Hallicrafters T-54

[cork]

This should be a work-in-progress report on the rhab. of a T-54. So far replaced about 5 lbs of capcitors--all the film cap's, the CRT and a 6J6. This is the early T-54 with 12SN7s, and 6SH7 IFs. RF and IF allingment went OK. But the resolution is just barely 200 lines both horiz and vert. It kind of hints that the CRT resolution isn't that hot. Both horiz and vert lineartiy were terrible to start with. I added some RC + diode ckts to both the horiz and vert sweep ckts. As the pix shows vert lin is good now, but horiz needs a bit more compensation. As it was built this set has no lineartity adjustments; its poor little 12SN7s are driven to saturation just to fill the screen with the HV set to where it is supposed to be. So linearty suffered. This set has no horiz.AFC, just direct sync injection into the horiz MV. And there is no horizontal stab. L-C circuit (ringing coil). So things are a little wild with the horiz swp; its prone to line jitter and tearing. Another problem I can't get on top of is faint hum bars at 60Hz. This is a hot chasis half wave power supply.
The 150V supply has a filter choke; the -150V is RC filtered as is the 270V supply. No amount of additional filtering makes any difference in the hum bar problem. It's not mag. interference from the filter choke or some other device. Shielding the CRT makes no diff. I even tried pure regulated DC on the heater string, and still no improvemt.
Anyhow, this old timer has been an education for me. Its designers sure didn't have things sorted out totally. It was a long way from a 630, which was about the same time, but more money.