Adding Ferrite Beads to TV-7B/U Tube Tester (to stop oscillations)

[Garry777]

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.

 

[arts]

You can just install them on every pin, that way the damping will be effective regardless of tube type being tested. This will cause no problems whatsoever. Also, you only need to do one socket, as the effect will carry over to the other sockets in the unit.

 

[arts]

These are the ones I use. They're big enough to pass 18 gauge wire, but small enough to fit 7 & 9 pin sockets without interference. Order extras; you'll be dropping lots of them

https://www.digikey.com/en/products/detail/fair-rite-products-corp/2643000501/8593902

 

[Garry777]

You can just install them on every pin, that way the damping will be effective regardless of tube type being tested. This will cause no problems whatsoever. Also, you only need to do one socket, as the effect will carry over to the other sockets in the unit.

Thanks for the info.

These are the ones I use. They're big enough to pass 18 gauge wire, but small enough to fit 7 & 9 pin sockets without interference. Order extras; you'll be dropping lots of them

https://www.digikey.com/en/products/detail/fair-rite-products-corp/2643000501/8593902

Thanks for the info.

 

[Retrovert]

Ferrite beads are great tools to effectively and inexpensively remove VHF/UHF frequencies.

An additional option to remove the lower-frequency RF oscillation — typically in the AM band up to where the bead kicks in — is the addition of grid and screen stopper resistors. Both form RC circuits with the tube's Miller capacitance, and thereby ruin the Q of the circuit in the AM band and upwards. This is one of the ways that high-gain front-ends have the AM radio signals removed. I would expect, given the mountains of wiring underneath the chassis, that antennas abound.

I had not considered the potential for oscillation in my testers and never even looked for it. Now, the problem has become obvious! Must make modifications! Excellent question by @Garry777 and excellent pointer to beads from @arts.

What's funny is that whenever a tube is intentionally used as the heart of an oscillator minor issues in construction will damp or otherwise confound the oscillation, yet when oscillation is undesirable the tube happily sings all day long. This is a great mystery. I believe the Illuminati is involved.