myself and jamesd have concocted this amp
it has been a few months in creation
any opinions would be appreciated.....
power supply is valve rectified LC or sometimes LCLC
(i can't fit the second choke onto the board)
i have tried CLC which gives @510V HT with droppers to give 460V on driver
but choke input sounds better in this case
the driver stage has further LC decoupling
i am considering some form of shunt regulation or minimal reactance type psu
6n6p operating point was actually derived for ecc99
so we may tweak this but it does sound substantially better with 6n6p
i would like to thank jamesd for his support in this project
it was he that led me through all the calculations etc
so without him it wouldn't have happened
hope you like it.....
dave dove
it has been a few months in creation
any opinions would be appreciated.....
power supply is valve rectified LC or sometimes LCLC
(i can't fit the second choke onto the board)
i have tried CLC which gives @510V HT with droppers to give 460V on driver
but choke input sounds better in this case
the driver stage has further LC decoupling
i am considering some form of shunt regulation or minimal reactance type psu
6n6p operating point was actually derived for ecc99
so we may tweak this but it does sound substantially better with 6n6p
i would like to thank jamesd for his support in this project
it was he that led me through all the calculations etc
so without him it wouldn't have happened
hope you like it.....
dave dove
Attachments
A couple of comments on Dave's amp.
In many ways this amp is a tribute to JRB of Tubecad fame. His ideas abound in it. The pentode Aikido is a super idea. It allows the nice low Gm audio pentodes to have a real chance of driving DHTs. ANd a very good job they do of it. I've used and like high Gm pentodes driving DHTs but had often wondered what an EF86 would sound like doing the same task - now I know 🙂.
The idea to use partial feedback around the 300BXLS came from Dave and is again inspired by JRB. John and Steve Bench's T-Rex amplifier design provided the template and Dave adapted it for this amp.
James
In many ways this amp is a tribute to JRB of Tubecad fame. His ideas abound in it. The pentode Aikido is a super idea. It allows the nice low Gm audio pentodes to have a real chance of driving DHTs. ANd a very good job they do of it. I've used and like high Gm pentodes driving DHTs but had often wondered what an EF86 would sound like doing the same task - now I know 🙂.
The idea to use partial feedback around the 300BXLS came from Dave and is again inspired by JRB. John and Steve Bench's T-Rex amplifier design provided the template and Dave adapted it for this amp.
James
Aikido
Nice work Dave,
Looking forward to hearing it at the next Eggborough meeting .
I see this as the logical extension of the WE91 circuit . The beauty of it is , you still have only one gain stage , with one coupling cap , you retain the high gain of the pentode , but with the extra current from the Aikido . As James has said , the pentode alone looks to be slew-limited into the 300B grid, but the Aikido should get around this .
James, do you know what the output impedance of the 300B with the feedback loop should be ? - Interested to gauge what the damping factor could be . Has the circuit lost much gain from this tweak ?
I'll be following the same path most likely, but first I'll built Thorten's WE91 variant, so we can get the max education out of this ..
Mark
Nice work Dave,
Looking forward to hearing it at the next Eggborough meeting .
I see this as the logical extension of the WE91 circuit . The beauty of it is , you still have only one gain stage , with one coupling cap , you retain the high gain of the pentode , but with the extra current from the Aikido . As James has said , the pentode alone looks to be slew-limited into the 300B grid, but the Aikido should get around this .
James, do you know what the output impedance of the 300B with the feedback loop should be ? - Interested to gauge what the damping factor could be . Has the circuit lost much gain from this tweak ?
I'll be following the same path most likely, but first I'll built Thorten's WE91 variant, so we can get the max education out of this ..
Mark
Hi Mark,
Without going through the math to check how this circuit changes things, I would say about 150R based on JRBs example Tubecad Partial Feedback .
Hope that helps.
Looking forward to you joining the club 🙂 I'm toying with the idea of adding it to my PT15 PP amp. Since these are driven by an IT phase inverter - it is a challenge to work out what values to use...
ciao
James
Without going through the math to check how this circuit changes things, I would say about 150R based on JRBs example Tubecad Partial Feedback .
Hope that helps.
Looking forward to you joining the club 🙂 I'm toying with the idea of adding it to my PT15 PP amp. Since these are driven by an IT phase inverter - it is a challenge to work out what values to use...
ciao
James
Thanks for sharing with us James and Dave! I'm afraid I'm going to have to ask the inevitable question and ask..."How does it compare to other amps you've heard?"😀
bas
i've had this breadboard going for over a year now
kr300bxls output valves at loads of operating points
originally with lundahl output transformers
now with partridge output transformers
it has had the following driver stages:
6j5gt > 6ah4gt very good big dry sound k&k audio style
half ecc99 very polite, not enough energy for me
6em7 both cap coupled and direct coupled.... yuck
417a which i loved but had to try....
