She's a runnin, kinda
 

:banana:
Well I got that 1966 Magnavox combo powered up tonight.. I recapped the entire electrolytic plethora on this chassis the last 2 days. What A PaIn In The ***!!! Who were the elves that wired this chassis, the filters in this set are buried! And the chassis is totally compact compared to the RCA chassis im familliar with. But anyway this set is full of gremlins!

First and foremost (the concerning part), when the raster comes up upon startup the horiz hold is way off and the left side of the screen is shrunk in an inch. Will stay this way until I start adjusting the horiz hold a little, then you can hear the set come in and the left comes back out, raster gets brighter and then I can stabilize it. Good bright raster and plenty of contrast and focus. If I turn the set off and right back on, same scenerio, horiz way off and left side shrunk. I move the horiz hold dial far left and back to where it was and problem solved..

That may or may not be related to the 2nd issue. The Raster after 10 minutes of use gradually darkens, goes out of focus, shrinks on both sides and a little on the top and bottom. If I turn the brightness up picture blooms bad and shrinks worse. If I turn the set off and back on over a minute period, problem solved except the movement of the horiz hold dial to get the pic back into sync.

3rd issue. really bad pincushion top, bottom and sides of the screen.

4th and last issue, Colors way off, but im sure this is due to a flaky demod and agc sync seperator tubes. I should have this fixed soon, (also completely deteriorated bakelite sockets on the x and z demod tube locations.

Any help is greatly appreciated, and you guys are always the best!
Thanks!
Shawn

Blooming and shrinkage at the same time? wow, that's an odd one. However I may be able to help out by splitting the symptoms up for you.

First, check out the damper and HO section. Low voltage could be the cause for the oscillator drift and shrunken raster. Shrinking on the sides is almost always attributed to B+ boost problems with the Damper tube or HO tube. Check the tubes.

Poor focus, blooming, and dimming are caused by weak HV, bad HV rectifiers, poor or NO HV regulation. However if you are getting this symptom along with a 4 sided shrink, then I might go back to the power supply and check for bad solder joints. If this set has an inrush limiter in series with the transformer primary, it may going up in resistance. You can check by measuring the voltage at the primary of the transformer. If its less than the voltage coming out of the wall then trace it back from the transformer and see where the voltage drop is.

Another problem is the use of Fuseistors, or fuseable resistors. These were often used in place of circuit breakers or fuses in the B+ circuits of some color sets. They will usually be 7 ohms at 5 watts or something like that. They will sometimes increase in value as they warm up, killing the B+ voltage.

Measure the B+ after the rectifier(s), and see if it changes after the set warms up. Then you can get somewhat of an idea of where to proceed from there. Follow the B+ line and see if there is anything like a dropping resistor that might cause voltage problems.

And check ALL the tube sockets! They may not be making good contact. I've seen it a lot in 5 tube radios from the '60's.

And yes, those filter cans are the devil to change. My T933 has one behind the power transformer and two behind the HV cage. Those are certainly not ones that you will change in 10 minutes!

That sounds exactly how my chassis is too, everyone that has a maggie chassis seems to start with a T, mine is a U, but none the less im sure these chassis are the same. On the topic JPDylon brings up a great point, (Bad HV regulation), If i have a 3A3 that reads into the question mark area, althought AK'rs tell me that this tube is like a diode, Im going to start with replacing that 3A3, just seems to me that I should start there, then start checking voltages and rectifiers along with those flake fusistors. Do you guys think that the 3A3 could be a culprit here, at least to the loss of HV regulation?

I was advised by a member of AK to use a 3CU3 in place of the 3A3 in my Magnavox. The reason is that the internal structure of a 3CU3 is fixed so the filament can't sag and short like a 3A3 can.

If you are having trouble with HV regulation, I'd check the 6BK4 tube and it's associated parts.

The "U" was on older prefix used before the "T" chassis. I think all the tube color Magnavox chassis were very similar. The "T" series chassis were used up to the early '80's. I think the T809 was the last 19" color set and the T815 was the last console.

Hey guys, where can I get tube sockets to replace for the demod tubes in this chassis? The ones in there are completely deteriorted. I need 2 of them. These sockets are for the smaller tubes, the tube type is 6GY6.. Thanks!

check out tubesandmore.com

just search for "9 pin socket" or "7 pin socket"

dunno how many pins that tubes uses. i'm guessing 7

Coool, thanks man, got 'em ordered...

