4 6SN7GTB of my home made 211 power amp are connected in 2 SRPP.
The filaments are supplied by one single 6.3V with the CT connected to 75V
DC.
What is the use of that 75V DC?
Please give comments on the circuit:
http://www.geocities.com/hkbirdslover/index.html

"·à¤l¤f" wrote:

4 6SN7GTB of my home made 211 power amp are connected in 2 SRPP.
The filaments are supplied by one single 6.3V with the CT connected to 75V
DC.
What is the use of that 75V DC?
Please give comments on the circuit:
http://www.geocities.com/hkbirdslover/index.html

The 75v biases the heaters at +75v, so the voltage difference between the
cathode and heater of top and bottom 6SN7 triode is less than 80v.
This prevents short circuits between K and H.

Old fashioned paralleled tubes with resistance loads would work OK
in the amp you have.
If you bypass the driver tube cathodes' Rk, consider using 330 uF, not just 33
uF.
The input 6SN7 has a small anode current, consider using 2.2k for rk in lieue
of 4.7k.
The driver tube might also benefit from more current, Rk = 1.8 k perhaps.
Sometimes I have used say 1.8k for the bottom Rk and 2.2k on the top tube Rk,
so a slightly
higher voltage is across the top tube of the SRPP stage.



Patrick Turner.

Probably to elevate the dc potentioal on the 6sn7 cathodes to a value
that both the upper and lower tube can tolerate without too much
Heater-Cathold voltage differential.
Also to reduce hum.

Bob

"·à¤l¤f" wrote:

4 6SN7GTB of my home made 211 power amp are connected in 2 SRPP.
The filaments are supplied by one single 6.3V with the CT connected to 75V
DC.
What is the use of that 75V DC?
Please give comments on the circuit:
http://www.geocities.com/hkbirdslover/index.html


Bob H.

Just grab that plate in one hand, the chassis in the other,
and FEEL the power of tube audio!!!
(not literally, of course, just kidding. DON'T DO THAT!)

On Sat, 15 May 2004 06:44:43 +0800, ·à¤l¤f wrote:

4 6SN7GTB of my home made 211 power amp are connected in 2 SRPP.
The filaments are supplied by one single 6.3V with the CT connected to 75V
DC.
What is the use of that 75V DC?
Please give comments on the circuit:
http://www.geocities.com/hkbirdslover/index.html

It reduces the heater-cathode voltage to something that the valve will
stand. I'm not sure of the safe rating, but grounding one side or the
centre tap of the heater winding would put 135v from heater to cathode -
probably well outside the limit.

--
Cheers...
Mick
Gave up on viruses & trojans - moved to Linux... :-)
Nascom & Gemini info at http://www.nascom.info

Thanks for your explanation.
Now I understand why the CT of the 6.3V ac for the 6SN7 in my Techno push
pull power amp
is connected to the cathode of a power tube.

"Form@C" ¦b¶l¥ó
news
On Sat, 15 May 2004 06:44:43 +0800, ·à¤l¤f wrote:

4 6SN7GTB of my home made 211 power amp are connected in 2 SRPP.
The filaments are supplied by one single 6.3V with the CT connected to
75V
DC.
What is the use of that 75V DC?
Please give comments on the circuit:
http://www.geocities.com/hkbirdslover/index.html

It reduces the heater-cathode voltage to something that the valve will
stand. I'm not sure of the safe rating, but grounding one side or the
centre tap of the heater winding would put 135v from heater to cathode -
probably well outside the limit.

--
Cheers...
Mick
Gave up on viruses & trojans - moved to Linux... :-)
Nascom & Gemini info at http://www.nascom.info

Thank you.
At the very beginning due to lack of space I omitted
the filtering choke and put a 47 ohm resistor there.
When I switched on the amp the first time a noticeable hum
was heard 10 feet away from the speakers. Now a 5 H choke
was put inside the chaises. Without input signal it is now dead silent
at all volume scale. I'll take photo of it tomorrow for you all to see.

