The only advantage of feeding them with a current source is that it
reduces the switch-on surge, but again with heavy filaments that really
isn't an issue.

David.

Quite. I wrote a long screed on this subject and then trashed it as
counterproductive to Andy's purpose.Andre

Well, it's actually counter to the findings that a bunch of us DHT
users observed - current sources sounded better. Have you done direct
A-B comparisons?

Andy's on a learning curve,
and he won't know that all this regulation is a bridge too far -- I
mean the danger of creating an over-refined tube amp that sounds just
like a silicon amp but more expensive so -- until he hears it and
starts backing off to where he likes the sound. You gotta do it for
yourself; that's part of the fun. Andre

Well, I think we're all on a learning curve. But no way does clean DC
make a DHT sound like silicon. I am wondering, as you say, if there
are alternatives to voltage regs in the filament supplies, but right
now I only see huge caps and chokes - both bigger and heavier and (a
lot) more expensive. I'm open to all ideas, since I'm certainly
sticking with DHTs for the forseeable future, therefore a lot of
filament supplies are my self-imposed fate!!!

Incidentally, for the B+ it's all chokes, polypropylene caps and glow
tubes.

The reason I do it that way is it sounds better. I believe the reason
it
sounds better, is some of the signal appears across the fill in a
DHT,
and the voltage reg will try and regulate that away, with a current
reg,
the signal is common mode, so not affected. Nick

My findings exactly.

LM338K in the steel case will do all the business you require and
last
forever. Maybe pricey but worth it for an IC you intend sticking into
the furnace that is a tube amp.

It's a nice product, but around �7 a throw - OK for a one off special
but too expensive for continued building. Even the most basic 3 stage
all-DHT SET needs 6 filament supplies!

On Jan 18, 12:02*am, Andy Evans wrote:
The only advantage of feeding them with a current source is that it

reduces the switch-on surge, but again with heavy filaments that really
isn't an issue.

David.

Quite. I wrote a long screed on this subject and then trashed it as
counterproductive to Andy's purpose.Andre

Well, it's actually counter to the findings that a bunch of us DHT
users observed - current sources sounded better. Have you done direct
A-B comparisons?

I agree, a current sourced regulator sounds better than one without
the CC. My point was simply that I consider AC fils good enough
sonically.

About a dozen years ago, after I gave up on AC balance in PP amps, I
spent a lot of time on trying to improve the sound by messing around
with the fils. I tried everything including, under the influence of
Allen Wright, current sources. I agree that fixing the current is
better than fixing the voltage on the fils, but eventually I went back
to AC fils because anything more seemed to me to be unnecessary. But
don't let that influence you: you still have the pleasures of a
simplification kick in front of you!

Andy's on a learning curve,
and he won't know that all this regulation is a bridge too far -- I
mean the danger of creating an over-refined tube amp that sounds just
like a silicon amp but more expensive so -- until he hears it and
starts backing off to where he likes the sound. You gotta do it for
yourself; that's part of the fun. Andre

Well, I think we're all on a learning curve.

You're right. I didn't mean to sound patronizing. I'm watching you
like a hawk in the hope of learning something else I can use on my own
amps.

But no way does clean DC
make a DHT sound like silicon.

I have no problem with clean DC. But well-enough filtered DC is clean
enough (without necessarily going for those monster caps Patrick
Turner advocates). However, if you keep refining everything, the
cumulative effect on a DHT is eventually to make it sound over-
sophisticated, bland; where that point falls is a matter of taste. I
returned to tubes because I switched on the Bang & Olufsen setup in my
study one morning and noticed that the music had a chilling quality.
Admittedly that edginess of good quality silicon which is subliminally
so disturbing is caused by NFB, and the blandness of an overrefined
ZNFB DHT amp is of an entirely different nature and of a much lower
order, but eventually it just came to me in the library of a grand
house one day where I was listening to Steven Doane practice that even
fine instruments in expert and sensitive hands have their rough edges,
and that the rough edges are what gives them a humane scale that a
synthesizer will never share. It is entirely a personal attitude and I
offer it only as that.

I am wondering, as you say, if there
are alternatives to voltage regs in the filament supplies, but right
now I only see huge caps and chokes - both bigger and heavier and (a
lot) more expensive. I'm open to all ideas, since I'm certainly
sticking with DHTs for the forseeable future, therefore a lot of
filament supplies are my self-imposed fate!!!

I had a bunch of chokes given to me by one of the local hams that were
suitable and tried them too. The late Bill May, my technical guy but a
music-lover even as he never took his hand off the meter, loved that
sound even better than the everything-current-controlled-and-locked-
down sound we also tried around that time because we built so many
exactly similar amps (at someone else's expensive of course...) to
conduct a big transformer comparison, and could then use these amps
for other tests. But now you're starting to talk about a lot of real
estate that brings other niggling and some rather big problems with
it.

Incidentally, for the B+ it's all chokes, polypropylene caps and glow
tubes.

Did I ever tell you what my big T199 "Millennium's End" PSE Svetlana
SV572-xx did with the second transmitting tube on the chassis when
operated in its lowest (under 10W) SE mode? In that version the second
transmitting tube was turned into a shunt regulator for the remaining
signal power tube, a very wasteful procedure as a shunt regulator
immediately drops as much current as the operating tube -- but the
sound was one of the finest I ever heard. I should add that the shunt
reg was current-controlled; that was the final 20% trick of what was
already a very pleasing sound. But, of course, the heat and the
complication and the expense (just try buying an audio-quality switch
good to 1000V) and the lack of reliability because a lot of the
components were operating on the ragged edge, all of that made me
uncomfortable and not just because a kilovolt amp is intrinsically
dangerous -- it would make me uncomfortable on a 300B at less than
hallf that voltage.. But I learned something: shunt reg sounds better
than series reg by so many magnitudes it is no contest. Of course, I'm
talking about plate voltage now; I don't quite see anyone shunt
regulating all those mansized filament amperes...

Such fun to throw out alternatives when someone else is doing the
work! Pay no attention to what I liked or didn't, Andy. When it sounds
right to you, you're on the right track. And if it doesn't sound as
good as another idea, you're still on the right track, just
temporarily on a branch line. It's a journey without an end.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

PS I'm sure you know this already: the original and still the best of
the Lundahl power transformers comes with four separate beefy filament
supplies. I've always just bought the standard LL1651 and knocked the
6.3V down with a resistor for 5V DHT fils because I believe the
resistor provides an element of stabilization, but I should think Per
Lundahl will wind them for you with 5V fils if you ask.

On Jan 17, 8:05 pm, Eeyore
wrote:
Andre Jute wrote:
The ultrafidelista generally use AC fils because they sound best,

Because hum is good for fidelity ?

Graham

Yo, Poopsta, you have my sympathy. It must be really distressing
living down there in Boombox World as you do among people constantly
seeking to add distortion to their music. How many years does one have
to spend down there in Audio Hell before you start believing everyone
else is a moron without taste or musical education?

But your prejudice doesn't apply to people who know what they do with
tubes, who have the money for DHT and the skill to apply the
accumulated knowledge. Time to start educating you, Poopie. Say after
me, one hundred times: Properly implemented DHT DO NOT HUM. Proper
implementation almost never requires regulation in DHT. It means
paying attention to grounding and to the sizing and physical placement
of filament balancing devices (small subcircuits often called
humbusters, which is perhaps where you got your silly prejudice).
We're not talking about some little guitar-amp with 12AX7 of the sort
you are no doubt familiar with, we're talking about the mighty 300B.
Proper implementation of 300B fils is shown on my netsite, and
probably discussed in one of the chapters of The KISS Amp. I'll leave
you find the circuit and the text; at least that'll keep you out of
the pub and other dens of vice with boomboxes where you apparently
gather the misinformation you spread like disease on UKRA and RAT and
the protechtube conferences.

Don't bother grovelling in the dirt; a simple deep bow and a sincere
"Thank you, Master" will do the business.

