Updated 8-23-2009

August 2009 Column
Same 'Old Radio's, same 'Old Stories', same 'Old Place', only the name has changed .


Vintage Ham Scopes

Gold's Home Brew Scope

K2TQN's Multiphase MM2

WK9Q's National CRM

KB8TAD's National CRM

Heath HO-10

National CRO

Vintage Ham Scopes

Prior to 1935 hams relied on station
monitors or used their receivers to check
the quality of their phone signals.1 Unfortunately,
not every station sounded good
and a better method was needed. ARRL
encouraged hams to clean up their signals
and from the mid 1930s The ARRL Handbooks
provided schematics, so hams could
build a basic oscilloscope for phone station
use. At about the same time the National
Radio Company offered the CRO, a 3 inch
model of similar design. At $29.50 plus
the cost of the 3 inch 906 cathode ray tube
(CRT) tube and one #80 tube, this was
considerably more than the weekly wages
of the average ham.

But before the CRM could be developed,
it was RCA that designed and built
the new 913 tube that made it all possible
and then they reduced the cost to $5 each
(see Figures 1 and 2). National quickly
designed a new scope around that tube.
The CRM (see Figures 3 and 4) would sell
for $11.10 plus tubes. It was much more
affordable than their larger 3 inch CRO.
Thus, with the CRM, National made it
possible for most amateurs to improve their
AM phone signal.

John Dilks, K2TQN    125 Warf Road, Egg Harbor Township, NJ 08234-8501   e-mail: K2TQN@arrl.net