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Damper diodes as rectifiers



 
 
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  #1  
Old July 2nd 07, 05:48 AM posted to rec.audio.tubes
Maaark
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Posts: 1
Default Damper diodes as rectifiers

I've seen people use dampers as rectifier before, and I like the
premise.. but something confuses me.


In the datasheets for 6AU4, 6AX4, etc, they state that "use of this tube
as a power rectifier is not recommended".

Why is it not recommended? I don't see any flaws.
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  #2  
Old July 2nd 07, 06:02 AM posted to rec.audio.tubes
robert casey
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Posts: 340
Default Damper diodes as rectifiers

Maaark wrote:

> I've seen people use dampers as rectifier before, and I like the
> premise.. but something confuses me.
>
>
> In the datasheets for 6AU4, 6AX4, etc, they state that "use of this tube
> as a power rectifier is not recommended".
>
> Why is it not recommended? I don't see any flaws.


Not sure either, but be sure to not exceed the peak current rating. In
rectifier service, such a tube will see a big peak of current as it tops
off the B+ filter cap. Just like regular rectifier tubes. But maybe
those can take more abuse (a 5U4 is directly heated, vs a damper which
is indirectly heated). Choke input filters should help with this here.

A nice feature of most damper diodes is the high voltage ratings for
heater-cathode. Which means you should be able to run the heater off a
grounded heater supply. Also makes for slow B+ turn on.

A downside with damper diodes is that virtually all of them have only
one diode inside, so you'd need a pair of damper diode tubes to replace
say a 5U4 rectifier.
  #5  
Old July 2nd 07, 04:35 PM posted to rec.audio.tubes
John Byrns
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Posts: 1,441
Default Damper diodes as rectifiers

In article <Hs%hi.77733$NV3.12353@pd7urf2no>, Maaark >
wrote:

> I've seen people use dampers as rectifier before, and I like the
> premise.. but something confuses me.
>
>
> In the datasheets for 6AU4, 6AX4, etc, they state that "use of this tube
> as a power rectifier is not recommended".
>
> Why is it not recommended? I don't see any flaws.


An interesting question, didn't the damper diode provide the boost B+ in
old Televisions, which essentially makes it a power rectifier? I wonder
if the "not recommended" might have something to do with the published
ratings being given for operation at the horizontal line frequency, not
power line frequencies?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
  #6  
Old July 2nd 07, 10:45 PM posted to rec.audio.tubes
Ned Carlson
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Posts: 71
Default Damper diodes as rectifiers

Maaark wrote:
> In the datasheets for 6AU4, 6AX4, etc, they state that "use of this tube
> as a power rectifier is not recommended".
>
> Why is it not recommended? I don't see any flaws.


I'm guessing that statement was meant in the context of
power supplies of *television* power supplies. Most of the older
TV's with power transformers and rectifier tubes that I've seen
had 5U4, 5V3 or 5AU4's, probably because they warm up right away,
and cool off a lot faster, although there may have been other
considerations.

Marantz ignored that warning, BTW, and I don't recall ever hearing
about any problems relating to them in the Marantz amps that used
6AU4's.

--
Ned Carlson
SW side of Chicago, USA
www.tubezone.net
  #7  
Old July 3rd 07, 12:45 AM posted to rec.audio.tubes
Eeyore
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Posts: 8,474
Default Damper diodes as rectifiers



robert casey wrote:

> Maaark wrote:
>
> > I've seen people use dampers as rectifier before, and I like the
> > premise.. but something confuses me.
> >
> >
> > In the datasheets for 6AU4, 6AX4, etc, they state that "use of this tube
> > as a power rectifier is not recommended".
> >
> > Why is it not recommended? I don't see any flaws.

>
> Not sure either, but be sure to not exceed the peak current rating. In
> rectifier service, such a tube will see a big peak of current as it tops
> off the B+ filter cap.


It's quite normal with silicon rectifiers for the peak current to be ~ 10 times
the average. I expect the voltage drop of thermionic diodes reduces that ratio
but I dare say these diodes weren't intended to pass such high peaks.

Graham

  #8  
Old July 3rd 07, 01:48 AM posted to rec.audio.tubes
robert casey
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Posts: 340
Default Damper diodes as rectifiers


>
>
> It's quite normal with silicon rectifiers for the peak current to be ~ 10 times
> the average. I expect the voltage drop of thermionic diodes reduces that ratio
> but I dare say these diodes weren't intended to pass such high peaks.
>


Looking at various data sheets, it looks like a tube can handle only
about 5 times its average. It's something one needs to pay attention to.
  #9  
Old July 3rd 07, 07:31 PM posted to rec.audio.tubes
tubegarden
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Posts: 343
Default Damper diodes as rectifiers


> Maaark wrote:
> > In the datasheets for 6AU4, 6AX4, etc, they state that "use of this tube
> > as a power rectifier is not recommended".

>
> > Why is it not recommended? I don't see any flaws.


Hi RATs!

Um, some folks used WE 300B tubes as diodes. No accounting for design
muses.

This is not a mystery. Back when everybody made tubes, it was common
to diss "cross applications".

RCA radios had stern warnings: "Use RCA tubes for best performance."

So did many other brands ... some skepticism is recommended.

Of course, if you use TV dampers for a power supply and your dick
falls off, you can't say they didn't warn you.

Hi-Fi means whatever you think it means. Even if you are really,
really smart or whatever

Happy Ears!
Al



  #10  
Old July 3rd 07, 08:34 PM posted to rec.audio.tubes
robert casey
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Posts: 340
Default Damper diodes as rectifiers


> They advised that damper diodes be used only for their intended
> function for a reason.


Which could just be marketing.... But not likely, as no damper diode
ever had two separate plates like regular rectifier tubes had.
>
> Operation at less than specified filament voltage, or asking them to
> pass current before they are are fully warmed up, will cause shortened
> life. And even if operated "properly", the only effect will be that
> they have a sharper cutoff on the negative portion of the cycle, just
> like a silicon diode. So if silicon diodes are bad, the damper diode
> is too.
>


Other indirectly heated rectifier tubes, like the 6X4, would also have
that issue.
 




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