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Old 12th August 2007, 11:33 AM   #1
Fuling is offline Fuling  Sweden
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Join Date: Aug 2001
Location: Sweden (Mora)
Default What does R2D2, Mickey Mouse and a...

...crackpipe have in common?
Quite unexpected, they are building blocks in my latest amp project:
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Old 12th August 2007, 12:00 PM   #2
Fuling is offline Fuling  Sweden
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Join Date: Aug 2001
Location: Sweden (Mora)
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. Im 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.
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Old 12th August 2007, 12:48 PM   #3
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Join Date: May 2005
Location: near Duesseldorf
Hi,

without the "sand" 2SK2700 source follower: what do you think about a DET19 as output tube?

http://www.jogis-roehrenbude.de/Roeh...ioden/2C34.htm

Regards Andreas
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Old 12th August 2007, 01:01 PM   #4
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
Im hoping to find a pair of good PP OPTs in the 10k/8 range and build a DET19 PP amp some day. IIRC they are good candidates for a zero bias output stage.
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