Quote:
Originally Posted by John Folsom
Here is an interesting Philco tidbit. Philco made this kit to convert your 48-2500 projection set to a code 125 model. This is a 1X2 based tripler HV power supply sub assembly. I assume it is intended to replace the older 1B3 based tripler.
In addition to installation instructions, they have a sheet of service tips. Of interest is the suggestion that the DC restored tube be removed. This improves the focus performance in changes from light to dark scenes. They state the improvement in focus will more than offset the disadvantages of not having DC restoration
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Very interesting! The aspect of my 48-2500 that I find most disappointing is that the picture doesn't stay in focus between light and dark scenes. Mine is so bad that I don't really consider it tolerable. Interesting that Philco acknowledged that this was a problem.
When I received my set, the HV supply had been removed and replaced with a homebrew RF HV supply on a separate chassis. I never understood exactly why, and since the homebrew HV supply had developed its own problems, I removed it and rebuilt the original circuit using parts from another 48-2500 chassis with 1X2s. It works, but the focus problem is severe, and the cause appears to me to be due to sag in the HV with scene brightness (perhaps made worse by using a triode CRT) affecting the focus.
Perhaps the reason it had a homebrew HV supply was because a previous owner found HV sag to be the problem, and built a better HV supply.
Sometime in the near future I'll try the removal of the DC restoration tube. On the other hand, I'm not eager to live without DC restoration, so I'll be interested in whether there is some other fix. I've wondered if it would make sense to try to build a 6BK4 shunt regulator like that used in early color sets to solve the problem?
First, I'll wait to see if Eric's set shows less of this focus problem than I am seeing. There may be problems with mine beyond what these sets typically show.
09-09-2010, 05:12 PM
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