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 Post subject: Re: GE806 1949 with stand
PostPosted: Nov Sun 25, 2018 5:40 am 
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Tom Schulz wrote:
Frequenceme wrote:
Here is another video without the isolation transformer. Looks better.

Hmm... External magnetic fields can cause that sort of thing. How far away from the CRT was the isolation transformer? If was within about 4 feet, try hooking the set back to the transformer but put the transformer farther away from the set.

I move the TV further away and moved the isolation transformer out of there both, neither helped. I do have a florescent light above it but nothing changes if I unplug it. I did a bit more work on my GE 12" model 830, the contrast control on it effects the horizontal hold. Sure doesn't act that way in this 806.

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 Post subject: Re: GE806 1949 with stand
PostPosted: Nov Tue 27, 2018 3:38 am 
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I just now looked at your videos. I think that the videos with and without the isolation transformer are about the same.

About the possible causes of the now reduced wave.

You could still have some marginal electrolytic caps. You would not have seen any effect of jumpering in test caps because of the larger problem with the hot chassis. So you could try that again. I would concentrate on C383/384, C373 & C374.

You could have some tubes with heater to cathode leakage that your tube tester can not detect. I would concentrate on V20, V21 & V22.

It might be possible that the filter choke, L376, has a shorted turn. That would make it not really act like a choke or at least reduce it's effectiveness. A shorted turn may not reduce the resistance enough to measure, but you could try measuring the resistance anyway. The schematic I am look at says 55 ohms.

One last thought, are there any tubes that look like they are supposed to have a shield where the shield is missing?

Edit:
I am assuming that you have a U or W version of this set.

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 Post subject: Re: GE806 1949 with stand
PostPosted: Nov Tue 27, 2018 4:41 am 
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Yes this is a W version of the set. As far as choke L376 it did get attacked by the mouse. I assumed that since it tested close(53.6 ohms), I could not see any wires chewed in two and I had B+ volts that it was ok. May very well have a turn to turn short. I have some chokes maybe I will get luck and have one on hand to try.
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GE806-67.jpg
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 Post subject: Re: GE806 1949 with stand
PostPosted: Nov Tue 27, 2018 5:48 am 
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Looks like this is the closest I have on hand. The Stancor on the right is also 300 Ma
Attachment:
GE806-69.jpg
GE806-69.jpg [ 136.07 KiB | Viewed 259 times ]

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 Post subject: Re: GE806 1949 with stand
PostPosted: Nov Tue 27, 2018 7:34 am 
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Sams specs that choke at 1.2 Henry, so either of those you pictured should work.


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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Sat 01, 2018 3:43 am 
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Tom Schulz wrote:
I just now looked at your videos. I think that the videos with and without the isolation transformer are about the same.

About the possible causes of the now reduced wave.

You could still have some marginal electrolytic caps. You would not have seen any effect of jumpering in test caps because of the larger problem with the hot chassis. So you could try that again. I would concentrate on C383/384, C373 & C374.

You could have some tubes with heater to cathode leakage that your tube tester can not detect. I would concentrate on V20, V21 & V22.

It might be possible that the filter choke, L376, has a shorted turn. That would make it not really act like a choke or at least reduce it's effectiveness. A shorted turn may not reduce the resistance enough to measure, but you could try measuring the resistance anyway. The schematic I am look at says 55 ohms.

One last thought, are there any tubes that look like they are supposed to have a shield where the shield is missing?

Edit:
I am assuming that you have a U or W version of this set.

OK I tried everything here including replacing the choke. Nothing made a difference in the wave. I then rechecked some voltages and V21 pin 2 is still way low.
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GE806-70.jpg
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This shows old notes from last year, all the resistors with a red dot next too them checked within specs. The mica capacitors with a red dot next to them have been replaced. All paper and electrolytics also are new.Something that is hooked to V21 pin2 must be causing the low voltage and the wave?
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GE806-71.jpg
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Last edited by Frequenceme on Dec Sat 01, 2018 4:40 am, edited 1 time in total.

