"jh"

Hi Mr Philosopher,

it's very remarkable that you don't recognise one of the most polite
answers Phil.A ever made.

Let me assure you - his statement's correct, yours' not so...

There also were KT88 Marshalls, although they are a completely different
story. IIRC the indeed evolved from generic Mullard or the GEC designs.
But - the bread and butter Marshall began 1962 with the 5881/6L6/KT66
equipped JTM45 - an almost 100% copy of the 5F6-A - and they (Ken Bran)
have publicly admitted that they were clearly aware of that fact. The
evolvement to the usage of pentodes (EL34s) was mainly driven by
economical reasons. The similarities to the mullard designs may come from
the fact, that there ain't so many possibilities to connect a pentode or a
beam power tetrode to a circuit - and - the 5F6-A was also based on a
common available basical circuit (from WE or RCA IIRC).

The preamp of the marshall *was* the same as a 5F6-A and the future
evolvement was only incorporated by the addition/alteration of some
components to fit the sonic tastes of the upcoming rock musicians (cathode
Cs, mixer Rs, bypass Cs, different B+ filtering etc). Even the MV
Marshalls just rewired the existing preamp circuit to a cascaded design.
OK some Rs and Cs were added but that was all. Up to the generic JCM800
the circuit still clearly showed it's origins.


** The ECC83 phase splitter with 100k/82k plate loads and the use of 220k
bias feeds to the EL34's grids are standard across nearly all Marshalls,
plus the cause of problems with bias runaway. The direct coupled
ECC83cathode follower driving the tone stack is also a common feature across
nearly all models too, as is the presence control in the NFB path.

All come direct from the Fender 5F6-A schematic.

Fender wisely improved their basic design as time went by - ie changing to a
12AT7 phase splitter and 68k output tube bias feeds.

But Marshall never got the hint, even to this day.



...... Phil