"The Natural Philosopher"

Phil Allison wrote:

You can use a transformer to adjust power output via taps without
upsetting the impedance

** Very dodgy connecting a matching transformer to any old SS amp. Many
output stages cannot cope with the very low primary resistance and
propensity to core saturation at low frequencies.

Never had any problems with any of my designs attaching 100V transformers
to em.

** ROTFL - so ****ing what ?


LF response is pre tail;rerd to get rid of serious 'rumble' on most amps
anyway

** Saturation may easily well ocurr at 50Hz or higher.

You have no clue - do you ?

and SOAR protection mens teh worst that can happen is serious distortion
if you end up wit DC bias..

** You have even less than no clue.

FYI:

A great many hi-fi amps have no or useless SOA limiting and a mere switch on
thump will cause instant output stage destruction if a transformer is
connected to the output.


- but resistive pads are not good for bass units.


** Perfectly OK for the purpose of an extension speaker.


No not perfectly good. Acceptable. Barely.

** Yawnnnnnnnnnnn...

You a professional bull**** artist or what ?


The good old Vox A30 amplifier has an output impedance of some 80 ohms.
Driving an 8ohm pair of loudspeakers, the effects are dramatic.

** The speakers in an AC30 are series connected, giving a nominal 16
ohms.
At bass resonance, that will rise to about 60 ohms - so the amp's output
will rise by 4 times giving a 12dB peak at about 75Hz.


Are they? Been too long..but your figures are as I recall from tests in
terms of ferquency and gain..

** I overestimated the boost, with 80 ohms driving 60 ohms max boost is more
like 8dB.


Lotsa valve guitar amps use PP output pentodes with little or no NFB,
just
like the AC30.

Actually you would be surprised.

** No I wouldn't.

I make my living repairing valve guitar amps - among others.

Since 1973.

They do NOT.


Only the AC 30 (EL84) was in any way seriously high impedance.

** Oh, there are lots of others with impedances in the 50 to 200 ohms range.

All those with pentodes and no feedback.


Most EL34 naps had some feedback - Marshalls come out around 8 ohms and
the US amps (tetrodes) were much more 'hi fi' at less than an ohm.

** Nonsense.

Only one maker of valve "guitar amps" had such low output impedances -
Dynachord.


I concluded that Fender, being an ex radio engineer, designed decent
amplifiers.

** Fender amps vary a lot, but most have output impedances over 4 ohms even
with a 4 ohm nominal load rating.

1950s models ( SE and PP) had no NFB at all.


Whoever did the Vox was a post war penny pinching scoundrel,

** Huh ??

The main reason Vox used no NFB was that being class A, it was simply not
needed to reduce crossover distortion - as was the case with all Fender's
class AB designs.


and Jim Marshall was a carpenter,

** Fact he was a drummer and music shop owner who employed techs to do his
amp building.

They just copied a popular Fender design at first - then stuffed it up.


IN short the British 'valve' sound was entirely due to a serendipitous
coincidence of parsimony and incompetence.

** Describes Marshall to a T.

Swapping Fender's 5881s and 6L6s for EL34s was a master stroke of
incompetence.


Then of course both Jim Marshall and the Vox boys were chasing decibels at
low cost, so both employed ultra lightweight speaker cones that had vile
coloration and zero stiffness. But louder. One imagines Celestion were
glad to unload these at any price.

** ROTFLMAO !!

Celestion made their guitar ( and radio ) speakers to be as efficient as
possible plus suitable for open back enclosures.

Low cone mass and fairly high resonant frequencies are the name of the game,
plus limited VC excursion for safety.

Rest of your tripe snipped.



..... Phil