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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Sat 01, 2018 4:28 am 
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Frequenceme wrote:
This shows old notes from last year, all the resistors with a red dot next too them checked within specs. The capacitors with a red dot next to them have been replaced. Something that is hooked to V21 pin2 must be causing the low voltage and the wave?

V21 itself could be puling the voltage low if it is drawing too much current. It is after all connected to pin 2. :) The tube could draw too much current if the grid (pin 1) is just a little more positive (or less negative) than it should be. I don't see a red dot next to C397 and a bunch of others in that area.

Now it is the job of V22 to vary the voltage on the grid of V21 to keep the horizontal locked. If something is affecting the balance of that dual diode then that circuit might be operating with a offset or bias which could cause the grid of V21 run at a different level than it should. C384 is feeding the sync signal into that circuit and C397 is feeding a sample of the frequency of the horizontal oscillator (taken from the horizontal output) into it. The dial diode acts something like the detector in a FM radio and compares the two signals and develops a voltage depending on how close they are to each other.

Are there any capacitors in that area that have not been replaced? Have all the resistors been checked?

The voltage at the V21 pin 2 being low would not in itself cause the wave. But if the sync is weak or marginal than the circuit might not be keeping as tight of a control on the horizontal as it should be. Still it seems that 60 Hz from the power line is getting into things. Perhaps some component such as a capacitor laying on some of the wiring for the heater circuit. Any two conductors form a capacitor. So a capacitor and a heater wire form a capacitor which could couple in a unwanted signal.

Have you tried different tubes for V20, V21 & V22?

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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Sat 01, 2018 4:49 am 
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Sorry I should have said the Mica capacitors with Red dot have been replaced. All electrolytic's and wax caps are new including C397. I will try to recheck the heater wiring and see if I have a solder blob I missed or a component touching. And no not all resistors have been checked.Thank you!

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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Thu 06, 2018 6:52 pm 
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I am a major contributor to the GE Monitor Top Refrigerator forum. http://monitortop.freeforums.net/ One of our members (Cablehack) from Australia is a former TV repair man. I recently posted a link to this thread for him to find and he has this explanation for the wave I am seeing. Also bless him possible remedies!

Quote from Cablehack "Nice couple of post war sets! I haven't read though the entire Antique Radio forum thread, but from what I've seen and the youtube video, I gather the complaint is a slow horizontal weave in the picture. First, I'll explain why it occurs. The signal source; DVD player or digital tuner, etc, uses a crystal timebase. Therefore, the vertical sync pulses will be exactly 59.94Hz (close enough to 60, but had to be changed slightly when colour was introduced). And,the set is operating from the public electricity supply, which is also 60Hz. However, the frequency of the public supply is not rock steady and drifts very slightly, back and forth over time, but it's average over time is still 60Hz - good enough for clocks. What you're seeing on the TV screen is the weave is moving up or down at a frequency that is the difference between the power station frequency and the vertical sync frequency from your signal source. At different times of the day, it may seem to move faster or slower - as the loading of the generators changes.

So why is it visible at all? Basically, it's due to imperfect filtering in the set's power supply. I note two selenium rectifiers and no power transformer. Undoubtedly, the two rectifiers are connected in a voltage doubling circuit - to provide about 250V B+ from 120V mains. As such, it's a half wave circuit, and a good deal harder to filter than a full wave circuit. The reason being with a half wave circuit, the ripple frequency is 60Hz, and with a full wave circuit it's 120Hz. Filter capacitors and chokes work better at the higher frequency. The fact there is only one "band" of the weave shows it's 60Hz ripple - there are two bands when this happens if the set has a full wave power supply. Imperfect filtering means something in the horizontal circuit, operating at 15,734Hz is being modulated by the 60Hz ripple present on the B+ supply. Most likely it's the horizontal oscillator, but could also be the sync separator (or sync amplifier, if there is one). It could also be the horizontal output circuit.

