[Tube747]

Did anyone try either 211? What's your comment? Thanks!

[Patrick Turner]

On Mar 12, 5:45*am, Tube747 wrote:
Did anyone try either 211? What's your comment? Thanks!

No but I have compared KR845 to Chinese Shuguang 845A which are close
copies to the original RCA 845.

In a pair of SE amps I heard virtually no dramatic differences in the
sound quality. So I concluded that the much higher cost of the KR
tubes did not justify their purchase. But then just WHO designs and
WHO builds the amp and HOW the circuit is configured and WHAT input
and driver tubes are used and HOW much NFB is used will determine the
sonic outcome. The sonic outcome WILL NOT only be determined by the
choice of output tube.

Usually all audio amps using 211 will need some NFB because the Ra is
about 4k, and if the load was say 10k, then the damping factor = 10k /
4k = 2.5, which is rather poor because typical speakers have varying R
and thus reflect an anode load to a tube which may vary between 5k and
50k. So thus one might prefer Ra to be 2k at least, and of course the
tube that gives this result without loop NFB is the 845. But there's
one possible better tube, the KRT100.

KRT100 details are.....
Maximum Plate Voltage 1000 V
Maximum Plate Current 140 mA
Plate Dissipation 100 Watts
Va 650 V
Ia 90 mA
Vg -87 V
Transconductance 4.4 mA/V
Amplification Factor 5.3
Filament Voltage 5 V (DC/AC)
Filament Current 2.0 A

One would be an idiot to use the tube set up on the maximum rated Ea
and Ia. For SE class A with one tube I'd use Ea = 850V x Ia = 90mA
giving Pda at idle = 76.5W.
Class A load = ( Ea / Ia ) - 2Ra = 850/0.09 - 2x1,300 = 6,844 ohms.

If you wanted PP class A, you could use RLa-a = 13.69k, but then for
good class AB1 operation use RLa-a of about 1/2 the class A load, ie,
6.84k.

The damn trouble with the KRT100 is that it needs a cathode supply =
5V x 2A which is a complete PIA if one ever wanted to use 845 or 211
in the same amp.

Just WHY KR audio ever decided on 5V x 2A instead of making the
cathode heating the same as their 845 and 211 is a complete mystery.


For KR211 details go to
http://www.kraudio.cz/

You will see that the KR211 has cathodes requiring 10V x 1 amp or
either ac or dc but of course ONLY true engineers would only ever
apply well filtered dc heating current to the 211 cathode. Now the
cathodes in KR211 and KR845 seem to be identical and are in fact dull
glow oxide coated wire cathodes similar to that used in a 300B.
So if you want to make an amp capable of using either KR211/845 or
KRT100 or Shuguang 845A or B, then you MUST make the heater supply
adjustable to give 10Vdc at 1A or 3.3V or 5V at 2A. This means having
a heavy duty transformer winding with at least 5 taps at the right
place to be able to trim the Vdc to where you want it for particular
tube choice. One does NOT want any series resistance between rectifier
circuit and such cathodes because you'll waste heat.
In 845 amps I built 2 years ago I used a choke input filter with a
thick wire solenoid choke 30mH and very large C values and taps
around 12Vac so that the cathode supply voltage could be changed. If
left unchanged, and the owner switched to Shuguang 845A/B, then Ik =
3.3A, not the 1A for KR845, so Vdc will sag to less than 9Vdc with the
increased Ik.

In MY ever so humble opinion, I would urge caution when using KR Audio
845/211/T100 tubes with Ea exceeding +900V.
The cathodes are more fragile than the bright emitter thoriated
tungsten as found in old RCA and the Shuguang 845A/B types. It has
been said elsewhere by others that oxide coated cathodes tend to be
eroded much more easily by positive ion bombardment within a tube when
Ea is above +1,000Vdc. The reason is that the higher Ea increases the
sppeed at which +ve ions hit the cathode and therefore their eroding
effect is greater. To conclude, I have NO IDEA whether the KR triodes
with their dull emitter cathodes will last as long as the older
original designs. I would be extremely surprised if they lasted
longer. With 211, the use of Ea = +1,200V with Ia = 60mA is quite OK.
If the circuit is for PP, one might use even higher Ea for 211/845
etc, but I would not use KR triodes in such designs.

With 211, in order to get a reasonable amount of class A1 SE or AB1
PP, the use of a high Ea over 1,000V is needed to get a usefull anode
voltage swing without the drive amp being limited by grid current and
hence get a useful amount of output power. But in the old days many PP
amps had the 211 driven by a pair of low Ra triodes in PP and with a
1:1 driver transformer which could thus drive the 211 well into class
AB2 and thus extract awesome amounts of power.
When using 845, class A2 or AB2 can also be done but the increase in
power does not justify the expense of the driving transformer.
And of course if you want bandwidth at full power between 14Hz and
50kHz, then the OPT and IST are very difficult to design and there
ain't many one can buy off the shelf.

