Does anyone have knowledge about adding ferrite bead(s) to a TV-7B/U Tube Tester circuit to stop oscillation in a tube being tested. I'm having problems with an old 6L6GB tube that goes into oscillation when tested on my TV-7B/U tube tester. I know that a ferrite bead is used on a wire going to the 8-pin test socket (I just cant remember the pin #). Thanks for all replies.

It probably doesn't matter. I'd select the plate or control grid first.

Some testers use ferrite beads on every lead, to every socket. More's better. If you have the beads, and the time, I'd add them to at least the sockets you use most. I'm not sure if the later TV7's had them or not, but many of the non military Hickoks do.

My TV-7D/U has them everywhere. I think that’s exclusive to the “D/U� version.

Peace,
DrRick

Curious about the observed symptoms when it goes into oscillation. What happens?

FWIW, my Hickok 6000A has ferrite beads on all the socket island leads at the mating plug.

I have always wondered: Which ferrite beads? Or does it matter?

John

I added beads to the 7, 9, and octal tube sockets on a TV-7A. Testing 6DJ8/6922 tubes on the TV-7A was almost impossible without them. Even getting your hand close to that tube would cause the meter to jump upscale during testing.

In this case, it probably makes little difference which bead you use. You are trying to suppress high frequency oscillations in a circuit where everything else is at relatively very low frequency. Nothing critical here.... other than the fact that they have to fit in there mechanically

The easy way to do it is to just make a socket adapter with a resistor, typically 4.7k to 10k in series with the g1 grid. You could also place a 47R resistor in series with the anode, or both. This will kill the parasitic oscillations, better than the ferrite beads.

Have you checked the 2700pF capacitor , designed to suppress HF oscillations, in the anode circuit of the tester ?