It’s been a long since I last posted here some project stuff. I’ve been busy with work and family. On my spare time, spent mostly listening to music, developing some synthesiser modules and playing music as well!
I missed ETF this year, sad to say. Work commitments made it impossible to travel to France. Hope that’s not the case next year as am keen to get back. I’ve seen some pictures and feedback and seems it was a blast despite the COVID restrictions.
On my exchange with Rod Coleman regarding this post, I asked him to send me a pair of his latest DHT filament regulator (version 9) to test them on my 801a preamp with a cathode bias resistor (degenerated or un-bypassed):
These regulators are design with the objective in mind of having a larger impedance path in the cathode. The negative terminal in this version always need to connect to the cathode resistor.
I will modify the VT-25a/801a preamp I built back in 2016 to use these regs. I will need to remove the filament bias element and replace with the cathode resistors. I will also upgrade the gyrator boards and get these boards for the FT-3 caps I have in place:
Some new holes will have to be drilled I think on this nice aluminium top plate. Let’s see how it turns out.
The circuit has already been presented:
I won’t be adding initially the low gain attenuator network (R2 and R3) nor the source follower. The rest is the same as above