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Old 24th March 2005, 07:50 PM   #1
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Question EZ81 tube rectifier

HI,

to everyone, I am new in this forum and I hope I can share with you my audio experinces. Well, I am not so good in DIY as you guys but I like to understand and doing things, that is why I joined this forum.

I was forgetting to say sorry for my really bad English grammar!

So my question is abut power supplies. I would like to build a power supply using the EZ81 tube rctifier, like the hybrid schematics a' la Counterpoint. I should have 25V ac as my output, I couldn't find any schematics on the web, do you you have some suggestion?

Thank you,
KEPha
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Old 24th March 2005, 07:54 PM   #2
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A tube rectifier is not usable below 100 volts, go with a ss diode recifier bridge.
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Old 25th March 2005, 01:47 PM   #3
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HI!

Thank you, anyway I am still curious how to that, I have a poweramp to which I have to tweak the supply, I would try with that, have you any reference,

bye
KEPha
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Old 25th March 2005, 02:04 PM   #4
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Can you be more specific ?
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Old 25th March 2005, 02:14 PM   #5
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HI,

I will try to be clearer. I want to have a look to some schematics of power supplies which use the EZ81.

I have never seen one, but I heard that they are excellent in their job.

I heard about this tube because Counterpoint used to in its amp systems. I don't know more than this.

Thank you, have a nice day
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Old 25th March 2005, 02:24 PM   #6
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Its like any tubeamp power supply with a rectifier tube, centertapped transformer winding about 300v per side, 6.3v filament winding. Max capacitance you can have on the EZ81 cathode is about 50F, if higher the tube breaks sooner. I had a amp with EZ81, it only had RC links in the power supply but if you have a choke you get cleaner B+ with less hum. The anodes goes to the transformer and the cathode is the DC output.
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Old 28th March 2005, 12:04 AM   #7
anatech is offline anatech  Canada
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Hi KEPha,
The Counterpoint SA-100 uses a SS rect bridge for an HV output of approx +330 VDC. You can use an EZ-81 if you want. In any case, you will want to use a voltage regulator to isolate the voltage amp stage from variations in the DC level. Your amp will motorboat if you don't.
The SA-220 uses a tube rectifier and much higher DC voltages as they tried to filter these variations out. Not terribly successfully.

Counterpoint has many problems, so don't copy it or you will too!

-Chris
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Old 28th March 2005, 09:47 AM   #8
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Than you Guys, very helpfull,

Cheers,
KEPha
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Old 28th March 2005, 06:38 PM   #9
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EZ81's ain't so EZ. I find them frightfully scarce and would not design any circuit around them. They are used in my Heathkit EA-3's and I cannot find anything else that will sub without going to an octal socket change and using perhaps a 6X5.

My advice, go with a 5U4. heavy duty and you can find them all over the place. Needs 5V dedicated filament supply however. The B+ output will appear on this circuit.
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Old 28th March 2005, 10:39 PM   #10
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EZ81/6CA4s aren't that scarce (I think Electro-Harmonix distribute new production 6CA4s...), but nowadays IN4007s and the like are so common

Failing that, you could always use a pair of TV damper diodes, which will likely have a lower voltage drop, higher current capability and are most likely cheaper (plus, they look nicer).
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