Doug, is your GE 805 the "W" version or the earlier version.

Carl

Mine is the Early version. Sams has very limited info on the early version, but Riders has muxh more.

Can you test the Thermal Cut Out using an Ohmmeter?

I don't understand the Power Supply circuit in my GE 805.
Do you? The Early Version circuit I understand and that one has two fewer Electrolytic Capacitors.

Carl

No, I did not understand my power supply circut. I remember there was one big resistor in that chain of electrolytics that started to burn and broke. I could find nothing in the schematic resembling it. Before it broke, I measured it and was able to sub a wirewound which worked find. That thermal cutout should act like a curcut breaker, and you should be able to check it with an ohm meter.

Inside the High Voltage cage, this is what I have:


Is this where the two 75 ohm Resistors go?
Mine only has one and it measures 350 ohms.

Will an ordinary 75 ohm resistor work ok?

Carl

That's weird. I had 2 resistors in mine. Both measured good, but I went ahead and replaced them with 2 wirewound units, and they worked just fine. That doesn't even make sense to me on how yours is done. I could see a 105 ohm (75X2) to cut it down to 1 unit, but not a 350 ohm. What's that black wire on the left of your resistor going to that seems to be disconnected? On 2nd view, it's a white wire that seems to be burned at the end.

Let's face it: You and I both acquired sets that someone had worked on at some time previously that either didn't know what they were doing or just made mistakes and gave up. Now we have to correct what they did plus normal restoration. Mine uses a 12SN7 in the sync. All other versions use a 6SL7, but MINE HAD a 6SL7 in the socket. My cabinet had no paper telling me what I had for a model (805, 10T1), and I had a time trying to figure out what model I have. I had to sit and trace out the schematic on both the early version and W versions to realize I did have an early version, and someone had put the wrong tube in the sync. And yes, after I fianlly got it restored enough to get a pic, I tried both the 12SN7 and 6SL7 in the sync just to make sure. Only the 12SN7 worked thus proving I have an early version.

Good Luck
Doug

Carl, I went back and pulled up my old thread when I got mine. I thought I had posted a pic of the resistors in the HV cage, but I didn't. These are the only two I had, which doesn't do much good, but you can see the 2 resistors next to the tube. Are you using a Riders or Sams? There's a pretty good shot of the HV cage in the Sams on Pg 9.

Doug

Excuse me for bothering you guys, but, mine also has only one resistor
It's a 75 ohm, but, higher wattage.
John Folsom says that on different versions to save money they put the two strings in parallel, with one resistor.
Your thermal cutoff my be defective. They were known to go bad.
Remember, on the rectifiers to put a slightly higher value resistor in becuae silicons have less internal resistance, so, create higher voltage.
Bill Cahill

Doug, Bill, thanks. Like you mentioned Doug, I concur, our TVs have been hacked on. Mine also had a couple of modern capacitors and several modern like resistors.

Bill, my Thermal Cut Off is open. I'm going to bypass it. Also, have to trace out the wiring to figure out if I need one or two 75 ohm resistors.

Also, my TV was missing the 4 ohm resistor in series with the Selenium Rectifiers. I've replaced the Seleniums with 1N4007. I'm going to install a 20 ohm (actually using x2 10 ohm 10 watt resistors) as Tom Albrecht mentioned in his notes when he restored his GE 805.

I guess I'll find more surprises as I get on with this restoration.

Bill, does that power supply circuit I posted earlier make sense to you?

Thanks for your help.

Carl

I just looked at your posted power supply circuit. That is a fairly standard voltage doubler circuit. Let me see if I can explain. On a negative going half cycle of the AC line, the two 150 uf caps charge up to around 150 volts as the diode you pointed to clamps it's end of those capacitors to ground. Then on the positive going half cycle the input end of the capacitors rise to positive 150 volts. That plus the 150 volt charge on the caps gives you around 300 volts into the other diode and the following filter cap.

The only strange thing is the use of 2 150 uf caps instead of one 300 uf cap. Perhaps by using 2 caps, each cap would have only half the total current flowing through it. They may have been worried about over stressing the caps with too much current. Or perhaps no one made a 300 uf cap.

