Thanks BobC.
I see now that using a lower voltage power transformer might get the B+ about correct using diode rectification, but then using a choke to reduce hum would decrease it perhaps to too low a level. So better to use a higher voltage power supply so that techniques that one would want to use such as chokes (and or valve rectifiers) to reduce hum, but also decrease B+ won't leave one with not enough. Does that sound correct?
I just spied a site:
http://www.tube-and-valve-electronics.co.uk/product_information/SV83_Electron_Tu... that listed 300V as the maximum plate voltage for SV83 (6p15p). Nevertheless, I am inclined to go with your experience re a 300V B+ sweet spot. With regard to measuring the B+, I know I can measure it with a multimeter connected to speaker ground and the socket for pin 7 for the 6p15p, but I am curious how does B+ relate to point “A” or “B” on the Zkit1 PCB in the “Pre-Flight Check” in the manual?
https://www.decware.com/newsite/ZKITmanual2020.pdfWith regard to diode rectification, you suggested adding a 120ohm 5W resistor after the diodes before the power supply filter / 1st cap. Would that be placed after the 1K resistor in series with it?
The CL90 NTC definitely sounds like a good idea. Where would it be placed? After the diodes before the 1K power resistor?
With regard to a rectifier valve, I have never heard an amplifier with one so I don't know what I'm missing and I note that the well regarded bottlehead amplifiers don’t have them, so I am inclined towards the cheaper option of diode rectification if it can sound great. Can you tell me what benefits you got when you went with valve rectification?
With regard to a choke, it sounds like a sensible way of improving hum. My, now not working, Transcendent Sound SOB has two chokes. In a diode rectified Zkit1 where would the choke go and approximately what values would you think might be sensible?
With regard to more capacitor filtering, I am inclined not to go overboard, but your suggestion of two 100uF, I presume in place of the 33uF after the diodes and resistors (?), sounds like a good idea. Perhaps I will go with the motor run version.
Removing the 3.3uf/10K decoupling network before the preamp tube and changing the 47K resistors changes to 56K would simplify things a bit too.
With regard to the grid resistors, so with the lower the B+ a lower grid resistance from 1K down to 300 Ohm can be used. Easily done.
Sounds like I have find out what choke to use with diode rectification that would reduce hum and adjust resistance in the power supply values to get/keep B+ at 300V. Does that sound right?
Did you use a program to help with power supply calculations? If so, may I ask which one?
Kind Regards,
Ben