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#46
04-22-2026, 09:46 PM
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Thank you sir.
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#47
04-24-2026, 01:51 AM
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I proceeded by installing the 5U4 used in the 300 volt supply. That's enough to get the AM and FM radio modes working
Neat to see the 0C3 gas regulator fired up. First time a tube glowing purple in a TV is good thing.  When you are in FM or TV mode, the signal strength meter on the left is activated. Later Dumont models used a 6AL7 indicator tube. Sound is weak and the tuning dials are off - especially in AM mode, but I do have sound.  
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#48
04-24-2026, 11:27 AM
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The service info is a little lacking. No alignment info for the AM radio for example.
It's a basic 6BE6, 6BA6, 6AT6 design so I think I can muddle my way through it. I'll start by peaking the IF cans for the 456kHz IF frequency and try to get the dial scale back on track. I'm not sure if it's off mechanically or the trimmers need tweaking, but it's pretty far out. I'm picking up AM 820 around 1100 on the dial for example. Can't seem to find AM 720 at all which should be booming.  
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#49
04-24-2026, 07:37 PM
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I decided to forge ahead with a full power up.
The delay relay has been replaced with one having a 10K coil resistance. Series resistor was dropped from 33K to 27K. Seems to work fine. Still using the original 10uF oil filled filter cap. Nothing much happed at first other than a more powerful hum out of the power supply. Not the easiest set to troubleshoot. A handheld scope with a X100 probe was used to poke around. I quickly determined the horizontal oscillator was not running.  Those are the parts mounted on the vertical CRT support. No getting around it so out comes the CRT. Four paper caps were lurking back there including this very distressed 01.uF.   Ok oscillator running now and output waveform looks right. However, the signal on the yoke is only a fraction of what it should be. This signal is used to control the HV (EHT) circuit. The goal is the HV should be extinguished if the deflection circuit fails. Remember, no flyback in this set. Deflection and HV supply are independent. The phosphor could easily be damaged without this safety circuit. We should have 50VPP at this point - not 6.6  Nothing obviously wrong with the circuits so I started tweaking the many controls. Hor. size got me to about 30 volts. Hor. peaking took it the rest of the way. I could hear the telltale squeal once I hit about 45 volts. I'm using a little test CRT at the moment. Looks like we have horizontal ringing and the vertical tends to collapse. Even so, it's wonderful to see a raster of any sort.  
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#50
04-26-2026, 09:04 PM
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Making progress! I had a bad connection on the video amp plate supply resistor. Fixing that resulted in video on the CRT face.
However, sync is terrible. Barely there horizontally, not there at all vertically. The original 1947 Sylvania 1N34 is still good.  I really see what you mean about the tuning indicator now. I do get a strong meter deflection when I have the TV sound tuned in just right. 
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#51
04-27-2026, 06:19 PM
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I found a 5.6K resistor in the sync amp circuit measuring 3.2K and replaced it.
It's only the second bad resistor I've found in the set. Perhaps because they used all 1W or better even though the factory parts list calls for 1/2 watters. Here's a size comparison with a 1/2 watt resistor on the left and the bad 5.6K on the right.  That helped but after running a couple minutes instability returned. Swapping out the sync amp 6SN7 seems to have finally solved the problem.  Need to do a bit of work on the geometry and shift the image over to the left.  Bandwidth is pretty good. I expect it will improve with a better setup. I'm currently feeding it from a Sencore VG91 with alligator clips on the 72 ohm screw terminals. Live video source is a cheap OTA converter box feeding the VG91 external video modulation.   
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#52
04-27-2026, 11:42 PM
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#54
04-28-2026, 10:42 AM
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Yes, that is with the original 12RP4 picture tube.
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#56
04-29-2026, 09:02 PM
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New 807s arrived today and I had just enough time to pop one in and give it a try before I get ready for the convention.
I haven't measure the HV output, but I can already tell it's working better. I can vary the brightness over a large range and the image stays sharp and focused. Before it would bloom and get blurry.  The tuner needs a deep cleaning. Tuning is a bit of a challenge right now, but when it's locked in, it looks really good. Sounds could use an alignment as well but that will have to wait. 
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#57
04-30-2026, 02:03 PM
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Quote:
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Linear Mode
