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'[EE] Power tubes near speakers could cause tuble r'
2009\05\11@223224 by Xiaofan Chen

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Add [EE] tag but I do not know anything about tubes.

On Tue, May 12, 2009 at 10:11 AM, Richard Prosser <spam_OUTrhprosserTakeThisOuTspamgmail.com> wrote:
{Quote hidden}

2009\05\11@224503 by John Gardner

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Xiaofan said >  I do not know anything about tubes...

Sure you do - Think high voltage FETs   :)

2009\05\11@225048 by John Gardner

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Thinking about it - 450V... Class A?

Edson, I suspect you're melting the 6L6s... Just a hunch.

2009\05\12@084654 by olin piclist

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>> Since the grids etc. are sitting in a vacuum they will not be subject
>> to speaker vibration directly,

Or course they are, just not thru the air.  They are mounted to something,
which is mounted to something else, which eventually can be vibrated by the
speaker.

That said, microphonics is unlikely a issues in the final stage of a power
amp.  There isn't enough gain between there and the output.  Since you are
using tubes for some bizarre reason, you probably have a 12AX7A or the like
for the front end.  There microphonics can be a issue.  Tap it lightly with
a screwdriver and you can probably hear it in the output.  Try the tap test
on the final tubes and you probably won't hear it.

>>> Can a speaker's magnetic field interfere with tubes/valves and
>>> damage it?

Very unlikely.

>>> They are just prototypes I'm making while studying tube
>>> circuits.

Why?  Is this because you want to learn about tubes, or because you
prescribe to silly audiophool theories about sound purity, oxygen free
cables, and whatnot.  If so, get a dead fish and start waving.  It's just as
effective and a lot cheaper.

>>> They uses a pair of 6L6 in the power section and gives
>>> close to 40W maximum output power.

6L6 were common audio final tubes back in the day.  Does anyone even make
these things anymore?

>>> Tapping the tubes with a finger while holding it near the ear, I can
>>> hear something vibrating inside the tubes.

That's normal.  There are metal structures suspended inside.  At some
frequency, parts are going to resonate mechanically.


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Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\05\12@084727 by olin piclist

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John Gardner wrote:
> Xiaofan said >  I do not know anything about tubes...
>
> Sure you do - Think high voltage FETs   :)

With pilot lights.

********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\05\12@085029 by olin piclist

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John Gardner wrote:
> Thinking about it - 450V... Class A?
>
> Edson, I suspect you're melting the 6L6s... Just a hunch.

He said 450V at 45mA.  That comes out to 20W.  I don't remember the specs on
a 6L6, but it's not obvious to me off the top of my head that this is out of
line.  From their size and remember how hot they got in normal operation,
20W sounds normal at first glance.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\05\12@093336 by Alan B. Pearce

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Olin wrote:
>John Gardner wrote:
>> Xiaofan said >  I do not know anything about tubes...
>>
>> Sure you do - Think high voltage FETs   :)
>
>With pilot lights.

Yeah, think 'hot source FETs' ...

2009\05\12@095522 by Mark Rages

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On Tue, May 12, 2009 at 7:49 AM, Olin Lathrop <olin_piclistspamKILLspamembedinc.com> wrote:
>
> Why?  Is this because you want to learn about tubes, or because you
> prescribe to silly audiophool theories about sound purity, oxygen free
> cables, and whatnot.  If so, get a dead fish and start waving.  It's just as
> effective and a lot cheaper.
>

No, he is talking about a guitar amplifier, not hi-fi.  Guitar
amplifiers are intentionally overdriven, and tube overload
characteristics are definitely different than normal solid-state
circuits.  Some of the DSP simulators get very close though.

>>>> They uses a pair of 6L6 in the power section and gives
>>>> close to 40W maximum output power.
>
> 6L6 were common audio final tubes back in the day.  Does anyone even make
> these things anymore?

6L6GT are very common output tubes.  They are still in production.

http://www.groovetubes.com/tubes_list.cfm?ObjectGroup_ID=108

Regards,
Mark
markrages@gmail

--
Mark Rages, Engineer
Midwest Telecine LLC
.....markragesKILLspamspam.....midwesttelecine.com

2009\05\12@150601 by M. Adam Davis

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On Tue, May 12, 2009 at 8:49 AM, Olin Lathrop <EraseMEolin_piclistspam_OUTspamTakeThisOuTembedinc.com> wrote:
> prescribe to silly audiophool theories about sound purity, oxygen free
> cables, and whatnot.  If so, get a dead fish and start waving.  It's just as
> effective and a lot cheaper.

But not as lucrative if you're in the business of selling tube amps to
said audiophiles.

-Adam

2009\05\12@211845 by Tony Smith

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face
> > prescribe to silly audiophool theories about sound purity, oxygen free
> > cables, and whatnot.  If so, get a dead fish and start waving.  It's
just as
> > effective and a lot cheaper.
>
> But not as lucrative if you're in the business of selling tube amps to
> said audiophiles.


Fish make excellent speaker stands.  Especially blue fin.  Just replace
every new moon.

Tony

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