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There is supposed to be one of the Mesa guitar amps that uses 12 power
output tubes in some sort of push-pull parallel - parallel manner. I'd
like to look at the schematic, just to see how it's wired. Most or all
guitar amps have online schematics, but there are 50 or more models made
by Mesa, so I dont know which model to look at.

Does anyone know which model this is?

I'd also be interested in URLs for any other amps that use more than 4
power tubes.... I did find a poorly made drawing of a Fender 400, which
has 6 tubes. The schematic is hard to view though.

I've always wondered if there was any limit on the number of tubes that
could be paralleled to gain huge power wattage outputs. (Of course I
know the size, weight and cost of the output transformer sets limits).

Thanks

[Peter Wieck]

http://www.mesaboogie.com/support/ou.../bass-400.html


This one.

Keep in mind that guitar amps are not audio amps - any more so than a Hummers are Ferraris.

Peter Wieck
Melrose Park, PA

[Big Bad Bob]

On 02/21/17 05:16, Peter Wieck so wittily quipped:
http://www.mesaboogie.com/support/ou.../bass-400.html


This one.

Keep in mind that guitar amps are not audio amps - any more so than a Hummers are Ferraris.

ack - they're designed specifically for guitar or bass, including
capacitor values and transformer characteristics, and often add their
own "color" to the sound that's unique. You might call that a form of
'distortion'.

Additionally, guitar amps are typically designed to overload with
predictable characteristics. The phase splitter of a guitar amplifier
will often be designed so that it clips a certain way in the output
stage long before the splitter overloads, and has reasonably even
distortion pattern across a wide band of overload conditions. there may
also be too little negative feedback for an audiofile's ear to be pleased.

In short, the amplifier becomes "part of the instrument" in determing
the sound and quality.

but hey, us guitar players knew that, heh. It's why so many prefer
tubes, because they have "that sound" as opposed to a transistorized
amplifier that overloads, well, like a transistorized amplifier.


There's a certain behavior you get when a "Cathodyne" phase splitter
overloads, which differs from a 'long tail pair'. It's almost a
frequency doubling effect in the Cathodyne when it goes into overload.
You can prevent this (somewhat) with a series resistor of sufficiently
high value in series with the grid, since it's apparently due to grid
volts cathode (causing grid current).

Or you can use the 'long tail pair' which seems to be the preferred
method in a lot of guitar amps.

http://www.300guitars.com/articles/a...hase-inverter/

Older hifi circuits seem to use the 'cathodyne' because a) they're not
expected to overload, b) it uses one less triode than 'long tail pair',
and c) it's well suited to using a 12AU7 for preamp + phase inverter to
drive a pair of 6L6's (or similar) directly, coupled with NFB, and fed
directly by the volume control knob.

(pre-amps leading up to that would use 12AX7's as needed for tone
controls, phonograph, etc.).

In any case, the guitar amp's phase inverter circuit makes a difference
in how it overloads, at what point it overloads, and how it recovers
from transient overloading. All of that changes the sound considerably.

So yeah. I expect a lot of people already know this, but I'm saying
anyway, just because.


--
your story is so touching, but it sounds just like a lie
"Straighten up and fly right"