Project impossible? bringing a magnet-box back from the dead?
 

Well I have always been a sucker for hard luck cases, and WELL, I have really found one this time!

I'm always looking on FB for vintage TVs, and found one a week ago for the fantastic price of FREE!
All I could see at the time was a CRT and a chassis that looked like it had been unceremoniously removed from the cabinet for no doubt some horrific use of a dog bed or fish tank or the like, all I could see was cut wires and it was clearly missing the tuner, but, HEY, it was free!
I got it today.

NO markings at all on the chassis, but it did not take me long to ID it...

same as in this thread.
http://www.videokarma.org/showthread.php?t=38726

A look at the CRT
https://i.imgur.com/hpVtGeS.jpg

OK,,,,
https://i.imgur.com/ELiQIcf.jpg

NOT looking good here, that first element looks VERY dark.
hooked it up to the B&K tester

https://i.imgur.com/mrWLCSS.jpg
NOPE, not looking good.:no:

after 2 hours
https://i.imgur.com/YFSgxAo.jpg
came up a bit, but still very tired.

and finally , the murdered chassis, no tubes, and cut wires, ( i had a few tubes )
https://i.imgur.com/8ECWBpM.jpg

Sad that they do that.

I am gonna try to bring it back to life.

Starting with horizontal /HV then Vert and so on.

gonna have to work out what wires are what and where they go
but since the tuner is gone, this will most likely end up AV/input if it ever DOES work.

Its not a "magnet box", the correct term is "maggot box".

When I was a little kid we had them. The pictures were incredibly sharp, and
in 1954 started showing dot crawl stupefyingly clearly.

Houston, we have power!
https://i.imgur.com/54cwucJ.jpg

took a bit to work out which wires but! :)

https://i.imgur.com/NfzdA5Q.jpg tubes nice and glowing, no smoke

As mentioned in the other thread, the SAMs is CLOSE, with slight differences, some tubes are not the same. like it shows a different damper, so I had no idea which one to use, looked through my old tubes , found a 6DW4B, did a quick check, it matched up perfectly for the way the socket was wired, so i put it in, I see no reason why it should not work in there, a damper is a damper, the ratings for it seem good enough.

I'm now waiting for other tubes horz osc and the HV rect, to come, to see if I can get HV up.

The original damper tube was probably a 6AY3.
I have a newer Mag chassis that uses a 6GB5/EL500. I picked it off the street because I wanted the little stereo amp, 2 6BQ5's. That's awhile ago!

Wasn't 6AY3 a compactron base? IIRC it was used in a lot of RCA B&W sets of the day.

Well, I have been able to confirm that although THIS chassis does not use the damper as shown on the SAMS I have, ( 6DA4A) And is wired for a 6AY3/ 6DW4B type, the latter being a bit more beefy, it is wired for a 6GW6 HOT, which i had, and I THINK worked, not really sure. :(

From what I can see, the 24AHP4 is one of the largest BW CRTs made, and a bit rare to find one at all, let alone in good working order.
It's going to be interesting to see what kind of picture the one I have can make, but first I will be trying to bring this chassis up on the 8YP4 Test CRT.

Again, it really sucks that the tuner is gone, all the missing controls, I can re-create, but the tuner, not so easy, although, I do see NOS tube tuners for sale on eBay, trying to tack on some alien tuner, and get it to work correctly and align up and be nice and happy with AGC and everything would be near impossible.

But on the upside, it looks like the input to the video output , right out of the detector is 1.5v ptp, so it would be easy to feed in composite video.

I have a Magnavox combo that has a rebuilt 24AHP4, which seems to be perfect! I took it for the PPP 6V6 mono amp. If I could give the set away to a collector, I'd leave it intact. :thmbsp:

Maggie also made 27 inch sets for a little while. The 24 and 27 inch CRTs were wide-deflection, small neck types that tended to go flat right away. To find a still-good unrejuvvied one would be a rarity indeed.

If I get a house in the next couple of years I may have to take a look at it...

If you were not so far away from me T_T

because shipping is murder! :(


But now I have another problem to work out, I did not notice that the video going into the output tube is inverted , YES it's 1.5 ptp, but it is upside down, and gets fed into the CRT cathode at 50v
so now I gotta work out how to invert a composite video input. Because I don't think this will work to well off IF with my tuner subber as a source.

I am thinking of this a a AMP. But I do not know op-amps very well. :(
https://www.eleccircuit.com/simple-v...ifier-circuit/

they do not make DIP LM359 chips anymore and I don't trust the ones from china, FAKE! So all I can find are surface mount.

