Predicta 17" HV question

[DaveWM]

yep that would get messy oh well maybe someday somebody will find a micro connector that is no larger than the wire itself. Too bad, it would be nice to be able to easily separate the pcb for easy access.

[Phil Nelson]

Well, the Molex female terminals are about as small as anything can get and still allow you to solder onto it. A few of the board's WW pins would be easy, since the old leads have enough slack to simply attach a Molex terminal on the end. A number of leads are tight and would need lengthening. There are at least three WW pins with two wires attached.

Meanwhile, the new K7 couplate works fine, but the height is still deficient.



The 400V boost voltage measures 400V on the money. On the 6DR7 vertical tube, the voltage at the oscillator grid is low (-.03V rather than -3.5V) and the plate is somewhat high (155V rather than 115V).

As with the horizontal section, caps & resistors around that tube have already been replaced, which leaves couplates K4 and K5, I guess.

Phil Nelson

[Phil Nelson]

I've been puttering around with the height problem, still seeking a solution. Height is 1/3 of the screen at most, and linearity is poor.

I wonder if the vertical output transformer could be funky?

I have subbed known-good 6DR7 vertical tubes, replaced the K4 and K5 vertical couplates, checked or replaced Rs and Cs around that tube. The pots for hold, height, and linearity are working and have the right resistance. The 400V boost voltage is normal. Here's a piece of the Sams schematic:



Voltages are close except that pin 7 (grid) is only -0.5 volts rather than -3.5. Resistance of the vertical windings on the yoke looks normal.

On the vertical output transformer, the secondary measures 2.6 ohms (expected 2.5) but the primary measures 410 ohms where it should be 425 (or 430 in the Philco schematic).

Could a few shorted turns in the output transformer account for the lack of height? I feel like I've eliminated just about everything else. This problem existed before I did any restoration.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html