Hi all, I was wondering if you could give me some pointers or background on using batteries for biasing my driver stage 6n1p.
I bought the same batteries Gary Pimm uses for his battery biased CCS (CR1225FV / Lithium 3V)
I want to try them on my design instead of the 330 ohm resistor. See schematic.
The voltage across the cathode resistors is 2,6V now. That means around 7,9mA running through the 6n1p.
I bought the same batteries Gary Pimm uses for his battery biased CCS (CR1225FV / Lithium 3V)
I want to try them on my design instead of the 330 ohm resistor. See schematic.
The voltage across the cathode resistors is 2,6V now. That means around 7,9mA running through the 6n1p.
Attachments
Hi Bas,
It'll mean the stage gain will go up a bit, because at the moment you have an unbypassed cathode resistor.
I don't know if there will be any sonic benefits. This valve has such a low Ra, and with the active load....
But it's worth a try...
Cheers,
It'll mean the stage gain will go up a bit, because at the moment you have an unbypassed cathode resistor.
I don't know if there will be any sonic benefits. This valve has such a low Ra, and with the active load....
But it's worth a try...
Cheers,
Hi Dhaen,
How about bass? Usually bypassing with a cap improves that. I still think my system needs more bass, even after the improvements after the plate resistor increase, and bypassing the ouput stage with a Black Gate...
So I'm going either bypassed with a cap or battery.
But do you have any idea how many batteries to use in series?
Cheers,
Bas
How about bass? Usually bypassing with a cap improves that. I still think my system needs more bass, even after the improvements after the plate resistor increase, and bypassing the ouput stage with a Black Gate...
So I'm going either bypassed with a cap or battery.
But do you have any idea how many batteries to use in series?
Cheers,
Bas
Hi Bas,
Aha, it depends on why the bass is lacking in the first place.
If it's lacking because of an inadequately sized cap, then a bigger value will bypass down to a lower frequency.
Or,
If an anode inductor (choke or transformer) has inadequate inductance (H), then bypassing the cathode will reduce Ra, and reduce the inductance required to get down to a given frequency.
In the case of a resistively loaded stage with no bypass at all, adding a suitably large value will increase the stage gain over the entire audio band. If the valve is running at a low current, or has a high Ra, it might improve the top end response slightly, by the reduction of Ra.
If that's as clear as mud, I'm sorry 😉
Cheers,
Aha, it depends on why the bass is lacking in the first place.
If it's lacking because of an inadequately sized cap, then a bigger value will bypass down to a lower frequency.
Or,
If an anode inductor (choke or transformer) has inadequate inductance (H), then bypassing the cathode will reduce Ra, and reduce the inductance required to get down to a given frequency.
In the case of a resistively loaded stage with no bypass at all, adding a suitably large value will increase the stage gain over the entire audio band. If the valve is running at a low current, or has a high Ra, it might improve the top end response slightly, by the reduction of Ra.
If that's as clear as mud, I'm sorry 😉
Cheers,
The circuit shown in the picture is a mu-stage. Be careful with battery biasing there bacause the bias point is set by the upper penthode. It's a fixed current system instead of fixed voltage. In a mu-stage you won't find much difference in gain if you bypass the triode's cathode resistor or not because of the anode load (the penthode) wich is very high compared to the triode's cathode resistor.
Battery bias works just fine in anode follower or choke/transformer loaded circuits wich are actually fixed voltage systems. Tubes really like it if you run them in a fixed quiesent current or in a fixed cathode voltage, you can't do both, one factor has to vary with the grid voltage otherwise it's not an amplifier anymore.
Battery bias works just fine in anode follower or choke/transformer loaded circuits wich are actually fixed voltage systems. Tubes really like it if you run them in a fixed quiesent current or in a fixed cathode voltage, you can't do both, one factor has to vary with the grid voltage otherwise it's not an amplifier anymore.
Sjef,
You are soo right, about this. I tried bypassing this morning with a capacitor. I could hardly hear a change in volume. It did sound different though. Maybe even better...
What I don't understand though is...the mu-follower determines the current.....so why do we need a cathode resistor at all?
Regards,
Bas
You are soo right, about this. I tried bypassing this morning with a capacitor. I could hardly hear a change in volume. It did sound different though. Maybe even better...
What I don't understand though is...the mu-follower determines the current.....so why do we need a cathode resistor at all?
Regards,
Bas
Mu-followers work very well with fixed bias on the lower valve, whether it is battery bias (on grid or cathode), diode bias (cathode), or a PSU to supply grid bias. The gain doesn't change from unbypassed resistive bias, but the power supply noise rejection improves...
CATHODE BYPASSES AGAIN.
Hi,
While this theory is correct,bypassing the cathode R on SRPP circuits will add its' own colouration to the circuit.
It is a given that a mu follower_approaching a CCS_ is still very sensitive to PSU regulation.