The lower the Ea and higher the Ia becomes, the lower the anode RL can
be and thus it more likely falls into the range of values available
from tranny winding companies. Some PP trannies available off the
shelf may well be used for an SE design if you have a choke feed of dc
to the anode and you cap couple the anode to the PP tranny to stop the
DC flow.
The primary of the OPT is thus at 0V potential, but the caps need to
be very well rated for the high dc.

I have a MingDa amp here which has PP Shuguang 845 with Ea = 1,220Vdc
and Ia = 50mA max. Bias = -199Vdc so the drive voltage before grid
current = 140vrms approx. With 211, the bias would be much less, and
drive voltage lower for the class AB1. But it begins to become high
when you run into class AB2, and of course the driver amp Rout needs
to be LOW, less than 1,000 ohms. There will still be rapid distortion
onset after the start of the grid current drive region but if there is
global NFB this will be minimal. And probably of no concern if you
only want a few watts max where all the audio power is created by the
class A1 region of working.

I would be very wary of using any Chinese Tianjing Full Music 845 or
similarly made 211 with dull emitter cathodes.
I plugged a quad of TJ845 into the MingDa amps and these tubes just
arced internally very badly at turn on and then later in a test
circuit with Ea = +1,100V. They were found to have cathodes needing
10V at 0.6A, so when used in a circuit which normally requires tubes
with 10V x 3.3A cathodes, the Ek will rise to perhaps +13Vdc because
the TJ cathode current does not load down the heater supply. With the
higher cathode temp, the TJ become very unhappy. But that was not the
cause of the arcing; in my test circuit I made sure the cathodes were
heated properly with 10Vdc maximum.



Patrick Turner.

[popilin]

Originally Posted by Patrick Turner

On Mar 12, 5:45*am, Tube747 wrote:
Did anyone try either 211? What's your comment? Thanks!

No but I have compared KR845 to Chinese Shuguang 845A which are close
copies to the original RCA 845.

In a pair of SE amps I heard virtually no dramatic differences in the
sound quality. So I concluded that the much higher cost of the KR
tubes did not justify their purchase. But then just WHO designs and
WHO builds the amp and HOW the circuit is configured and WHAT input
and driver tubes are used and HOW much NFB is used will determine the
sonic outcome. The sonic outcome WILL NOT only be determined by the
choice of output tube.

Usually all audio amps using 211 will need some NFB because the Ra is
about 4k, and if the load was say 10k, then the damping factor = 10k /
4k = 2.5, which is rather poor because typical speakers have varying R
and thus reflect an anode load to a tube which may vary between 5k and
50k. So thus one might prefer Ra to be 2k at least, and of course the
tube that gives this result without loop NFB is the 845. But there's
one possible better tube, the KRT100.

KRT100 details are.....
Maximum Plate Voltage 1000 V
Maximum Plate Current 140 mA
Plate Dissipation 100 Watts
Va 650 V
Ia 90 mA
Vg -87 V
Transconductance 4.4 mA/V
Amplification Factor 5.3
Filament Voltage 5 V (DC/AC)
Filament Current 2.0 A

One would be an idiot to use the tube set up on the maximum rated Ea
and Ia. For SE class A with one tube I'd use Ea = 850V x Ia = 90mA
giving Pda at idle = 76.5W.
Class A load = ( Ea / Ia ) - 2Ra = 850/0.09 - 2x1,300 = 6,844 ohms.

If you wanted PP class A, you could use RLa-a = 13.69k, but then for
good class AB1 operation use RLa-a of about 1/2 the class A load, ie,
6.84k.

The damn trouble with the KRT100 is that it needs a cathode supply =
5V x 2A which is a complete PIA if one ever wanted to use 845 or 211
in the same amp.

Just WHY KR audio ever decided on 5V x 2A instead of making the
cathode heating the same as their 845 and 211 is a complete mystery.


For KR211 details go to
http://www.kraudio.cz/

You will see that the KR211 has cathodes requiring 10V x 1 amp or
either ac or dc but of course ONLY true engineers would only ever
apply well filtered dc heating current to the 211 cathode. Now the
cathodes in KR211 and KR845 seem to be identical and are in fact dull
glow oxide coated wire cathodes similar to that used in a 300B.
So if you want to make an amp capable of using either KR211/845 or
KRT100 or Shuguang 845A or B, then you MUST make the heater supply
adjustable to give 10Vdc at 1A or 3.3V or 5V at 2A. This means having
a heavy duty transformer winding with at least 5 taps at the right
place to be able to trim the Vdc to where you want it for particular
tube choice. One does NOT want any series resistance between rectifier
circuit and such cathodes because you'll waste heat.
In 845 amps I built 2 years ago I used a choke input filter with a
thick wire solenoid choke 30mH and very large C values and taps
around 12Vac so that the cathode supply voltage could be changed. If
left unchanged, and the owner switched to Shuguang 845A/B, then Ik =
3.3A, not the 1A for KR845, so Vdc will sag to less than 9Vdc with the
increased Ik.

