[west]

Setup: Speakers efficient enough that if I cut the amp's power in half,
there is no discernible volume difference to the ears.
The way I cut the amps power in half is by switching the output tubes to
triode and adjusting the volume to have the same SPL in pentode.
I understand the theory but I would love to hear your opinions on what if
any differences can you hear between the 2 modes. I know this subject has
been beaten to the ground but the theory always obfuscated the sound changes
for me. Can we just talk about the sound in your words? It will help me
plenty. Thank you.

Cordially,
west

[John Byrns]

In article zpkGh.215$Ih.208@trnddc02, "west"
wrote:

Setup: Speakers efficient enough that if I cut the amp's power in half,
there is no discernible volume difference to the ears.
The way I cut the amps power in half is by switching the output tubes to
triode and adjusting the volume to have the same SPL in pentode.
I understand the theory but I would love to hear your opinions on what if
any differences can you hear between the 2 modes. I know this subject has
been beaten to the ground but the theory always obfuscated the sound changes
for me. Can we just talk about the sound in your words? It will help me
plenty. Thank you.

There is a completely different change in sound depending on whether the
amplifier has negative feedback or not. You need to tell us whether the
amplifier in question uses negative feedback or not before we can
comment on the sonic differences between the two modes.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Patrick Turner]

John Byrns wrote:

In article zpkGh.215$Ih.208@trnddc02, "west"
wrote:

Setup: Speakers efficient enough that if I cut the amp's power in half,
there is no discernible volume difference to the ears.
The way I cut the amps power in half is by switching the output tubes to
triode and adjusting the volume to have the same SPL in pentode.
I understand the theory but I would love to hear your opinions on what if
any differences can you hear between the 2 modes. I know this subject has
been beaten to the ground but the theory always obfuscated the sound changes
for me. Can we just talk about the sound in your words? It will help me
plenty. Thank you.

There is a completely different change in sound depending on whether the
amplifier has negative feedback or not. You need to tell us whether the
amplifier in question uses negative feedback or not before we can
comment on the sonic differences between the two modes.

Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

The argument about pentode&beam VS triodes has been going on now
since about 1933, some 74 years.

Contestants in the argy bargies over the ssue usually
assume the triodes have little NFB, say 12 dB, and the
pentodes have heaps, say 20dB, which is 2.5 times more GNB
than the triode case. This way the pentode amp will have about the same
Rout
as the triode amp and a fair comparison can be made.

We should also incude comparisons with Ultralinear, and Local Cathode
FB, a la Quad-II amps.

All the people I know cannot tell the slightest difference between
triode sound and UL
sound when switching the screen supply to the anode, or OPT screen tap.

I've tried to get ppl to detect the differences, but none have.

Pure Pentode or beam tetrode SHOULD be far more easily detected by the
golden ear brigades
because the harmonic spectra of a pentode in PP or SE is a far richer
mix
of high numbered harmonics which all spoil music, especially
if the circuit works in near class B PP conditions.

But the GNF applied around a typical multigrid circuit reduces the
spuriae of all kinds
by the amount of NFB applied and this is usually by a factor of 0.1
even ib a near class B amp which usually produces a low amount of pure
class
of say 3 watts before the amp lurches into rougher working in class AB
which produces the
most objectionable spuriae, and IMD especially.

At 1 watt most ppl still hear ZERO difference between 2 x EL34 in class
A triode with 12dB GNFB, good for 12 watts max,
and the same tubes in pentode class AB good for 35 watts max.

The pentode may in fact measure less THD / IMD than the triodes ( or UL
for that matter )
although the mix of residual spuriae with pure pentode will be a richer
mix.
Triodes may have some 2H, 3H, and then very low levels of anything else,
but the PP pentodes will have 2,3,4,5,6,7,8,9H, but in declining
quantities.
The levels of say 4,5,6,7,8,9H at 1 watt from typvcal class AB PP
pentode amps at a watt
is usually negligible, along with resulting IMD.
Hence we don't hear the spuriae; its eclipsed by everything else.

But applying say only 10dB GNB around a pure pentode or beam output
stage will produce Rout that is
much above the triode case with 12dB GNB, so the speaker response won't
be the same, and the sound WILL change
with apparently more level wherever the speaker Z is high.

Triode without any GNFB are usually listenable at low levels, but
pentode amps are a disaster, and awful,
unless the load is kept at a constant R value, which is practically
unviable for most ppl to arrange.

UL or local CFB gives intermediate Rout; the Rout is usually about = RL,
with no GNFB.
Pure pentode Rout can be typically 40 ohms with a pair of EL34.
Triodes without GNFB are about 4.5 ohms with the same OPT ratio used in
pentode.
Triode connection prefers 10k RLa-a instead of 5k a-a, and if this is
the case
triode Rout = 2.3ohms approx, including some OPT winding resistances.

