[Penthode]

I did some more work on the set this past weekend. Thanks to Matthew D'Asaro, I managed to get my HP8601a sweep generator running again. I have had the HP8601a for years and it is a great machine. You may recall the RF Output lead slipped off and hit the 5U4 rectifier while on, when I was in the process of beginning IF alignment. This blew up the Hybrid output amplifier and thanks to Matthew's reverse engineering skill, he duplicated the HP Hybrid amplifier!

The audio IF alignment was slightly off and it has been fixed. The 4.5MHz trap (on the chrominance chassis) was way off: this would have accounted for the bad 920kHz beat. I initially just swept the video IF amplifier to study the response. The response was extended incorrectly to the sound region. I later found the overcoupled transformer between the first and second IF stages was misaligned. The traps and rest of the stages were touched up and it looks fine. I have not examined the tuner nor the chroma chassis alignment just yet.

I decided to "bake" the chassis in the cabinet. This gave me the opportunity to set up the purity and convergence properly for the first time. I had no problem with purity and given time, the convergence ended up pretty good. It was reassuring to find all the convergence controls worked. In the CTC5, I especially like the location of the controls on the front which made it very convenient to simply sit in front of the screen as you make the adjustments.

Despite the 21AXP22 testing excellent, the picture is still pretty dim by modern standards. But I can get an acceptible picture without blooming so long as the room lighting is subdued.

Bothered by the rather poor DC clamping in the video, I tried reverting the contrast control to original: I will open this in a separate thread.