Wonderfull Crazy mod on SA2000
Johnson, Thank you for the info and show us a such
interesting example for showing the possibility of the way to get very good
sounding stuff without huge investment. Think this is the sample of
Labor with the Passion that is one of most efficiency investment to get very good sound. Hope I might not be wrong?
Here under is Johnson's comment.
...continued can be viewed with crick next.
Some details about this crazy SA2000.
I bought it on Ebay from someone who thought its broken.
Turns out only 2 RCA connectors are broken and the
Source/Tape Mon selector is not installed right.
So I fixed them and then did the following:
Bypassed input PFET, changed input from Cathode to route to Grid.
Installed battery to provide adjustable (2Megaohm trim pot) bias to
No Cathode resistor.
Added 100kOhm resistor to plate so effective plate resistor = 33.3333k.
adjust bias so that it's always 4.5-5mA idle current.
Use Nichicon low impedance lytics for B+ filter (180uF)
replaced all 22uF caps to 68uF Nichicon low impedance.
replaced filament cap from 2200uF to 3300uF, Nichicon KW.
Input cap to grid is now Russian Teflon FT3 0.1uF
B+bypass is now Jensen 0.015 + 62uF Solen PB 400V
Note that I'm using quick disconnect plugs so I can switch between
Solen, Blackgate, ASC386 for comparison.
Output is Jantzen 3uF.
wired 6922 socket to 6SN7 tube socket.
Replaced the 2 drop resistors to regulator transistor with chokes
Can't find a way to put choke right after 6CA4 before 180uF cap.
Otherwise I'd think smoothing before it goes to series pass transistor
might be much better idea.
May re-enable Mosfet follower later.
That's pretty much all.