Greetings Friends. I've been thinking on this amp all summer, when I wasn't doing fun summer stuff, and I've found two promising schematics on these forums for a cathode-biased Gu50 SEP amp with a 6e5p driver. The first was posted by @quikie22 with help from @Wavebourn
The second posted by @Ejam
In both circuits there is some type of voltage regulation for the screens. I'm unfamiliar with the methods used, and was curious about using Zener diodes as described in the @blueglow 807 SE amp. 75v + 75v + 100v diodes makes 250v:
and 75v + 75v makes 100v for the driver tube. Zener diodes are noisy; what size filter cap could I use? Blueglow used 10uF 350v caps for that - I think they should be rated for the no-load voltage, 600v here. Also, does the supply cap for the driver tube really need to be 100uF? How about each driver tube gets its own 25uF supply?
As far as the power supply - with a b+ of 450v it's gonna require caps rated for 600v and the WIMA DC Link lineup looks pretty sweet, especially that 25uF 600v that's only $7.20 at Mouser. I've knocked up a PSU schematic - with thanks and apologies to @Suncalc
Can I have less capacitance in the power supply if the caps are higher quality? The first schematic calls for a PSU with a 720vct PT and a 47uF-10H-330uF circuit. Films have come a long way (down in price) since these circuits were drawn. Are the values I've drawn in (the top half) suitable for this amp?
Any thoughts, advice, tidbits of wisdom are welcome, thanks for taking a look!
w
The second posted by @Ejam
In both circuits there is some type of voltage regulation for the screens. I'm unfamiliar with the methods used, and was curious about using Zener diodes as described in the @blueglow 807 SE amp. 75v + 75v + 100v diodes makes 250v:
and 75v + 75v makes 100v for the driver tube. Zener diodes are noisy; what size filter cap could I use? Blueglow used 10uF 350v caps for that - I think they should be rated for the no-load voltage, 600v here. Also, does the supply cap for the driver tube really need to be 100uF? How about each driver tube gets its own 25uF supply?
As far as the power supply - with a b+ of 450v it's gonna require caps rated for 600v and the WIMA DC Link lineup looks pretty sweet, especially that 25uF 600v that's only $7.20 at Mouser. I've knocked up a PSU schematic - with thanks and apologies to @Suncalc
Can I have less capacitance in the power supply if the caps are higher quality? The first schematic calls for a PSU with a 720vct PT and a 47uF-10H-330uF circuit. Films have come a long way (down in price) since these circuits were drawn. Are the values I've drawn in (the top half) suitable for this amp?
Any thoughts, advice, tidbits of wisdom are welcome, thanks for taking a look!
w
Connecting a capacitor directly across a Zener diode does not do much to filter their noise,
because of their fairly low internal impedance. The capacitor needs a significant source resistance
located before it (but after the Zener) to develop the low pass filter action. The corner frequency f = 1 / (2Pi x R x C)
The parallel capacitor can make a soft start, though.
because of their fairly low internal impedance. The capacitor needs a significant source resistance
located before it (but after the Zener) to develop the low pass filter action. The corner frequency f = 1 / (2Pi x R x C)
The parallel capacitor can make a soft start, though.
Would a simple capacitance multiplier work well enough for the screen grid power supply? That's easy to make because the pass device won't have to drop much voltage, which means it shouldn't need a large and expensive heatsink.
If you get one of those Antek toroid power transformers with two 180V primaries, you could 'stack' them to rectify 180VAC and 360VAC. Maybe something along these lines...
If you get one of those Antek toroid power transformers with two 180V primaries, you could 'stack' them to rectify 180VAC and 360VAC. Maybe something along these lines...