motorola vt71 ts4j 3rd if issue- it wont light
 

Tried the tube it is not at fault. I don't think its the ground. Every tube inside lights but this one and there's no signal because of this. Any ideas? Thanks

Did you check for continuity between the tube pin sockets on top of chassis, and the solder tabs below chassis? On a wafer type socket the connection can become broken between the two wafers. Other than that, it could be a real dirty or damaged contact.

It's a series strung set so the only way it's possible is if the filament pins are shorted together. Check for continuity between pins 3 and 4 on the socket.

So if pin 3 & 4 are shorter that is the problem? If you pull the tube everything stays lit so it is making the series still work so must be something odd. Its not a wafer socket but one of those light brown or tan plastic type sockets.

Do you have a schematic for it?

Yes, pins 3 and 4 are the filament. They must be shorted otherwise the other tubes could not be lit up with that tube pulled out.

The schematic shows 5000pf heater bypass caps in the IF strip. Check for a shorted cap. Also, one of the tubes in the same string may have an H-K short.
The tubes are in a series-parallel arrangement. :scratch2:

I have a schematic and will have to check the pins. I think the 5000pf cap is a disc.

I could say if you pull the 2nd if tube some go out butnot after this 3rd if. You have pull a tube after the 3rd if to get the others to go out.

I made a mistake on the disc caps. 250pf.
There has to be a fault on tube socket between pins 3&4. Maybe a solder splash or????. :sigh:

Sorry, I completely spaced out that it's a series heater string. But that's a weird thing you have going on there.

So the tube that don't light up, did you try another one and did it light up on the tester if you tested it?

I tried another tube and even switched it with the second if and no lighting. When I can will check the pins and socket.

Pin 3 and 4 have no continuity so I checked pin resistance and pin 4 has none. I looked at the wiring and it looks like a resistor was changed. Here's something v4 going to v5 the tube that wont light v4 connects to pin 3 of v5 but v5 goes to v6 from the same pin 3. Shouldn't pin 4 of v5 be going to v6?

Is a ts-18 8 inch Motorola similar so I could compare the wiring?

According to Sams, yes, pin 4 of V5 goes to pin 3 of V6 via a choke.

TS-18 is pretty darn similar but don't know if the tube wiring in that area is 100% the same.

I see a resistor not a choke. I guess someone wired it wrong bypassing it and this would explain why the tube wont light.

IIRC I think that resistor is a 1 ohm between sockets. The ts18 versus the 4d or 4j are different, I would stick with a print of that chassis not others. But they are very similar .

Looking at my schematic of a TS-4J, pin 4 of V4 goes to pin 4 of V5, connectd between those two is R-F-C L-46, a choke. Also on pin 4 of V4 is a 250mmf to ground. Does V-16 (6AL5) light?

The chokes look a lot like resistors. Here's a photo of one of mine you can use for reference. It's hi-res and you can zoom in for a closer look: https://flic.kr/p/f3QtaC

Here I've circled a couple of the chokes.
https://farm2.staticflickr.com/1501/...9140d209b7.jpg

Ah ha thanks for the pic. One of those chokes Has a resistor on it like it was added and looking at this pic I can see it was wired wrong explaing wht it wont light. When I hook it right I will expect the house to light up lol. Ok I will update what happens for real.

Thanks now the tube lights and there is a signal withe usual minor touch ups to make the buzz go away etc. I'd like to report that the house lit up too but it didn't.

The manufacturer may have decided that resistors were cheaper than coils, and it being a series string they probably had excess string voltage to burn off. The resistors were probably chosen to act like decoupling coils (resistance = coil reactance at the IF frequency) to avoid unwanted feedback in the IF strip. They'd then reduce the ohms of the dropping resistor between the high side of the powerline to the top tube of the heater string.

This resistor looks like someone added it to the one choke so I checked the choke and its not open. .... also removing the resistor might increase the signal but wont know for sure till I do more....... I don't know how or why the choke was wired wrong but without that tube lighting there would be no signal.