Dynaco SCA-35 project "Start-Me-Up" with EFB™
Last week the new power board with EFB (Enhanced Fixed Bias) arrived from Canada from http://audioregenesis.com
This board is meant for a Dynaco SCA-35. Funny detail is that I am one of the first of getting this board. You will see a photo coverage of the process of rebuilding a Dynaco SCA-35. The amplifier will be provided with new boards from Audioregenesis. The preamp board PC-11, a complete new power supply board which will replace the both can capacitors but with a extra feature!! EFB !! and the PC-10A output board in stead of the PC-10. The PC-10A is using 6GH8A or 6U8A. These have the same quality as the rare and expensive 7199 tube. The biggest change will be the extra feature EFB. If you want to read everything about this, just visit http://tronola.com/A_New_Look_At_An_Old_Friend.pdf
First I had to make a choice which SCA-35 is most suitable for the new boards. I have 4 SCA’s with one already with new audioregenesis boards (exept the EFB but with PC-10 boards). My choice was to pick the SCA with the best looking chassis.
This one is ready for restoring. The original pertinax (pressed paper) boards are a bit discolored because of the heat of the tubes.
The bottom of the circuit board was a bit a mess.
The new PC-10A boards are in place, the old stuff besides it.
At the output tubes it is becoming crowded already.
To connect the wires for the input selector takes a bit more time! Lots of spaghetti on a square cm.
This is the new Power Supply Capacitor Board with EFB™ . The board has double layers and the holes for the wires are full metal throughout the hole. The screws for attachment are already there. The manual is sent with the board, and very good I must say. If you want to see the manual for this board, visit http://www.audioregenesis.com/manuals/pdf/SCA35-CAPR05_Installation.pdf
This is the bottom of the can capacitors. One of these capacitors is not available anymore. The other one is, but sending it to the Netherlands, Europe is very expensive. In fact a complete power board with EFB is almost cheaper.
If you want to read more about David Gillespie's EFB™, go to http://tronola.com/A_New_Look_At_An_Old_Friend.pdf
Fine, these are gone. Two yawning holes stay behind.
The new power board is placed within a minute, it fits just perfect. Connecting the leads can start.
Everything has finished! I check all the wires again. With a magnifying-glass I even check the soldering. This is a good thing when you use the old wires again. I partially renewed the wires.
Now I can put in the new tubes. I have new matched EL84 from JJ and the 6GH8A are RCA. The preamplifier became the old 12AX7. Give pressure to the bottom side of the boards when you put in the tubes! Isn't it a fantastic view?
Now I can connect it to 'the grid' and set the right bias on the power board. This is possible with the decent test sockets. The average voltage for left and right channel has to be 0,27V what is a bias current of 27mA. The original design has a bias current of 35mA. The power dissipation is lower and thus extending the lifetime of the tube. A new (extra) feature is using an EFB modified ST-35 or SCA-35 as a pseudo tub tester to match output tubes for bias current. The EFB circuit makes this possible, it would not work with the stock, cathode bias circuit. As I understood, there will be a procedure for that soon!
A CD of the Rolling Stones is lying ready to play with the song "Start Me Up" under the play button. On the multimeter you can see the voltage 0,27V.
The cover can be attached! Listen to some music
How does it sound? I will report in the next post.
Excuse me for my bad English language