What's your favourite voltage regs?
 

"Jim Lesurf" wrote in message
...
In article , David Looser
wrote:
"Ian Iveson" wrote in message
o.uk...


Isn't this just an alternative description of the same phenomenon? How
is cathode loading nothing to do with feedback?

Well maybe it is. In which case Jim Lesurf has a very odd way of
describing it.

I think we are talking at cross-purposes. I was dealing with what I
thought
Andy and Nick were referring to. i.e. external resistors in the heater
PSU,
or their equivalent in terms of employing a 'constant current' heater PSU.
The external resistance would be in series with any the cathode *signal*
and the rest of the system via the PSU.

The discussion was about the difference between a low-impedance voltage
regulated filament supply, and a high impedance current regulated one.
Whilst clearly a similar effect to a current regulated supply could be
obtained by the use of a high-value resistor in series with a voltage
source, such a plan would be extremely wasteful of energy and generate
significant extra heat, so it would not be a viable option and no one
suggested it.

The impedence of the filament supply is in shunt with the resistance of the
filament itself, in the case of a constant current PSU no cathode current
will flow through it, in the case of a constant voltage PSU a proportion of
the cathode current will flow through the PSU via the end of the filament
distant from the cathode connection.


You are, I think, talking about the internal resistance in the valve used
for heating.

Indeed.

I have no idea which of these has any significant in an audio amp. :-) I
was simply commenting that if their is some loading via the PSU then
resistors would help reduce this. Seen equivalent effects in mm wave
oscillator tubes.

But that has no relevance to the point at issue here.

From the values people quote, though, the heater resistance in the valve
seems only to be of the order of 10 Ohms for the DHTs (?) If so, given the
other impedances I'd be surprised if that had a significant effect. But as
I say, I've not built or studied these types of amp...


Rather less than 10 ohm I think. As to whether it is significant I cannot
say, but users of DHTs say that they sound "better" when the filament is fed
from a current, rather than a voltage, regulated PSU so presumably *they*
think it is significant.


The problem Andy/Nick were referring to was, I think, that the PSU is
*not*
perfectly isolated/floating. However if I have misunderstood, perhaps they
can say.


Not at all. It was nothing to do with whether the PSU was floating or not,
it was about whether it was voltage or current regulated. As I said in a
common-cathode amplifier there is usually little or no signal at the cathode
to shunt.


David.

What's your favourite voltage regs?
 

In article ,
David Looser wrote:
As I said in a common-cathode amplifier there is usually little or no
signal at the cathode to shunt.

Be interesting to know just how the heater supply makes any difference to
the sound quality, then?

--
*Organized Crime Is Alive And Well; It's Called Auto Insurance. *

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

What's your favourite voltage regs?
 

On Mon, 21 Jan 2008 11:07:09 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
David Looser wrote:
As I said in a common-cathode amplifier there is usually little or no
signal at the cathode to shunt.

Be interesting to know just how the heater supply makes any difference to
the sound quality, then?

As interesting would be a couple of sets of measurements to show just
what the difference is that they are hearing.

d

--
Pearce Consulting
http://www.pearce.uk.com

What's your favourite voltage regs?
 

In article ,
Don Pearce wrote:
On Mon, 21 Jan 2008 11:07:09 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
David Looser wrote:
As I said in a common-cathode amplifier there is usually little or no
signal at the cathode to shunt.

Be interesting to know just how the heater supply makes any difference
to the sound quality, then?

As interesting would be a couple of sets of measurements to show just
what the difference is that they are hearing.

Don't think you're allowed that sort of question here anymore. People
flounce off in a huff. ;-)

--
*Artificial Intelligence is no match for Natural Stupidity *

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

What's your favourite voltage regs?
 

On Mon, 21 Jan 2008 11:20:41 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Don Pearce wrote:
On Mon, 21 Jan 2008 11:07:09 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
David Looser wrote:
As I said in a common-cathode amplifier there is usually little or no
signal at the cathode to shunt.

Be interesting to know just how the heater supply makes any difference
to the sound quality, then?

As interesting would be a couple of sets of measurements to show just
what the difference is that they are hearing.

Don't think you're allowed that sort of question here anymore. People
flounce off in a huff. ;-)

Oops! I'll shut up...

d

--
Pearce Consulting
http://www.pearce.uk.com

What's your favourite voltage regs?
 

"Dave Plowman (News)" wrote in message
...
In article ,
David Looser wrote:
As I said in a common-cathode amplifier there is usually little or no
signal at the cathode to shunt.

Be interesting to know just how the heater supply makes any difference to
the sound quality, then?


