as something that only need be set up once, and then left alone. We'll see how much that is true once the set it running. I will say that the vertical height, hold, and linearity interact with each other a good deal. If that vertical hold control was on the front of the set, in the hands of the average Joe, you could probably really mess up the picture.

The RCA 630TS has a manual gain control in front, labeled Picture control. Kinda weird until you get used to it.

My DuMont RA-103 is the same. I was initially dubious, thinking the designers were just a bunch of showoffs. Turns out that the horizontal and vertical are absolutely solid, even with different video sources, changing channels, etc. None of my other restored TVs has that kind of stability.

By the way, did you ever clean the contacts in the tuner?

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

On my 1-108 chassis Sylvania the horizontal and vertical controls are underneath the chassis. Accessible, but not easily. Once set, they are very stable. The horizontal circuit is an RCA design.

John

This thing has pretty well killed my resolve to work on televisions. I have never done so much work to get so little done on a television. Where I stand with this thing now is that the am radio only works, and I get only a very silent white noise sound for audio on FM and television. I get a raster, but no image on the screen. I've tested all of the components I can get to, and I have replaced all of the questionable parts, and put in a new lineup of tubes in the receiving/IF sections with no changes.

Trying to inject signals into the set, but my B&K analyst is just too iffy to get any results. I've been scouring ebay for a sweep generator and marker generator, but I've been outbid on all of this gear for the last month.

I'm pretty sure this set is out of alignment, as many of the circuit adjustment screws that were sealed in blue locktite have clearly been fooled with. If anyone in southeast PA has the appropriate alignment equipment that could be used to analyze this set, I'd love to see what it's issues are.

Failing that, is it possible to simply put a/v jacks into this? Here is a schematic for the 801, which has nearly identical audio/video output sections. If someone is aware of how to properly do this, I would like to know how.

http://www.one-electron.com/FC_Radio.html

All that aside, here is some of what I did do:
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Attachment 166683

Here it is, the power supply for this set. Using a transformer for an RCA 12" set, a Crest power transformer, and some surplus transformer, I had enough to power the tv. It is mounted to a cake pan, and all routed out to a European-style terminal strip. You can also note the two Dale-type power resistors mounted to the angular heat sink on the top of the power supply. The whole thing weighs 35 pounds. I am still very happy that I was able to create something like this, but I need some way to continue to move forward with this set.

Nice job on the PS :thmbsp:

Is you BK working well enough to inject video at the grid of the video amp (V7) ? That should allow you to get the sync circuits working and see an image. I believe you could inject a composite video signal here too for your A/V jack, but you'd need to play around with the level and polarity.

As for audio, you can add a jack at C41 on the volume control for AUX. Maybe replace that 2 position TEL / RAD switch with a 3 position one :scratch2: