Wednesday, March 15, 2017

PARC meeting picture, progress and not on the TV 3 tube tester


Here is a picture of the meeting we had at PARC with some of the original researchers who built parts of the Alto.


I removed the meter from the tester chassis, opened it up and was delighted to find that the series wirewound resistor was open! As long as the movement itself works, I only have to install a substitute resistor to repair this.

Cover off, next to remove faceplate
Shunt wirewound resistor in series with movement

Resistor is an open circuit!
The meter movement moves fine on its own, restricting the repair to a replacement for this. It was helpfully marked on the face with its precision resistance - 1,640 ohms - which is the value I must shoot for in a substitute.

Anchor electronics parts list
If I combine the 1.6K resistor, accurate to .05% in series with the 40.2 ohm resistor accurate to .1%, the target resistance is 1,640.2 with a max deviation of about 0.84 ohms. The higher value resistor can have a value between 1599.2 and 1600.8 ohms, while the smaller resistor will be somewhere from 40.1598 to 40.2402. I will buy several of each and cherry pick the best combination, both on the low side, to get closest to 1640 exactly.

While I am going there, I cataloged the capacitors that must be changed to finish the restoration. One challenge is that I can't locate one of the capacitors shown in the manual I downloaded. It has clear pictures of where it should be, but the location is somewhat different and there is absolutely no capacitor there.

The manual I found was from 1949, for the TV-3/U while my unit is a TV-3A/U from 1950 or 1951. I bit the bullet and ordered a manual reprint from ebay which should arrive on Saturday. It may be that one of the three capacitors I ordered do not even exist in this unit, but I have visually verified two of them.

Parts in hand, I began soldering the replacement components on the tester. Somehow, while preparing to solder the series precision resistors into the meter, I managed to pop the movement off its bearings. I suspect this is now totally broken, by a stupid mistake, when it was almost salvaged.

The capacitors went on, anyway, so that when I either repair or more likely spend a fortune to replace the meter, the tester will then work. Building the solid state rectifier tube replacement now.

No comments:

Post a Comment