"Edward Knobloch" wrote in message
news:n6gvk.335$1a2.107@trnddc04...
Hi, Gang

If you enter the terms "hp-200 Hewlett thesis" in to
Google search,
one of the results is Google Books, which has some of Jim
Williams'
book "Analog Circuit Design". Chapter 7 of the book is an
appreciation
of the HP-200, and an attempt to better its distortion
performance
using modern parts. It's a fascinating chapter, giving a
glimpse
of how an expert designer thinks. Also fascinating are
excerpts
from Bill Hewlett's 1939 Stanford thesis about the
original design.

73,
Ed Knobloch

Bill Hewlett's original patent on the Wein bridge
oscillator is USP 2583649. It can be found on either the
patent office site at http://www.uspto.gov or on Google
patents. Google has the advantage that one can download a
PDF directly. There is likely also additional stuff on the
Hewlett-Packard Memory Project site at: HP Memory Project
I don't think they have the Stanford thesis there but I
have downloaded the IRE paper somewhere, probably Google
could help find that too.
The performance of late versions of the well known -hp-
200CD could be made much better than the specs by careful
choice of tubes and lamps. The lamps especially have a
significant effect on the distortion. Stock lamps were aged.
I now forget the exact method but it seems to me that it
involved running the lamp at red heat for a few minutes and
reducing temperature slowly. This probably relieved strains
in the filiment. In any case I was often able to get the
distortion down to perhaps a quarter of the spec. For very
special applications where very low distortion is required
one can reduce the feedback level. This will cut down the
distortion but also makes the oscillator have amplitude
instablility so there is a limit. I seem to remember an ap
note covering this but its been forty years since I worked
for -hp-.
Of course, the company developed solid state versions
of the oscillator with better distortion and stability
characteristics than the vacuum tube versions. These all are
still very servicable instruments.
Note that there were many changes made from the first
to the last production and the later versions are
significantly better than the early ones. The same is true
of the 400D/H voltmeter. The early ones should be avoided
except as collector's items, they barely met specs to begin
with and were completely redesigned. Late ones will meet
half specs.


--
--
Richard Knoppow
Los Angeles, CA, USA