Tom, I should have mentioned that the hoirz frequency has to be maxed out for me to even get the horiz hold to try to sync if it's maxed out. Sometimes even if both are maxed out, it's not enough for me to get a pic in sync. The horiz drive is a trimmer cap. It realyy doesn't have any effect except turning it all the way in reduces pic width.

Doug

Have you tried a different 12AU7?
Sounds like that is part of the problem. I'd also go with sync seperator, and, sync amp.
Perhaps a pwr. supply feed resistor is off, causing this?
Have you tried tapping, wiggling tubes?
I may be wrong, but, didn't I read in another GE post somewhere that there is a high value mica cap on 6SQ7 aud det., and, amp that has something to do with the sync??
I know on some of the RCA tv's they used the 6AV6 aud. amp as a agc rectifier. If that circuit acted up, agc would be off, causing lack of sync.
Bill Cahill

Have you tried a different 12AU7?
Sounds like that is part of the problem. I'd also go with sync seperator, and, sync amp.
Perhaps a pwr. supply feed resistor is off, causing this?
Have you tried tapping, wiggling tubes?
I may be wrong, but, didn't I read in another GE post somewhere that there is a high value mica cap on 6SQ7 aud det., and, amp that has something to do with the sync??
I know on some of the RCA tv's they used the 6AV6 aud. amp as a agc rectifier. If that circuit acted up, agc would be off, causing lack of sync.
Bill Cahill

Bill, the 12AU7 has been replaced and subbed. I checked the voltages on it last night and they are ok. I'll check into the 6SQ7 to see if I have a mica cap. Wiggling tubes doesn't seem to help. BTW, you have mentioned several times about the AGC circut, and I keep forgetting to reply about that. I may be naive in this, but I don't think this set has an AGC citcut. I can't find one on the schematic. I've even looked thru the AGC chapter in my 1956 Sams "TV servicing Guide", and can't find a circut in their examples thjat resembles my set.

Doug

I just found that I have a copy of Sams set 96 folder 4. If that is the correct one for your set or is close, then I know a little better what we are talking about.

This set does not have the gated AGC circuit as used in more modern sets. Instead it uses the voltage developed by the video detector diode for the ACG voltage and the contrast control is the adjustment.

You quite possibly have two separate problems. One is that the horizontal oscillator can only be brought near the correct frequency with extreme adjustments of the controls. The other is weak sync.

The schematic that I am looking at shows a 6AL5 as a horizontal sync discriminator (it works similar to a FM audio discriminator). Problems with that tube and the associated capacitors and resistors could pull the horizontal off frequency. Some TVs use a set of solid state diodes instead of a 6AL5 for that circuit. If your set is different and uses diodes, those could be the problem.

The weak sync could be caused by problems with the sync amp and the sync separator circuits, and possibly by weak video feeding those circuits. I suspect that this has already been mentioned, but have you checked the video detector diode?

Tom, my set is an 805 found in Sams 78-4. What you have is for the GE 10T1. When I got the set, there was no model # on it or even paper inside the cabinet, so I havd to figure out what I had. It turns out I have the EARLY version of the 805 which differs from the later versions found in Sams 78. Sams gives complete douumentation on the later 805, but only gives a schematic for the ealy versions. The main difference is the early version uses a 12SN7 for sync and the later uses a 6SL7. I acutally have tried both tubes just to make sure, but the 12SN7 seems to be more stable. There are parts differences too between the two versions, and after studying the schematics, I'm positive I have the early version.

This morning I tried it and couldn't even get the horiz to sync at all even with the horiz hold and horiz frequency maxed out. According to the schematic, I don't think my set uses a diode for video. My set uses a 6AL5( which I have replaced) as the ratio detector/DC restorer.

Doug

What type of circuit does your set use for the horizontal afc (the stuff just ahead of the horizontal oscillator)? Perhaps you could take a close up photo of just that part of the schematic and post it.

Tom, I had a breakthrough of somwhat this afternoon. Normally, I prefer Sams over Riders, but in this case Riders has more info on the early verision. Sams does not have a voltage chart for the early versions, but Riders does. I had downloaded and printed it out. However, I was using the wrong one. The top of the page says Early, S,T versions, but the bottom only says, S&T versions. I scrolled thru it again and found a different voltage chart for the early versions. I printed that out and started checking the sync voltages. This time my sync voltages were right except pin 1 was low about 35 volts. Pin 1 SB about 90volts. Coming off pin 1 is a 270mmf which goes to pin 5. Pin 5 has the right voltage, and I had replaced that 270 with a new unit. I got out my substitution box, and the closest it has was a 220. I tried that anyway, and the pic cleared up briefly. I let the TV cool off for an hr and retried it, but this time I couldn't get it to sync. However pin 1 was now where it SB. Therefore that new 270 cap was bad. The closest I had on hand was a 251, so I put that in and fired it up. The sync voltages are now all correct. The horizonal still won't lock in like it should. I then started checking the horiz oscilator voltages (now that I have the right voltage chart), and I have some descrepancies on pin 2 and 3.

