Thanks it's what I thought for the voltage.
For the other values I think I will just get other caps
Thanks nickytheshaft
I was thinking of using 6.3v to 5v drop resistor. However can I use the values indicated in the layout of post 65 with any corrections indicated in the following posts? Since many components do not correspond to those printed on the pcb. Just to have a starting point and not see magic smoke right away.
I was thinking of using 6.3v to 5v drop resistor. However can I use the values indicated in the layout of post 65 with any corrections indicated in the following posts? Since many components do not correspond to those printed on the pcb. Just to have a starting point and not see magic smoke right away.
With such low AC voltage (even at 230V it's only 334V) the cathode bias of 300B not the optimal solution.
The PSU DC output about 350V, and -with cathode biased 300B- the estimated power (A1) is only 3.2W (70mA anode current, Ug 100Vpp on 700R cathode resistor, the OPT has 3k5:8 connection).
Over it the distortion growing rapidly.
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The OPT datasheet recommend 80ma anode current, so the estimated current of HT PSU (one channel) about 88-90mA (power tube current + driver tubes current), the aggregated current is about 180mA.
You may choose some options (depending of OPT primary connection, cathode biased 300B):
- low/er/ impedance (2k or 3k5) with higher distortion but higher maximum power;
- high impedance (apx. 5k) with low distortion, but lower power.
The higher impedance represents higher DCR (the 5k total DCR is 184R), so with higher impedance the anode voltage will be a little lower (few ten Ohm * 80ma= about 2...5V).
If you choose this version, must be the HT B+ higher for -estimated- 350..400V Vak.
The B+ voltage:
Voltage on cathode resistor + estimated Vak of 300B + voltage on OPT (DCR*estimated current).
Sample: 68V + 350V + 15V = 433V (at 80mA anode current).
If you want 433V (at 180mA load) B+, the power transformer secondary must be -about- 390..420V (dependig of rectifier tube, PSU desing etc...etc).
p.s.
If you have MS-3221 power transformer from ISO, it's designed for fixed bias amplifiers (from the 70V AC point generating negative bias voltage of 300B grid).
You may choose some options (depending of OPT primary connection, cathode biased 300B):
- low/er/ impedance (2k or 3k5) with higher distortion but higher maximum power;
- high impedance (apx. 5k) with low distortion, but lower power.
The higher impedance represents higher DCR (the 5k total DCR is 184R), so with higher impedance the anode voltage will be a little lower (few ten Ohm * 80ma= about 2...5V).
If you choose this version, must be the HT B+ higher for -estimated- 350..400V Vak.
The B+ voltage:
Voltage on cathode resistor + estimated Vak of 300B + voltage on OPT (DCR*estimated current).
Sample: 68V + 350V + 15V = 433V (at 80mA anode current).
If you want 433V (at 180mA load) B+, the power transformer secondary must be -about- 390..420V (dependig of rectifier tube, PSU desing etc...etc).
p.s.
If you have MS-3221 power transformer from ISO, it's designed for fixed bias amplifiers (from the 70V AC point generating negative bias voltage of 300B grid).
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Some of this OT choice should also be based on the actual impedance of the speakers you are going to drive. Given that the impedance seen by the tube is a reflection of the speaker impedance, and rarely does a speaker present a constant impedance load across all frequencies, it's a good idea to try to look up the measured impedance curve of the speakers you plan to use, and setup the OT accordingly.
Hello,can you tell me why you did not place the 22pf?
My kit came with 33pf instead.
Thanks
