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#46
10-09-2010, 07:42 PM
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Indeed, my set seems to be finally coming along and I couldn't be more pleased considering where it started from! Based on the suggestions I've heard on here, as well as some insight from various trouble-shooting booklets from the 1950's, I've looked over my schematics and have compiled a checklist of things that might need some attention before I can call it done. Hopefully, a couple tubes and maybe a few more resistors will iron out these deficiencies.
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#47
10-09-2010, 08:03 PM
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Quote:
jr
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#48
10-09-2010, 09:28 PM
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Schematics
Alrighty, here's a scan showing the last stage of the video section, and the vertical section is visible below it. I left all that in there because the AGC is controlled by half of the 12AX7.
 Again, the symptoms include a washed out picture and virtually no contrast when the picture is adjusted to maximize sound output. Turning down the AGC improves contrast somewhat at the cost of sound, and eventually an unstable image. Brightness on the whole is fair, I suppose. It wouldn't look so great in a well-lit room.
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#50
10-10-2010, 12:23 PM
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That sounds like a good test!
Looking at the circuit, I don't see an obvious DC restore circuit.... I would check again the value and connection of C-33 (.1uf) and also make sure that r-33 is the correct value as well. L-20 would be a peaking coil to check....perhaps the contrast control is open ? Do you have a scope? jr
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#51
10-10-2010, 03:32 PM
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Nah, I've been really wishing I had a scope, though. Most of them I've seen are a bit expensive, other than a Tektronix? 555 I saw recently for $50. Didn't feel comfortable bidding on something I know nothing about.
I found that R31 ( 1k ) was out of tolerance awhile back and replaced it, but it didn't change anything. I think I recall that 220k tested okay, but I'll have to pull the chassis out again tonight and take another look. Not sure about the .1 capacitor, though. My multimeter can check capacitance but only once I've pulled it out of the circuit. The contrast control has been making the brightness go up and down as if the pot is working, but it's not "contrasting" anything. I'll be sure to look at those peaking coils, too.
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#52
10-11-2010, 06:56 PM
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I ran out last night to check and see if Home Depot had those adapters for the 300 ohm connections in the back of my tv. They didn't, so I waited and got one from Radio Shack today since the old one was messed up. But, to make the trip worth something while I was at Home Depot, I picked up some Howard's Restore-A-Finish in mahogany for my cabinet and a pack of fine steel wool. Today, the weather was nice so I immediately jumped at the chance to do something I've been wanting to do for a long time; fix up that scratched cabinet! It really didn't look too bad already, especially from the front where there were maybe only a dozen or so very small nicks that were somewhat noticable. The sides and top didn't fair so well. They still looked "okay" but were scratched beyond belief in some spots, especially the left side.
The Howard's stuff really did wonders for this type of damage without too much work at all. I think it took a couple hours with a bit of drying in between. I was pretty liberal with the top and sides, but very light with the front where I wanted to merely "touch up" the trouble spots. I still ended up rubbing a thin coat over the whole front end, although careful to avoid to the grille cloth.     The scratches are practically invisible and that color is just amazing! It's like I'm slowly turning the clock back 50 years. I could still touch up a few more spots and maybe wax it, but for now I'm happy with it. Now I'm just waiting on some rather expensive Krylon gold paint to get here so I can finish up the control panel. I've still got the chassis out so I'll be investigating the video output section tonight. More to come soon!
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#54
10-11-2010, 08:54 PM
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Concerning using a DVD player: Most VCRs will have a set of AV inputs (Yellow/White). You can hook your DVD player into this and just set the VCR to use the inputs.
A 6BA6 may also work in place of a 6AU6 if you have one to test with.
__________________
Death: Man how old is this TV?, You probably get the DuMont network on this thing!
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#55
10-11-2010, 09:09 PM
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Oh yeah, I forgot to mention that I did figure that out recently! I had been playing cable channels and a DVD player by hooking it up to the VCR input jacks. The VCR actually makes it so that I don't really need a converter box, since I can flip through all of our cable channels on it. ( We only have basic cable, and this VCR goes up to like 200 channels or something ) No remote, though.
I already have a NOS Zenith 6AU6 on the way, but... I do have a GE 6BA6 on hand that came out of the same RCA radio chassis that I borrowed the audio output transformer from. I had set it aside as a possible replacement for my television because at some point, I swear I saw it in the tube lineup. Then, I checked back and didn't see a 6BA6 and dismissed the idea because I realized that I must have been thinking of the 6BE6 which is used in my set. I didn't know they were compatible. Last edited by RitchieMars; 10-11-2010 at 09:18 PM.
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#56
10-12-2010, 02:39 AM
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Well, I swapped out that 6AU6 for the 6BA6 and it didn't seem to help. If anything, I think the buzz got worse. I tried making minor adjustments to the sound cut-off coil, no results. I tried the intercarrier coil, but it didn't feel like my allen wrench fit it. I know putting the tool down into the coil made it louder. I would have taken some voltage readings, but at one point I reached and turned the fringe lock and I heard two sharp cracks. That scared the crap out of me, but I checked and found no capacitors blown, no visible signs of arching. Maybe a shard of the steel wool I used earlier got into something? I did find that the way I had things positioned, the speaker wire was up against the low voltage rectifier tube and it got stuck to it and when I pulled it off, I realized it had melted slightly from the heat. That's the hottest corner of the chassis, so I made sure to reposition the speaker wire afterward.
I checked a bunch of resistors in the video output section but I swear I can't find anything amiss. I think I found one of those peaking coils, and it looks like something coated in wax with a red dot on it. It measures 8 ohms, compared to the 10 listed on the schematic. Either way, the picture is still washed out when I adjust for the best sound output. I can make it contrast better by turning the AGC down, but then the buzz gets really loud. On one channel, I actually got the sound to work pretty good and the buzz was barely noticeable. Then a commercial came up and it was buzzing again. Last edited by RitchieMars; 10-12-2010 at 02:43 AM.
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#57
10-12-2010, 12:42 PM
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Could the video signal coming in be to hot? I know some modulators are on the hot side. I notice this with my 53 zenith.
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#58
10-12-2010, 01:31 PM
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Quote:
http://www.solidsignal.com/pview.asp...u=853748001293 RS sells/sold them also but I have not see one in a RS for a while. Note that on the RS unit "min" means minimum attenuation, NOT minimum signal. jr
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#60
10-12-2010, 04:40 PM
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Quote:
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Linear Mode
