I didn't realize that Tom. I've been going thru my junk box of tubes looking at all the 9 pin tubes trying to find a 6J6. A lot of things are weird on this set. I've seen 4 instances of two resistors in parallel on it. However that was mentioned in the Sama saying "Some models use paralel resistors in various application to obtain desired value." In each case, it's noted in the resistor section of the Sams. I'll investigate this Sams more closely and see if I can find something about a prodection change. Thanks for letting me know.

Doug

I'm making SOME progress. After checking all the tubes and replacing one, I fired it up again and got weak audio coming thru but with a stong buzz. I first looked at tuber. This set uses coils that have to be excanded & contracted for adjustment, but there is one trimmer. I adjusted the trimmer and got it a little better, but I ened up unscrewing it too far and had a time getting the screw back in.

I looked in my 1956 edition of Sams "TV Servicing Guide" under both sync & intercarrier buzz. One symptom it listed is a bad filter cap in the ratio det. I have that circut in my set using a 6AL5 det with a 10mfd @ 50V coming off pin 7. I had replaced that earlier and thought I had put it in right. Looking at my Sams schematic, it has the pos going to straight ground, and the neg going to pin 7. I hooked it up the normal was with pos going to pin 7. Do you think my Sams is misprinted, or have any of you heard of a filer cap being installed reverse in this type of circut. I don't want to reverse it without some clarification 1st.

Doug

I need someone to answer a question about my filter choke. Until last night, I could power up the set and get excellent sound even though I had no usable CRT. Last night, my 5U4 tube burnt up. Thinking the tube was bad, I borrowed one out of another set, and it burnt up as well. This time I heard a hiss and saw wax leaking from the filter choke. The Sams lists is at 55 ohm @ 1 Henry. I found a new one at a parts place rated at 56 ohms at 1.5 Henry. Will that work.

Thought I had a lead on a CRT on Ebay, but I've been outbid upto $110. I don't want to put any more than that into a CRT not knowing the condition of the other major components: yoke, vert output trans, ect. Oh well, maybe another one will come along.

Doug

I would think that Filter Choke would work as long as the Filter Choke
can handle the current draw.
I wonder if you have something shorting causing this?

BTW, what CRT are you looking for?

Carl

Thanks Carl, I'll see about ordering the choke.

On the CRT, I need a 16KP4 or equivalent. The Sams list 16RP4, 16GP4, and 16TP4. Actually, if I could just even get hold of a test CRT like a 5AX4, I would be satisfied for the time being so I could know what I'm facing as far as video restoration in this set.

Doug

Carl, as far as the current on the choke. The new one is tared for 200ma. The Sams rates the old one at .150A

Doug

When you get your new one, I'd put an amp meter in series to see if
you have a short that is drawing a lot of current. If it exceeds 150ma,
I'd quickly remove power and take a detailed look see.

Carl

Doug, I went to the ETV and there were some 5AXP4 and 8XP4 CRTs there for not that much. Wished I had known, I would have gotten one for you. There was also a number of other CRTs.

Carl

Maybe I'll post an ad in the Classified for a 5AX4 and see if I get any responce.

Doug

I'm back on this set again for a few days while I wait for my next project (Dumont RA392) to arrive by mail. The last time I tried a power up, the 5U4 burnt up. I grabbed another 5U4 from anonther set, and it burnt up too, and I saw wax bubbling from filter choke L1. This choke comes off the 410V line and feeds the 400V line, C2A(45mfd) and horiz centering control.

The centering control, a 30ohm wirewound pot, had sparked previously, and I had just subbed a reg 25ohm pot while I looked for a replacemt. I've gotten a correct 30ohm wirewound pot and am ready to install it. I have a replacement choke coming tomorrow.

However, I checked my old choke with the ohmmeter, and it reads 55 ohm like it should. That worries me that something else may be bad. I see in mbear2k's thread about his Crosley, he checked the power transformer resistances against his Sams. I've got the Sams with resistances measurements and tried checking the resistances on the 5U4 socket with no tube installed (one lead in socket and other to ground) and couldn't get a reading. Am I doing this right? How is the best way to check a power transformer like this? Does the 5U4 need to be in or out while making these checks? This transformer has the 5U4 mounted in the transformer case.
Thanks
Doug

Transformer question:

My filter choke came in today. I installed it and decided to do a slow redcued power up. I started out on 40V then increased it to about 50 after 20 min. I could see the filaments of the larger tubes starting to glow, then I smalled something burning. The new 5U4 tube was so hot, that I couldn't touch the glass. I then pulled the plug. Can I now assume that my power transformer is shot. Would it be safe to pull the 5U4 and try another reuded power up to do some voltage checks on the transformer?

