On Sat, 08 Oct 2011 08:07:32 +0100, N_Cook wrote:

Bill wrote in message
...
On 10/7/2011 12:36 AM, N_Cook wrote:
wrote in message
...
On 10/6/2011 10:46 AM, Dave Heil wrote:
On 10/5/2011 15 35, Jeffrey Angus wrote:
On 10/5/2011 10:16 AM, N_Cook wrote:
No etching of this material. Plain board , punched to take
eyelets
and
then
wires or component leads fed through the eyelet and soldered.
Very dark grey
almost black , well 40-50 years on it is

I believe what you're referring to is called "fish paper". A
heavy, stiff grey/black cardboard.

Phenolic was between orange and brown, considerably stiffer and
would crack if bent. Commonly used at the time for those tag
strips. Having rows of turret terminals down both sides.

A lot of "That turned out to be a bad idea" techniques were
attempted in the late '50s through the early '70s to eliminate
point to point chassis wiring.

Not all items, and especially "consumer" items were designed with
the idea "This should last forever". That as many items built as
far back as the '20s are still serviceable is more by accident and
over engineering that by conscience design.

It is indeed fish paper and a really heavy version of it. I've seen
a number of amps where it has held up well. I'd guess these were
stored not in garages or basements but in interior rooms or
closets.

will a penetrating epoxy poured onto it fix the problem? it
would
at
least prevent/block moisture.


It requires some knowledge of the failure mode first, which so far in
this
thread has not been explored. Because of its microphonic behaviour I
suspect
some sort of capacitance efffect. Hinted at by it only seems
necessary
to
separate the "active" board and the backing insulation "grounded"
board
to
stop the rustle and microphony. More permanent fix by securing some
rigid
paxolin FRPB between the 2 boards. I suspect something in the core of
the
material goes conductive enough to create a capacitor surface around
high
voltage points.



my guess about the penetrating epoxy is that it would turn the stuff
into a sort of instant FRP

But any conductive pathway in the core would remain unaffected

Bake in 250 degree oven for 2 hours first, allow to cool naturally, then
seal.