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So that's what I propose, change high resistors if very off
or attached to changed capacitors, or if it is in a voltage divider or
timing circuit. This leaves out lots of resistors in the
RF-IF and heater chains.
But I noticed a bizarre circuit twist. The HV supply supplies
the CRT anode. That sucks some current. There is a voltage
divider chain that provides the DC voltage bias
for the deflection plates, which presumably take no DC current,
and the focus, which likely doesn't either. The focus control wiper
is bypassed to ground. But the divider chain continues on
to lower voltage .. but not ground. It terminates (for DC) in
the plate of the first vertical sweep output tube! The
total resistor chain is about 9 megs.
If the first vertical amp tube were to lose transconductance
a lot, the plate voltage would drift up to about 2 kV! I do
of course note that the plate resistors in the deflection circuits
are all in the megohm range, as this is electrostatic deflection
which should draw no current. Its not high power like in magnetic
deflection/flyback HV generation sets.
What would happen to a 12SN7 with 2 kV on the plate?
(And to its socket?)
Also ... if the bypass on the focus put wiper is too low the
huge vertical sweep AC voltage will get onto the focus
electrode. The plate resistor (for AC) of the sweep tube
is about 3 megohm, depending on the focus control setting.
Do people agree that this is bizarre? Why did they not simply
add a resistor to ground?
Doug McDonald
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