[R-390] Resistor Tolerances

Mon, 29 Jul 2002 08:20:40 -0400

Scott,
no need to be precise on most of the resistor values, the ultimate answer
will be found when you finish your work, align the radio and make some
measurements.

How sensitive the circuit is to the resistor value depends on where the
resistor is in the circuit.
The resistor values  used in B+ decoupling (2.2k), grid input, grid
parasitic suppression, or audio plate are not critical at all.

The values used in the voltage dividers for the screens are a little more
important , and the cathode resistors probably make the most impact as they
set the bias level for the tubes.
(Don't forget that tubes have fairly wide tolerances too and drift over
operating age as well).

If you measured all the resistor values in your radio and you didn't find
anything that was way out or broken then you already made great progress. In
the past when I have done this I've found resistors that were 50% or more
out, or even one that was 10 times out (somebody in depot repair didn't pay
attention to the last color band). 390nonA power supplies are another
matter, there's always crispy critters in there!

73,
John
.
----- Original Message -----
From: scott <[email protected]>
To: <[email protected]>
Sent: Monday, July 29, 2002 7:45 AM
Subject: Re: [R-390] Resistor Tolerances

> Well I never buy NOS resistors and certainly not caps.  Baking resistors
> before measuring
> tolerance is just not the real world, even though most boat anchors do
just
> that.  :-)
> The real question I have is: If the tolerance needs to be held to original
> specs on any specific
> areas of this set.  I am trying to rely on someone's experience to save me
a
> lot of
> needless work now or in the future.........