[Penthode]

Success on the weekend! I have a reasonably good picture on my CTC-5 and it is running well. I have roughly set up purity and static convergence: I haven't touched the dynamic convergence just yet. Pictures to follow.

The third video IF was intermittent and I ended removing the tube socket because of the pin connections. I slightly bent the socket pins and re-installed the socket with virtually no damage to the copper trace: a good solder sucker is indespensible. The alignment of the third stage was affected. I plan to go through and test the complete RF/IF alignment shortly. In the meantime I simply touched up the last IF coil.

The 12BY7 developed control grid current after running a few minutes. That was the only bad tube in the set. (All the tubes looked original although the 12BY7 video amplifer had possibly been changed before: the rest of the RCA tubes read made in USA and the RCA 12BY7 read made in Canada.

I was beginning to investigate the alignment a couple of weeks ago when the RF Output lead of my HP8601A slipped off and hit the 5U4 rectifier socket while the set was on. Needless to say, it blew up the output hybrid amplifier of the generator. Fortunately, I recalled an article in which Matthew D'Asaro reverse engineered the HP hybrid and is offering them for sale. I purchased one and once it arrives I trust I will have my alignment equipment back in the running.

Lastly, after examining the video off the CRT with the contrast control modification, I am beginning to have second thoughts about keeping it. I notice with the contrast control advanced, the black level varies with picture CONTENT. At low contrast, it doesn't appear that bad. I believe it may be due to the bypass capacitance loses the DC level. I will look at this more and may consider modifying the contrast circuit back to original.

It is interesting that the interaction of brightness and contrast control adjustment is removed with the modification at the expense of superior DC coupling. I'd be curious to hear from others with similar thoughts or alternative arguements.