Roundie left edge purple

[DaveWM]

FIXED, AND i AM AN IDIOT


after consulting with some folks over at fun with tubes, I check the line voltage AT THE CHASSIS, turns out it was low, I still had the set on the variac and thought I had 117v at the chassis, wrong, voltage drop across the line/switch must have been doing me in.

The orig problem of under scan was prob fixed when I replaced the osc driver tube, as this improved the scan width, but by then I had the set on the variac.

[DaveWM]

added some "active cooling" as a precaution on the fly, will monitor its effect on overall temps.

[DaveWM]

Not so fast. the concern for the hot fly had me recheck the HOT grid voltage, should be -60 was -40

I scoped it, 120v pp correct waveform, but should be 190vpp

checked the osc tube all forms and PP looks good on that tube.

on the osc tube a 6BL8 screen volts look good cathode voltage looks good so short of a bad tube I cant see why the wave form would be down (but I will try subbing some tubes to see the effect anyway).

[DaveWM]

I am going to check the wave shap network cap, its a 680pf tube precision cap, comes off a resistor that is at the plate of the osc tube. If leaky I assume it could drag down the output.

I subed some other tubes (all test good on my hickok 533) for the horz osc, best I could get was 140pp. Low drive would sure explain the hot flyback and the fact that I have to turn the horz out bias all the way down to get the cathode current in check.

I have a local tube guy I may go to his place and check a bunch of nos 6BL8's and pick the strongest he can find (if the 680pf is ok).

[DaveWM]

hmmm lifted one leg of the horz wave form shaper network, very leaky and would not even open the eye of the cap tester at all. going to remove it completely and check again. This could be the answer i hope.

[DaveWM]

oh well once I got it completly out it was fine. turns out having the oscope attached to the TV was causing the bad cap reading with one leg lifted.

I recheck my oscop calibration, my grid drive to the horz osc tube is low 100v should be 170v so I will be looking into the feed back loop on that next.