"Bob Hedberg" ¦b¶l¥ó
¤¤¼¶¼g...
Probably to elevate the dc potentioal on the 6sn7 cathodes to a value
that both the upper and lower tube can tolerate without too much
Heater-Cathold voltage differential.
Also to reduce hum.

Bob

"·à¤l¤f" wrote:

4 6SN7GTB of my home made 211 power amp are connected in 2 SRPP.
The filaments are supplied by one single 6.3V with the CT connected to
75V
DC.
What is the use of that 75V DC?
Please give comments on the circuit:
http://www.geocities.com/hkbirdslover/index.html


Bob H.

Just grab that plate in one hand, the chassis in the other,
and FEEL the power of tube audio!!!
(not literally, of course, just kidding. DON'T DO THAT!)

Hi Patrick, the sound of my 211 SE amp is not as good as my 300B SE amp.
There are 13 layers of windings in the 10K 211 output transformer (7 primary
and 6 secondary)
With despair I tried the 5K CT of the output transformer. The sound is much
better but the output
power is dropped. I want to add one more 211 tube each channel to match the
impedance.

"Patrick Turner" ¦b¶l¥ó
¤¤¼¶¼g...


"·à¤l¤f" wrote:

4 6SN7GTB of my home made 211 power amp are connected in 2 SRPP.
The filaments are supplied by one single 6.3V with the CT connected to
75V
DC.
What is the use of that 75V DC?
Please give comments on the circuit:
http://www.geocities.com/hkbirdslover/index.html

The 75v biases the heaters at +75v, so the voltage difference between the
cathode and heater of top and bottom 6SN7 triode is less than 80v.
This prevents short circuits between K and H.

Old fashioned paralleled tubes with resistance loads would work OK
in the amp you have.
If you bypass the driver tube cathodes' Rk, consider using 330 uF, not
just 33
uF.
The input 6SN7 has a small anode current, consider using 2.2k for rk in
lieue
of 4.7k.
The driver tube might also benefit from more current, Rk = 1.8 k perhaps.
Sometimes I have used say 1.8k for the bottom Rk and 2.2k on the top tube
Rk,
so a slightly
higher voltage is across the top tube of the SRPP stage.



Patrick Turner.

Hi,

Quite interesting !
My guesses:
-Halving the turns halves the DC induction, reducing the risk of steel
saturation, better basses.
(Could be checked by temporary by overbiasing the 211 to reduce DC in the
tranny)
-Surely less leakage inductance, better highs.

If secondaries are accessible, it's perhaps possible to rise the reflected
load using a different wiring ?

This could void doubling the power supply current too ;)
.... at the risk of returning to steel saturation.

Do you have some precisions about this tranny ?

Yves.

"·à¤l¤f" a écrit dans le message de news:
...
Hi Patrick, the sound of my 211 SE amp is not as good as my 300B SE amp.
There are 13 layers of windings in the 10K 211 output transformer (7
primary
and 6 secondary)
With despair I tried the 5K CT of the output transformer. The sound is
much
better but the output
power is dropped. I want to add one more 211 tube each channel to match
the
impedance.

[ . . . ]

"·à¤l¤f" wrote:

Hi Patrick, the sound of my 211 SE amp is not as good as my 300B SE amp.
There are 13 layers of windings in the 10K 211 output transformer (7 primary
and 6 secondary)
With despair I tried the 5K CT of the output transformer. The sound is much
better but the output
power is dropped. I want to add one more 211 tube each channel to match the
impedance.

If you halved the primary winding size by connecting the B+ to the OPT CT,
then the load seen by the tube reduces 4 times, say from 8k to 2k, and I fail to
see
how that could improve the sound, since maximum PO will be a lot less,
thd will be 5 times greater, and Ro will be 4 times higher .
Also the P inductance will reduce 4 times and the LF cut off will
occur at an F of 4 times what the Fco is when all the primary
is in the circuit.
Your schematic doesn't show a primary CT, but i assume there is one.

Maybe someother thing is not quite right, something you cannot see...