6c45pi which i didn't love even with some extreme battery biased operating points
then this which sounds like the music in my head
particularly since applying feedback around 300bxls
it has bandwidth, control, speed, transparency and loads of funk
and i haven't even started on the power supply yet
and all the caps, resistors and wire are cheap and nasty
we designed it to use ef86 and ecc99 which i had lying around
but changed to 6n6p because i really don't like ecc99
and it sounds wonderful
dave dove
i've had this breadboard going for over a year now
kr300bxls output valves at loads of operating points
originally with lundahl output transformers
now with partridge output transformers
it has had the following driver stages:
6j5gt > 6ah4gt very good big dry sound k&k audio style
half ecc99 very polite, not enough energy for me
6em7 both cap coupled and direct coupled.... yuck
417a which i loved but had to try....
6c45pi which i didn't love even with some extreme battery biased operating points
then this which sounds like the music in my head
particularly since applying feedback around 300bxls
it has bandwidth, control, speed, transparency and loads of funk
and i haven't even started on the power supply yet
and all the caps, resistors and wire are cheap and nasty
we designed it to use ef86 and ecc99 which i had lying around
but changed to 6n6p because i really don't like ecc99
and it sounds wonderful
dave dove
Mmm this schematic looks very interesting as a tube and a couple of resistors and a cap or two...is cheaper than some good choke.
further to this thread
we showed the amp at a gathering in the UK the other week
it proved to be very very good indeed
very fast and good top to bottom balance
have removed safety resistors
changed 6n6p cathode resistors to 690R
cheap russian coupling caps
cheap 2W metal films
choke input psu:
500-0-500 > 5u4gb > 5H > 20uf > 5-9H > 220uf
single feed to partridge output transformers
then into 20H choke on to driver stage
no decoupling cap - don't ask me why but it sounds better
are you going to try it bas?
dave dove
we showed the amp at a gathering in the UK the other week
it proved to be very very good indeed
very fast and good top to bottom balance
have removed safety resistors
changed 6n6p cathode resistors to 690R
cheap russian coupling caps
cheap 2W metal films
choke input psu:
500-0-500 > 5u4gb > 5H > 20uf > 5-9H > 220uf
single feed to partridge output transformers
then into 20H choke on to driver stage
no decoupling cap - don't ask me why but it sounds better
are you going to try it bas?
dave dove
Thinking of trying this circuit, I am having problem finding 620K 5W resistor.
May I ask how do you come up with the value of Rg2 (620K)?
May I ask how do you come up with the value of Rg2 (620K)?
Rg2 follows standard pentode calculation practice. So
It is based on the voltage drop between the B+ it is connected to and the required Vsg i.e V(Rsg)= B+ - (Vsg+Vk) where Vk is the voltage on the cathode. And the screen grid current under static conditions (i.e. no signal). Isg can be found by examining the datasheets for the valve and finding the screen current at the operating point (Va, Vsg, Ia, Vgk). Alternatively it can be estimated from the anode current Ia. As a general rule (their are exceptions) Isg is about 25% of Ia.
So Rsg = {B+ - (Vsg+ Vk)}/Isg.
The decoupling capacitor should work with the screen grid input impedance and Rsg to decouple the screen grid with a 1Hz time constant. Ideally to the cathode (not to ground) but it can be to ground if the cathode is also bypassed to ground...
hope that helps
James
It is based on the voltage drop between the B+ it is connected to and the required Vsg i.e V(Rsg)= B+ - (Vsg+Vk) where Vk is the voltage on the cathode. And the screen grid current under static conditions (i.e. no signal). Isg can be found by examining the datasheets for the valve and finding the screen current at the operating point (Va, Vsg, Ia, Vgk). Alternatively it can be estimated from the anode current Ia. As a general rule (their are exceptions) Isg is about 25% of Ia.
So Rsg = {B+ - (Vsg+ Vk)}/Isg.
The decoupling capacitor should work with the screen grid input impedance and Rsg to decouple the screen grid with a 1Hz time constant. Ideally to the cathode (not to ground) but it can be to ground if the cathode is also bypassed to ground...
hope that helps
James
I'd love to adapt this to the 6C33C-b and build. I've never built a tube amp before, and this looks like an interesting project but for cost reasons for an unknown outcome, seeing as its my first build, I'd like to use the much cheaper 6c33c-b.
Do you see any issue in modifying it for the russian IHT? I also have the C3g and C3m pentodes to play around with, so maybe I'll try them in lieu of the EF86.
Do you see any issue in modifying it for the russian IHT? I also have the C3g and C3m pentodes to play around with, so maybe I'll try them in lieu of the EF86.
It should be a good driver for a 6C33. The only noteworthy thing I can see is the requirement for a high B+ for the Aikido relative to the 6C33 B+. If your happy with two psu in your amp then it should work well.