Let me play around with that tonight and I'll post my results.
Doug

After working with it tonight, I can now get the pic to sync IF the brightness is turned up all the way. Turning the brightess down loses the horiz sync. In an earlier post, I had mentioned about a capacitor that was labeled 222 which I had used for a 220, but it actually read 2000. Well, I found another one of those tonight underneath one of the boards. I put in a 251 which was the closest I had. The sync voltages are all ok, and the horiz osc volatges are ok except for pin 3. The Riders voltage diagram shows 85V, and I have about 9-11. I redownloaded that chart and looked closely on the monitor to make sure it wasn't 8.5.

Anyway, I'm going to put this on hold for a few days and order the correct capacitors. I've got 251s in where I need 220s and 270s, and I want to get a correct 2000mmf for the grid of the horiz osc.

Do order mica caps instead of ceramics.

Well I'm back in business today. My new caps arrived today, and they are micas. I got them put in, and the sync is somewhat more stable. Vertical is fine but horizontal is still somewhat touchy. However now the pic is washed out. I'm going to start tracing out the video amp circut and see what I can find

still sounds like AGC to me.

The only problem is that I don't see an ACG circut in the schematic. This set uses a 6AL5 for a DC restorer and video detector. It has a 12AU7 for Video Amp. I checked the voltages on the 12AU7 and all were normal except pin 1 & 7 were way low. Pin 1 SB 100V and I have 38. Pin 7 SB 25 & I have about 2. I've been tracing that circut out and replaced all resistors. One is puzzling though. The schematics (both riders & Sams) call for a 39K around pin 1. Pin 1 connects to a peeking coil, then thru a 3300 ohm resistor, then thru a 39K. In my set, I see an 8200 ohm resistor where that 39K should be. It's nothing I've changed though. I think I am gonna sub a 39K and see of anything changes.

Doug

Update: I think I just found my problem: the peeking coil coming off pin 1 on the 12AU7 video amp is bad. It SB 6.9ohm, and I couldn't get a reading on it. I found a peeking coil in my junk box that read about 9 ohm and subbed it. My pin 1 voltage jumped to 71V. That's still about 30V low, but the pic was much sharper. I will try to get the correct peeking coil this week and see what happens.

Doug

I think I've got the problem about licked. I found a peaking coil toayd on a junk chasis I had in my shop. It read 7.1 ohm, and I figured that was as close to 6.9 as I could get. I put it in, and the voltage on pin 1 of the 12AU7 went to 75V. Still about 25V too low, but the picture was now watchable. I turned again to that questionable 39K resistor in that circut. Last night I found an 8.2K in its place, but both Sams & Riders call for a 39K. I put a 39K in, and I think that had a hand in bringing the voltage down. I got out my substitution box and started experimenting with different resistors ranging from 33K down to 10K. I found 15K gives me about 100V which is what I need with a pretty decent pic.

I've got one little vertical problem now. The pic wont quite fill the bottom of the screen no matter how the size and lin controls are adjusted. I'm going to try another 12SN7 vert output tube and see if that helps before I start digging into the vert circut. Horizontal is still somewhat touchy, but at least I can sync the pic now. I think I need to adj the horiz lin control for that.

The set has played for about 20 min now with good results as you can see.

Doug

You can't really tell what inductance a peaking coil has by measuring it's resistance. The resistance reading on the schematic is just so you can see if the coil has had some type of failure such as a short or an open. Choosing a replacement by matching the resistance is unlikely the get you a coil with the correct inductance. Does the parts list give you an inductance value for the coil? If so, you could try to buy a coil with the correct inductance. You do not need to get one that matches the resistance. Do you have any type of meter or other test equipment that measures inductance? If so you could measure the coils in your junk box and find a match. Some coils have colored stripes or dots on them that give the inductance.

Tom, thanks for letting me know about that. The old peaking coil was open. This coil seems wo work fine, so I'm going to go with that. I had contacted Mayer, but they didn't have one. The set played for an hor last night with a sharp pic. I just had to adj the verticl hold one time during play.

One new problem. During the many times I turned the set over on it's side, I tore the rotten speaker cone in several places. I super glued it, but it's torn again. Being that it has a field coil, I'll need to get it reconed rather than replace it. Does anyone know a good place to do these?

Thanks
Doug

you should use a scope and take a look at the signal PP starting at the detector. switching values from what was installed (unless it was clearly a repair that may have been done wrong) to try and resolve a problem is not a good idea. It may work ok but prob not as good as it should. Unless the parts are marked as 5/10% then generally you can have large variances and the circuit will still work fine (some circuits are more critical but if they are you will generally see precision parts installed).

Sounds like you have a gain issue, a PP reading at the video detector is a good starting point. if its good there, then you can trouble shoot going forward. If the PP is low then I would be looking at AGC voltages, and gain at the IF tubes. Or even a weak detector (diode or tube).

The effect of a wrong value peaking coil would be to either make sharp edges and fine detail overly pronounced or somewhat blurry, depending on which way it is off. If a peaking coil is open then anything, even a jumper across it, will be an improvement. If the picture looks good to you then don't worry about getting the right value coil.

I've got the speaker & field coil removed and sent off for reconing. The place says 4 week turnaround, so it will be another month before I can report any more progress. In the meantime, I'm turning my attention to the cabinet. I've gotten a Novus kit and plan to start restoration this weekend. There is a small hairline crack in the top, but I think I can fix that where it will be virtually unnoticeable.

Doug