[R-390] B+ current

[John Wendler]

Roger,

I understand your point about way too much science and from a "do it and
move on" point, you are absolutely correct.  This is a proven tolerant
design with an approved field mod.  From a reliability standpoint, however,
I would rather take the heat in some cheap, hyper-margin (25 W is about as
cheap as 7.5 W) power resistors by the supply than elevate the temperature
of the older stuff? (Your mileage may vary, and from a practical point, it
may only be a few degrees difference spread out over the rest)

I have not been getting enough circuit design activity at work recently, so
it will come out in the darndest places.  I learn a ton by modeling and
reverse engineering something.  If I can get several independent pieces of
data to correlate, then I have reason to believe that I am approaching some
measure of truth.

The voltage concern comes from reading the Pearls - there is an emphasis on
the 115 VAC vs. 120 VAC and using a variac to reduce the modern voltage.  I
was lucky that the filter killer cap was not leaky; it was the first thing
I replaced.

The series regulator idea was suggested by someone else in an off-list
e-mail to me.  The voltage limiting aspect was something that I picked up
from a white paper on Dr. Schmid's website.  I think he was selling solid
state replacements for the rectifier tubes at one point.  (
http://www.schmid-mainz.de/26Z5W.pdf) As you note, a regulator would help
reduce ripple; I do not have enough of my radio up and running to know if
hum is an issue, or what my major sources might be.

BTW, did you do the checklists?  I printed those things out in a flash and
they are part of what is guiding me in my restoration.  I am writing the
manufacturer and serial number of each module on the relevant checklist as
I hit them.  I also write restoration notes, and may yet stick photos on
the back. (I have been taking  before and after pictures as I have been
going along, but I am not sure of the best way to share them with the
group.  They are running between 3 and 4 MB each.)

Thanks to the several people who have sent me the diagram from the Y2K
manual too, that has been very helpful!

TNX & 73,

John