What's your favourite voltage regs?
 

Don Pearce wrote:


I will repeat with the 2a3 again later.

But I just thought of a possible reason, see wht you think. unlike a
300b, the 2a3 I used has dual anodes, its effectivly two 45 in parallel
in the one envelope. I wonder if regulating the fil supply with a
current source instead of a voltage source is allowing different fil
temperatures in each half, and that inbalance is whats causing the
higher distortion.

Just a thought.


Provided they are wired in parallel they are pretty much
self-aligning. If a fil is at a lower temperature its resistance will
be lower, so it will take more current, hence more power. That will
apply whether they are voltage or current driven.. Of course if you
run them in series, whichever finds itself a little hotter will tend
to run away at the expense of the other.

d

Yep, I was just about to post that the last should be ignored, as it was
rubbish, a voltage on the valve pins, is a voltage, don;t matter how its
derived.

--
Nick

What's your favourite voltage regs?
 

I'm full of admiration for Nick and Don's research here - do you want
me to send you a ready built Rod Coleman supply to test? could be
interesting!

If so just email and I'll put it in the post. Andy

What's your favourite voltage regs?
 

Andy Evans wrote:

I'm full of admiration for Nick and Don's research here - do you want
me to send you a ready built Rod Coleman supply to test? could be
interesting!

If so just email and I'll put it in the post. Andy


I would certainly be interested, but given what we have found so far I
don't know if we wioll manage to measure any difference.

But I would love the chance to try.

--
Nick

What's your favourite voltage regs?
 

On Sat, 26 Jan 2008 09:43:56 +0000, Nick Gorham
wrote:

Andy Evans wrote:

I'm full of admiration for Nick and Don's research here - do you want
me to send you a ready built Rod Coleman supply to test? could be
interesting!

If so just email and I'll put it in the post. Andy


I would certainly be interested, but given what we have found so far I
don't know if we wioll manage to measure any difference.

But I would love the chance to try.

Have you found any clues yet to the odd distortion change in that last
test? I was wondering if you had been able to repeat it.

d

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

What's your favourite voltage regs?
 

"Jim Lesurf" wrote in message
...


I know exactly what this thread was about before your first contribution to
it. It was about the difference between driving the DHT filament with a
voltage source, and a current source, and that's all. The issue of how
"perfectly" the PSU was floating didn't come into it.

The comments you made in your first post did not address this issue at all,
but were, apparently, based on the misapprehension that we were discussing
the effect of the PSU not floating "perfectly". This suggested to me that
you had not read the thread properly before contributing, I still think that
to have been the case.

What I wrote was to clarify what Nick had said and give a better worded
explanation for a point he made.

In view of the fact that you were addressing an entirely different issue to
the one we were discussing, it did not "clarify" anything, rather it
confused the issue.

He emailed me later to confirm this.

Well so you said before, but I note that he has not taken the opportunity to
say that here.

David.

What's your favourite voltage regs?
 

Don Pearce wrote:

On Sat, 26 Jan 2008 09:43:56 +0000, Nick Gorham
wrote:


Andy Evans wrote:


I'm full of admiration for Nick and Don's research here - do you want
me to send you a ready built Rod Coleman supply to test? could be
interesting!

If so just email and I'll put it in the post. Andy


I would certainly be interested, but given what we have found so far I
don't know if we wioll manage to measure any difference.

But I would love the chance to try.


Have you found any clues yet to the odd distortion change in that last
test? I was wondering if you had been able to repeat it.

d


No, not yet, I admit I am skeptical that its real, I will repeat today,
I thought I would use my wave analiser to get another way of measuring
the same thing. Not that its more accurate than the PC (its not, only
good to -80dB), but its quicker as its in the same room as the test amp.

--
Nick

What's your favourite voltage regs?
 

On Sat, 26 Jan 2008 10:51:57 +0000, Nick Gorham
wrote:

Don Pearce wrote:

On Sat, 26 Jan 2008 09:43:56 +0000, Nick Gorham
wrote:


Andy Evans wrote:


I'm full of admiration for Nick and Don's research here - do you want
me to send you a ready built Rod Coleman supply to test? could be
interesting!

If so just email and I'll put it in the post. Andy


I would certainly be interested, but given what we have found so far I
don't know if we wioll manage to measure any difference.

But I would love the chance to try.


Have you found any clues yet to the odd distortion change in that last
test? I was wondering if you had been able to repeat it.

d


No, not yet, I admit I am skeptical that its real, I will repeat today,
I thought I would use my wave analiser to get another way of measuring
the same thing. Not that its more accurate than the PC (its not, only
good to -80dB), but its quicker as its in the same room as the test amp.

At the levels we are talking about, -80dB is just fine.

d

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

What's your favourite voltage regs?
 

Nick Gorham wrote:



Have you found any clues yet to the odd distortion change in that last
test? I was wondering if you had been able to repeat it.

d


No, not yet, I admit I am skeptical that its real, I will repeat today,
I thought I would use my wave analiser to get another way of measuring
the same thing. Not that its more accurate than the PC (its not, only
good to -80dB), but its quicker as its in the same room as the test amp.


Ok, confusion over, at 2.5v output, the voltage reg was going into
shutdown, so reducing the fill voltage to about 1.6v, so all we were
seeing was the effect Steve Bench had already seen that you can get
lower distortion by reducing the fill voltage. Making sure the voltages
remain constant, the measured distortion stayed the same between the I
and V supply.