Fancy making a set like that! Well, it's not as bad as it seems - back when the set was made - it's old enough to use what looks like a 10BP4, TV stations often had their vertical frequency locked to that of the power station. Thus, imperfect filtering could be gotten away with because the horizontal weave remained stationary. With the advent of colour, TV stations could no longer do this - the colourburst, horizontal, and vertical frequencies have to be all exact multiples of each other for the colour system to work. So, instead the TV station timebases were independent of the mains supply.

What to do about it? I note the set uses a series heater circuit. Depending where particular tubes are placed in the heater string, some have fairly high heater to cathode voltages - which stresses the heater to cathode insulation. Also, given the set's age, proper series heater tubes hadn't been designed yet, with controlled warm up time and better heater to cathode insulation. So, there's a possibility that if the horizontal oscillator tube had poor heater to cathode insulation, the horizontal oscillator will be injected with 60Hz from the heater supply. Having the horizontal frequency modulated by 60Hz would certainly cause the problem.

Assuming that's not the fault, then the power supply filtering has to be improved. Increasing the filter capacitance is one way - doubling the filter capacitors either side of the filter choke will help. If the horizontal oscillator has it's own B+ decoupling capacitor, increasing its value will also help. Because of cost, the minimum value of filter capacitors they could get away with was often used.
There is also another effective trick, and that's to resonate the filter choke at 60Hz. In the basic pi-filter circuit (i.e. an electrolytic either side of a choke), the choke simply acts as a high impedance to AC - which is why the ripple is a lot less on the output side of the choke. However, the choke's impedance can be made even higher by resonating it. In theory, the impedance would be infinite (and thus a very effective filter!), but due to various losses in the choke (like winding resistance) it isn't quite that good. The way to resonate it is to connect a capacitor across the choke winding. You could calculate the capacitance required using the formula for resonance, if you know the choke inductance or can measure it. Or you can simply try various capacitor values while looking at the B+ ripple on a CRO. Typically, start with 1uF and increase or decrease to see the effect. The right capacitor is the one that provides least ripple. The effect is quite marked once you find it.
Some radios and televisions actually did leave the factory with the choke resonated, but cost cutting meant that most didn't. In the day, a large paper capacitor was required for the purpose. But of course, now we have cheaper plastic film capacitors which are a lot better.

And one other thing, anything such as a transformer near the neck of the picture tube will also cause the same effect. In that case, the magnetic field deflects the beam directly. For this reason, proper TV power transformers have a shorting strap around the laminations to reduce the radiated field."
Thanks again Frequenceme

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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Thu 06, 2018 9:18 pm 
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The formula to find the correct cap to resonate the filter choke is .02530/fxfxL where L is the inductance in henrys and the capacitance comes out in farads.

My arithmetic says you would need a 7 uf cap for a 1 henry choke. For a 1.2 henry choke you would need a 5.86 uf cap. But a cap half that size should have some effect.

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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Fri 07, 2018 8:08 am 
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Frequenceme, I don't mean to divert attention away from your specific problem, but the similarities to how this is playing out are so relevant to what I experienced back in 2011 that I've been having bad dreams about it. :lol: Unfortunately my videos are no longer viewable but I think you can easily read between the lines. If you have the time I think you'll find this both educational and a little entertaining. At the very least you'll feel better knowing that you're not the only one that's ever struggled through a situation like this. :wink: viewtopic.php?f=3&t=181161


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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Mon 10, 2018 1:47 am 
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Thank you Tom for calculating the cap size. And Thank you Kevin for the link to your old post. It does look like we had very similar problems. Now I have some bad news I have been avoiding posting the last few days cause I will look like a idiot. I let the magic smoke out of L316 :cry: . I set up four jumper leads on the power supply caps so I could see what added capacitance did to the wave. I then stupidly turned on the set without watching the watt meter as I normally do. I soon had a hot smell and then smoke before I could look at the watt meter and shut it down. I know I fried L316. What are that chances I didn't hurt too much else? I feel terrible as we all had so much work in this set to get it this far. I believe one of my alligator clips slipped and shorted + side of C384 to chassis. Sure wish I would have been watching the watt meter instead of thinking about what I was going to do next.

