The way I found the socket, the filament went to pins 9 and 12. The regulator plate lead went to pin 9 and jumper went from 9 to 4. The 2nd anode lead went to pin 4, as well as the jumper going to the metal cup.
I, like a fool, removed the jumper and installed the resistor. It looked like the jumper was installed by a tech. Didn't look like factory issue.
Just remove the resistor, install the jumper and wire, per these instructions.

OK, so my thinking was right about it not making sense to connect both ends of the resistor or jumper to internal cathode connections. #4 being an NC (no connection) will just be a tie in as someone else has mentioned. I was just mixed up between 4 and 5 which in my socket are both pulled out and there is just a hole there. Anyway, I will give it a try hopefully this weekend.

Thanks!

[QUOTE=Zenith6S321;3126651]The 25MC30 schematic shows the 1.5K resistor connects to pin 1 and 9 of the 3AT2. The 3AT2 PDF shows that pin 4 is a no connect. So pin 4 could be used as a tie point for connecting the other end of the resistor to the anode lead. The schematic does not show this, so I'm guessing.

Dave

Hi Dave, is there any way that you can post something showing this resistor connected to pins 1 and 9. Reason being is that if it shows it there then both ends are interconnected to the cathode. According to the .pdf on the tube, pins 2, 5, 6, & 9 are the same as pin 1. Now the second anode lead does for sure connect to one end of the resistor, but I dare to ask is it at a no connect as a tie point or is it at 1 and 9. There is a big difference that presents obvious concerns. My lack of completely understanding the circuit may lend to this.

Sorry to keep going back to this, but what I am reading surely makes me wish that I could see a for sure Zenith reference to this.

[QUOTE=Tubejunke;3126823]Here is a picture of the HV area of the Goodman 25MC30 schematic. It does show pins 1 and 9 together going to one end of the resistor. The other end of the resistor could go to pin 4(NC) to anchor the anode lead. Looking at the 3AT2 pdf I thinks that's ok as pins 2 and 9 are the cathode so they are at the same potential and already internally connected to pin 1 (one end of the heater). The other end of the heater is pin 12 which the schematic shows going to through the 2.35 ohm resistance wire to the flyback heater winding. Goodman does credit Zenith with a good portion of the illustrations in his service manual but he does not specifically say that the schematics are from Zenith. Did you take any pictures of the socket before you disassembled as a cross-check of the schematics?

Dave

OK thanks! This diagram drives home the fact that everyone was right but me. I just wanted to see it in black and white as my Sams's schematic only shows the heater connection. Your schematic clearly shows the corona ring being bonded to pin 1 which is the same as pin 9 where that connection is made on mine with one end of the resistor and the plate cap of the regulator. Makes no difference. So the other end along with the second anode lead are at pin 4 of NC just as we all suspected and as DieselJeep has it.

I didn't get a picture because the initial connector pulled out with the tube clean of solder and somehow I had it stuck in my head that it was on pin 4. Duhhh! GeeZ! When I pulled the assembly apart the split resistor, connector and anode lead fell to the bottom of the cage leaving me with two adjacent open holes. In the name of not looking like a complete idiot; at least I suspected that what I had in mind would have caused some major issues and all of this might have been for nothing.

Thanks once again for advice and more helpful information. My 25LC30/U is not going to serve me well in this. I didn't realize that Zenith had that many design changes in only a few years. The set pictured on my folder looks like my set. Maybe next time I will have good news.

I thought I could get the HV cage off without removing or pulling back the chassis as I got all but one screw out. That one screw is mid way deep and close to the cabinet. Can't win em' all, but removal of the cage will make the job much easier than trying to work through the cover.

Is HV actually set to 25kv on these? What is the procedure for setting the efficiency coil?

25Kv is generally where most people seem to set them and many manufacturers recommended. The efficiency coil is used to set the cathode current of the horizontal output tube. You have to place a meter in series with the grounded cathode of the tube. There are a few opinions on the ins and outs of how the meter is set up, but I simply broke the cathode to ground connection and ran two leads out so I could check this current anytime I want. Some people believe in placing a capacitor across the two leads to protect the meter. You may want to look into that, but I didn't worry with it and had good results.

Other than that you operate the set normally and turn the slug slowly and find what is called the "dip" point or the point where the lowest current flows and that's about it. If you are like me, you won't be satisfied with that current as it may still be too high due to some other component causing that condition. I hope this helps. I think you can Google setting the cathode current on a vintage color television" and there is a pretty in depth article on this topic, but it is a bit scattered in nature. If you find it you will see what I mean.

You will not get an accurate current reading without that capacitor. The inductance of the meter will change the tuning of the output circuit, and you will get inaccurate readings.

Try it again with a .47uF cap (any voltage >10 should work). You should get different readings, and they may be lower....

Remember the goal of measuring equipment is to load or disturb the behavior of the circuit under test as little as possible. The meter will have very low DC resistance, but may have higher AC impedance, the cap neutralizes that impedance by giving AC an alternate path to follow.

Here are pictures of the whole schematic, if that helps.

Dave

Thanks Dave! That should help a lot.

Anyway, today I got everything reassembled and powered it up. Nothing bad happened, but nothing good either. No HV and only a blue glow in the top portion of the rectifier. I put it on my B&K tester and it is dead as a doornail like the heater is open.

Not sure where or why that would have happened. So, now I will hunt another 3AT2. A local supplier here has International Servicemaster brand which I don't want to get. If anyone has a supply of these and needs anything of that style base; I have a box of these type tubes which I have no use for including some pretty expensive sweep tubes. Just throwing it out there.

Two birds with the same stone on this one? :beatnik:

http://www.ebay.com/itm/NOS-Zenith-S...p2054897.l4275


Zenith branded for true authenticity, and you no longer need to worry about heater juice. Sounds like a good deal to me. :yes:



(No affiliation with seller.)

Have you ever tried a solid state replacement? My only experience is watching a video by one of our members on YouTube where he tries one and the set absolutely would not operate correctly with that type rectifier in it. He went back to the vacuum tube and all was fine.

I just suspect that the arching that went on in more than one place with my old socket got the best of the tube. Months ago before any of the socket issues developed I put and International Servicemaster in the set and it only lasted a few minutes. The one that I just pulled out and tested bad was used before that and up until the socket issue of late. Hopefully another decent quality tube will take care of things.

For the price including free shipping, I would definitely give it a try if the set was on my workbench. The advantages of the solid-state replacements are: reduced loading on the horizontal output tube and flyback, as there's no filament to heat up, and you can drastically simplify the connections to the socket. Literally all you need is the connection to the anode lead/HV regulator tube coming out the bottom. I'd unhook the filament loop, insulate the ends, and tuck them away in case they're needed in the future.


The voltage withstanding and current handling capability of the S-3AT2 replacement exceeds the specs for the normal 3AT2 (A/B) series.

Send me a PM with your email address and I can send you the full resolution pictures of the schematics. Upload to this site compresses the heck out of them and makes them look really fuzzy. A quick look at http://www.vacuumtubes.net/Prices%200A1%20to%203Z4.htm
shows they sell 3AT2s for $3.00. Other places are probably similar prices. I usually get two of each tube I order to have a spare and in case one is not so good.

Actually, a bad 3AT2 matches the Goodman description of the burnt resistor problem.

Dave

The only time, I used a SS replacement, was when the filiment loop was punctured through and arcing. I cut it short or tried to remove it completely.
Never had any problems. Usually on an RCA or one of the clones.