I hear,once again,a lot of people dismissing this kind of circuit on the basis of hearsay and a basic misunderstanding of what it can do.
No circuit topology is ever perfect but the next step up to the mu-follower is a CCS loaded stage triode.
How you achieve this is open for debate but I think a few semi-conductors around the top penthode are doing less damage to the sound then a cathode bypass soundwise.
Just my 2 cents,😉
Hi,
While this theory is correct,bypassing the cathode R on SRPP circuits will add its' own colouration to the circuit.
It is a given that a mu follower_approaching a CCS_ is still very sensitive to PSU regulation.
I hear,once again,a lot of people dismissing this kind of circuit on the basis of hearsay and a basic misunderstanding of what it can do.
No circuit topology is ever perfect but the next step up to the mu-follower is a CCS loaded stage triode.
How you achieve this is open for debate but I think a few semi-conductors around the top penthode are doing less damage to the sound then a cathode bypass soundwise.
Just my 2 cents,😉
Hi bas, you still need a cathode resistor.
Normaly you set the bias current with the cathode resistor by a given anode voltage. Lets say that the upper penthode is a true constant current source. The bias current is then set by this current source. The cathode resistor of the triode now doesn't set the current anymore but it sets the amount of voltage on the anode of the triode.
What where the audible differences in bypassing the cathode ?
A mu-stage is not the same as a SRPP.
Normaly you set the bias current with the cathode resistor by a given anode voltage. Lets say that the upper penthode is a true constant current source. The bias current is then set by this current source. The cathode resistor of the triode now doesn't set the current anymore but it sets the amount of voltage on the anode of the triode.
What where the audible differences in bypassing the cathode ?
A mu-stage is not the same as a SRPP.
SRPP.
Hi,
Yes and no,it is a derivative of the SRPP.
Again,yes and no.It primary use is to polarize the grid.
Tie that cathode to ground and you'll see what I mean.
Cheers,😉
Hi,
Yes and no,it is a derivative of the SRPP.
Again,yes and no.It primary use is to polarize the grid.
Tie that cathode to ground and you'll see what I mean.
Cheers,😉
batteries
Hi Bas ,
I only see a problem with using a cathode battery on this if it's a lithium like you stated . The battery must be a rechargeable type . I use NimH (nickel-metal hydride?) for SE input stages and find it an improvement over an LED or bypassed resistor , quieter than unbypassed resistor too . All down to personal taste but it's cheap so maybe try it
316a
Hi Bas ,
I only see a problem with using a cathode battery on this if it's a lithium like you stated . The battery must be a rechargeable type . I use NimH (nickel-metal hydride?) for SE input stages and find it an improvement over an LED or bypassed resistor , quieter than unbypassed resistor too . All down to personal taste but it's cheap so maybe try it
316a
Hi Sjef,
For interest sake:
I read Allan Kimmel again. The bypass cap does indeed not increase gain but does however lower output impedance
Was a very short listening periode but it appeared that the midrange seemed accentuated more than the bottom and top end..providing a seemingly "bigger"" soundstage.
I bypassed with a 2200uF Rubycon.
Bas Horneman said:
Bas, then "Allan Kimmel" is wrong. Bypassing the cathode resistor DOES increase gain, because the tube is no longer subject to degenerative effects - ie. negative feedback from the AC signal presented to Rk.
Hi Joel,
Actually Alan Kimmel's verbatim words were :
"This will have minimal effect on the gain"
I tried this and he is right. Don't forget it is a Mu-Follower.
Cheers,
Bas
Actually Alan Kimmel's verbatim words were :
"This will have minimal effect on the gain"
I tried this and he is right. Don't forget it is a Mu-Follower.
Cheers,
Bas
Bas, I'm sorry - I didn't see that this was a mu follower!
I was referring to a standard common cathode voltage amp.
I was referring to a standard common cathode voltage amp.
Gain variation
Bas,
I must admit that I was uneasy when I posted my comment about the gain increase with added cathode bypass cap on this circuit, but actually it is by practical experience.
Perhaps this means that my mu stage is not working right? I'll have to invesigate this further.
Cheers,
Bas,
I must admit that I was uneasy when I posted my comment about the gain increase with added cathode bypass cap on this circuit, but actually it is by practical experience.
Perhaps this means that my mu stage is not working right? I'll have to invesigate this further.
Cheers,
MU-FOLLOWERS.
Hi,
This is quite possible.
Having built some of these circuits, I can say that in fact adding a bypass cap shouldn't change the gain of the mu-follower at all.
Could it be you made the calculations for your stage with a bypass cap in place?
Cheers,😉
Hi,
This is quite possible.
Having built some of these circuits, I can say that in fact adding a bypass cap shouldn't change the gain of the mu-follower at all.
Could it be you made the calculations for your stage with a bypass cap in place?
Cheers,😉
- Status
- Not open for further replies.