Well, I checked the 6JE6 yesterday, upon startup, it's reading 208ma. After 10 minutt will drop all the way to 145ma. As it slowly drops down, crt starts to lose focus and a little shrinking on the left side of raster at 184ma. It will start geting wonky and horiz will start to flutter after it's been on for a while. Now whats interesting, it will drop quick if I turn up the brightness, but it can stabalize and eventually it will come back up and stay around 190ma and the raster looks good, although the horiz flutters a bit. Upon startup I have to turn the horiz hold all the way over and back to get a raster or it's way off. Haven't checked line voltage at the trans taps yet. Im stumped though, why would the b+ come back up after it drops way down? When I check this and attach my meter and disconnect the lead to ground and run my meter in series, this is checking B+ right?

Also I forgot to add that the vertical takes a bit to stabilize too, and is touchy. The horiz when I say is wonky, it has a tenency to flutter a bit back and forth like im barely turning the knob.

Hey Guys, just wanted to update.. I had my suspiciouns about the HO tube, on the meter, it would read great (115%), after a minute of being on the meter it kept dropping, so I replaced it with NOS. The srunken rater thing went away upon startup, horiz is correct now. The only deal is that after 10 minutes of being on the horiz wants to flutter and come in and out of phase a little. After 30 minutes, it's hard to lock, and gets really touchy. Cathode current is staying at an even 214ma to 210ma. The grid voltage stays at -54 vdc. At the transformer tap on the pc board is labeled 120v, i read 88vdc from the trans. Now this reading is taken before I power up the set, powering it up oes not change that voltage reading. Another tap going to the board is labeled 128v, I get nothing, ever... (and the set runs).. Any ideas? Also vertical hold flips like crazy upon startup and stabizizes after a couple minutes, if I stabilize it upon startup, it will start rolling when the set warms up..
Thanks

You need to set the meter to read ac voltage not vdc when checking the voltage on the primary side of the transformer. Voltages on the primary side of the transformer should be at or near line voltage. The B+ supplies are usually checked at the positive terminals of the main filter capacitors. There will be several B+ supplies. Usually 400V, 395V, 260V, 195V 130V. Something like that anyway. Set the meter to read DC voltage and connect the - lead to chassis ground, then you can touch the + lead to the power supply sources and check the readings. I do not know the chassis number of your set, but the U904 also uses a 6GC5 tube for a voltage divider to derive the 130 volt supply from the 260 volt source. The 395, 260, and 130 volt sources are all used in the sweep section. It would help to know what the chassis number is. I should have the schematic if you can post the chassis number. Check the voltages and componants in the Horiz afc and oscillator circuit for thermal faults. Before it gets hot use a soldering iron to heat the componants and see if that causes it to fail sooner. Be sure to check any high value or high wattage resistors in the sync circuits as well as the HV regulator circuit.

Bill R

Does this set have have a pincushion adj for the vertical circuit? The chassis is a U9109BB chassis. Thanks guys. BTW I am getting steady 391 vdc at the horiz sweep so not thinking b+ is an issue now...

what is the grid voltage on the Horizontal output when the failure starts occurring? If the HO is loosing bias it will greatly effect the sweep and size. The oscillator is responsible for biasing the HO tube, so you might see if the HO oscillator is ok. If you have a scope, look at the waveform at the output of the oscillator for a clean looking sawtooth around 17.5 khz

In some cases like this its sometimes best to simply sub out the HO and damper to make sure its not either of those two tubes. tube testers will test basic emission and shorts. Most don't have enough supply voltage to test sufficiently for leakage. It may show as good, but after the tube heats up driving the Horizontal sweep and HV section, it can be bad in circuit.

What HO and damper does it use? I may have them kicking around here somewhere.

Sounds interesting, The grid voltage of the 6JE6 HO is -54vdc constant, no change as opposed to heat.. The damper is a 6DW4.. There is a small sprague wax cap next to the horiz effenciency coil, Im thinking it's prob a good time to change it..

-54 volts is good as far as HO bias goes.

I'll check my tube stock this evening.