The driver was producing -50dB of second harmonic, so I think I will try
and repeat this next time I have a real SET on the bench with a more
capable driver stage.

But so far, "notying to see here, move along"

--
Nick

What's your favourite voltage regs?
 

In article , David Looser
wrote:
"Jim Lesurf" wrote in message
...


I know exactly what this thread was about before your first contribution
to it. It was about the difference between driving the DHT filament with
a voltage source, and a current source, and that's all.

Actually, that is incorrect. It started with a call from Andy to suggest
what PSU designs we favoured for applications like heating in the context
he gave. (cf below)

What you refer to was one of the various topics that subsequently arose.

The issue of how "perfectly" the PSU was floating didn't come into it.

Indeed. Nor have I ever said otherwise. Once again you are jumping to
erronious conclusions.

I am afraid that your habit of taking things out of context and snipping
away what has been responded to has confused you again if you assumed
otherwise. :-)

The comments you made in your first post did not address this issue at
all, but were, apparently, based on the misapprehension that we were
discussing the effect of the PSU not floating "perfectly". This
suggested to me that you had not read the thread properly before
contributing, I still think that to have been the case.

I am afraid that your habit of snipping what others have said and then
taking things out of their context is still confusing you. Above you state
various opinions as if they were facts. It may therefore be useful to
copy some of what was actually written to restore some relevant context.
So, according to my records the first posting I made in this thread was
actually as follows:


] Newsgroups: uk.rec.audio From: Subject:
] What's your favourite voltage regs? Date: Wed, 16 Jan 2008 13:35
]
] 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. :-)
]
] So I have tended to use variations on the kind of topology shown on
]
] http://www.audiomisc.co.uk/Armstrong/700/730PSU.gif
]
] As you can see, the zener sets the nominal voltage, and a capacity
] multiplier pass device smooths over the noise and gives a slow
] start/stop.
]
] That example was for about +/-20V up to about 100mA, used for the rails
] in a preamp. But the same topology has been used many times by my old
] research group for voltages in the few V region at currents up to a few
] amps, so may serve your purpose. [1] Just alter the components to suit.
] Make the pass transistor a form of darlington pair if needed. I found a
] single device was usually fine for currents of the order of an amp or
] two. But if you need high current the single-pack darlingtons made for
] cheaper SS amps might well do that well if you wanted. But these may
] need to be checked for oscillation problems.
]
] Main advantages of the topology are low noise and a gradual windup and
] rundown rather than coming on or going off with a crack. Kinder for your
] valve heaters, perhaps. You may also like the fact that it has no
] overall feedback. :-)
]
] No idea if it will suit you, but since you mentioned my name...
]
] For power amps, though, I always just used a decent transformer and
] large caps, then designed the amp to reject power line variations. So no
] need for any active smoothing/stabilisation/regulation.
]
] Slainte,
]
] Jim
]
] [1] e.g. for the PSU for 5-12V 1A Gunn diodes where noise from the PSU
] needs to be minimal as it would introduce noise sidebands to the 94GHz
] output. If you want I can see if I can dig out a diagram of the variable
] and fixed versions used for that, but they are in essence the above.


It was in other postings later one we got to various other topics...

What I wrote was to clarify what Nick had said and give a better
worded explanation for a point he made.

In view of the fact that you were addressing an entirely different issue
to the one we were discussing, it did not "clarify" anything, rather it
confused the issue.

I appreciate that it has confused you, since that was a different posting
on another issue to the above. As above, your problem here seems to be
that you have conflated and confused various issues and points that have
arisen in this thread. Since you have lost awareness of what I actually
wrote here is the first posting I made on the topic:


] Newsgroups: uk.rec.audio From: Subject:
] What's your favourite voltage regs? Date: Fri, 18 Jan 2008 09:35
]
] 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
]


And as I pointed out, Nick and I then exchanged emails about this.

I also made responses to other points you made. Unfortunately, due to the
way you snip and then take things out of context, these then became
conflated in your mind, leading to more confusion on your part.

The question of 'floating' PSU is clearly relevant to the above point since
it may be a factor in whether or not the above has an effect on
performance. Indeed, you might note the phrase "...if the PSU common mode
isolation is poor..." :-)

But, as I have said countless times, since I have never made or tested a
DHT audio amp I can't comment on the extent to which any of the above may
matter in practice. I was just trying to clarify what others had said. So
you could even note the use of "...*if*..." in the above. ;-

Well so you said before, but I note that he has not taken the
opportunity to say that here.

I could also note that neither he, nor indeed anyone else, has supported
your own confusions. :-) TBH I assume that he and others have had better
things to do, and are content to let me waste my own time. Nick has been
reading this group for long enough to know how patient I can be. ;-
Indeed, Nick and Don have had quite an informative discussion in this
thread.

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

What's your favourite voltage regs?
 

Yes - as the original poster I was looking for any useful input, which
has been richly provided by all concerned. I don't think it was about
one thing and not another - I meant it as an open thread about
different ways of supplying the filaments on DHTs, which covers a lot
of potential ground.

I particularly appreciate the input from guys like Jim who may not
have ever used DHTs but are still ready to throw their considerable
expertise into the ring. I think the basic elements are pretty close
to building a good linear PSU, something which I expect most of us
have done several times!

Particularly interesting input on how filaments work from Dave, Nick
and Don - I'm sending Nick some boards to test!