[Patrick Turner]

Andre Jute wrote:

On Jan 2, 10:45 pm, Ian Bell wrote:
Andre Jute wrote:
On Jan 2, 11:46 am, Patrick Turner wrote:

The other thing is that loading the top tube cathode does slightly make
the circuit work as a SRPP, but the effect is minor.

Actually, any circuit which works even partially like an SRPP is a
good circuit, especially if the advantage of the SRPP it mimics is a
low impedance. I'm not always so sure that the mu-follower is truly
worth the additional complication over an SRPP

If you want low distortion then the mu follower is much better than the
SRPP; definitely worth the extra complexity.

for anyone except the

purist who can, as a consolation for the extra expense and
complication, mutter to himself over and over, "Yes, but an SRPP isn't
a real current source and a mu-follower is an exemplary current
source... It's true, it's true!" An SRPP with a single extra resistor
to arrange a voltage lift can in most instances be arranged to work
for practical purposes as well, and probably more reliably, than a mu-
follower.

OK, then show me an SRPP design with a 6SN7 that does significantly
better than 0.4% at 20Vrms out into 10K at 2KHz.



Okay, I don't want to sound like a cost accountant, but someone must
be realistic.

Indeed, and if you want to save a few pennies at the expense of a whole
lot of distortion then SRPP is the way to go.

Quite a bit of other good stuff, some of it at least arguable on
grounds of taste, some of it indubitably right, snipped in the
interest of bandwidth.

LOL

Cheers

Ian

Andre Jute
The tubes tend to make people believe in a god, and SS leads them to
the
devil. -- Patrick Turner

You're missing my point, Ian, probably unsurprisingly. You're
interested in pre-amps and therefore need to extract the maximum of
silence as well as a big gain. I use CD and integrated two stage amps
(mostly); I start with 2Vrms of clean signal. Virtually any 6SN7
circuit that is competently built is silent enough for me, though in
fact I use high-mu 417A/5842 almost exclusively these days. And I have
many other trade-offs if I want addtional silence, as I usually do. I
can trade tube longevity by running the tube at very high voltage and
current. I can and do move the quiescent operating point well away
from any possibility of grid current. I can and do flatten the
loadline along which the signal swings by very high loads so that a
real accountant would tear out his hair at the "waste" -- like
building a 10 litre V16 engine for a car and then choking it back with
the silencers to a whisper and a miserable 200bhp when it is capable
of 600bhp. Everyone else makes a 300B give 8W; mine deliver 3.8W...

Say you set up an SE 300B amp which can make 8W into 5 ohms, while
dissipating no more than 30W at idle. Then you may find that maximum
clipping power will decline with loads below 5 ohms and above 5 ohms,
but it is an ideal way to set up a 300B to deal with speakers that are
nominally 8 ohms, so tht when indeed the load is 8 ohms the PO might be
much less than 8 ohms but fidelity and DF is higher.

In fact, the 300B set up as I suggest will indeed put up with speakers
nominally 4 ohms if the levels expected are low because one great
feature of triodes is that they are fairly load tolerant. But where the
host of the party is a triode, don't abuse his hospitality by inviting
too many guests who will draw excessively from the limited barrel of
amps available.

If very few guests turn up and the load is deemed to be 16 ohms then
decorum and convivialty will prevail and without the distortions of bad
behaviours.

The secret to partying well on one 300B for each channel is to have
sensitive speakers!

The more sensitive the speaker is, the less important is its impedance,
and the sweeter the sound if you can make a sensitive speaker work
properly.

Patrick Turner.





Andre Jute
Refinement beyond price