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 Post subject: GE 806 selenium rectifier replacement help needed
PostPosted: Feb Sun 25, 2018 3:54 am 
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I replaced the selenium rectifiers with 1N4007 diodes and 68 ohm 10 Watt resistors in series, but when I turned the set on the resistors started smoking. What could be wrong, I've replaced all the electrolytics?


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Feb Sun 25, 2018 4:01 am 
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cpisinde wrote:
,,,when I turned the set on the resistors started smoking.
What could be wrong, I've replaced all the electrolytics?

If the 1N4007 is wired right, smoking 10W resistors can only be one of two things...
1) You wired one or more of the electrolytics backwards, or
2) You shorted some point in the B+ line to ground.

- Leigh

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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Feb Sun 25, 2018 4:07 am 
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I'm sure they are wired correctly. I'll double check the electrolytics. Won't get a chance till next week though. Thanks


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Feb Sun 25, 2018 4:16 am 
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Check for a paper cap on the B+, there usually is one, often far away from the power supply.

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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Feb Sun 25, 2018 5:04 am 
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68 ohms is too high of a series resistance for a voltage doubler in a TV. More like 15-25 ohms is what you want, and even for that small resistance you'll need at least a 10 watt resistor.

68 ohms is in the right ballpark for an AC/DC radio, but here you have much higher current.

With 68 ohms in series, you may be generating tons of heat. So I think you probably have everything wired correctly; just the resistance is too high.

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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Feb Sun 25, 2018 6:34 am 
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Yes I concur. A 68 ohm resistor would dissipate around 25 watts because of the ripple current.

You may need to use 4, in series-parallel. The selenium rectifier used to dissipate a lot of power too.

You may also need to adjust that resistor value to get your target B+


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Feb Sun 25, 2018 5:10 pm 
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Thanks for the tips. I'll look into it next weekend and post the results. Thanks


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Feb Mon 26, 2018 5:45 am 
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Here is a link to the work on my 608 I replaced the selenium's with diodes and had no problem other than adding more resistance to dropped the voltage back down. viewtopic.php?f=3&t=332554

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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Sat 03, 2018 4:09 am 
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UPDATE: I noticed that R82 (the 1Watt 1500 ohm vertical output plate decoupling resistor) was also burned up. I changed that resistor and also the other resistors mentioned above with much lower resistance. The result was that the resistors in series with the 1N4007 are fine, got warm but not too warm. Problem is that R82 still burnt up. Any ideas where to look?


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Sat 03, 2018 12:01 pm 
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What is your B+ voltage now? If it's too high, your plate decoupler will have to work harder.


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Sun 04, 2018 3:06 am 
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Location: Bear, Delaware 19701
What would cause the B+ to be too high?


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Sun 04, 2018 4:19 am 
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The resistors in series with the diodes too low.....


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Sun 04, 2018 7:15 pm 
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cpisinde wrote:
UPDATE: Problem is that R82 still burnt up. Any ideas where to look?

If the B+ is less than 10% high then it is not a problem. A lot depends on just how the resistor burnt up.

If it quickly burnt to a crisp then there is a short to ground in the vertical circuit. A tube with a plate to cathode short could do that. Or the bypass cap could be shorted, even if it is new. You may be able to see that with your ohmmeter and could disconnect parts and find the bad one with the ohmmeter.

If the resistor just ran hot and slowly cooked, then the circuit is drawing too much current. A leaky cap from the plate of one tube to the grid of the next will cause the second tube to draw too much current. A gassy tube will draw too much current. A leaky bypass cap could draw too much current. New parts can be bad. Electrolytic caps can be leaky if they have been sitting on the shelf somewhere for a long time.

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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Mon 05, 2018 6:28 pm 
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Even if the B+ was 20% high it would not cause a resistor to burn up or overheat enough to have noticeable damage in a time frame less than several days. B+ that high would be somewhat hard on some parts. Electrolytic caps might be running close to or at their voltage rating. That might cause them to age more quickly than you would like. And tubes would be running hotter than they should which would reduce their lifetime.

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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Tue 06, 2018 12:28 am 
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Tom Schulz wrote:
If the B+ is less than 10% high then it is not a problem.

Schematic voltages generally have a toleranve of +/-20%.
Any value in that range is OK.

That's due primarily to resistor tolerance.
It's also influenced by variations in characteristics from one particular tube to another.

- Leigh

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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Sat 10, 2018 5:10 am 
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Ok, I changed R82 with a new 1.5k 1W resistor. As for the resistors in series with the 1N4007 diode I have an 18 and 5 ohm 10W resistors is series for a total of 23 ohms to replace one and the other one has a 5 and a 15 ohm 10W resisyors in series for a total of 20 ohms. That's the best I can do with what I have in stock. The result was the resistors in series with the diode got warm but not too warm, the R82 resistor took a long time to get hot, but it did. I could feel the heat from it about 6 inches away. After the power was disconnected, I touched R82 and it was piping hot! I'm sure it would have burned up in a few more minutes. Should I increase the resistance again for resistors in series with the diodes? Thanks in advance.


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Sat 10, 2018 6:01 am 
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cpisinde wrote:
Should I increase the resistance again for resistors in series with the diodes? Thanks in advance.

No. Once you have everything working you may want to adjust those, but they are not the cause or your problem with R82 getting hot. There is something wrong in the vertical circuit causing it to draw too much current. You have to troubleshoot that.

Do you have the CRT connected and do you see anything on the screen? If so, what? Does the cathode resistor of the vertical output tube also get hot? If the cathode resistor gets hot then the vertical output tube is drawing too much current. If is does not get hot then the current is flowing somewhere else. Try disconnecting the bypass cap at the junction of the 1.5 K resistor and the vertical output transformer. Does that fix the overheating?

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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Sun 11, 2018 5:38 am 
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I always power up tvs with the crt and speakers connected. I replaced the 1500 ohm R82 again. Made sure all caps have been replaced in vert section. No raster yet. Some caps do not exist in this chassis compared to the SAMS schematic and even compared to other chassis. There was never an issue with the cathode resistor. I then disconnected C9 bypass cap at the junction of the R82 1.5k resistor and vertical output transformer. R82 remained cold after sufficient time had passed! Does this mean C9 is the problem?


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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Sun 11, 2018 5:38 pm 
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cpisinde wrote:
I then disconnected C9 bypass cap at the junction of the R82 1.5k resistor and vertical output transformer. R82 remained cold after sufficient time had passed! Does this mean C9 is the problem?

Yes, C9 is bad. Make sure that C9 has a high enough voltage rating.

I was looking at the schematic shown in the Riders book, available here http://www.earlytelevision.org/pdf/ge-805-rider-tv3.pdf . I see that there is a 5 ohm resistor in line with the power going to the rectifiers. You could put one set of extra resistors in series with that resistor instead of one set in series with each diode. It will work the same either way.

The Riders schematic details a lot of production changes.

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 Post subject: Re: GE 806 selenium rectifier replacement help needed
PostPosted: Mar Thu 15, 2018 5:02 am 
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The C9 cap was bad. After replacing it, R82 no longer burns up. Thanks to everyone for the help. Now I can proceed to the next section.


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