Andre Jute wrote:
Patrick Turner wrote:
West wrote:
"Patrick Turner" wrote in message
...
The 845 amps I have been strugling to find time to build
are approaching a stage where I must decide
on the actual working points that would be most suitable for
both 211 and 845 including class A2 operation,
by means of cathode follower buffer choke loaded to the
fixed bias supply.
So far having Ea at 1,000V and Ea at 80mA with RL = 12.5k
could seem OK but it means Pda = 80 watts,
and only KR845 or KR211 look able to take this idling condition,
one reason being that the KR heaters are 10V at 1A instead
of the RCA GE use of 10V at 3.3A.
RCA data gives Pda = 67 watts, and if Pd-filament = 33 watts,
the total tube Pd = 100 watts
Anyone here with actual experience of using either tube
in an SE amp???
ALSO, anyone here have longterm experience of use of Shuguang
845?
Patrick Turner.
I remember reading, not long, ago that the Boss (AJ) found 2 sweet spots
with his 845's, 970v & 1046v. The voltages are rough approximates that are
the best my memory can do at the moment. Good luck and keep us posted on
this venture and why not ping him?
960 and 1040V. And I was talking strictly about the 845. I never got
on with the brittle sound of the 211 but it is well known that the 211
starts to sound better nearer its 1250max. Kondo got around the 211s
problems at less elevated voltages (he ran his Ongaku at 960V at the
plate, I seem to remember) by loading it with a 20K (claimed, probably
16K in real life) transformer.
Kondo has his schematic shown at
http://www.drtube.com/schematics/an/ongaku.gif
The output 211 doesn't have a cathode shown, but let's assume it is
taken to 0V.
Ea sure is 960V, and bias at about -47V, and the CF drives the 211
directly to get the +53V max applied to the grid to give a total drive
voltage of
about +/- 100V pk or 70Vrms.
So Kondo knew how to get lots of power but not have to use 1,250V to
avoid the grid current.
he knew the first 10 watts class A1 up to onset of A2 was going to be
utterly blameless.
Then he said its due to silver wire and special cores and a lot of BS
followed about it all
and oh how the $$ rolled in. What a masterful stroke of luck he
engineered!
Hats off for Kondo.
I have heard 211 and find 'em real goooood.
It depends who made the darn thing, and all the other issues in the amp,
and boy do thay matter because there isn't any NFB loop
to correct sonic or technical problems.
( No NFB to further muddle a sound either, but its all not as simple as
some
would asert..)
Well yes, between 970V and 1,050V seems about right...
Hey, Max, I'm not impressed with that 760V 845 you found. It may sound
fine to the owners if they haven't heard an 845 as it should be built,
in fact better than any other amp they ever heard, but it ain't the
real thing, which is worth a lot of trouble, as any 845 owner will
tell you. Back in the days of the Joenet still, there was a craze
among the Japanese for 500V 845. This was one of the dumbest ideas I
ever heard.
But why so dumb? if the Ea = only 760V, and Pda = 75 watts,
then Ia would be 100mA, and load whatever to suit, and you get a
reasonable
15+ watts and listen with 2 watts.
I bet a bunch of golden eared auio buffs would not hear
any difference beteween an 845 and 3 paralled KT88 in triode,
or 3 x 300B.
Perhaps its good wine for all three options.
The 500V option isn't ideal, but if Ia = 100mA, Pda = 50W
and if RL = 5k, you get +/- 160V peak across a 5k load
for 2.6 watts.
But many japanese are happy sipping their drinks very slowly
rather than guzzling it down like a round eye westener.
And volume is low in their small roomed houses with paper walls.
so they marvel at the 845, and its sweetness even at low power.
But whatever thei pin onto the 845 isn't all that is tickiling their
ears;
its all the other tubes in the line up as well....
The last option is to whack up the Ea, and whack up
the RL, to have the triode act more like a voltage device than a current
one,
thus provoking its internal NFB loop to create more heaven in sound by
coping with the devils
of distortion better.
