Hi! Most of the main power supply, bias supply, the power tubes and relays is wired up and running. Martin's proposed alternative power supply for the driver stage is running great! I'm getting a stable +147V and -147V from the power transformers 50VAC winding (without load).
Relay supply is also working fine with the 5V regulator mounted in the back. Relais are wired up and tested, still have to wire up the XLR socket but will do that towards the end to keep some things more accessible for soldering. Looking at the picture I now see that I labeled the pcb "FET Power Supply". It's the "Relay power supply" of course, must have been late at night:D
Output transformer is also wired up, just missing the NFB wire:
...and finally the ground bar above the potentiometers and the front panel light:
Next up is the remaining parts of the power supply near the reverb transformer, the remaining parts of the bias supply and the phase inverter stage.
Cheers
Last edited by captaincoconut on Sun Mar 09, 2025 5:08 pm, edited 1 time in total.
Sorry for being so slow with building but spring's around the corner and I try to spend as much time as possible outside of my workshop Spent an hour this weekend determining the outer foil on my capacitors....
Phase inverter, CF and bias circuit almost fully wired up now. I went with Marshall values (820R/10K) for the PI and with a 100k NFB resistor from the OT's 8 Ohms tap as a starting point. I'm short of some fitting trimpots for the bias balance and PI balance, but have them on order. Additionaly, I have to wire up the Presence and Master Volume controls, but haven't decided yet about the best space to route them, so I will wait a little and do that at a later point.
Next thing I will do is finish the reverb circuit, the Switchcraft footswitch jack and then the FET boost with the input wiring proposed by Martin here .
Great looking build so far. I agree with what's been said about your lead dress, SUPER!
Did you paint your OT Secondary wires black where they exit the chassis? If so nice detail.
Edit: I see you Primary wires have also been Blackened. Also great job of documenting. As I read through some of these other builds I often can't recall precisely what I did and find myself looking back through my builds, frequently wishing I had documented mine better.
GAStan wrote: ↑Sun Mar 30, 2025 3:39 pm
Did you paint your OT Secondary wires black where they exit the chassis? If so nice detail.
Edit: I see you Primary wires have also been Blackened.
I use Hammond transformers in this build and the first few centimeters coming out of the transformers are almost all solid black but have different colors after that. Probably has to do with how they paint them.
Thanks to everybody for the nice words, keeps me going as I'm sometimes thinking I'm losing my mind building this haha!
captaincoconut wrote: ↑Sun Mar 30, 2025 3:58 pm
I use Hammond transformers in this build...
What part numbers are you using for the PT and OT, and what will your power stage look like, i.e. what tube type and is it distributed load?
Following this schematic. Using the same Hammond 373FX power transformer, but Hammond 1760W (Twin Reverb) OT with 6L6 tubes.
Could anyone give me some input on a ballpark value for the voltage divider resistors used to power the FET board? The linked schematic replaces the traditional HAD designed FET booster with an EP booster and divides B+5 down to around 9V. I would like to use the traditional FET booster design, though.
Spent an hour this weekend determining the outer foil on my capacitors....
