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From: malte@techfak.uni-bielefeld.de (Malte Uhl)
Subject: Re: The use of Phase Splitters (12AX7s)
Date: Tue, 17 Aug 1993 15:17:52 GMT

: transformer.  I believe that older (pre-1940s) amps often used transformer
: coupling between stages and I guess this may have included phase reversal
: for pushpull output stages.  Given that my moving coil stepup device is a
: transformer and it produces little distortion without any feedback, I would
: expect that transformer coupling could be used sucessfully.  I would also
: like to hear peoples' thoughts on this.

: Peter Campbell (peterca@ento.csiro.au)
: C/O Div. Entomology, C.S.I.R.O.
: Box 1700 Canberra A.C.T. 2601    Ph.61-6-2464158 (w), 61-6-2516213 (h)
: Australia                           61-6-2464173 (fax)

High quality transformers like the ones used in studios for microphone adaptors
are much more expensive than another tube stage, even today.
And because they have to be shielded against electromagnetic influences,
they are quite heavy, too.

However, before 1940 engineers had to use transformers because there weren't
any tubes (triodes) with enough amplification. Pentodes had come up just a few
years earlier, e.g. in 1936 the EL12, a 7 Watts power pentode. Pentodes like
EL34, EL84, EF86 and their american equivalents are inventions of the early
1950's. The american 6L6, a child of the '30s, was known for its bad audio
quality because of its metal container.

Transformers were used in (some) guitar amplifiers, too. But their
frequency response was intenionally anything but flat.

Malte