FPALB
Active member
I've been working on this unit for a while now and thought I should begin a thread to document the rebuild. With the budget available the criteria was simple - Get the main mono out working (with front panel volume control) as well as provide a direct out from each of its preamp cards (also with their front panel volume controls)- Amplifier and booster cards for monitor path are not necessary. Id like to have shut off switches for each channel post fader as well - easy to do with so many unused switches. The unit is in disrepair with many wires cut, all the tubes missing, and the power supply is completely stripped of components except for the mains transformer, and 6 can caps installed by a different tech. All the cards and transformers are present.
Game plan: Rebuild the power supply, the preamp cards, and the program amplifier card. Remove all wiring and keep any shielded wiring that is still good. Rewire just the circuits im using and send direct outs to new jack on the rear of the unit.
The guys over on this thread did a ton of heavy lifting for me , so thank you to them.
Where I currently am:
PSU: Fully rebuilt the power supply (replaced 4CR1 with diodes- still need to add a resistor to drop the voltage down slightly).
Kept the same can caps that the last tech put in as well as added a couple other stand alone they are as follows:
4C1(A,B,C): 40uF, 40uF, 20uF
4C2(A,B,C): 40uF, 40uF, 40uF
4C3: .47uF film
4C4(A,B,C): 40uF, 50uF, 50uF
4C5(A,B,C): 50uF, 50uF, 20uF
4C6(A,B,C): 50uF, 50uF, 50uF
4C7: 2200uF
Cards: cleaned and rebuilt all of the cards that I will be using.
Next step: remove the riser plate from the chassis and use it to create a test platform on my bench to test the power supply loaded with all of the cards.
Issues im still pondering -
- Im not going to be using the monitor section at all, and because the PSU is a non regulated unit im assuming ill have to put loading resistors in place to keep the PSU happy - is this correct thinking? Im a bit of a novice when it comes to unregulated supplies like this.
-Direct outs: Can an unbalanced direct out post 1C5 be sufficient for a direct out into a converter? How does one calculate this? Do I need a transformer here or a buffered circuit?
Thank you for all of your shared knowledge in advance.
Game plan: Rebuild the power supply, the preamp cards, and the program amplifier card. Remove all wiring and keep any shielded wiring that is still good. Rewire just the circuits im using and send direct outs to new jack on the rear of the unit.
The guys over on this thread did a ton of heavy lifting for me , so thank you to them.
Where I currently am:
PSU: Fully rebuilt the power supply (replaced 4CR1 with diodes- still need to add a resistor to drop the voltage down slightly).
Kept the same can caps that the last tech put in as well as added a couple other stand alone they are as follows:
4C1(A,B,C): 40uF, 40uF, 20uF
4C2(A,B,C): 40uF, 40uF, 40uF
4C3: .47uF film
4C4(A,B,C): 40uF, 50uF, 50uF
4C5(A,B,C): 50uF, 50uF, 20uF
4C6(A,B,C): 50uF, 50uF, 50uF
4C7: 2200uF
Cards: cleaned and rebuilt all of the cards that I will be using.
Next step: remove the riser plate from the chassis and use it to create a test platform on my bench to test the power supply loaded with all of the cards.
Issues im still pondering -
- Im not going to be using the monitor section at all, and because the PSU is a non regulated unit im assuming ill have to put loading resistors in place to keep the PSU happy - is this correct thinking? Im a bit of a novice when it comes to unregulated supplies like this.
-Direct outs: Can an unbalanced direct out post 1C5 be sufficient for a direct out into a converter? How does one calculate this? Do I need a transformer here or a buffered circuit?
Thank you for all of your shared knowledge in advance.