Serious stereo tube amp questions.

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   I have always like exposed tube equipment. Since I was a little
kid. So I have been thinking about getting a small stereo tube amp for
the living room to replace the typical modern amp we have. That no
longer works.
   All the modern small amps have outputs of several tens of watts.
But all of the small tube amps I see and remember only have outputs of
less than ten watts. Is there something sneaky about the how the
output of modern amps is rated? I know there is gonna be some puffing
up of numbers but it seems drastic. And if the modern amps have hugely
inflated numbers does that mean a tube amp rated at 5 watts is really
only a watt or so?
   There are a couple amps I have some interest in and would like
opinions on them if anybody here has the time to check out the links.
Here's the first:  
https://www.ebay.com/itm/Stereo-6P1-Vacuum-Tube-Amplifier-Class-A-Single-Ended-Power-Amp-6-8W-2-Black/253343561504?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D3d9e7203be8141d5a456d24eb0de6f49%26pid%3D100675%26rk%3D7%26rkt%3D15%26mehot%3Dpp%26sd%3D232926640491%26itm%3D253343561504&_trksid=p2481888.c100675.m4236&_trkparms=pageci%3Afade2d01-dd65-11e8-b2c7-74dbd180c23c%7Cparentrq%3Acc7d86731660aadab4e3bf87fffadd9b%7Ciid%3A1

   Sorry about the mile long link. Does this amp look any good for the
money? Can someone even tell from looking at the description? I'd buy
an older used amp with exposed tubes if I could find one that I knew
worked and wasn't really expensive. I want something that sounds OK. I
am by no means an audiophile, my ears aren't that good and I know it.
But I can still hear hum and hiss.
  
Here's the second amp link:
https://www.ebay.com/p/APPJ-Assembled-Fu32-Single-ended-Tube-Amplifier-Stereo-Power-Amp-Board-HIFI-DIY/716663897?iid28%2415070393&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20131231084308%26meid%3D403303410e0041a1b0482a2943aa48ae%26pid%3D100010%26rk%3D4%26rkt%3D12%26mehot%3Dpp%26sd%3D263867889779%26itm%3D282415070393&_trksid=p2047675.c100010.m2109
  
   Another long link. There's probably enough info in that link to
describe the position of every particle in the universe. Anyway, I was
just interested in the power tube, the FU32. I have never seen a tube
like that. Is it actually just two tubes in one glass envelope?
Sharing some pins I assume? Anyway, are these types of tubes common?

   The last thing I was wondering about was what determines the output
power of an amp. Is it just the tubes? Transformers? Or a combination
of tubes and transformers?
Thanks,
Eric

Re: Serious stereo tube amp questions.
snipped-for-privacy@whidbey.com wrote:
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 ** So you might as well replace it with something completely useless.  



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 **  No.  

 The Chinese tube amps you are citing are mere toys.

 Ornaments or conversation pieces for oyur desk or mantelpiece.



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 ** No - its a toy amp.  


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**  Another toy amp, the Chinese are laughing all the way to the bank.


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** Totally off with the fairies.


.....     Phil


Re: Serious stereo tube amp questions.
On Wed, 31 Oct 2018 17:19:04 -0700, snipped-for-privacy@whidbey.com wrote:

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It is determined by how much power goes to the speakers.  That, in
turn, is usually dependent on the voltage the amp is running on, by
ohms law.  Power (watts) is the amps times the volts.  If you have 8
ohm speakers and are pushing one amp through them you have 8 watts of
power and are using 8 volts to do it.  Really high power transistor
amps use power supplies capable of 200 volts and can produce a few
thousand watts at the speakers.

The voltage a tube amp runs on is not as important because you
generally have an output transformer and aren't driving speakers
directly.   But the power is still important and it still takes more
iron, copper and money to produce more power in conventional tube
amps.

Class A produces heat because when the amp is just sitting there with
the sound muted it is still dissipating the full power through the
tubes or transistors, class AB is static power is determined by the
bias point (how much current is allowed to flow with no sound out -
higher bias = more heat and better sound due to less cross-over
distortion)

Everything gets larger in conventional (linear) amplifiers as power
increases.  More copper, more iron, bigger filter caps, more money. At
some point, if you really like music and have golden ears, the money
is better spent developing a good music room rather than shelling out
more for amps.  There is such a thing as a law of diminishing returns.
For $50 you can build a pretty decent amp but to make it sound
significantly better might take $500....

We had some audio power amps in the navy that were used to drive a
deflection yoke in a direction finding display.  Old tube technology.
The amp used direct drive and had a whole chassis of nothing but big
tubes with graphite plates running cherry red and producing huge
amounts of heat to push the relatively low voltage through the
deflection coils.  It was all done to produce a very low distortion
signal so the display would show a perfect circular light trace on the
screen.  Any deviation from perfection resulted in a DF bearing being
off by a degree or two. (which translates into miles of error)

They were replaced with solid state devices and better technology.

Re: Serious stereo tube amp questions.
wrote:

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Thanks for the replies. The amps I have been considering are all class
A amps. I am not interested in hybrid amps. And even though  I listen
to MP3 players every day and will be playing an MP3 player through
whatever amp I get I still want a purely analog amp.
Eric

Re: Serious stereo tube amp questions.
snipped-for-privacy@defaulter.net says...
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I bought a couple of the 5 watt or so switching amps form China to play  
with.  Put them on a scope and it was interisting.  Instead of seeing a  
sine wave, it looked like a bunch of pulses.  It sounded ok to my  
untrained ear for voice quality.


Re: Serious stereo tube amp questions.
On Thu, 1 Nov 2018, Ralph Mowery wrote:

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I remember a 555 based class D amplifier in Elementary Electronicsi n the  
mid-seventies.  And it relied on the speaker, and the ear, to do the  
filtering.  So of course on a scope it would look digital, but might sound  
'fine".

I've not paid enough attention to more serious work to know how much  
relies on the speaker to do the filtering and how much is doen by  
deliberate filters.

   Michael


Re: Serious stereo tube amp questions.
On Thu, 1 Nov 2018 12:34:19 -0400, Ralph Mowery

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Sometimes it takes some magic to get a good reading with a scope and
digital sound source.  A ground loop or sometimes just the way the amp
is laid out and shielded will allow switching transients through...
and other times it is just not filtered all that well, particularly
those elcheapo Chinese amps where most of the design effort is in
marketing bling rather than quality components like low ESR caps and
suitable magnetic components.

Re: Serious stereo tube amp questions.
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you can trim those:

https://www.ebay.com/p/X/716663897

--  
  When I tried casting out nines I made a hash of it.

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