Thanks Tom for the explanation. It makes sense now and I appreciate how you clearly explain how circuits work.

I'm planning on replacing the 4 ohm resistor with a 20 ohm to compensate for the internal resistance the Selenium rectifiers because I'm using 1N4007's - from Tom Albrechts posts on this TV. I assume the charge/discharge of those two capacitors will work the same, and work similarly with both versions of this circuit - see below.

You have piqued my interest in circuit theory. This TV has two versions of the power supply circuit. The power supply circuit I had in the prior post was for the "W" version of this TV - "W" is the one I am restoring. The "Early version" of the same TV has the power supply circuit like this:

This circuit accomplishes the same thing, Voltages the same, is more understandable to me as I can easily see the voltage doubling here, and uses fewer Electrolytics - no 60uf Caps. Why would GE engineers "improve" the circuit by adding two more Electrolytics? Looks to me that adding those capacitors significantly increased the manufacturing cost. No Muntz engineering here:-)

Below is the "W" version of this circuit for easy reference:


Carl

I only have the Riders version for this TV. Don''t have Sams.

Apparently my 75 ohm Globar Resistors (R373 and R374) are toast.

Do you think an ordinary 75 ohm say 10watt Resistor will work OK?

Carl

Yes. As stated, that is a standard voltage doubler power supply circuit...
Bill Cahill

Finished recapping this TV. Replaced 26 capacitors.
Someone mentioned that this TV has "crappy controls" - well I had one that
came apart that I had to fix.
I left the 1600volt capacitor - the one under the neck of the CRT thinking it would be OK.

Got 2 issues to resolve before powering up this TV:

1- Can a pair of 75 ohm resistors be substituted for the Globar Resistors?
2- Need to replace the 1700 ohm power Focus resistor topside.

The terminal strips in the HV cage holding the Globars was burned.
I've installed new terminal strips readying installation of resistors.

Now I know what you guys say about these mounting boards under the chassis - they are not fun to work with and they are fragile.

This thing had some crazy wiring. The circuit shows two 150uf Electrolytics in parallel. The mounting was such that one was under the chassis and the other on top of the chassis. I went ahead and moved the top one to the chassis bottom.

I'll recheck everything again before powering up.
Getting anxious to get this TV playing.

Attached are some pictures.



Carl

75 ohm 10W wirewound resistors will work fine. That's what I used in mine.

Doug

Hey thanks Doug.
BTW, can you supply the URL to your restoration thread?

Thanks

Carl

Carl, Try that for my thread.
Doug viewtopic.php?f=3&t=182182ug

Doug, thanks for the thread url.
I read through it.
Did you find a replacement peaking coil?
I think I'll ohm out all the coils before applying power.

Where did you purchase your 75 ohm wire wound 10w resistors?
Like to find a place I can order these fast.

Carl

Carl,

I can't remember whereI got those resistors. I just checked Just Radios, and the closest they have are 68 and 82 ohm. Maybe I used 82 ohm instead. Ebay lists 75ohm @10W but these sellers are in Hong Kong, and you know how long that will take. I checked my stash of 10W resistors, and all I have is one 82 ohm, and I could make another 77 ohm by putting a 47 ohm and a 30 ohm in series.

You live in NC, and I live in GA. I'll send you those 3 resitors for you to use for the time being until you can locate the correct 75 ohm if you are interested. As far as the peeking coil, I used one I had in my juink box, and it worked fine.
Doug

You would have to ask the engineers, but that might be quite difficult now. One possibility is that they were having a high failure rate on the electrolytics due to the high ripple current running through them. Using two capacitors in parallel will cut the current in half for each of them. I suspect that you could have used a single 300 uf cap in place of the two 150 uf caps and a single 120 uf cap in place of the two 60 uf caps. Especially now that you can buy capacitors rated for high ripple current and low ESR (Equivalent Series Resistance).

Both DigiKey and Mouser ship quickly and offer several types of shipping. Overnight if you want it. If I remember correctly, DigiKey can ship by first class mail if the weight is low enough. First class mail to my location takes two days.