Hi everyone,
My 575 curve tracer’s DC balance on front panel won’t calibrate properly. I am following the calibration procedures in the manual. The dot won’t center, with the pot range switch at the end of its range. It is within 1 graticule though. Also, changing the vertical or horizontal sensitivity causes the dot to shift around a bit.
I noticed the DC pots had been changed from the 10k value for my serial no. to 100k. I got the 10k figure from the parts list in the manual. I am assuming that parts list includes all serial no’s.
My serial is a later one, and has the 122C modification. My serial is 012947.
The scope makes nice looking curves and works well.
Thanks for any help here.
Jack

Not sure if this problem is on the vertical or horizontal amp, but the trouble-shooting should be similar.
First, the balance pot: on early s/n's this was 5k, changed to 10k on s/n 6630 up . 100k will reduce the DC's on the screen grids.
Most likely candiate for imbalance is the 12AU6 valves, so you could try swapping over the relevant pair and see if the imbalance is similar but in the opposite direction. Ditto with the following 6AU6 tubes.
If it's not the valves, there are a host of resistor pairs to check: you're looking for symmetry across the two halves of the differential amps - the DC voltages measured with the balance (and differential) pots centred should provide a clue.
John