Jackson 648-S tube tester died

[electra225]

This was my stepdad's old tube tester from when he had his TV repair shop. I was testing a tube then the filament went out. When I turn the tester on, it will center the meter, but I don't have any filament voltage for tube testing. I didn't find a fuse and the schematic pasted to the cabinet doesn't show one. Anybody have an idea where to look?

[Hi-Fi-Mogul]

Greg,
Here is a nice write up on the Jackson 648 series testers.

Towards the end of a rather exhaustive review of his
tester, he says there is no fuse.

https://tubesound.com/rebuild-calibrati ... kson-648a/

[electra225]

I like your avatar, Mr. Mogul. Thanks for sharing it......

Thank you for the link. That will give me a place to start.

[hermitcrab]

are all the tube filament voltages dead?

[William]

That is a cool Avatar, Mr. Mogul.

Bill

[Hi-Fi-Mogul]

Greg and Bill,

When I saw that "Hi-Fidelity Incorporated" photo,
I knew that's where I wanted a job.

Now, if I can only find that time machine I had
around here....

[William]

When you find that time machine, I would like to borrow it.

Bill

[electra225]

I have no filament test voltage. I have AC up to at least the primary of the filament transformer. The plate and screen voltages work fine, and use a different power transformer. There is a switch "S2" that I can't find. It is called the "filament switch". The only filament switch I see is the round one where you choose which filament voltage you need. This switch is drawn on the schematic as a regular old switch, not a switch with several positions. Hmmmm.

[electra225]

Bummer. The filament transformer is out.

[William]

Another transformer malfunction does that mean a transformer or is there a work around for this problem. I sure hope it is a simple fix.

Bill

[electra225]

Well, now I don't know what to believe. I initially thought the filament transformer primary might be open. Now, I'm not sure about that. It "ohms out" good. The only schematic I have is the one pasted to the bottom inside of the cabinet and it's not the best. According to that schematic, if I read it right, power goes from the line, thru the primary of the filament transformer and the other transformer, then thru the "filament" switch, S2. I have determined that S2 is the "life test" switch. I seem to be getting AC thru the filament transformer primary, but not thru that silly life switch. I am not 100% sure how to troubleshoot that. This thing quit suddenly. No smoke, nothing smells like it's been hot, nothing looks burnt.

[hermitcrab]

The life switch on mine is a momentary slide switch , it places the tube under a load as if it were in a circuit, I wouldn't think that would have anything to do with the Filament voltage, but they made so many variations of the 648 , it could be possible.

[electra225]

I've been putzing with this thing some this afternoon, deciding whether to toss it or not. That S2 switch I was looking for is the "life" switch. It's okay. Something strange is going on. The primaries of both transformers seem to be okay. The multi-position filament voltage switch is a mystery to me, how to troubleshoot it. It seems like the secondaries of both transformers may be where the issue lies. And, since I don't see a rectifier anyplace, I am to assume that all the voltages in this instrument is AC? That doesn't seem right. Maybe I need a schematic better than the one pasted to the bottom of the cabinet. What am I overlooking? The issue has to be something simple.....