But I can assume, if I swap the + & - inputs, I will get inverted ( negative ) output ? And adjust R1 /R3 till I get close to 1 to 1 or slightly higher gain from it? Am I guessing right?

Google inverting op amp circuit (or read the Wikipedia page on op amps) and that will give you the schematic and maths to make a circuit.

Personally I'd try getting a tuner for it. That almost certainly uses the modern IF frequency and generally they aligned TV tuners and IFs to be interchangeable... as long as you don't try something silly like making a late 40s 21MHz tuner work with a 60's 44MHz IF TV.

I replaced the 27" CRT in a mid-60's Magnovox set that was probably the first solid-state set. It was a 90 deg CRT.

I have found stuff like this ,, no idea if it would work or not :o
https://www.ebay.com/itm/18459874966...wAAOSwzEpf6Su2

I have a tuner and all the controls from a similar Mag set I scrapped.
Unfortunately, I can't get to my warehouse because of health issues.
Be patient, that set don't have to be finished in the next day or so!

but I do have one of these, but it has no ACG control
https://www.ebay.com/itm/313573344093

exactly
this will be brought up in stages

horz /HV first
then vert
then try to get a raster on the test CRT
then try to get video
I'm just thinking ahead :P

I tend to do that :)

Chassis number is on a small paper tag. It can be anywhere on the chassis
or large part. usually starts with U, V, or T followed by numbers.
They fell off all the time so see if its in the cabinet.
Maggy model numbers are rarely useful in Sams. The used to sell
the same sets with totally different chassii. Same goes for audio.
Seperate chassis ##'s than the TV.

You can build a tuner subber & get other uses from it.
Get a solid state tuner with antenna isolation OR add isolation.
Needs 9, 12, 18, or 24 volts to run it. Also need a variable bias for AGC 1-3 VDC. Short the AFT to ground. Put it in a box & get a long IF cable with an RCA at the end. You seem like a builder so no big deal making it.


My father had the 27" magy. No UHF so pre march 1964.
Lasted abt 4 yrs & jug went soft. Bought a Zenith color then.
Other than that they were a well built set.

73 Zeno:smoke:
LFOD !

https://i.imgur.com/AIQwxRy.jpg

got some tubes in

https://i.imgur.com/E0jx7yD.jpg

horz osc is working,,, but the HOT I got last year on eBay is BAD, works half the time, and I don't think the damper I found laying around is any good also.

can't get stable HV,, can SOMETIMES draw an arc from the HV rect cap, but nothing ever out out of the CRT anode.

Got to get MORE new tubes, and start checking resistors / caps in the sweep circuit.

but this IS progress for a chassis that i picked up from someone's front porch!

an I can't find any ID numbers on it as I mentioned...

Oh, maggie chassis numbers are nuts. The same set might have different numbers based on the tuner used. Best I can tell, that’s the only fiff between the CT-220,221,222. Maybe. I dont think anyone knows.

Oh HELL yes, I have bad resistors...

https://i.imgur.com/MdXL3cN.jpg
I'm VERY sure that this CAP is bad, cause it's paper, and it's getting hammered by the horz yoke output.

on a lark, i checked the other side.
https://i.imgur.com/zKsZBMN.jpg

R75 checked at 56 ohms :O

I was expecting bad resisters,, but WOW.
no wonder HV was unstable , even with a wonky HOT, it was acting VERY weird, this is why.

Dang. That's an interesting way of obtaining the feedbback pulse. What condition is the dual diode in? This is the first time I've ever knowingly seen a series dual diode in use. Most always it's the common cathode version.

hard to tell, not easy to test those silly selenium dual diodes on a DVM, the only one that DID seem to show it as a diode had it as 1.9v one direction, and infinite the other for both junctions, never tested on like this before, so not sure if its good/bad or ugly.

The phase detector is most likely bad, this is the second Selenium diode type phase detector that I have come across so far, the first being in the one in my CTC-16 which it fine, but not this one, which almost every tester on diode test can't see it as a diode, even the fancy multi tester ( transistor/cap/resistor ) thinks that it is a capacitor.

But now the question is, what type of diode to replace it with, I'm sure there are many to choose from, but what one? :o

just randomly searching, came up with the Mouser # 78-SD101A-TAP

no idea if It's right to use as a replacement for it or not. :/

went over the entire sweep PCB, did not find that many bad resistors, only 3-4 not counting the big 2 watt one I mentioned before, and they are not THAT far off, unlike that big one.

Ordering a mess of parts now, mostly electrolytic capacitors & that really bad 2w resistor, still unsure if the selenium phase detector is good or bad, seems the only real way to test it is to run it in the correct circuit and see what happens. I saw in a few places, that a BAT86 diode is a workable replacement, so a pair of them is ordered in case it is bad.

