Tag: FT-3

FT-3 Coupling Cap PCB

As several DIYers out there, I’m a big fan of the Russian teflon FT-3 capacitors in my preamps. I normally use the 220nF/600V ones as have plenty of them in stock. These are superb in my view, however mounting them is a royal pain in the back. I used turrets for some time, but I ended up building a simple PCB which has a cutout to fit the FT3, solder it firmly on big copper pads and then solder the connections from the PCB. Also added a bias resistor (either for charging/discharging the cap or for fixed bias) which is connected to a GND terminal. This GND terminal could be used for the negative fixed bias if required. The PCB can be stacked very easily as has 4 M3 hex standoffs:

Populated PCB (Without resistor) and empty PCB
lateral view with the FT-3 cap soldered on PCB

 

UV-201a final version – finished!

After doing all the soldering part (which I enjoy much), the preamp is now finished. It sounds as good as the original breadboard:

For the curious ones, here you have a picture of the inside:

The teflon sockets are bolted straight into the 4mm top aluminium plate. No microphonic noise this way. Rod Coleman V7 regulators set to 200mA. A pair of Russian Military NOS wire-wound resistors in parallel provides the filament bias. The gyrator PCB is set as per original circuit and each valve at 3mA. These are DC coupled to the MOSFET follower PCB set at 10mA each. The output is then taken out from a pair of FT-3 teflon caps. 

Now to enjoy this beauty!