From: META000 <META@UNB.CA>
Subject: RE: Built your own amp?
Organization: The University of New Brunswick
Date: Thu, 12 Nov 1992 21:51:45 GMT

In article <1992Nov8.144635.25201@mnemosyne.cs.du.edu> cpeckham@nyx.cs.du.edu (Chris Peckham) writes:
>Anyone out there made their own amp?  Do you use it?
>Have you copied the circuit diagram of a 'classic'
>old tube amp and managed to recreate the sound you
>were expecting?
>
>Reissue tube amps are typically more expensive than
>comparable solid state amps.  The parts cost more,
>and maybe you're paying for the 'concept',  as if you
>were buying the real thing.  Maybe you're paying
>for something I can't think of, too.  Is it viable
>to copy the electronics?  Would this cut the cost?
>
>What are your thoughts on building your own tube amp?
>
>Someone thinking of having a go
>Chris
>.
>.
While I haven't built any (tube) amps from scratch, I've rebuilt one
or two,and gazed at schematics from hundreds.  In general, tube amps
are fairly simple to build.  Many classic designs consist merely of
three to five tubes (unless you want multiple channels, vibrato,
etc), and accompanying capacitors, resistors and controls.  The HARD
part is getting hold of power and output transformers, and trying to
stay unfried.  A large part of the distinctive sound of a vintage
amp seems to be what kind of plate voltage the power tubes are
seeing (that's the magic in the variac, by increasing the line
voltage from the wall to the power transformer, the transformer, in
turn, sends a higher plate voltage to the tubes), and a glance
through a book of schematics reveals that there is much variation to
be obtained, and much variation demonstrated in tube amp designs.
If one is REALLY interested in getting a vintage sound, rather than
futzing around from scratch, look for a pawn-shop special that has
the basic ingredients, and use what you can glean from schematics to
turn a black horse into thoroughbred.  For instance, virtually any
amp that uses two sections of a 12AX7 pre-amp tube for its' first
two driver stages can probably be reworked with Fender-style EQ
controls.  If the amp uses 12AY7, or 12AU7, or 12AT7 pre-amp tubes
in the front end, you can replace them with a 12AX7 for higher gain
and a more easily overdriven sound.  Many mid-power tube specials
use a pair of 6L6GC power tubes, and these can sometimes be rebiased
(depending on design) so that EL34 ("Marshall" tubes) can be
installed in the same sockets.  Virtually any amp with a pair of 6L6
or EL34 power tubes can also be modified to have a master volume
control.  Lastly, many otherwise sucky amps can come into their own
when matched with a decent set of speakers for a change.  Lest
anyone think that such delights only exist in the mid to high power
realm, I hasten to point out that the 6-watt one power-tube tweed
Princeton I own is one of the most luscious tone machines you'll
ever hear, and a delight of my life.  I am constantly surprised by
how virtually identical it is in design to a myriad of other single
power tube amps produced during the 60's and early 70's, that
appeared to be bargain basement cheapos.  You'dbe surprised at what
often lies under the hood of a Wards-Airline or Silvertone amp!  I
suppose there is a certain satisfaction to building one's own
"vintage" amp from scratch. However, considering the kinds of
"half finished" semi-vintage tube amps there are out there at garage
sales, considering how hard it is to get appropriate transformers,
and considering the sheer weight of planning one of these things out
(remember, if you start from scratch, you won't be able to ear test
it until it's done), my vote goes for the reclaimed mutt rather than
for thegenetically engineered purebred.

Mark Hammer

Xref: sparky alt.guitar:9821 aus.music:1684