Doug

sounds like a short in the B+, check the current at the input to the choke and do a slow ramp up, the schematic should say what the current should be. The fact that the 5u4 is over heating would make me think the PT is fine. with everything unplugged check the resistance of the B+ rail, should be 10k to 15k after the filter caps charges up from the VOM.

Thanks Dave, Will do that. I'm hoping that PT is fine. If not, this set may be parted out. After all I have no working CRT for it, and the cabinet has no venere and is going to cost a good deal to revenere and refinnish. A bad PT may seal this set's fate.
I've got my new Dumont on the bench now, but I'll check those resistances tomorrow and post back what I find.

Doug

You have a short on your B+ line. It could have been a short from the windings to the chassis in the old choke, but that has now been replaced. The short is on the B+ line at the end of the choke farthest away form the power transformer and 5U4. Just to be sure you could disconnect the B+ by disconnecting the choke and then power it up on the variac as you did the last time.

The short could be caused by a bad electrolytic cap or one installed backwards (which is now bad).

Tom, that makes sense. The horiz centering control went bad which was a 30 ohm wriewound pot. Not having one, I used a reg 25 ohm while I ordered the correct one. That control comes directly off choke L1 (the one I replaced) then goes to the next filter choke L2. When I got the correct control, I noticed I had wired that temp control in wrong. I'll bet that caused an electrolytic to short. I'll get out my checker and check all the electrolytics tomorrow. Thanks for the tip.

Doug

Ok, I'm back working on this again and have the same problem. I have replaced C1A (45mmf) and C2A (45mmf) and the choke L1 that is in between the two. With the 5U4 pulled, I powered it up on the variac and got it up to a full 110V with the tubes glowing. I put in the 5U4 and started another power reduced power up. By 50V AC, the 5U4 was already getting warm, and I was not reading any B+ on my 410V or 400V line. I pulled the plug before I ruined another 5U4.

Should I just disconnect everything coming of the 5U4 (filters, chokes, horiz centering coil) and start hooing think up one by one til I find a short?

Doug

what is the resistance at the filament of the 5U4 to the ground (assuming chassis ground it B-). This is what the 5U4 sees and should be between 10k to 15k (just a guess) AFTER the filter caps charge up. the resistance will be lower but should quickly drop to that 10-15k range. If not then you have a short somewhere. No need to keep powering it up until you find that.

IF you find its shorted, then disconnect the B+ at the last filter cap, so the power supply is only seeing the 5U4, filter cap/choke/filter cap.

Check it again and see if the resistance rises to 10-15k with that. If it does then you have cleared the likely suspects (bad filter caps). Now the fun begins, you will need to triple check the B+ wires to all the tube sockets, looking for solder blobs, pushed up wires in contact with things they should not be, and then decoupler caps on screens and also check caps on audio transformer primary.

A close visual inspection here is key. I had a shorted disc cap that was taking out my B+ on a color tv set. I should have seen it, looked like it had been shot with a BB.

Anyway you will need to start disconnecting various B+ connection to circuits to find it. Don't forget pass thru type caps like those used on tuners.

Dave, the filmaents on 5U4 are pin 8 and pin 2. Both pin 8 & 2 come off the 5V winding of the power transformer. It is a chasis ground. Do I check between pin 8 and ground or between pin 2 and ground, and I assume the 5U4 is to be removed while making this test.

Doug

leave the 5U4 in (it should not matter as the filament windings connects the two, one of the pins goes the the 1st filter cap), power off, read the resistance from either pin 2 or 8 and chassis ground. Resistance will read low at 1st prob in the hundreds of ohms, the quickly rise to the thousands. the filament of the 5u4 is the cathode this is where the B+ is taken off as a full wave rectifier (the B- is the center tap of the secondary HV section of the power transformer) from there it gets filtered to get the ripple out by the caps and choke.

Note on some sets the B- is NOT the chassis ground, the RCA I am working on is like that, the B+ and B- are connected to a voltage divider with the center attached to the chassis. This provide a easy way to get neg bias voltages as required. You can be pretty sure of a neg chassis ground if you see un insulated filter caps. If all the filter caps are floating then its likely the B- is NOT the chassis. Need to replace the paper covers on those if the can stays attached to the circuit to avoid a nasty shock hazard. Doubler low voltage supply circuits generally have a single floating can as well but will have a grounded filter cap.