New Project - RCA 8PT

[compucat]

Originally Posted by maxhifi

Noticed a new 'defect', or possibly characteristic. When contrast is cranked up, text can get fuzzy. Plate voltage on video amp is off spec, quite a bit too high. Since contrast control works by varying bias on 6aw8 pentode video amplifier, and current is too low, i'm guessing either tube is bad or resistors have drifted. This design doesn't appear to have a lot of headroom built in.... Effect not terrible, it just means one has to balance contrast with sharpness. Will work on this one once new flyback installed. In the mean time have been using this as my only tv... Works great... Wonder how long until i start to dream in black and white?

When I turn the contrast all the way up on mine it almost looks like overloaded agc. I think what you are seeing is just a characteristic of the design and not a defect. The picture and fine tuning controls need to be adjusted for the best overall performance which on a set like this is invariably a compromise. I expect this was typical of 1950s sets. The one thing these little RCA sets would have benefited from is an aluminized tube.

[maxhifi]

Originally Posted by compucat

When I turn the contrast all the way up on mine it almost looks like overloaded agc. I think what you are seeing is just a characteristic of the design and not a defect. The picture and fine tuning controls need to be adjusted for the best overall performance which on a set like this is invariably a compromise. I expect this was typical of 1950s sets. The one thing these little RCA sets would have benefited from is an aluminized tube.

I agree completely, just for the sake of improved contrast. If attached advertising (radio & tv news, July 1954) is credible, it would have been a pretty big improvement. I wonder if any aluminized replacement CRTs were made for this set.