From left to right: DET20 input tube, 808 output tube and RK60 rectifier.
The input tube is quite similar to 1/2 6SN7 and will operate with a CCS load and 280V B+, the driver stage will be a 2SK2700 source follower with +300 and -150V rails direct coupled to the grid of the 808.
808 has an amplification factor of 49 so it requires positive grid bias to work in an SE amplifier, about 30-35V should be about right to pull 90mA through the tube at 350V plate-cathode.
The output transformers are Mars 3,5K 10W units with 0-4-8-16 ohms secondary windings. I´m going to use the 16 ohms taps for cathode feedback.
808 is one thirsty bottle when it comes to filament current, 7,5V 4A is what it needs to be happy and there seems to be no way to get rid of the hum unless they are heated with clean DC.
The filament PSUs will be massive, as in MASSIVE: 11VAC transformers followed by 35A rectifiers and LCLC-filters made from 1,1mH 10A transformer core chokes and 27000uF caps.
Somthing like 1,1+1,1mH - 27000uF-1,1mH - 27000+27000uF.
The filament ransformers also has 230 and 110V low current windings that will supply the input and driver stages with +300 and -150V.
The output stages will have their own power supplies based on 385-0-385V 150VA transformers, RK60/1641 rectifiers and CLC filters (with low input C).
The amp will be built as mono blocks.
The input tube is quite similar to 1/2 6SN7 and will operate with a CCS load and 280V B+, the driver stage will be a 2SK2700 source follower with +300 and -150V rails direct coupled to the grid of the 808.
808 has an amplification factor of 49 so it requires positive grid bias to work in an SE amplifier, about 30-35V should be about right to pull 90mA through the tube at 350V plate-cathode.
The output transformers are Mars 3,5K 10W units with 0-4-8-16 ohms secondary windings. I´m going to use the 16 ohms taps for cathode feedback.
808 is one thirsty bottle when it comes to filament current, 7,5V 4A is what it needs to be happy and there seems to be no way to get rid of the hum unless they are heated with clean DC.
The filament PSUs will be massive, as in MASSIVE: 11VAC transformers followed by 35A rectifiers and LCLC-filters made from 1,1mH 10A transformer core chokes and 27000uF caps.
Somthing like 1,1+1,1mH - 27000uF-1,1mH - 27000+27000uF.
The filament ransformers also has 230 and 110V low current windings that will supply the input and driver stages with +300 and -150V.
The output stages will have their own power supplies based on 385-0-385V 150VA transformers, RK60/1641 rectifiers and CLC filters (with low input C).
The amp will be built as mono blocks.
Hi,
without the "sand" 2SK2700 source follower: what do you think about a DET19 as output tube?
http://www.jogis-roehrenbude.de/Roehren-Geschichtliches/Trioden/2C34.htm
Regards Andreas
without the "sand" 2SK2700 source follower: what do you think about a DET19 as output tube?
http://www.jogis-roehrenbude.de/Roehren-Geschichtliches/Trioden/2C34.htm
Regards Andreas
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