Good to know. I'm just using one of these set to 110V and I drop 51V with a zener and use the rest for biasing... I originally was going to wire for Triode and needed the extra voltage. In my new 6P45S build in triode mode, I'm using the same module for bias, but I'm using an AB-4 autobiasing board from Pavel at
audioamp.eu
DC-AC Converter 12V to 110V 200V 220V 280V 150W Inverter Boost Board Transformer | eBay
Automatic bias control module for four push-pull (PP) tube AB-4. Dimensions 74x77 mm. TES
Just thought I'd let you know I reconfigured for Triode operation on my build. 300V B+, fixed bias @ 60ma per tube. Very nice sound even if it's only 27W...
Thought I'd give an update. I changed back to tetrode mode. Triode mode at the op and load I was running has no balls! (By that, I mean less than 1/4" excursion)
audioamp.eu
DC-AC Converter 12V to 110V 200V 220V 280V 150W Inverter Boost Board Transformer | eBay
Automatic bias control module for four push-pull (PP) tube AB-4. Dimensions 74x77 mm. TES
Just thought I'd let you know I reconfigured for Triode operation on my build. 300V B+, fixed bias @ 60ma per tube. Very nice sound even if it's only 27W...
Thought I'd give an update. I changed back to tetrode mode. Triode mode at the op and load I was running has no balls! (By that, I mean less than 1/4" excursion)
Thank you for the information!
He he he i was expecting this as the triode mode does not offer anything significant in this amplifier.
My final build outputs 80w rms with 0.3% THD @ 20db GNFB and 98 db SNR.
Basically i have reinvented the Williamson amplifier but with a tone stage and mosfet mu follower active loads even at the LTP stage and some tricks.
I have tried all configurations by now and i found that the mu follower stages with mosfets have the best characteristics (low thd, SNR of 100db and bandwidth of 400 Khz @ 6db) so i adopted them for all amplification stages.
I have also made nice PCB's for all stages including an LTP, a tone stack and a power supply stage.
The stage visible is the preamplifier with Concertina and voltage regulator, resting on top of the amplifier's power supply (600V, 400V, 200V, -24V, 12,6V, 6,3V
Chris
He he he i was expecting this as the triode mode does not offer anything significant in this amplifier.
My final build outputs 80w rms with 0.3% THD @ 20db GNFB and 98 db SNR.
Basically i have reinvented the Williamson amplifier but with a tone stage and mosfet mu follower active loads even at the LTP stage and some tricks.
I have tried all configurations by now and i found that the mu follower stages with mosfets have the best characteristics (low thd, SNR of 100db and bandwidth of 400 Khz @ 6db) so i adopted them for all amplification stages.
I have also made nice PCB's for all stages including an LTP, a tone stack and a power supply stage.
The stage visible is the preamplifier with Concertina and voltage regulator, resting on top of the amplifier's power supply (600V, 400V, 200V, -24V, 12,6V, 6,3V
Chris
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Here are the most interesting sections.
I have tested all of them BUT SOME PARTS ARE THERE AS AN OPTION for example in the Concertina preamplifier i have a feedback rc from output to input grid that it is ment for a different configuration as the pcb i have made are multi purpose.
Actually all of the local feedback rc networks found at the tonestack, preamplifier and Concertina are needed only in special cases and their values are adjusted as needed depending on where i wish to apply local feedback, to the input grid or to the cathode.
GRID STOPPERS must be small in value 1k or smaller otherwise the bandwidth is compromised.
The LTP stage does not have the DC input bias circuit that the concertina has for the 829B output tube because an LTP stage is not needed in my build which uses the 829B.
Chris
I have tested all of them BUT SOME PARTS ARE THERE AS AN OPTION for example in the Concertina preamplifier i have a feedback rc from output to input grid that it is ment for a different configuration as the pcb i have made are multi purpose.
Actually all of the local feedback rc networks found at the tonestack, preamplifier and Concertina are needed only in special cases and their values are adjusted as needed depending on where i wish to apply local feedback, to the input grid or to the cathode.
GRID STOPPERS must be small in value 1k or smaller otherwise the bandwidth is compromised.
The LTP stage does not have the DC input bias circuit that the concertina has for the 829B output tube because an LTP stage is not needed in my build which uses the 829B.
Chris
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FINISHED!
I finally finished my amplifier and now it lives with me.
I took some final measurements which are:
Bandwidth 20Hz to 30Khz limited at the input.
THD below 0,1% at 70W rms and 19db NFB using the B&W 603 S2 speakers connected to the 4 Ohm tap since they can go below 4 Ohm at certain frequencies.
With no NFB Distortion is 0,7% at 25W rms and 1% at 60w RMS
S/N 98db with 19db NFB and ~80db without.
Sensitivity 0,25V rms FOR 70W output with NFB and ~25mv without.
I want to also try a P channel Mosfet Concertina against the 6SN7 and also use a 6SL7 for the tone control instead of the 6sn7 just to check the distortion and the S/N
Also i consider changing the enclosure because i don't really like wood now that i see it finished....
Here are two pictures, in the second one i couldn't resist not to include my RC Jet.
Now i need to clean the house because i have really messed it up and my wife does not forgive without money
I finally finished my amplifier and now it lives with me.
I took some final measurements which are:
Bandwidth 20Hz to 30Khz limited at the input.
THD below 0,1% at 70W rms and 19db NFB using the B&W 603 S2 speakers connected to the 4 Ohm tap since they can go below 4 Ohm at certain frequencies.
With no NFB Distortion is 0,7% at 25W rms and 1% at 60w RMS
S/N 98db with 19db NFB and ~80db without.
Sensitivity 0,25V rms FOR 70W output with NFB and ~25mv without.
I want to also try a P channel Mosfet Concertina against the 6SN7 and also use a 6SL7 for the tone control instead of the 6sn7 just to check the distortion and the S/N
Also i consider changing the enclosure because i don't really like wood now that i see it finished....
Here are two pictures, in the second one i couldn't resist not to include my RC Jet.
Now i need to clean the house because i have really messed it up and my wife does not forgive without money
Attachments
Last edited:
I forgot to mention that when i say no NFB (Negative Feed Back) i mean without any type of feedback local or global.
All stages are designed to run open loop with the GNFB removed although i have made experiments with local feedback especially in the tone control stages.
What i use now is 19db (i can go up to 30db) GNFB (Global Negative Feed Back) because i think the bass region is soft a bit without it although i believe that the overall sound is better or more natural, i don't really can tell....
Chris.
All stages are designed to run open loop with the GNFB removed although i have made experiments with local feedback especially in the tone control stages.
What i use now is 19db (i can go up to 30db) GNFB (Global Negative Feed Back) because i think the bass region is soft a bit without it although i believe that the overall sound is better or more natural, i don't really can tell....
Chris.
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