In MY ever so humble opinion, I would urge caution when using KR Audio
845/211/T100 tubes with Ea exceeding +900V.
The cathodes are more fragile than the bright emitter thoriated
tungsten as found in old RCA and the Shuguang 845A/B types. It has
been said elsewhere by others that oxide coated cathodes tend to be
eroded much more easily by positive ion bombardment within a tube when
Ea is above +1,000Vdc. The reason is that the higher Ea increases the
sppeed at which +ve ions hit the cathode and therefore their eroding
effect is greater. To conclude, I have NO IDEA whether the KR triodes
with their dull emitter cathodes will last as long as the older
original designs. I would be extremely surprised if they lasted
longer. With 211, the use of Ea = +1,200V with Ia = 60mA is quite OK.
If the circuit is for PP, one might use even higher Ea for 211/845
etc, but I would not use KR triodes in such designs.

With 211, in order to get a reasonable amount of class A1 SE or AB1
PP, the use of a high Ea over 1,000V is needed to get a usefull anode
voltage swing without the drive amp being limited by grid current and
hence get a useful amount of output power. But in the old days many PP
amps had the 211 driven by a pair of low Ra triodes in PP and with a
1:1 driver transformer which could thus drive the 211 well into class
AB2 and thus extract awesome amounts of power.
When using 845, class A2 or AB2 can also be done but the increase in
power does not justify the expense of the driving transformer.
And of course if you want bandwidth at full power between 14Hz and
50kHz, then the OPT and IST are very difficult to design and there
ain't many one can buy off the shelf.

The lower the Ea and higher the Ia becomes, the lower the anode RL can
be and thus it more likely falls into the range of values available
from tranny winding companies. Some PP trannies available off the
shelf may well be used for an SE design if you have a choke feed of dc
to the anode and you cap couple the anode to the PP tranny to stop the
DC flow.
The primary of the OPT is thus at 0V potential, but the caps need to
be very well rated for the high dc.

I have a MingDa amp here which has PP Shuguang 845 with Ea = 1,220Vdc
and Ia = 50mA max. Bias = -199Vdc so the drive voltage before grid
current = 140vrms approx. With 211, the bias would be much less, and
drive voltage lower for the class AB1. But it begins to become high
when you run into class AB2, and of course the driver amp Rout needs
to be LOW, less than 1,000 ohms. There will still be rapid distortion
onset after the start of the grid current drive region but if there is
global NFB this will be minimal. And probably of no concern if you
only want a few watts max where all the audio power is created by the
class A1 region of working.

I would be very wary of using any Chinese Tianjing Full Music 845 or
similarly made 211 with dull emitter cathodes.
I plugged a quad of TJ845 into the MingDa amps and these tubes just
arced internally very badly at turn on and then later in a test
circuit with Ea = +1,100V. They were found to have cathodes needing
10V at 0.6A, so when used in a circuit which normally requires tubes
with 10V x 3.3A cathodes, the Ek will rise to perhaps +13Vdc because
the TJ cathode current does not load down the heater supply. With the
higher cathode temp, the TJ become very unhappy. But that was not the
cause of the arcing; in my test circuit I made sure the cathodes were
heated properly with 10Vdc maximum.



Patrick Turner.

Patrick:Congratulations, you know that you say, it is very usefull to me, I am designing an amplifier using 211/VT4C and I save your explanation as a reference, but in one point I disagree, because the geometry of the 211 cathode, if you put DC on them there is an asymmetrical distribution of electron emision then an asymmetrical distribution of electrons in the anode, not seems good to me for the Phisics of a valve.
The goal to put clean DC in a cathode-filament is the noise, but we talk about of a power triode with an amplification factor of 12, the noise is not the devil here, with a well designed circuit you can "kill" the electric field of 50Hz (for you 60Hz) and no noise, the grid don´t see that.
I am not sure, but Kondo San, when made the Ongaku used 10V AC for the cathode-filament and the result, well you know.
Because of you I am looking for a 845 now, for the best damping factor (better bass response and dynamics) if I understood your explanation.
I love graphite anode and thoriated tungsten catode, which valve is better for me at a low cost?
Forgive my english, I am a poor physicist of the third world.
Best regards.
popilin