I would like to modified my Ampex 602 preamp into a two mic preamps.
I'm thinking of using the original design for the first preamp but to replace V2 (6AW8A) with 12AT7 so instead of triode and pentode I'll have two triodes at V2 position.
For doing this replacement I'll need to do the following mod in the heaters supply :
With the 12AT7 heaters wired this way for 6 volt operation, it will draw 300 mA, while the 6DJ8 heater draws 365 mA. The 100 ohm resistor in parallel with the 12AT7 heaters balances the voltage across the two tubes.
So this is the routing for the first mic channel:
mic input > T1 > V1 (both sides of 12AX7) > first half of V2 (12AT7) > V4 (6DJ8)>output transformer (T2).
For the second preamp I'm thinking to use the reproduce amp channel in combination with the bias driver components:
(J2) converted into mic input > additional input transformer (T11) > V3 (both sides of 12AX7) > second half of V2 (12AT7) > V5 (both sides of 12AU7) > additional output transformer (T104).
Since I already have an Amperx 601 output transformer and since I'll use a 12AU7 to drive the second output transformer (T104)
I'll copy the output stage of the Ampex 601 for my second mic pre.
I made this schematic for my design:
Before I'm starting to order parts, do you have any comments / can you see some errors on this design?
Fore reference here's the original 602 schematic:
http://i63.tinypic.com/2m346l5.jpg
I'm thinking of using the original design for the first preamp but to replace V2 (6AW8A) with 12AT7 so instead of triode and pentode I'll have two triodes at V2 position.
For doing this replacement I'll need to do the following mod in the heaters supply :
With the 12AT7 heaters wired this way for 6 volt operation, it will draw 300 mA, while the 6DJ8 heater draws 365 mA. The 100 ohm resistor in parallel with the 12AT7 heaters balances the voltage across the two tubes.
So this is the routing for the first mic channel:
mic input > T1 > V1 (both sides of 12AX7) > first half of V2 (12AT7) > V4 (6DJ8)>output transformer (T2).
For the second preamp I'm thinking to use the reproduce amp channel in combination with the bias driver components:
(J2) converted into mic input > additional input transformer (T11) > V3 (both sides of 12AX7) > second half of V2 (12AT7) > V5 (both sides of 12AU7) > additional output transformer (T104).
Since I already have an Amperx 601 output transformer and since I'll use a 12AU7 to drive the second output transformer (T104)
I'll copy the output stage of the Ampex 601 for my second mic pre.
I made this schematic for my design:
Before I'm starting to order parts, do you have any comments / can you see some errors on this design?
Fore reference here's the original 602 schematic:
http://i63.tinypic.com/2m346l5.jpg