You don't need to build it (though I did) to know it will sound like
****. Just check the Ia-Ea-Eg curves, and ask yourself what sort of a
primary impedance you will have to put on the tube to get any power
whatsoever, and I mean less than 2W.
5k and 500V at 100mA is a good way to get 2.6 watts
of nice power. Like a 2A3 on steroids.
A big bottle full in fact.
Its like using an elephant to shift a matchstick,
and a limited elephant at this Ea and Ia, without being allowed to
flex muscle with A2.
If the circuit is made to work A2 you get 15 watts.
The tube will last forever....
Suddenly it becomes clear that
the entire negative-going half of the signal, to the right of the
quiescent operating point, stands chin-deep in sewerage, and if
Pavarotti breathes heavily the entire cast drowns in slurry.
Not if the Ia is made high enough to stop the Ea +ve swinging into Ra
curvature
when Ia becomes low.
I also
tried about 800V and while it sounded infinitely better than 500V, and
much more like the real thing, it still wasn't the best the 845 is
capable of.
I agree.
My customers all prefer a much higher power ceiling than
japanese who don't mind low levels.
211 has Ra = about 3.3k and 845 has Ra about 1.9k.
So the damping factor of the 211 is poorer and NFB would seem to me
to be almost unavoidable.
It seems to me perverse to consider the 211 and the 845 as
interchangeable in any way whatsoever. All they share is the glass
envelope and a requirement for very high voltages to give their best.
Well, the fact is that the same load at the same Ea and Ia can be used
to get
a maximum of around 31 watts where Pda quiescent = 67 watts and
operation is A2.
If you dissallow A2, and toy stipulate you want 20 watts,
then the op points will have to change for the same Pda; the 211
will have higher Ea and RL and lower Ia than 845.
Because the the anode load will about 33% higher than for 845,
then the damping factor difference is reduced, and both become
usable without any NFB.
If the Ra = 3.6k at 55mA with 211, and load = 20k, then DF = 5.5, quite
good.
845 would have Ra = 1.8k and RL = 14k and DF = 7.7, only marginally
better.
It means that if the speaker coils suits 6 ohms, and 6 ohms is the load,
then allowing 0.6 ohms total winding R, Rout varies between 1.8 ohms,
211,
and 1.5 ohms. So with either tube used wisely, you get DF 4 with
either triode
without any loop NFB.
I can say that 10dB of NFB will not destroy the sound, and probaably
make bass sound tighter
etc, but NFB is optional when Rout gives a DF 4. (( IMHO ))
The A2 operation means THD tends to rise when grid current happens...
A SRPP with a pair of EL84 in triode looks promising to make the needed
150Vrms drive at low impedance for the 845, and with a choke to bias the
845 grids so the
bias can't change easily when in A2.
While I understand the need to drive the 211 into Class A2 to get any
real power, it is too high a price to pay for a little extra power to
drive the 845 into Class A2.
To get the 211 to make power in A1, you simply have to use a high Ea,
hence 1,250V
is about right, maybe a little more even, as long as the
required OPT is available....
OPT with 20k primary loads for operation with HV are thin on the ground.
The A2 allows operation of both 211 and 845 at a lower Ea than one might
use. But if one insists on A2 AND having Ea high, then RL
must be higher to allow the wider swing without cut off.
meanwhile if this becomes the case for eithewr tube then at
the op point with high ea, and high RL the tube
has very low THD/IMD for the first A1 watts before it moves to A2.
Then of course the driver tube surely must have a large effect
because its 2H cancels the output tube 2H whether you like that or not.
To what extent the cancellation occurs depends on a lot of things,
and the actual load in use.
There may be almost perfect cancelation with 8 ohms at the speaker,
but at 4 ohms or 12 ohms the cancelation makes hardly any difference.
But my customers say they like clean sound of my SE amps.
