Sencore CR70

[tvcollector]

I'm noticing with my Sencore CR70, When I was testing a color roundie tube that after a few times shutting off and setting and turning back on to test each gun, I'm not able to get the filament voltage to 6.3, it goes to about 5.5 with the variable setting all the way up... Seems like after it's been on for a while the big load of the tube puts a toll on the tester.. Even switch to 8 volts it's goes up a bit into the 6volt range... If I take take the tube off the tester I'm able to get the range.. I'm guessing there are some bad caps or maybe some resistors in the Sencore.. I don't have a schematic for this thing If I were to look into it...

I'm able to test the the tube at 5.5 volts but it not going up to 6.3 volts.. I sure I'm not getting the full results..

[kvflyer]

Let me throw this out. I have two of these guys and they are quite different "under the hood". I think there is an early and a later model. One may have DC on the filament and the other may have AC? I am going from memory here since one of mine is in FL and the other one is in MD.

If yours is supposed to put out DC, there "May" be a problem with that circuitry. An old capacitor or bad diode. I don't think they used selenium rectifiers.

Hopefully, this will trigger some more information for you...

[tvcollector]

Thanks for the info.. I ended up buying the service info and all that on a data cd off Ebay.. It's got the updated settings chart, and all the schematics...

[kvflyer]

Originally Posted by tvcollector

Thanks for the info.. I ended up buying the service info and all that on a data cd off Ebay.. It's got the updated settings chart, and all the schematics...

Did your service data indicate that there were two versions of the CR70 (with no different model number)? Glad you got the updated list of settings. I know that one of my CR70s has for instance a listing for the 7JP4; the other one does not.

I will admit that I took my first one apart two times because I thought there was a problem with the filament supply. It turned out to be my misunderstanding of the instructions (known as a stupidity attack) when using the universal adapter. Both of them work now (actually, always did!) Please keep the thread going and let us know what you found. Happy Hunting!

[6GH8cowboy]

This is a DC regulated fillament supply.
In this case the fillament regulator transistor was bad (under load). I am of the opinion that this is a most over engineered fillament supply. Both voltage and current! There is absolutly no reason for it. Once the CRT is pluged up and lit, the load is constant. What ever the final setting is to manualy bring the fillament voltage back to spec. that's where it stays. No fancy regulation nesessary. AC mains wont change that drastic while your testing in even the worst part of the world.
This had to be some kind of marketing thing.

Oh yea, the instructions say to set the switches first. That's because misconfiguration can present itself as a short on the fillament line if misconfigured.

Set the switches first, check the settings again... turn it on.

[bandersen]

Keep in mind that in the auto/manual restore modes the current through the filament is increased in a controlled manner.