In an indirectly heated valve the whole cathode is effectively at the same
potential. However in a directly heated one there is a voltage gradient
across the filament due to the filament supply. This means that the
effective grid bias also changes across the filament and thus the standing
current will be weighted towards the negative end of the filament. As long
as the valve is operating strictly within it's linear region it can be
approximated to the whole filament being at the mean filament voltage.
However once it strays into a non-linear region that no longer applies and
different parts of the filament will enter the non-linear portion at
different values of grid voltage, in the extreme one end of the filament
could be cut-off, or saturated, whilst the other was still providing some
variation in anode current. This will improve the linearity a bit compared
to the uni-potential case, which *might* explain the supposed sonic
advantage of the DH valve.

Also the cathode current flows through the filament, but how much of the
filament it flows through depends on which part of the filament it flows
from. Since the filament has resistance this will introduce an element of
negative feedback into the valve, but again how much feedback you get will
depend on which bit of the filament that particular little bit of current
flows from.

Whether any of this is enough to justify the use of DH valves in modern
amplifiers is another matter entirely. I'm quite happy with my Quad 44 and
405-2.

David.

What's your favourite voltage regs?
 

On Mon, 21 Jan 2008 11:54:52 -0000, "David Looser"
wrote:

"Dave Plowman (News)" wrote in message
...
In article ,
David Looser wrote:
As I said in a common-cathode amplifier there is usually little or no
signal at the cathode to shunt.

Be interesting to know just how the heater supply makes any difference to
the sound quality, then?


In an indirectly heated valve the whole cathode is effectively at the same
potential. However in a directly heated one there is a voltage gradient
across the filament due to the filament supply. This means that the
effective grid bias also changes across the filament and thus the standing
current will be weighted towards the negative end of the filament. As long
as the valve is operating strictly within it's linear region it can be
approximated to the whole filament being at the mean filament voltage.
However once it strays into a non-linear region that no longer applies and
different parts of the filament will enter the non-linear portion at
different values of grid voltage, in the extreme one end of the filament
could be cut-off, or saturated, whilst the other was still providing some
variation in anode current. This will improve the linearity a bit compared
to the uni-potential case, which *might* explain the supposed sonic
advantage of the DH valve.

Also the cathode current flows through the filament, but how much of the
filament it flows through depends on which part of the filament it flows
from. Since the filament has resistance this will introduce an element of
negative feedback into the valve, but again how much feedback you get will
depend on which bit of the filament that particular little bit of current
flows from.

Whether any of this is enough to justify the use of DH valves in modern
amplifiers is another matter entirely. I'm quite happy with my Quad 44 and
405-2.

David.


I'm aware of what is happening, and how the effect operates. What I
don't have is any kind of feeling for the magnitude of the effect.

A measurement would be simple. A current source feeding the heater,
and an optional capacitor from one end of the heater to the other to
make it a voltage source at audio frequencies.

d

--
Pearce Consulting
http://www.pearce.uk.com

What's your favourite voltage regs?
 

"Don Pearce" wrote in message
...

I'm aware of what is happening, and how the effect operates. What I
don't have is any kind of feeling for the magnitude of the effect.

A measurement would be simple. A current source feeding the heater,
and an optional capacitor from one end of the heater to the other to
make it a voltage source at audio frequencies.


I no longer have access to the required test kit (my ex-employer wouldn't
let me keep the Audio Precision analyser when I left :-( ) so I couldn't do
that. I'd be interested in the result if anyone else can.

David.

What's your favourite voltage regs?
 

On Mon, 21 Jan 2008 12:14:05 -0000, "David Looser"
wrote:

"Don Pearce" wrote in message
...

I'm aware of what is happening, and how the effect operates. What I
don't have is any kind of feeling for the magnitude of the effect.

A measurement would be simple. A current source feeding the heater,
and an optional capacitor from one end of the heater to the other to
make it a voltage source at audio frequencies.


I no longer have access to the required test kit (my ex-employer wouldn't
let me keep the Audio Precision analyser when I left :-( ) so I couldn't do
that. I'd be interested in the result if anyone else can.

David.


Even the cheapest sound card is more than man enough for this job.
What I lack is a DHT amp.

d

--
Pearce Consulting
http://www.pearce.uk.com

What's your favourite voltage regs?
 

Don Pearce wrote:
On Mon, 21 Jan 2008 12:14:05 -0000, "David Looser"
wrote:


"Don Pearce" wrote in message
...

I'm aware of what is happening, and how the effect operates. What I
don't have is any kind of feeling for the magnitude of the effect.

A measurement would be simple. A current source feeding the heater,
and an optional capacitor from one end of the heater to the other to
make it a voltage source at audio frequencies.


I no longer have access to the required test kit (my ex-employer wouldn't
let me keep the Audio Precision analyser when I left :-( ) so I couldn't do
that. I'd be interested in the result if anyone else can.

David.



Even the cheapest sound card is more than man enough for this job.
What I lack is a DHT amp.

d


I could set up something simple, want to describe what you need setting
up and I will see what I can do.

--
Nick