I suppose I could say why; less than 0.1% THD at any load from 4 ohms to
12 ohms for the first 10 watts
out a total of 35
At 2 watts and 5 ohms the CFB 35 had less THD than most PP amps of the
same max power
and even with 6 dB more global NFB..........
Because the 845 and 211 present pretty low THD at listening levels,
AND because the driver stage has to work a bit even to produce these
levels,
there is a fortitious amount of non contrived natural and unavoidable
distortion cancelling going on.
Usually the output stage of any amp makes more THD than any of its
driver stages,
but where output tube gain is low, then the driver stage has to work
hard and thus
it produces considerable distortions, and in SE design it cancels where
all the tubes
involved are triodes.
The 845 is a tube that naturally and
natively lives in Class A1, where at an entirely feasible 80mA and
around 1000V it delivers near as damnit 20 single-ended watts of
unequalled glory. To drive it into Class A2 for some "engineering" wet
dream of extracting maximum possible power will unbalance its sound,
in particular by giving it a bloated bass.
Well, I fail to see the slightest reason why adding a CF to simply
extend the A1 range a bit into A2 would have any sound effect.
Remember, its the overall thinge here, and who has made the amp,
and how far they went, and at what sort of trouble......
I like the idea of SRPP EL84 -- one of my favourite tubes. But with
what you're going to have to charge for this amp, you may as well go
the whole hog and drive the 845 with another DHT. I've always had good
luck gilding the lily by driving kilovolt transmitters with 300B
idling along very, very, very quietly in the driver spot.
SRPP EL84 in triode has faded in my mind in favour of
a simple anode gain stage driving a direct coupled CF using a secong
EL84 triode.
The reason I favour EL84, it have it capable of 180Vrms for 845 drive,
and only need 10Vrms input, so a nice drive tube like 6SN7, 12AU7, 6CG7
can be used for
an input voltage not more than 1Vrms, without global NFB.
Using as pair of 845 in parallel improves the sensitivity.
211 may require a little bit of GNFB, but because its gain is twice 845,
GNFB can be used, and sensitivity is still sensible, under 1.5vrms
input.
And while I'm giving advice that you probably don't need, don't even
think of loading less than 10K on the plate of the 845. (And higher on
the plate of the 211 -- the need for impossible impedances is what
makes these tubes difficult, not the high drive requirements; to my
mind the impossibility of finding the correct output transformer for a
211 rules it out for anyone who isn't himself a winder.)
I agree entirely.
I want to have about 6k minimum for the two paralleled tubes,
so 12k each.
SE loads refelected from speakers vary.
Many speaker makers lie all their way to the bank
about Z and sensitivity.
Nearly all speakers have a low Z between bass and midranges
where most power is needed because crossovers
shunt a portion of the current if they are second order and damped
properly.
an Xo set for typical 6 ohm driver has Zin = 4.5 ohms at Fo
and if the Fo of bass and mids is the same, then Zin = 2.3 ohms at Fo.
I try to avoid this horror by overlapping the bass-midrange,
so that Zmin is 4 ohms perhaps, over a wider F band.
I arrange my PP amps to make max PO at 3 ohms,
and SE amps to peak at 4 ohms.
But in the real world a load mismatch often cannot be avoided, and
still we get blameless sound from SET class A where the clipping
ceiling is way above the peak levels used, even with the wrong load.
But a couple of my customers cheat, and are sneaky to a point.
Thy have bought ZeroImpedance load matching toroidal transformers,
and both say they like having a 2:1 Z ratio change so that an 8 ohm
speaker
looks like a 16 ohm, and a 3 ohm load at some point along the AF band
becomes a more reasonable 6 ohms.
They don't like the reduced sensitivity and lower ceiling, but they say
it sounds better.
AJ may not be reading the group at the moment.
I was happily designing my new bike when some well-meaning lurkers
wrote to say that I am wanted. So, like the Good Scout, here I am to
help you across the street. Dib-dib.