I also had to order the audio output tube, even though I'm not ready to get sound working yet, because this thing uses the cathode bias of it to source the 120b+ for the set, though that voltage does not seem to be needed for sweep, it IS needed for IF and video.

The diode isn't critical. A fast switching diode like a 1N914 or 1N4148 will work or a Schottky type. Use a 1N400X series in a pinch

That bad 18 ohm resistor is most likely the main reason I could not get stable HV, that and the .047 cap that I suspect was leaky, with that resistor over 3x the rated value, it was like trying to run it with the yoke disconnected, and the HV circuit HATES that! :O

What I don't get is how can this HOT that got last year ( 6dq6a ) be stronger than the one in my stromberg carlson when it DOES work, but be very intermittent but nit seem to be shorted that I can tell :o

The failing 18 ohm resistor has been changed, ( reads 61 out of circuit ), replaced main bias filters, not to dredge up this whole reform / replace debacle, but this does sort of add fuel to it.
At this point, I have had power on for over 2 hours, most of it bringing it slowly up.

https://i.imgur.com/IAcROGx.jpg

C1, C2a, C3a have been replaced, when tested ( after being isolated), C2a & C3a seemed to check OK, although a bit high, I have no way to do a full power leak test, however.
BUT... I could get no reading at all on C1, it was very dead. :(
I now have a matching set of 150uf in the voltage doubler circuit.

USPS says that the NOS HOT will be here today, I will see if I can get stable HV now.

YES! YES!
:banana::D
https://i.imgur.com/B8hgItl.jpg

We have liftoff!

Its alive!!! It's alive!!! :lmao::yikes::beer:

https://i.imgur.com/pLjN5Nj.jpg

https://i.imgur.com/g2ndhPl.jpg

Now have a full raster, this is a major step forward, but the audio output tube 6GC5 did NOT come today like USPS said it would, so I can't bring up the IF/video without it yet, cause as mentioned, it is the source of the 120v for the video circuits.

I have rigged up temp controls for horz / vert hold, and they seem to work, but I still need to rig up a contrast control, for w/o it the cathode of video output is just left hanging and thus inert.

first images of video..

NOTE,,
I have no brightness control yet, and I have not got IF input to work yet, this is video input direct.
and I'm seeing the same issues that I saw with 8yp4 that I saw on the Arvin, it just NOT seem to work well with cathode input, but loves G1 input.

https://i.imgur.com/AgPCWfA.jpg

https://i.imgur.com/DNijuP1.jpg
I dread having to rig up something to hold the 24ahp4 tube, or the 21aup4a out of my SC again :(

Does anyone have experience with the 8YP4 Test CRT? And may have any idea why it seemed to work so well with my FADA 895 ( rca 630ts clone ) 12LP4 G1 video input, but work poorly with the arvin model 5204cm chassis 21EP4B and now this magnavox one using a 24ahp4 both with cathode video input, are the voltages just too far out of range for the 8YP4 to work well, is a 20+ sized just too much for it? I'm not sure why it is not liking it, it IS hooked up right. :(

First video using the native CRT. it IS a bit weak, but it's pretty damn good for a weak tube.
came up to this level after 90 sec or so.

https://youtu.be/KmF9YlAy-U8

Impressive!

Video response and focus look great - see all those chroma dots!

It seems that the 24AHP4 is not as bad as I thought, ( or what the BK 490B told me it was,)
The unstable brightness issue seems to be due to me not having the correct control for brightness yet, calls for a 200k pot, tied to 120v and gnd, with the center post going to CRT G1, using what I had on hand used a 500k trimpot.
Obviously now, not a good idea, because I noticed that it's overheating and causing an unstable picture, too small to take to load, so until I can get the right parts for it, I intend to replace it with 2 ½ watt 100k resistors, with the CRT G1 hooked to the center, this should give a decent pic, otherwise I would have to adjust the values.

As for sound, that too is a bit tricky, since I have not gotten IF up yet, it did not seem to work with the tuner subber, direct input at the audio output where the volume control USED TO BE, gave too weak of a output, (point 32) , I have found the output of the detector, which used to go to the tone control, (point 31 ), these can be linked to enable sound at full blast.

https://i.imgur.com/22toG2w.jpg

From what I have read, the 6DT6A is very close to the 6BN6 which was used in my Arvin, which had a AUX/phono input hooked to the detector at G3 (point 30) via a resistor and bypass cap, gonna try to see if something like that will work here as well.