OK, I've never seen/heard a decent explanation of what goes on with a valve
amp with 4 and 8 ohm taps when it is hooked up to speakers of 6 ohm nominal
impedance.

Instinctively I use the 8 ohm tap but, quite recently, one of the yoofs in
HFW wrote 'simply use which one sounds the loudest' or words to that effect.
I know it doesn't appear to make a lot of odds, but summat must happen
differently in the amp on each of these tappings. I've seen references to
the valves 'working harder' one way and the trannies 'not liking it' another
and so it goes on.

Anybody really know? - I would love to hear the correct explanation....

I won't go into technical details here - somebody else can - but I think the
helpful concept to have is that a transformer can transform down "less" or
"more" according to the output taps (if there are any). Put it on its 15 ohm
tap and it transforms down "less". On the 4 ohm tap it transforms down "more".
So with the same speaker, the "less" the transformer transforms down the louder
it will be, the "more" the transformer transforms down the higher the impedence
the valves will see, so the happier they are in terms of less distortion, but
the quieter they are in terms of output. There is an optimum point where it's
both quite loud and quite undistorted. If it goes louder than that it sounds
woolly, if you go the other way it tightens up the sound, which is initially
satisfying but steadily becomes unnecessary in terms of diminishing returns. If
you had 8 ohm speakers, putting the amp on the 4 ohm tap would be cleaner and
tighter, using the 15 ohm tap would be louder and a bit more ragged. Neither
will damage anything, and frankly you can set it at whatever sounds preferable
to your ears.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

Andy Evans wrote:
If
you had 8 ohm speakers, putting the amp on the 4 ohm tap would be cleaner and
tighter, using the 15 ohm tap would be louder and a bit more ragged. Neither
will damage anything, and frankly you can set it at whatever sounds preferable
to your ears.

Not so. I clearly remember seeing an old valve amp go up in smoke when
the wrong tap was used.

Well yeah and I wish my valve amp, and others, had multifilar
secondaries, so you could choose, for example, whether to
connect 2 4-ohm secondaries in series for 8 ohms, or in
parallel for 2 ohms with less voltage but a lower o/p impedance.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

In article ,
Fleetie wrote:
Well yeah and I wish my valve amp, and others, had multifilar
secondaries, so you could choose, for example, whether to
connect 2 4-ohm secondaries in series for 8 ohms, or in
parallel for 2 ohms with less voltage but a lower o/p impedance.

As a rule of thumb, the greater the turns ratio the more inefficient a
transformer becomes.

--
*Corduroy pillows are making headlines.

Dave Plowman London SW
To e-mail, change noise into sound.

"Andy Evans" wrote in message
...
I won't go into technical details here - somebody else can - but I think
the
helpful concept to have is that a transformer can transform down "less" or
"more" according to the output taps (if there are any). Put it on its 15
ohm
tap and it transforms down "less". On the 4 ohm tap it transforms down
"more".
So with the same speaker, the "less" the transformer transforms down the
louder
it will be,

OK


the "more" the transformer transforms down the higher the impedence
the valves will see, so the happier they are in terms of less distortion,
but
the quieter they are in terms of output.


OK


There is an optimum point where it's
both quite loud and quite undistorted. If it goes louder than that it
sounds
woolly, if you go the other way it tightens up the sound, which is
initially
satisfying but steadily becomes unnecessary in terms of diminishing
returns. If
you had 8 ohm speakers, putting the amp on the 4 ohm tap would be cleaner
and
tighter, using the 15 ohm tap would be louder and a bit more ragged.
Neither
will damage anything, and frankly you can set it at whatever sounds
preferable
to your ears.


OK, so you're really saying, all in all, the 4 ohm tap would be best then?
I'll give it a try and see if I can hear an improvement.

Thanks for that - nice to get information from someone who *knows*.... ;-)

Keith G wrote:




OK, so you're really saying, all in all, the 4 ohm tap would be best then?
I'll give it a try and see if I can hear an improvement.

Thanks for that - nice to get information from someone who *knows*.... ;-)




Only other thing to consider (don't disagree with what Stew has posted)
but using the 4R tap with 8R speakers, will mean the output valves see a
reflected load thats 4 times bigger. Thi sis good in that it will tend
to reduce the distortion, but it will also severly limit to output
power, maybe more than the advantages of using the 4R tap give.

Thats why I originally mentioned reflected loads and load lines.

--
Nick

"Nick Gorham" wrote in message
...
Keith G wrote:




OK, so you're really saying, all in all, the 4 ohm tap would be best
then? I'll give it a try and see if I can hear an improvement.

Thanks for that - nice to get information from someone who *knows*....
;-)




Only other thing to consider (don't disagree with what Stew has posted)


??


but using the 4R tap with 8R speakers, will mean the output valves see a
reflected load thats 4 times bigger. Thi sis good in that it will tend to
reduce the distortion, but it will also severly limit to output power,
maybe more than the advantages of using the 4R tap give.

Thats why I originally mentioned reflected loads and load lines.


OK, I'm taking it as 'tap down for less distortion but quieter' and 'tap up
for louder but more ragged' as a general rule of thumb then.

On Fri, 5 Nov 2004 23:07:52 -0000, "Keith G"
wrote:

OK, I'm taking it as 'tap down for less distortion but quieter' and 'tap up
for louder but more ragged' as a general rule of thumb then.

Succinct, and accurate! :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Thu, 4 Nov 2004 19:22:55 -0000, "Keith G"
wrote:

OK, I've never seen/heard a decent explanation of what goes on with a valve
amp with 4 and 8 ohm taps when it is hooked up to speakers of 6 ohm nominal
impedance.

Instinctively I use the 8 ohm tap but, quite recently, one of the yoofs in
HFW wrote 'simply use which one sounds the loudest' or words to that effect.
I know it doesn't appear to make a lot of odds, but summat must happen
differently in the amp on each of these tappings. I've seen references to
the valves 'working harder' one way and the trannies 'not liking it' another
and so it goes on.

Anybody really know? - I would love to hear the correct explanation....

Pretty obvious, really. On the 4 ohm tap, it will have .7 of the
output voltage, 1.4 times the available current, and half the output
impedance. Generally, this should give better results.
--

Stewart Pinkerton | Music is Art - Audio is Engineering