The amp you have uses a lot of global NFB and using only 1/2 the OPT prim means
the gain of the output tube reduces because the load is 1/4 of normal, so there
is less
effective applied FB.
At low levels, say a watt or two, the thd will still be low despite the mismatch
of load to the tube,
but the speaker response might be giving you mush more bass due to the higher Ro
of the amp,
and the tendency of bass speakers to put out more due to the resonant impedance
somewhere
between 40 and 100 Hz. With a higher Ro, the response will be different to when
Ro = 1/10 x speaker Z.
Ro still should be low even with your drastic change because of the NFB.

A 300B amp with no global FB and with a load of 3.5k at the anode, and a tranny
with
3.5k to 8 ohm impedance match will translate the 1.1k of anode resistance to
about 2.4 ohms at the secondary, ( that's what I measured on a 300B amp last
friday ).

What is the Ro of the 211 amp with and without FB?

Patrick Turner.





"Patrick Turner" ¦b¶l¥ó
¤¤¼¶¼g...


"·à¤l¤f" wrote:

4 6SN7GTB of my home made 211 power amp are connected in 2 SRPP.
The filaments are supplied by one single 6.3V with the CT connected to
75V
DC.
What is the use of that 75V DC?
Please give comments on the circuit:
http://www.geocities.com/hkbirdslover/index.html

The 75v biases the heaters at +75v, so the voltage difference between the
cathode and heater of top and bottom 6SN7 triode is less than 80v.
This prevents short circuits between K and H.

Old fashioned paralleled tubes with resistance loads would work OK
in the amp you have.
If you bypass the driver tube cathodes' Rk, consider using 330 uF, not
just 33
uF.
The input 6SN7 has a small anode current, consider using 2.2k for rk in
lieue
of 4.7k.
The driver tube might also benefit from more current, Rk = 1.8 k perhaps.
Sometimes I have used say 1.8k for the bottom Rk and 2.2k on the top tube
Rk,
so a slightly
higher voltage is across the top tube of the SRPP stage.



Patrick Turner.

Yes, you are right, better high but less bass.
The current was raised to 60ma in order to bias propperly for 5K primary.
Finally I have changed back to 10K primary and quite satisfied with the
quality
of the sound which approaches to 300B SE but much more power especially in
punchful
bass. The schematic and photo could be find in:
http://www.geocities.com/hkbirdslover/index.html
http://www.geocities.com/hkbirdslover/211_photo.html


"Yves" ¦b¶l¥ó
¤¤¼¶¼g...
Hi,

Quite interesting !
My guesses:
-Halving the turns halves the DC induction, reducing the risk of steel
saturation, better basses.
(Could be checked by temporary by overbiasing the 211 to reduce DC in the
tranny)
-Surely less leakage inductance, better highs.

If secondaries are accessible, it's perhaps possible to rise the reflected
load using a different wiring ?

This could void doubling the power supply current too ;)
... at the risk of returning to steel saturation.

Do you have some precisions about this tranny ?

Yves.

"·à¤l¤f" a écrit dans le message de
news:
...
Hi Patrick, the sound of my 211 SE amp is not as good as my 300B SE amp.
There are 13 layers of windings in the 10K 211 output transformer (7
primary
and 6 secondary)
With despair I tried the 5K CT of the output transformer. The sound is
much
better but the output
power is dropped. I want to add one more 211 tube each channel to match
the
impedance.

[ . . . ]

You are right, I changed back to 10K primary to get more power output.
Your advice made me remove the NFB cap. The high freq was too loud and
distorted then.
I added a 1K ohm resistor in series with the 211 coupling cap, the problem
was tackled.
The schematic and photo could be find in:
http://www.geocities.com/hkbirdslover/index.html
http://www.geocities.com/hkbirdslover/211_photo.html

"Patrick Turner" ¦b¶l¥ó
¤¤¼¶¼g...


"·à¤l¤f" wrote:

Hi Patrick, the sound of my 211 SE amp is not as good as my 300B SE amp.
There are 13 layers of windings in the 10K 211 output transformer (7
primary
and 6 secondary)
With despair I tried the 5K CT of the output transformer. The sound is
much
better but the output
power is dropped. I want to add one more 211 tube each channel to match
the
impedance.

