A hard learned lesson

As per my recent post about the Zenith 6 S 152 I had much difficulty tracking down a intermittent problem. The set would change volume level and AGC level at random intervals and momentarily grounding the adjusting screw on the SW trimmer would bring it back to normal, sometimes for several hours. Well it turns out I had four intermittent 6A8's and one intermittent 6K7. NOS 6A8 and a 6K7 from a known good set did the trick. Tried each of the 6A8's again one at a time and the problem came back, then tried each one in another set and the problem occurred in that set too. The odds of having four tubes that tested great but all had the same problem are pretty long but it did happen. The grid caps on these tubes were nice and tight but I re-soldered them anyway and will test them again sometime in the future. Regards, Ed.

Thanks. I'll keep that in mind when I return to tv rebuilding.

What brand's and types of 6K7, 6A8?? Were these glass style G or GT or metal tubes?

Tung-Sol, Crosley, Ken-Rad. All tubes were G envelope.

Good fine Ed, those are the toughest of problems. Often time my scope comes into use for something like that. It is nice to view what is going on where. Great job.
Jerry