Don Buska d.buska at ADVANTEST.COM
Fri May 4 12:08:04 EDT 2001

On Fri, 4 May 2001 06:45:46 -0700, H. W. Petersen wrote:

>When did National stop installing round transformer cans in the HRO and
>use rectangular ones?
>Pete Petersen

Hi Pete,

Per an article by Charles Fisher in an old AWA Journal on dating the early HRO's the
round IF cans were replaced to rectanglar with the P-series (first letter of serial
number begins with the letter P) which were made during Aug 1936 through Feb 1937.  So
it appears the round cans disappeared in late summer 1936.  Production started with
the D series in Jan 1935 and the hole series of HRO5's went to well after WWII with
the HRO5TA1 up to around 1947/48.  Then it was replaced by the more modern looking


Don N9OO

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