If you halved the primary winding size by connecting the B+ to the OPT CT,
then the load seen by the tube reduces 4 times, say from 8k to 2k, and I
fail to
see
how that could improve the sound, since maximum PO will be a lot less,
thd will be 5 times greater, and Ro will be 4 times higher .
Also the P inductance will reduce 4 times and the LF cut off will
occur at an F of 4 times what the Fco is when all the primary
is in the circuit.
Your schematic doesn't show a primary CT, but i assume there is one.

Maybe someother thing is not quite right, something you cannot see...

The amp you have uses a lot of global NFB and using only 1/2 the OPT prim
means
the gain of the output tube reduces because the load is 1/4 of normal, so
there
is less
effective applied FB.
At low levels, say a watt or two, the thd will still be low despite the
mismatch
of load to the tube,
but the speaker response might be giving you mush more bass due to the
higher Ro
of the amp,
and the tendency of bass speakers to put out more due to the resonant
impedance
somewhere
between 40 and 100 Hz. With a higher Ro, the response will be different to
when
Ro = 1/10 x speaker Z.
Ro still should be low even with your drastic change because of the NFB.

A 300B amp with no global FB and with a load of 3.5k at the anode, and a
tranny
with
3.5k to 8 ohm impedance match will translate the 1.1k of anode resistance
to
about 2.4 ohms at the secondary, ( that's what I measured on a 300B amp
last
friday ).

What is the Ro of the 211 amp with and without FB?

Patrick Turner.





"Patrick Turner" ¦b¶l¥ó
¤¤¼¶¼g...


"·à¤l¤f" wrote:

4 6SN7GTB of my home made 211 power amp are connected in 2 SRPP.
The filaments are supplied by one single 6.3V with the CT connected
to
75V
DC.
What is the use of that 75V DC?
Please give comments on the circuit:
http://www.geocities.com/hkbirdslover/index.html

The 75v biases the heaters at +75v, so the voltage difference between
the
cathode and heater of top and bottom 6SN7 triode is less than 80v.
This prevents short circuits between K and H.

Old fashioned paralleled tubes with resistance loads would work OK
in the amp you have.
If you bypass the driver tube cathodes' Rk, consider using 330 uF, not
just 33
uF.
The input 6SN7 has a small anode current, consider using 2.2k for rk
in
lieue
of 4.7k.
The driver tube might also benefit from more current, Rk = 1.8 k
perhaps.
Sometimes I have used say 1.8k for the bottom Rk and 2.2k on the top
tube
Rk,
so a slightly
higher voltage is across the top tube of the SRPP stage.



Patrick Turner.

I order the output transformers form a local winder in |Hong Kong
They are heavy. The primary is 0, 5K 10K in 7 layers
There are 6 separate secondary, each 0.9 ohm embedded in 6 layers in the
primary.
I get [(0.9x3)^2]/0.9=8.1 ohms net secondary in 3 pairs of pp 0.9 ohm
connected in series
as the following:
___0.9___0.9___0.9___
0.9 0.9 0.9

"Yves" ¦b¶l¥ó
¤¤¼¶¼g...
Hi,

Quite interesting !
My guesses:
-Halving the turns halves the DC induction, reducing the risk of steel
saturation, better basses.
(Could be checked by temporary by overbiasing the 211 to reduce DC in the
tranny)
-Surely less leakage inductance, better highs.

If secondaries are accessible, it's perhaps possible to rise the reflected
load using a different wiring ?

This could void doubling the power supply current too ;)
... at the risk of returning to steel saturation.

Do you have some precisions about this tranny ?

Yves.

"·à¤l¤f" a écrit dans le message de
news:
...
Hi Patrick, the sound of my 211 SE amp is not as good as my 300B SE amp.
There are 13 layers of windings in the 10K 211 output transformer (7
primary
and 6 secondary)
With despair I tried the 5K CT of the output transformer. The sound is
much
better but the output
power is dropped. I want to add one more 211 tube each channel to match
the
impedance.

[ . . . ]