Andre Jute
Charisma is the talent of inducing apoplexy in losers by merely
existing elegantly

In article , Eeyore
wrote:


Nick Gorham wrote:

Ian Iveson wrote:

and the voltage reg will try and regulate that away, with a current
reg, the signal is common mode, so not affected.

UH ?

Can only speculate at this point as I have never tried using these circuits
for heaters in audio amps. However...

With 'direct' heating the heater psu is - I presume - connected to the
same physical place as the cathode signal. Having a 'constant current' PSU
means the PSU looks like a high impedance connection, so will be less
likely to have a loading effect on signal drive to the cathode if the PSU
common mode isolation is poor. i.e. the problem is that the cathode signal
has to drive any loading it sees due to the PSU, so a high impedance might
be preferred.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html

i.e. the problem is that the cathode signal
has to drive any loading it sees due to the PSU, so a high impedance might be preferred.
Slainte, Jim

Yes, you're right on the nail - that's a common reason given by those
who have developed and use current sources - the high impedence. Here
is a useful reference on DHT filaments which refers exactly to this.

http://www.tentlabs.com/Products/Tub...ent/index.html

http://www.tentlabs.com/Products/Tub...ingmethods.pdf

"Jim Lesurf" wrote in message
...
In article , tony sayer

wrote:
In article , Jim Lesurf jcgl@st-
and.demon.co.uk scribeth thus
In article
,
Andy Evans wrote:


So - which voltage regs are your fave choices here? Good quality
output important, but cost also a consideration. This looks right up
Jim's street for starters.

FWIW I tried various types of 'IC voltage regulator/stabiliser chip'
some years ago and decided I wasn't keen on any of the common types.
Too prone to oscillations or excess noise, etc. Newer ones may be
better, but I lost interest in using them. :-)


Shouldn't you valve types be using DC from batteries;?...

The only valves I've done PSUs for were klystrons or carcinotrons. I
suspect the battery stacks for those would have been quite large. ;-

**"Carcinotron"? I had to look that one up. A type of travelling wave tube.
I thought I'd heard all the names, but the choice of the name: carcinotron
was sure an unfortunate one.

Trevor Wilson

In article , Trevor Wilson
wrote:

"Jim Lesurf" wrote in message

Shouldn't you valve types be using DC from batteries;?...

The only valves I've done PSUs for were klystrons or carcinotrons. I
suspect the battery stacks for those would have been quite large. ;-

**"Carcinotron"? I had to look that one up. A type of travelling wave
tube. I thought I'd heard all the names, but the choice of the name:
carcinotron was sure an unfortunate one.

It was a common description in my experience. I think at least one of the
makers of BWOs (backward wave oscillilators) for 100GHz used it. It may
have been Thompson CSF but I can't recall as it was ages ago.

I assume it was on the basis that the backward wave was - in conventional
TWT terms - a parasitic growth than extracted power from a forward beam
mode. Analogy with the way a cancer growth takes resources from the normal
body processes or disrupts their operation.

So for a conventional TWT it was unwanted, but turned out to be useful for
power at higher frequencies.

Advantage of the tubes was that you could get them up to about a THz, and
they had a wide electronic tuning range. The snag was what brought them to
mind for this thread. The wide electronic tuning range meant that you
needed to control all the applied voltages with exceptional care if you
wanted output stable to a few kHz or better.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html

"Jim Lesurf" wrote in message
...

Can only speculate at this point as I have never tried using these
circuits
for heaters in audio amps. However...

With 'direct' heating the heater psu is - I presume - connected to the
same physical place as the cathode signal. Having a 'constant current' PSU
means the PSU looks like a high impedance connection, so will be less
likely to have a loading effect on signal drive to the cathode if the PSU
common mode isolation is poor. i.e. the problem is that the cathode signal
has to drive any loading it sees due to the PSU, so a high impedance might
be preferred.


No, it's nothing to do with loading. What is actually happening is that the
resistance of the filament is partially in series with the cathode current.
So it acts as an unbypassed cathode resistor creating a little bit of
negative feedback. Effectively shorting that out with a low impedence
filament supply reduces this negative feedback.

David.