Fred Nachbaur wrote:



Tom Schlangen wrote:

Hi Robert,


Did a little simulating in Circuitmaker.
Using a remote cutoff pentode like
a 6AR11 (compactron with a pair of identical
pentodes) as an emitter follower



You surely mean _cathode_ follower ;-)


looks to give good compression of the level
signal. [...]



Thank you very much, this suggestion is interesting
to me since it would provide real signal dynamics
compression (not only limiting).

But I must admit that I can't find said compactron
(and suitable socket) for a reasonable price over
here in Germany.

Are there any alternatives with more "common" tube
types and sockets? I understand that one single double
triode for _both_ channels can't emulate two
remote cutoff pentodes ... but a real compressor
function is appaling, if it could be done easily with
few usual/common parts. No need for audio quality
compression, it is only an optical feature.

Tom


For your "meter compressor" you don't really need two channels. Just
sample the sum of both channels, unless you listen to a lot of music
with everything in one channel you'll be alright. ;-)

As for common tubes - look for the tubes used in IF stages of AM
radios. These will almost always be remote cutoff, allowing gain to be
varied with DC control voltage (AVC). Here the most common is 6BA6
(and 12BA6), I don't know what the equivalent is in Euro radios.

Thought a pair of eye tubes were desired..... At least I'd want a
pair. Anyway, the
remote cutoff tubes need not be pentodes, a 6ES8/ECC189 variable mu
triode would do.
Heard that someone with a large supply of 6ES8s relabeled them as 6DJ8s
and sold
them as such..... If you happen to have a "6DJ8" that sounds
terrible, it might be
one of these.

Equivalents to a 6BA6 look to be: 5749, 6660, EF93, CV454, 6F31, CV2026,
CV5037, PM04, W727. Shouldn't be too hard to find a pair of these. Also
remote cutoff pentodes intended for TV sets should be easy to find. 6BZ6,
EF183, 6GM6, etc.