[Penthode]

I have repaired/ restored a number of TVs over the years. If the set is more than twenty years old, I make a habit of checking alignment. I generally find that even changing tubes is enough to change the IF alignment noticably.

With practice, IF and RF alignment becomes very straightforward and does not take long to perform. I recently went through the alignment of my RCA 9TC275 in about two hours. And like other aspects of this hobby, it is fun!

The interesting thing is that prior to alignment, the picture and sound on the set was pretty good. However after alignment the picture was noticably better and the audio was louder and clearer. I have attached some snapshots of the RCA's IF response (full IF and the overcoupled transformer between the tuner and 1st IF stage) and the 21.25MHz sound discriminator. The full IF has markers at the adjacent channel video (19.75MHz), sound carrier (21.25MHz), 22.1MHz, 25MHz, video carrier (25.75MHz) and adjacent channel sound (27.25MHz). Note that the KCS29 chassis has two adjacent video, two adjacent sound and two sound traps in the video IF strip.

I particularly like the earlier sets (prior to 1953) because many sets then had four IF stages. The four IF stages were needed to get the four MHz bandwidth. After color was introduced, three or even two stages were the norm which limited bandwidth to 3MHz or less.

My opinion is that in the earlier days, the loss of bandwidth was not too noticable because broadcasters, especially remotely located network affiliates, were hard put trying to provide 4MHz on network programming. However today, with excellent quality DVDs and downconverted HD broadcast, the NTSC quality has never been so consistently good. The early four MHz sets can display the extra quality now to good advantage.