Re: Alan Dower Blumlein "garter" circuits now in triode mode EL34 P-P amp



John Byrns wrote:

In article <1g20f416fo3ak20ct5tk245lus39cfl7th@xxxxxxx>,
flipper <flipper@xxxxxxxx> wrote:

On Fri, 10 Oct 2008 19:43:02 -0500, John Byrns <byrnsj@xxxxxxxxxxxxx>
wrote:

In article <antse415gmbhqcpl3lm01v6av0baoed4sb@xxxxxxx>,
flipper <flipper@xxxxxxxx> wrote:

On Thu, 09 Oct 2008 08:17:24 -0500, John Byrns <byrnsj@xxxxxxxxxxxxx>
wrote:

In article
<dc9475d9-2f75-4b5a-a1f5-21efa88c7bd6@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
tubegarden <tubegarden@xxxxxxx> wrote:

Hi RATs!

Took me three and a half years to try eight resistors and four
capacitors :)

Doesn't meet the KISS principle, why use "eight resistors and four
capacitors"
when only one resistor and one capacitor will do the job?

The first task is, or should be, to define 'the job' and if current
balance is a part of it then the "one resistor and one capacitor"
doesn't do it.

Al's definition of the job seems to be first preventing "current imbalance
in
the output transformer", because it "gobbles bandwidth and sensativity", and
secondly insuring that "it sounds wonderful". Presumably Al's point is that
if
"current imbalance in the output transformer gobbles bandwidth" then it
won't
sound so wonderful. While that seems reasonable, I'm not sure how gobbling
"sensativity", what ever that is, will keep an amplifier from sounding
wonderful?

My requirements for the job are a little different than Al's. I start with
the
same requirement that the amplifier sound wonderful, however I don't feel
that
current balance in the output transformer is a necessary condition for an
amplifier to sound wonderful, so I don't make current balance a requirement
of
the job. Secondly for numerous reasons I prefer simplicity, so I don't like
solutions that take extra parts to implement, KISS.

Presumably the problem with current imbalance in the output transformer is
that
it can cause the transformer to saturate under some conditions, producing
distortion and restricting the power capability at low frequencies. An
alternate approach to the problem of current imbalance in the output
transformer
is to use a simple circuit and deal with the current imbalance by over
specifying the output transformer so that saturation won't occur with a
reasonably balanced pair of output tubes. While this approach may cost a
bit
more, it is only a hobby, and is harmonious with Al's maxim that "a penny
saved
is a world lost".

I don't know why you think using a hundred words for 10 'improves'
anything.

You don't care about balance, fine. He does so it is simply not true
that "one resistor and one capacitor will do the job" he set out to
do.

I also don't see why you feel the need to do nothing but denigrate
what he clearly finds to be an improvement to his amp.

Exactly how did I "denigrate what he clearly finds to be an improvement to his
amp"? What I said was that I preferred a simpler solution to the problem, I
didn't say his approach wasn't an improvement, what I said was it was too
complex for my taste. Read the thread again, if there was any denigration going
on it was Al's response to my first post where I indicated my preference for a
KISS solution.

But speaking of denigrating people, what is it with you today? First you attack
poor old Patrick, and now you are after me, clearly you are having some sort of
mood problem today.

But then I suppose I shouldn't expect anything less from someone who hides
behind a fishy alias, and is afraid to allow his posts to be archived.

--
Regards,

John Byrns

I would not worry about our fiesty fish amoung us. He ain't a shark. He
asks some pithy questions and makes some contentious comments, but I
believe he's actually fairly good natured most of the time. We all learn
from good natured argy bargy. But you have me right, I'm poor, and I'm
old, well, damn well not 30 anymore, but I do get over 500 hits a day at
my website and somebody finds it interesting. Maybe its not the best
tube audio site but together with others we make up a wealth of info on
how-to-do issues on the Internet, and its all completely free of charge.

Is the Garter better than two plain old R&C bias parts per tube in a
substantially class A PP amp? I don't see it being much better. But if
it is, then the betterment is marginal, and will only cost 1 extra
resistor per tube, for the two series R for each Rk. The only other
bother is that the total value of the two bias Rk must be twice what
you'd normally have with just two sets of separate R&C. The grid voltage
is determined by the voltage half way down the total Rk. So if you have
a circuit for class AB1 KT66 with Ea = 365V, and 30V of grid bias
voltage across 470ohms, then Rk total will have to be 940 ohms, and the
Ek will be +60Vdc, Eg1 = +30Vdc. The doubling of the total value of the
Rk definitely will improve natural idle current NFB regulation of Ia by
Rk. But you'll dissipate an extra 1.9W per cathode resistance but that's
not too much a price to pay. I didn't consider this aspect before. But
Ek rise due to class AB charge up currents in OP tubes
will be worse, but then if you also used my bias stabilizing circuit
with a power transistor and about 3 x R for each OP tube then you'd
control the Ek rise with class AB abd keep the circuit balanced at the
same time. Maybe this is the best, I don't know the full answer, because
so many ways can be thought of for achieving an outcome.

Patrick Turner.



Surf my web pages at, http://fmamradios.com/
.

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