What are my chances of finding a replacement for L316? There is a 806 on Ebay in poor shape but its a early version and does not have L316 in it.
It burnt were circled and who knows were else.
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I have these on hand.
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Thanks to Joe Sousa and the radio museum I found the specs on L316
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GE806-74.jpg
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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Mon 10, 2018 5:10 am 
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If that power supply caps plus lead touched the chassis, the chassis is isolated through that 470K resistor, so that alone should not have caused too much drama. I really don't see how that would have shorted across L316. Are you sure the coil is burnt completely open? At any rate that's a fairly common part from those vintage of sets. There's a good chance that Miller 6212 will work. I will go take a look at my GE 821 parts chassis(same basic chassis you have). If that part is there and checks good you can have it for postage.


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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Mon 10, 2018 6:21 am 
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Kevin Kuehn wrote:
If that power supply caps plus lead touched the chassis, the chassis is isolated through that 470K resistor, so that alone should not have caused too much drama. I really don't see how that would have shorted across L316. Are you sure the coil is burnt completely open? At any rate that's a fairly common part from those vintage of sets. There's a good chance that Miller 6212 will work. I will go take a look at my GE 821 parts chassis(same basic chassis you have). If that part is there and checks good you can have it for postage.


I am not sure what happened then, I know it was drawing almost 400 watts when I shut it down. I only had test leads hooked up at each side of C384 and C383 The other ends were hooked to one side of a cap with the other side of cap waiting to be hooked to the end of lead after things warmed up. If it matters it was C383 I believe shorted not C384 as I previously posted. I haven't ohmed out L316 but it was the component that was hot too touch afterwards. I am sure not drawing normal watts now.

I also found I have a Miller 6333.
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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Mon 10, 2018 6:48 am 
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Kevin Kuehn wrote:
Are you sure the coil is burnt completely open?

I removed two leads and L316 is not open. Have 111/64/47 ohms. Something else must have went south that caused it all?

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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Mon 10, 2018 7:51 am 
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So what exactly are the symptoms now when you power up? Drawing excessive currents/watts? No picture or sound, nothing?


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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Mon 10, 2018 3:25 pm 
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Looks like I have no picture and no sound. Drawing about 70 watts. B+ Voltages are 195, 305, 307. Looks like I am not lighting up all the hi voltage tube filaments.

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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Mon 10, 2018 6:49 pm 
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You have two sets of series strung filaments in parallel across the AC line, both share a common return to B- through the picture tube filament. If one filament in either group has gone open the rest from that group will not light. It's possible your clip lead accident shorted B+ across a section of filaments and blew one or more open. I'd start by re-testing those tubes that are currently not lighting. Assuming the tubes in the yellow box are the ones not lighting, you'd better test L374, R374 too.


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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Mon 10, 2018 8:15 pm 
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V13's filament is open, V21's filament is high resistance (2.2K). All other filaments in the string are good. R374 and L374 check good. I just bought over 1000 used and new vacuum tubes to go with what I had. Looks Like I may not have a spare 19BG6 though. I don't see that my clips were anywhere near any party of the filament circuit. The only thing I see they could have touched were chassis.

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 Post subject: Re: GE806 1949 with stand
PostPosted: Dec Mon 10, 2018 9:08 pm 
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It is hard to see how shorting the B+ to the chassis could have done anything. One possibility is that C409 could have been subject to a high enough voltage that it broke down and put B+ in the filament string. So you could check it to see if it is shorted. Another more likely possibility it that the 19BG6 just broke down and had a heater to cathode short. Horizontal output tubes sometimes just do that. Especially if they are vibrated as will happen if the chassis is moved around. You should check R374 to see if it is still OK.

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