If you use a C3g then you can do without the Aikido as its meduim high Gm lets you make a nice low impedance driver and gain stage in one. This needs a little extra attention to the psu for the driver stage to keep the noise down.
James
If you use a C3g then you can do without the Aikido as its meduim high Gm lets you make a nice low impedance driver and gain stage in one. This needs a little extra attention to the psu for the driver stage to keep the noise down.
James
pentode aikido driver for 845
Hi
I have 845s and was going to use the 45 as the driver stage for an 845 SE.
On the weekend it occurred to me to look into using the Aikido as the input stage (I have some spare boards from Bas’ group buy).
This circuit looks better in several ways than what I was starting to think of. 🙂
In a “mid-point” 845 implementation, compared to the 300B XLS, the 845 has nearly double the B+ (1000 v); and nearly 50% higher grid volts swing: 145.
I only know fragments of circuit design . . maintaining the attractions of this circuit, how would it be adapted to run 845s in particular, the higher grid swing?
(Though depending on what speakers end up being used, I may not need to maximise power).
Thanks
Hi
I have 845s and was going to use the 45 as the driver stage for an 845 SE.
On the weekend it occurred to me to look into using the Aikido as the input stage (I have some spare boards from Bas’ group buy).
This circuit looks better in several ways than what I was starting to think of. 🙂
In a “mid-point” 845 implementation, compared to the 300B XLS, the 845 has nearly double the B+ (1000 v); and nearly 50% higher grid volts swing: 145.
I only know fragments of circuit design . . maintaining the attractions of this circuit, how would it be adapted to run 845s in particular, the higher grid swing?
(Though depending on what speakers end up being used, I may not need to maximise power).
Thanks
amazing result
I would like to thank Dave for this design. I had some 6n6's and on impulse put together a breadboard version. It sounds delicious. Better than most 300b amplifiers I've heard. Oh dear, what am I going to do with my old amp now ???😉
Incidentally, I've found that it sounds indeed better with choke input psu. I'm so thrilled with the result that I think I'm going to make separate psu's for driver and output.
Thanks again
Fred
I would like to thank Dave for this design. I had some 6n6's and on impulse put together a breadboard version. It sounds delicious. Better than most 300b amplifiers I've heard. Oh dear, what am I going to do with my old amp now ???😉
Incidentally, I've found that it sounds indeed better with choke input psu. I'm so thrilled with the result that I think I'm going to make separate psu's for driver and output.
Thanks again
Fred
Update
Hi Dave and James, have you any further comments on this design.
I am going to build this, maybe swap in 6H30 as I have a few octal versions in stock - any comments, or changes you have implemented appreciated.
Hi Dave and James, have you any further comments on this design.
I am going to build this, maybe swap in 6H30 as I have a few octal versions in stock - any comments, or changes you have implemented appreciated.
GM70 Driver
Hi dave dove,
I've tried the driver at post 1, having a GS11 transmitter triode with a mu of 150 and the power half of a couple of 6GF7. The result is about right were i wanted it to be! For once, without tetrode or pentode, I get the definition and the power I wanted. Still just mono, plywood and first jiff of the modified driver, all direct coupled, pseudo-stacked psu,600v and 300v; Thank you for sharing this inspiring schematic. I will be two years that I am fiddling with the mighty GM70 by couples of hours a week, and YES, i am now nearer to sit and enjoy!
Jean Grégoire.
Hi dave dove,
I've tried the driver at post 1, having a GS11 transmitter triode with a mu of 150 and the power half of a couple of 6GF7. The result is about right were i wanted it to be! For once, without tetrode or pentode, I get the definition and the power I wanted. Still just mono, plywood and first jiff of the modified driver, all direct coupled, pseudo-stacked psu,600v and 300v; Thank you for sharing this inspiring schematic. I will be two years that I am fiddling with the mighty GM70 by couples of hours a week, and YES, i am now nearer to sit and enjoy!
Jean Grégoire.
Hi Dave,
I have recently come across this thread and it interested me greatly having had much success with Aikido line stages and as a diver for a Moskido.
I would really like to implement this but have some questions.
1 - if there any special consideration regarding the heater of the 6n6p - ie does it need to be lifted as is done with the Aikido linestage
2 - what is the going on around the 300b? is this some kind of feedback mechanism? the schematic seems to show 43k ->2.2uf > 1k > ground is this right? Or does the 2.2uf attach to the grid 300b?
Any help would be good for a relative newbee.
I have recently come across this thread and it interested me greatly having had much success with Aikido line stages and as a diver for a Moskido.
I would really like to implement this but have some questions.
1 - if there any special consideration regarding the heater of the 6n6p - ie does it need to be lifted as is done with the Aikido linestage
2 - what is the going on around the 300b? is this some kind of feedback mechanism? the schematic seems to show 43k ->2.2uf > 1k > ground is this right? Or does the 2.2uf attach to the grid 300b?
Any help would be good for a relative newbee.