Hi, I have a Heathkit TT-1 tube tester that works quite well except that when I test some EL34's the meter jumps up as soon as I switch to the test position. I have seen a couple references to the TT-1 "oscillating" with these types of tubes--is this the symptom? Also, is there a fix? thanks much,
John

Don't know about a fix. But this sight has the service information to download free for your model

http://www.vintage-radio.info/heathkit/

I must be misunderstanding what you mean by the meter "jumping up" when you put the switch in TEST.

The filament should heat up when you go to ON, right? Then, when you go to TEST, the meter should immediately pop up to whatever the tube's cathode emission is.
Doug

:I must be misunderstanding what you mean by the meter "jumping up" when you put the switch in TEST.
:
:The filament should heat up when you go to ON, right? Then, when you go to TEST, the meter should immediately pop up to whatever the tube's cathode emission is.
:Doug

Sorry I wasn't clear. On this tester, you rotate a switch to test for shorts and then are in the "test" position. After that, there is another switch that is activated to test for Gm and yet another that tests grid current problems. Normally, the meter does not move until the Gm switch is activated. Does that help clarify? thanks,
John

OK, I was screwed up. I was thinking of the Heath TC-1, which is a simple emissions tester. I'm unfamiliar with the TT-1. Sorry.
Doug

:
:Sorry I wasn't clear. On this tester, you rotate a switch to test for shorts and then are in the "test" position. After that, there is another switch that is activated to test for Gm and yet another that tests grid current problems. Normally, the meter does not move until the Gm switch is activated. Does that help clarify? thanks,
:John

Oscillation seems likely. To stop it, you may have to make a socket adapter with series resistors in the plate, screen and control grid leads. I'd try 10 ohms in the plate and 100 ohms in the two grids.

:Oscillation seems likely. To stop it, you may have to make a socket adapter with series resistors in the plate, screen and control grid leads. I'd try 10 ohms in the plate and 100 ohms in the two grids.

Very interesting. I assume the idea is to reduce the voltage on those connections? Do you think this was a design flaw in the TT-1 or deterioration with age? If it works, should I consider modifying the tester, or is it best just to use this change when the problem arises? I sure appreciate the help, John

I don't think you could permanently modify the tester - there are mucho combinations of the plate, screen, and control grid pin assignments.

I think that's why Alan suggested making a socket adapter. Buy an octal tube socket and get an octal tube base (dud tube with the with the glass busted off). Then wire between the base pins and the socket pins, sticking in the resitors in the appropriate lines for your specific tube.

Some old TRFs had such series resistors in the control grid ckt - called grid stoppers (they are to stop oscillation).
Doug

::Oscillation seems likely. To stop it, you may have to make a socket adapter with series resistors in the plate, screen and control grid leads. I'd try 10 ohms in the plate and 100 ohms in the two grids.
:
:Very interesting. I assume the idea is to reduce the voltage on those connections? Do you think this was a design flaw in the TT-1 or deterioration with age? If it works, should I consider modifying the tester, or is it best just to use this change when the problem arises? I sure appreciate the help, John

The tube is probably oscillating at hundreds of MHz, from the connecting wires acting as tuned circuits. The sereies resistors prevent the tube from "seeing" the wires. You can't modify the tester since other tubes will need direct connections to the pins.

Most recent testers use ferrite beads on the wires, acting as RF chokes. For whatever reason, Heath chose to use R-C networks. You could use beads too, but I don't know offhand where to get them or how to specify them. Resistors were a common fix for amplifiers or for series-regulated power supplies which often used banks of power tubes in parallel.

Thanks much guys, great info. I'll give it a whirl and let you know how it works. John

:The tube is probably oscillating at hundreds of MHz, from the connecting wires acting as tuned circuits. The sereies resistors prevent the tube from "seeing" the wires. You can't modify the tester since other tubes will need direct connections to the pins.
:
:Most recent testers use ferrite beads on the wires, acting as RF chokes. For whatever reason, Heath chose to use R-C networks. You could use beads too, but I don't know offhand where to get them or how to specify them. Resistors were a common fix for amplifiers or for series-regulated power supplies which often used banks of power tubes in parallel.

:Thanks much guys, great info. I'll give it a whirl and let you know how it works. John
:
::The tube is probably oscillating at hundreds of MHz, from the connecting wires acting as tuned circuits. The sereies resistors prevent the tube from "seeing" the wires. You can't modify the tester since other tubes will need direct connections to the pins.
::
::Most recent testers use ferrite beads on the wires, acting as RF chokes. For whatever reason, Heath chose to use R-C networks. You could use beads too, but I don't know offhand where to get them or how to specify them. Resistors were a common fix for amplifiers or for series-regulated power supplies which often used banks of power tubes in parallel.

OK, I finally got this thing built, and it seems to work like a charm--thanks so much guys. I also learned a lot from this. be cool, John

:Thanks much guys, great info. I'll give it a whirl and let you know how it works. John
:
::The tube is probably oscillating at hundreds of MHz, from the connecting wires acting as tuned circuits. The sereies resistors prevent the tube from "seeing" the wires. You can't modify the tester since other tubes will need direct connections to the pins.
::
::Most recent testers use ferrite beads on the wires, acting as RF chokes. For whatever reason, Heath chose to use R-C networks. You could use beads too, but I don't know offhand where to get them or how to specify them. Resistors were a common fix for amplifiers or for series-regulated power supplies which often used banks of power tubes in parallel.