From: Mike Monett
X-Mailer: Mozilla 2.02 (Win16; I)
Subject: Re: Prof Searle's 100MHz 30dB 1968-era 3-trannie amplifier
References: <3E2358BE.email@example.com> <3E2A0C89.7FAB@sneakemail.com> <3E2A4E8D.78BE@sneakemail.com> <3E2A868D.1D0E@sneakemail.com> <3E2AE81D.73AC@sneakemail.com>
Date: Sun, 19 Jan 2003 16:02:35 -0500
NNTP-Posting-Date: Sun, 19 Jan 2003 16:02:00 EST
Organization: Bell Sympatico
Jim Thompson wrote:
> The fourth transistor is a follower, and the feedback loop from that
> emitter is a *DC* loop. The AC loop is the same as Searle's; Searle's
> DC loop is different... mine sets Vo = Vcc/2.
> Searle's design uses discrete transistors, one of the hottest devices
> available, fT = 8GHz (were MMBRC941's available in Searle's day? ...I
> think not... there were 914's, but I don't remember 941's), mine uses
> a very early I/C process with 25.4um x 48.1um emitters, fT = 750MHz
> Searle's circuit uses 42mA, mine 12.5mA.
> ...Jim Thompson
Win was concerned that I used Prof. Searle's name as a title for the html
file, probably to avoid confusion like this. I used the title only to
identify the thread, and we only suspect this configuration is the one he
used. We don't know for sure.
The MMBR941's were not available in those days. They are in a SOT-23
package that didn't appear until later. I only used it since the 2N2222
didn't perform well, and I had the MMBR941 model already loaded so I
didn't have to hunt for ones like the 2N2369 or 2N918.
Usually the MMBR series is a t0-18 or t0-92 converted to the SOT package,
but the 2N941 appears to be a PNP according to an entry at
If this entry is correct, the 2N941 was not the forerunner of the MMBR941
and could not have been used in this circuit.
The SPICE version shown on my web site is only an initial stab to get a
feeling for the bias conditions. We have no idea of the actual supply
voltage or current drain of Prof. Searle's circuit.