[sdiy] Fwd: [funwithtubes] Vacuum Tube Multitasking - The Erla Superflex

cheater cheater cheater00social at gmail.com
Fri May 21 19:45:10 CEST 2021

I seem to remember a filter design where the audio and the CV were in
the same signal, and the CV was very large compared to the audio,
essentially a bias, that set the cut-off. Was that the Moog filter

I wonder if this is where the inspiration for such a filter came from.


---------- Forwarded message ---------
From: Mark <mark.erdle at gmail.com>
Date: Fri, May 21, 2021 at 2:14 PM
Subject: [funwithtubes] Vacuum Tube Multitasking - The Erla Superflex
To: <main at funwithtubes.groups.io>

In the early 1920s vacuum tubes and the circuitry to operate them were
expensive items, so there was a great incentive to get the most bang
for the buck out of each tube. As early as 1915, engineers realized
that it was possible to have a single triode vacuum tube amplify audio
and radio frequency signals at the same time. One of the more
successful reflex radio kits was the Erla Superflex of 1924/25, but
with the price of vacuum tubes dropping after an RCA patent expired,
the reflex design became obsolete by mid 1925 and the TRF and
superheterodyne took over the radio market.

Robert Lozier takes a look at an Erla Superflex in this video:

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