In the previous post about these mono blocks I already showed the building blocks of amps and power supplies and also the signal wiring. These amps are completed since a while and breaking in before they go to their new owner. So it is time for an update.
This is how the combo looks like, power supplies on the left and mono amps on the right:
As already described in the first part, the output stage s configured to only accept 45 or UX245 tubes. The driver stage can be switched between 45 (or UX245) and 10Y (or UX210, 801A, VT62, VT25A). In the photo above both stages are equipped with ST 45 tubes. The next photo shows the driver sockets with 10Y triodes plugged in:
Usually I do the output stage configurable for 45 or 2A3. Since these amps will be used with a very sensitive speaker, there was the wish to have the output tube filaments heated with DC as well like the driver, for which DC is mandatory. Due to the different filament currents of 45 and 2A3 that would have increased the complexity for the switching mechanism as the filaments are powered by completely passive filtered voltages.
This requires a lot of iron, therefor it made sense to build these as completely separate mono blocks with their own supplies. The photos below show the insert of one of the power supplies, assembled and pre wired, before it slides into the wooden frame and gets hooked up to the top plate which carries the B+ power transformer, oil caps and rectifier bridge.
The assembly inside the frame, before the top plate is added:
The whole space inside the chassis is needed for the chokes, filament transformers and caps of the filament supplies.
The amp chassis are a bit less crowded. Most of the parts are mounted on the top and all the signal wiring is done right under the top plate, using teflon insulated solid core silver wire with additional sleeving for mechanical protection:
B+ voltages are separately decoupled for driver and output tubes by their own LC section. The caps are on the top side, only the chokes are inside. Two more chokes for the filaments, which are the last choke in the LCL chain of the filament supply. No final cap across the filaments. The assembly inside the amp, all wired up before the bottom lid is attached:
Since the directly heated driver tubes have low gain, an input transformer steps up the voltage 1:4. It can be seen on the photo above in the top right corner.
The amps equipped with globe 45s in both sockets:
A close up:
UX210 in the driver position and UX245 output:
ST 45s in both sockets:
ST 10Y and ST 45:
A nice 'landscape' with tubes, transformers and oil caps:
The last photo shows the backside with the connection terminals:
These amps match in chassis style to the D3a LCR phono stage which I showed in earlier posts and will be complemented with a matching 10Y line stage.
I will give an update about the sound differences of 45 and 10Y driver in the next part. Stay tuned!