The NFB or not arguments revolving around percieved sound imageing
effects is all anecdotal.
When careful response measurements are made the sound changes probably
are due to varying
Rout and response contours.
Where the Rout is kept low for either case of with/without GNFB,
and where the response is maintained, with the same phase shifts, I bet
nobody notices the NFB
if its used.

Putting on my flame suit about right now...

Patrick Turner.

[Iain Churches]

"west" wrote in message
news:zpkGh.215$Ih.208@trnddc02...

Setup: Speakers efficient enough that if I cut the amp's power in half,
there is no discernible volume difference to the ears.
The way I cut the amps power in half is by switching the output tubes to
triode and adjusting the volume to have the same SPL in pentode.

Well, not even half.
Switching my UL pentode amps to triode
reduces the overall power from 50W to 32W, so in terms of
power, by shirtcuff calculation that's less than 2dB. With a
complex music signal, many people might be hard pressed
to notice the level change:-)

I understand the theory but I would love to hear your opinions on what if
any differences can you hear between the 2 modes. I know this subject has
been beaten to the ground but the theory always obfuscated the sound
changes
for me. Can we just talk about the sound in your words? It will help me
plenty. Thank you.

I have, on several occasions set up listening sessions with
groups of musicians and studio colleagues, all people
whose level of aural perception I respect.
None has been able to differentiate between the UL
and triode "sound". I would add that this amp has
18dB NFB.

However, sometime ago, I modified a VAC80W tube
amp from UL to triode for a friend who uses it with a pair
of open baffle speakers. The amp has very little NFB,
and a low damping factor.

Conversion to triode did not seem to alter any of the
performance parameters much except for ironing out a
lift of some 3dB at 20kHz.However, there was a marked
reduction in Zout and hence and improvement in the DF. See:

http://www.kolumbus.fi/iain.churches...ata/VAC_Zo.png

I returned the amplifier to its owner with one channel
only modified to allow him to compare triode with UL
and decide if he wanted to continue with the modification.
I did not mention anything to him about the comparison
measurements I had made. He claimed he could hear a
distinct difference, and mentioned that in triode mode
the bass was "leaner and tighter"

Regards to all
Iain

[[email protected]]

On Mar 3, 10:14 pm, Patrick Turner wrote:
Triode without any GNFB are usually listenable at low levels, but
pentode amps are a disaster, and awful,
unless the load is kept at a constant R value, which is practically
unviable for most ppl to arrange.

For "low-fi" and "mid-fi" applications (a couple watts output from
phonographs, car radios, etc), single-ended pentode miniature tubes
(e.g. 6AK6, 6AQ5) are commonly used and do pretty well with zero or
smallish amounts of feedback. Of course they're going into pretty
lousy speakers in abysmal environments, and a common theme is to shunt
a resistor across the load (usually on the speaker side of the output
transformer but sometimes the tube side of the output transformer). I
always thought the shunt resistor was there in case the speaker comes
unconnected, but maybe you have a point about keeping a more constant-
R load.

Tim.

[Patrick Turner]

wrote:

On Mar 3, 10:14 pm, Patrick Turner wrote:
Triode without any GNFB are usually listenable at low levels, but
pentode amps are a disaster, and awful,
unless the load is kept at a constant R value, which is practically
unviable for most ppl to arrange.

For "low-fi" and "mid-fi" applications (a couple watts output from
phonographs, car radios, etc), single-ended pentode miniature tubes
(e.g. 6AK6, 6AQ5) are commonly used and do pretty well with zero or
smallish amounts of feedback. Of course they're going into pretty
lousy speakers in abysmal environments, and a common theme is to shunt
a resistor across the load (usually on the speaker side of the output
transformer but sometimes the tube side of the output transformer). I
always thought the shunt resistor was there in case the speaker comes
unconnected, but maybe you have a point about keeping a more constant-
R load.

The old trick of shunting the a-a with R
will give a load when the speaker isn't connected.
Bass resonances of hi Z or other high Z peaks are controlled a bit, but
not a lot.
Then power is wasted into the shunt R.....

If R = 3 x speaker nominal Z, the DF is much better than having no R at
all,
and not too much power is wasted.

Patrick Turner.


Tim.

[Arny Krueger]

"west" wrote in message
news:zpkGh.215$Ih.208@trnddc02
Setup: Speakers efficient enough that if I cut the amp's
power in half, there is no discernible volume difference
to the ears.
The way I cut the amps power in half is by switching the
output tubes to triode and adjusting the volume to have
the same SPL in pentode.
I understand the theory but I would love to hear your
opinions on what if any differences can you hear between
the 2 modes. I know this subject has been beaten to the
ground but the theory always obfuscated the sound changes
for me. Can we just talk about the sound in your words?
It will help me plenty. Thank you.

Either all amplifiers sound the same, or exactly which amplifiers you use
will be signficant in this test.

There are a great number of other potentially significant, unspecified
parameters.

IOW, your proposed experiment is woefully under-specified.