[R-390] New Project Follow-up

[Bill Hawkins]

Well, see, the problem is that probability is everywhere. That's
why Murphy achieved immortality. There are people who get around
probability by changing everything - but they don't because there
is a probability that new parts will fail.

There are parts that will cause cascading damage if they fail, like
the blocking cap for the mechanical filters (no problem in the 390).
Reduce the probability of a catastrophe by substituting the probability
of failure of an old part with that of a new part.

Recognize that changing a part, with the heat of a soldering iron,
raises the probability of adjacent parts failing. Usually, the best
thing to do is to not replace a part until it fails. This is eloquently
expressed as, "If it ain't broke, don't fix it."

OTOH, getting at some parts in an R-390 class receiver requires a lot
of work. Deal with it. That's part of the charm of using the peak of
vacuum tube technology. You get to know how your radio works.

I know this doesn't help, but that's life. You can drive yourself up
a wall by demanding certainty.

Regards,
Bill Hawkins


-----Original Message-----
Carole White-Connor said:

Does anyone have a list of frequently troublesome resistors (like
Chuck's list of troublesome caps)?

I ask for a reason. I came across an article where Chuck notes that
R-614, a 560-ohm resistor in the AF section, frequently drifts,
sometimes to 700-800 ohms. Mine tested 1,000 ohms! I changed it out
and it made a tremendous difference in the audio. I'm wondering if
there are other known drifters.