Blink and you'll miss me for I do try to ride fast these days.....
Patrick Turner.
west
On longevity: the only 845 I ever accidentally popped dropped off the
table onto its head. Mine were all Chinese, some cheap rubbish bought
for less than ten bucks each in a wholesale box, some obsessively
selected. I ran them up to 84mA for several hours in tests. I detuned
the ones that left here to 72mA and sometimes up to 75mA. I ran one
for a couple of months at about 80mA and 960V, which sent Bill up the
wall (add the filament to the idling power and compare with spec).
Mine are all gone now to new deeply caring homes, but all the same I
haven't heard of one of those tubes that died a premature death in the
hands of new owners. Perhaps I have a thousand hours or two on 845,
perhaps even up to 5k hours, but that was across quite a few tubes,
maybe as many as twenty, and years ago (maybe current production is
even better than then), which doesn't really make my anecdotal
evidence the sort of hard-use information you want. But 845 are cheap;
so what if you have to replace them every couple of thousand hours? If
it bothers you, perhaps from a commercial fear for your reputation,
make the customer pay for Krone's fab tubes, which come with a
guarantee; I have KR 300B equivalents at least a decade old and
certainly with more than 10K hours on them.
Well, people say don't drop DH tubes because the cathodes are brittle.
KR have oxide coated DH cathodes, and probably having the tubes
turn on for a coupla minutes without B+ so that gass molecules
are absorbed by the getter BEFORE becoming stripped of electrons
and bombarding the cathode is a good idea.
Why don't you ever have easy problems, Patrick, say like how long KR
300B types will last, or whether gennie WE is worth the money?
I don't have a clue how long some tubes might last.
But a customer here has been running his 13E1 NOS made probably in 1960
for 5 years nearly every day for sometimes all day,
and there has never been smoke, always been real music,
and technically, they still measure almost as new'
last service I did 2 years ago all was as new except some grid
current had started to make grids slightly +ve,
so I reduced the Rg from 220k to 47k,
and changed the ECC32 paralleled driver to 6V6 in triode.
FB was effectively slightly reduced, and the client said the sound was
slightly better.
I will soon be giving the amps a check up again;
maybe swap the plain UL config to CFB if the OPT allows it.
Its 11 years since I made those amps, and because I thought I could
teach the local audio club that one didn't have to spend $140,000 on an
Ongaku,
a humble single big fat beam tetrode could do the business,
and without silver wire, and fancy-shmancy caps, resistors, chokes and
contacts et all.
I have a pair of KR300B I was given to demo to customers.
So I did, and nobody can pick them from any other 300B,
and they say well I have a spare dozen Sveltlanas, and don't need
anything else.
The KR can be run continuously at higher Pda than most other 300b...
Same goes for KR845 and 211, both of which have 10V x 1A cathodes, yea,
1/3 of the heat in the heaters!!!
Hence along with a bit of a fiddle hear and there the Pda of 100 watts
is OK.
But I wouldn't. Sooner or later someone will try to use an old RCA etc,
and there would be smoke.
Every audiophile should hear a good 845 at least once before he dies.
Otherwise he will have no reference to judge the music of the spheres
in Heaven.
Hmm, Angels have orbs they say, glorious wobbalititybitty spheres they
say.
If ever i go Upstairs, it'll be a case of Pardon me God,
lemme try to get a root here because they didna want root much where
I jus came from.
Sigh, but the rich guys will have all the shielas Up there I guess,
because in the latter day churches they now preach that
Prosperity Is Good. Go to Jesus with a millyun.
If ya poor, youse live in a drain pipe of Heaven.
But turds of gold don't smell as they float past though.
When ya see a discarded 845 float past, ya grab it.
I'm told the hills are slight and winds are favourable
when cycling around heaven and you never get a puncture.
Car drivers stop to salute, and wait until youv'e passed.
And there ain't no drug cheats in La Tour De Heaven.
Patrick Turner.
Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
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