[Penthode]

This evening I found the problem. It was a pretty obvious fault once I started poking around. A decoupling cap was open. I found the fault when I started moving the leads. The 1000pf capacitor was a chassis mount with the capacitor screwed into the chassis.

I could power the tuner portion on the bench while I took measurements. I have replaced the faulty cap with a silver mica cap and the response now matches the RCA notes. And there was a lot more gain!

It earlier worried me that as I changed the signal level the response shape changed. Now I can wind the input level up and down and the response remains the same!

Below are some photos and you can see from my previous post the response matches the published RCA notes exactly.