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From: kludge@pyr.gatech.EDU (Scott Dorsey)
Newsgroups: rec.audio,sci.electronics
Subject: Re: In defense of solid-state devices
Message-ID: <4128@pyr.gatech.EDU>
Date: Sun, 27-Sep-87 13:47:51 EDT
Article-I.D.: pyr.4128
Posted: Sun Sep 27 13:47:51 1987
Date-Received: Mon, 28-Sep-87 02:05:34 EDT
References: <729@alliant.Alliant.COM> <4124@pyr.gatech.EDU> <1895@ucbcad.berkeley.edu>
Reply-To: kludge@pyr.UUCP (Scott Dorsey)
Organization: Georgia College Of Universal Knowledge
Lines: 63
Xref: mnetor rec.audio:3452 sci.electronics:1436

In article <1895@ucbcad.berkeley.edu> max@eros.UUCP (Max Hauser) writes:
>I question this: the 12AX7's, 12AU7's, 12AT7's, 6L6's etc. that
>are so dear to tubophiles now are not only the same devices used
>in the 1950s and 60s, but in many cases actually were themselves
>built in the 1950s and 60s. Microphonics in particular are a function
>of the tube design.  Perhaps Kludge designs his own tubes;
>if so, he's the first such designer I've met (on the other hand,
>I design my own transistors: it's cheap and pretty easy).

   A 12AX7 that is twenty years old is apt to have a very different
internal structure than one constructed today.  In general, most of the
important parameters are the same, but some things have changed, things 
like support members to prevent microphonics, things like filament-
cathode coupling, etc.  It's true that microphonics are a function of
the tube design, but the fact that two tubes have the same designation
number does not mean that the design is identical, unfortunately.
 
>I would not for a moment question someone's preference for the sound
>of a tube preamp or power amp (even if it is more expensive, less
>reliable, and has an uncertain future as existing VT stocks get burnt
>out, or used by enthusiastic suburban kids as BB-gun targets).
>Also, I am not talking about the relative ease of designing good
>transformer-coupled tube amps and direct-coupled solid-state amps
>(except to note that direct-coupled TUBE amps are also tricky).

   What do you need in a stereo?  You need a good power amp.  A rather
simple thing to design using the 'brute force' approach; use big
output tubes running down near the linear end of their curve, use big
output transformers (and put them in the feedback loop, please), and
some form of relatively quiet driver (BY7 video pentode, AX7, etc.).
That's about it.  But to design a transistor amp, you need a lot of rather
sneaky tricks to keep waveform symmetry, try and soup up the slew rate,
and a lot of time is going to have to be spent to make it sound really
good.
   You also need a preamp.  Okay, I admit it, I use Analog Devices chips
for the high-gain input stuff.  They're pretty low noise, easy to work
with, and cheap.  And they are certainly easier to deal with for a high
gain application than tubes are.  But the equalization stuff and the
tone control stuff is all tube, for the same reasons described under the
power amp section.
   You also probably need a signal source.  I've got a tube tape deck,
because I couldn't afford a newer one.  It's pretty clean, and the amount
of amplifier noise is independant of the signal level (which is not true
with transistors, frustratingly).  But there's an integrated dbx box
attached, and an all-IC CD player next to it.
   It's not hard to build a spectacular direct-coupled, resistively-
coupled, capacitively-coupled, etc. tube amp.  Look in the RCA Receiving
tube Handbook.  It requires a lot less tinkering than even the RCA people
claim.  The only transformers in my stereo are in the output of the
power amp and in the power supplies.

>However, the broad statement that "transistor amplifiers are harder
>to design than tube amplifiers," unless qualified in the sense of
>"harder *for me*," is naive and not supported by hard facts.

   If this is true, why are there so few good transistor power amps
out there?  Why are there so few good transistor preamps out there?
Why isn't there any good tuner of any sort out there?
-- 
Scott Dorsey   Kaptain_Kludge
SnailMail: ICS Programming Lab, Georgia Tech, Box 36681, Atlanta, Georgia 30332
Internet:  kludge@pyr.gatech.edu
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