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Old 25th September 2002, 09:35 PM   #1
Ralph is offline Ralph  Netherlands
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Default Feedback wanted on PSU design

Hi all,

I'm currenty developing a 300B schematic. This is the amp I want to build: http://www.homepages.hetnet.nl/~rjonkers/300b.jpg

I'm having trouble getting a optimized 500V power supply, using PSU designer. I've come up with this supply so far, maybe you want to comment on it? And do you have tips to improve it (or to save some money by using less components)? I need 500V @ 110mA.

http://www.homepages.hetnet.nl/~rjonkers/psu.jpg


Thanks very much,

Ralph
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Old 25th September 2002, 09:44 PM   #2
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I'm certainly not an expert on tube rectifiers but... are they really significantly superior to diode designs? If slower switching is what you're after then would snubber networks across the diodes do the trick?

Don't want to start a tube vs silicon flame war but just wondered....
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Old 25th September 2002, 10:38 PM   #3
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Default PSU+300B

Hi,

I don't see anything wrong with it really.
Personally I would use ~6 mF as C after the rectifier,use the bigger self as the first one.
And I think you do the right thing by opting for the valves as rectifiers.
They don't introduce the noise all diodes do and ramp up the voltage for the output tube nice and slow.
On the cost side:
I wouldn't play cheap on a 300B amp but since you ask:
Selfs aren't cheap and you could replace the second one by something like this:
Click the image to open in full size.

I think your fellow Dutchman got it out of a Philips book, anyway it works fine and I think it would cost a fraction of a self.

Happy DIY,
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Old 25th September 2002, 10:45 PM   #4
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daatkins said 'I'm certainly not an expert on tube rectifiers but... are they really significantly superior to diode designs?"

One reason to use tube rectifaction is so the B+ doesn't come up right away, giving the tubes time to warm up. Applying B+ to a cold tube can cause cathode stripping and shorten the life of the tube. SS diodes can be used but then you'd need to delay the B+ turn on.....


Dave
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Old 25th September 2002, 10:55 PM   #5
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Default HEATERS

Hi Dave,

Pls read what I been said on:

DC Filament power supply

No standby switches please!
You're killing the tubes.

Cheers,
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Old 25th September 2002, 11:08 PM   #6
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I was referring to B+ rectifaction not filament....Its not good to have B+ applied before the tube filament is warm and happy Using a tube rectifier naturally delays the B+ to the other tubes as it has to warm up first....

Dave
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Old 25th September 2002, 11:15 PM   #7
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Default B+

Dave,

Sure,but I'd still not use any delay scheme with a diode bridge in B+ either.
You'd still create some cathode bombing.
Experience with CRT maintenance has proven this NOT to be a good idea.

Cheers,
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Old 25th September 2002, 11:21 PM   #8
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I only use tube rectifires, was only using that as an example to answer the question the other poster asked about why we use tubes instead of SS for B+ rectifaction...

Dave
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Old 25th September 2002, 11:31 PM   #9
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Default ELS + DIODES

Dave,


To answers two posts in one go:

Glad to see you know this stuff (rectif+tubes) and yes,I'm looking forward to see something on these beasts in the DIY Speaker section.

Remco,

Get in the starting blocks...


Cheers,
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Old 26th September 2002, 03:35 AM   #10
SHiFTY is offline SHiFTY  New Zealand
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Well I've got a radio that has a directly heated rectifier (5Y3), that heats up in about a second to 320V+, which then drops to about 260V (normal B+) as the tubes warm up. It has lasted for decades with all original tubes... (had to replace all the caps though.)
Tubes are not too delicate, they can handle short voltage spikes without too much trouble.

The indirectly heated rectifiers, like 5V4 would be a good choice for a slow B+ design without a standby switch.

There is also a way of calculating the value of that first cap so it minimises ripple in the power supply, does anyone have that formula?
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