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Here is my most recent 845 design.
Let the flames begin 8^D
DanL
Follow Ups:
That looks great, no flames required.
One thing I am considering in an 845 design is Power Drive. The right side of it anyway. You save the implementation of the interstage transformer/low mu tube and get A2 capability. I have used this with other tubes and it does sound good.
Dans is way better. The colors are so happy.
This area interests me but I want to do two stage.
Chris
I designed a GM70 amp with the power drive
for another inmate recently and know it well.
You still need to drive it with a 12K or
less tube to get the best from it though.
The 2SK2700 has some capacitance to overcome.
Personally I prefer interstages over the
cathode (or source) follower.
But to each his own.
DanL
For the Silk interstage, how did you settle on the 1:1?
What about the:
I-511SD
5.0K
30mA (36mA)
1:0.5+0.5
55H
1.25K+1.25K
20Hz - 75KHz
SE to PP or A2 drive circuit
8,800
Chris
I had a thread with that question in mind.
-- Link Below --
Naz pointed out that the core needs to be gapped
with tube current plus A2 current in mind so 30mA
for the 6EM7 and 25mA for the 845 A2 grid current so
you need a minimum of 50mA rating on the interstage.
The 25H inductance of the I-311S-2A3 will give me
an F3 of just under 5Hz so the I-311S-2A3 it is.
Also I am thinking of the Paul Joppa idea -
http://www.audioasylum.com/forums/tubediy/messages/20/206581.html
and my later reply -
http://www.audioasylum.com/forums/tubediy/messages/20/206758.html
for the PS transformers.
Vive Le OverKill 8^D
I was thinking my use of the "super mu follower"
in the first stage and my novel adaptation of
the Tent Bias Supply would get the attention.
DanL
"I was thinking my use of the "super mu follower"
in the first stage and my novel adaptation of
the Tent Bias Supply would get the attention."
The reason I popped in with the source follower was that you didn't seem to have an aversion to a little transistor action. I am interested in how the TentLabs circuit would sound in that arrangement. It seems to be solving a problem relating to bias stability that, in practice, I really have not run into. I don't mind checking things every few months (or years).
Alan Kimmel got me to order a low-capacity choke for that "Super Mu" position. Because it replaced a 1.5k resistor, with a 900 DCR choke, I did not find the improvement worthwhile, it may have even gone backwards.
I am all for trying new things. A regulated negative bias supply is always a plus.
Chris
The "Super Mu" has the benefit of a
"bare" resistor on the cathode which
is much better than anything else.
The "Super Mu" circuit multiplies the
choke's inductance by mu +1 so mine
is like a 3000H choke on the plate.
BUT it also multiplies any inadequacies
the plate choke you install there so
you need to use a high quality choke.
The Tent Labs has four channels but
only one bias setting so after some reading
I found that the sensing resistor on
the cathode circuit was a 10R sooo if
I changed a couple of 10Rs for 27Rs then
they would sense the same voltage at 30mA
that the other two channels would sense at
80mA and I have two stages of fixed bias.
I thought it was an efficient
use of their product.
DanL
Cerebral use of the Tent Labs Supply. Common sense but very smart.
DanL
There could be a problem with grounding between driver and output stages with the Tent labs bias supply. Just a thought. I love them. They are very quiet! But might not be as quiet used this way. I have used a standard fixed biasing supply between driver and output stages and found that it takes careful decoupling to make it work quietly. I guess I am saying there might be more to it than changing resistors. There might be ground returnes to consider.
Griboon
I can't see a problem as there
is only one grounding point.
From Product Sheet -
> > Find the ground connection where normally
> > the cathode resistors used to be connected.
> > Connect a single wire from that point to either
> > one of the ground inputs at connector J1.
DanL
I am just playing safe here. There are areas where shared biasing suplies need more consideration.
You should tell them that. I looked at the Tent Labs supply after seeing your sensing resistors and assumed that that was the common way of adjusting the current draw. Are you going to take a hack-saw to the board to put the other two channels in the other chassis?
Chris
No the power supply will be seperate.
I am thinking a sub chassis underneath so
there will be no umbilical cord problem.
Low B-Field from 240V transformers at 120V
so EMI won't be an issue from them.
All the signal tubes will be together.
DanL
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