Re: Whats wrong with LEDs for bias?


"Andre Jute" <fiultra@xxxxxxxxx> schreef in bericht
news:1136197370.933518.81930@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> Adam Stouffer wrote:
>> I ask this question because earlier in the evening I wired up a single
>> triode gain stage based on a 5610.
>>
>> http://www.nj7p.org/Tube1.php?tube=5610
>>
>> With a 5.6k plate resistor and 130 B+ the plate sees 78v at 10ma. The
>> cathode resistor was 220r and grid leak 470k. A 1v input gave 5v out
>> with a nice sinewave. Adding a 220uf or 1000uf cap on the cathode
>> resistor caused a noticable change on the bottom peaks, of course the
>> gain was higher at 7v out.
>>
>> Using a generic red LED on the cathode the output was again 7v and plate
>> current was now 12ma. The output looked much cleaner and had little
>> change from 20hz to over 100kz.
>>
>> Other than the stigma of using silicon in the signal path why isn't this
>> used in more designs?
>>
>>
>> Adam
>
> Essentially because a LED doesn't control the current but fixes the
> voltage bias. Fixed bias, though it gives better bass, to the golden
> ears unbalances the sound spectrum. So the ultrafidelista don't use
> LEDs for bias much. You might say it is hypocritical because battery
> bias, which is "acceptable", is also fixed bias.
>
> LEDs are sometimes used elsewhere, though not by the hardcore faithful.
> Designs by Eric Barbour and Steve Bench and others of the same
> practical stamp, often have LEDs, and designs by those acceptable to
> the untrafidelista DIYers because they are obsessively cheap, like Dan
> Schmalle of Bottlehead/Valve/Electronic Tonalities fame, sometimes have
> LEDs.
>
> There's a lot of hypocrisy in high end tubes, but you can make yourself
> unpopular by pointing out that an SRPP is not a constant current
> device, that a cathode follower adds negative feedback, that a DHT
> works so well because it has negative feedback built in, that trioded
> pentodes sound brilliant, that DHT in PP can sound better than in SE,
> and so on, a whole testament full of articles of faith contrary to
> known electronic theory and the experience of the open-minded.
>
> Of course, I could argue that LEDs should be acceptable because they
> are, specifically, not silicon...
>
> Another reason for the men, mostly middeaged, who build tube amps is
> that LED's are just too twee. A film cap is a big fistful of component,
> easily soldered in, costs plenty and looks like it. A Kiwame resistor
> is a fat green slug looking purposeful. A battery used for bias ditto.
> A LED shines like cheap jewellery. If we wanted to be in cheap
> itty-bitty parts, we'd build silicon amps.
>
> Andre Jute
>
An infrared LED will not shine cheap. And most of these take higher currents
than the visible ones.


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Relevant Pages

  • Re: Whats wrong with LEDs for bias?
    ... Adam Stouffer wrote: ... > triode gain stage based on a 5610. ... Fixed bias, though it gives better bass, to the golden ... LEDs are sometimes used elsewhere, though not by the hardcore faithful. ...
    (rec.audio.tubes)
  • Re: Whats wrong with LEDs for bias?
    ... Fixed bias, though it gives better bass, to the golden ... > LEDs are sometimes used elsewhere, though not by the hardcore faithful. ... SRPP is where the Rk of the bottom tube = the Rk ... triode untroubled by too low a load used in a gain stage. ...
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