[R-390] R390 B+ Expected Tolerance

[Jacques Fortin]

Hello Barry,

When you mention "new paper caps" did you really mean paper-in-oil caps ?
I do not trust any paper cap for a long time, except the sealed ones
(Sprague Vitamin Q, for ex.)
All "real", not vacuum sealed PIO caps develops leakage with time.
Better to use Mylar (polyethylene) or polypropylene ones, especially for
C608.

There are other causes that can make the output a little low in this
circuit:
R623 can be of an higher value than the tolerance range.
One of the two voltage divider resistors R616 and R617 can be out of their
tolerance range, or both.
V607 can have a higher transconductance than the "mean" value.
The sum of the voltage drops of V608 and V609 should be 170V: if it is
lower, the output of the regulator will be lower as well.

Just curious: what is the brand of the 5651 you have there ?
They vary by few volts from one maker to the other and when they age also
(they tend to go up when they age).

If nothing wrong can be found in the resistor values and you are still
unhappy with the 175V (which is not a bad result at all, IMHO), try to lower
the value of R626.
A 100K resistor bridged across the actual R626 should raise the output by
few volts...
Adjust value in consequence of the measured result.

Last comment: the HUM BAL. adjustment can "move" the output voltage also.
Be sure to adjust for minimum AC voltage at the test point J601.

73, Jacques, VE2JFE in Montreal