My original long reply seem to have gone missing in the ether. Here's a
condensed recreation.

John Stewart wrote:
Andre Jute wrote:

choke input .....
is traditionally built with two sections, meaning two chokes.

Not traditionally built in two sections at all.

RDH p1192ff. 1954 is traditional enough for me.

Presumably you're now on the right circuit:
http://members.lycos.co.uk/fiultra/T...trafi-crct.jpg

That is a special case.

Not at all. Rectifiers have spec limits on the value of capacitance
that may be applied in different power filters. The only way to get the
LC values desired is by using two sections. Many committed builders of
SETs use several sections: LCLCLCLC is not uncommon. Don't throw a
thrombie over the cost, John. If you're tonedeaf, before you start
dancing you should ask what the tune is. This tune has buggerall to do
with cost-engineering.

If you think I will give up square-rooting the noise left after one LC
section merely to save an additional LC section costing around a
hundred bucks, you should raise your head from your cheap junkbox amps
and smell the rich air of the 21st century.

If
you put one section in the -ve lead & the other in the +ve lead the common
mode voltages if they are present will be stopped.

I do it anyway, because I can. Everest; Hillary: "Because it is there."
Ultrafi; KISS; Jute: "Screw the cost engineers."

But then you need to be
aware of other possible problems!

List those "possible problems!", John, and then we'll compare them with
the known disadvantages (!) of the standard engineering method (cheap
single-coil choke on the positive lead) and with the extensive
advantages (!) of my screw-the-cost-engineers method of a split choke
with one section on the negative lead and one section on the positive
lead.

When it comes to protecting the rectifier(s) from excessive peak currents as
seen in cap input filters a single section choke of at least the critical
inductance will do just fine. No need at all for that 2nd
winding.

You haven't got it, pal. If the rectifier has to live dangerously and
be sacrificed occasionally in the service of better sound, I'd gladly
do. But in this amp the sonic imperatives dictate topologies that tend
to conservative use and protection of the rectifier. The second choke,
whatever its effect may be on the security of the rectifier, by
intention has buggerall to do with protecting the rectifier. From the
blank sheet, this amp was intended, cost no object, to drive noise into
the basement. That is what the second choke and cap do. It also
contributes to some other desirable features of the amp. Production is
not contemplated; it is a DIY amp; cost is immaterial.

You might ask what the design objectives are before you start
pontificating from the burning bush: "This is The Great P'Eng. Second
filter sections are an ostentatious abomination before my face. You
will burn in Hell for double-coil chokes, double filter sections, and
expensive tubes, because I am The P'Eng of The Cheap Junkbox." Sheesh,
man, what did they teach you at engineering school about determining
purpose as the first step? Or did you go only to cost-accounting
school?

JLS

Thanks for your thoughts. Let's hear some more about the "possible
problems!" of common mode rejection.

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

Henry Pasternack wrote:

"Patrick Turner" wrote in message ...
Well, Si diodes and high value cap input filters are better regulated than any
tubed choke input filter. Gone is the series resistance of choke and tube.
The choke input allowed the tube rectifier to conduct throughout the cycle;
there is no peak charging that had limits with tubes.

It seems to be a strong concensus among subjective-minded hobbyists that
choke-input filters sound better because a lot less RF hash is generated by
diode switching. Even Morgan Jones, who's a pretty no-nonsense guy and
not at all afraid of silicon, thinks so. The argument makes sense to me.

I have built a lot of PS in my time even with 500V at 650mA for my 300 watt amps there is *no*
problem with PS hash. The PS generates B+ using Si diodes, hundreds of uF, and a darn voltage doubler like
McIntosh
began to use all those years ago as soon as they could.
if someone cannot prevent rectifier noise getting into the signal they are a power supply novice.
I have never used tube rectifiers, and never had switching noise problems.
The SS 2 x 300watt amp I built in '96 has two 100,000 uFcaps for the rails and directly charged by 35amp
Si, bridge, and hum and noise is less than 0.25mV at the output.
I also find that using fast recovery diodes isn't any quieter than plain slow old cheap Si diodes.

But I am a careful with PS, prefering to have a mild steel sheet enclosure around the PS to stop magnetic
fields and electrostatic fields interfering.
I'd like to use a SMPS if I could lay my hands on a suitable design. Halcro do a SMPS in their amps
and they sell for $50,000 a pair, and have a good rep, and no noise.




This doesn't mean, though, that a given amplifier built with a cap-input
power supply will sound bad. There are many counter-examples.

Well if the choke is simply able to comply with RL / 1,100 where RL is
the Edc / Idc and Idc is considered at 10% of that normally drawn, the
choke is probably ok for choke input with a higher V ac HT winding
to produce the same B+.

There are a couple of concerns. The first is that the choke should have a
high enough current rating that it won't saturate with the large AC currents
flowing through it in this application.

The initial few charge up cycles with an SI rectifier can cause slight saturation; the wave forms are weird,

but really the chokes tend to limit inrush more than a cap input.
With class B the choke current is always on the move with signal and slight mains voltage fluctuations,
but because the swinger choke is designed to convey maximum dc at full power of a class B amp,
usually current demands through the choke won't be any higher than for this condition unless someone
connects a
shorted output or a load well below rated.

Manufacturers don't spec their chokes
for choke-input service and don't publish detailed design information, so
you have to make educated guesses.

Well ya gotta know what you buy, or don't buy it; I wind all mine.


The second concern is that the choke has to be made well enough that it
can withstand the added stress due to magnetostriction and core heating.
Hammond, which is the biggest supplier of affordable chokes in North
America, specifically states that their chokes are not rated for use in
choke-input filters. I don't know exactly what they mean by this.

Well, you can work it all out for a given choke. RDH4 has Hanna's method, supposed to be good for
filter chokes only with low ac across them. But if the DCR is low enough, Hanna works out OK with some
choke inputs where high ac is across the chokeas well as the dc flow. The sum of the
Tesla for dc and ac must not exceed about 1.5Tesla. Its the same issue with an SE OPT;
you have large ac signal across the L, and dc flow...


I have
a pair of Hammond 10H @ 300mA, 60 Ohm, chokes that run absolutely
cool and quiet as input chokes with a 1000VCT power transformer and
200mA DC load current.

Nobody is perfectly competent. I do not post with purpose to point out
mainly the incompetence of others, but more to offer an alternative which
may or may not appear to be truer than what else may have been said, or
to augment what has been said already.
I found teachers who came at me to primarily kick my butt of ignorance
to be rude.

Sometimes there is no choice but to kick the ass of a disruptive student.

I should keep my arse in a large steel bucket to prevent bruising eh....

Patrick Turner.



-Henry

John Byrns wrote:

In article .com,
" wrote:

Henry:

Just ignore Mr. McCoy. He is no technician certainly and his design
credentials are well-established.

Peter,

You are jumping into the middle of a blood feud, how can you expect Henry
to ignore Andre? Henry's only interest in this group is attacking Andre.
You may want to do some more reading in your psychology textbook.

This is similar to the situation that went on for so long between Patrick
and Phil A., where Patrick just couldn't ignore Phil's posts. Amazingly
however Patrick seems to have been able to ignore Phil recently, although
asking that of Henry may be asking too much.

Phil has kept out of many threads where he could have been a pest.
While that trend continues for awhile at least, I don't need to kick back.

Patrick Turner.



Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

John Stewart wrote:

Henry Pasternack wrote:

"John Byrns" wrote in message ...
This question is not meant as criticism of your general comments on
"swinging chokes". Are you sure that it is true that "The reason swinging
chokes are so rare nowadays is that the availability of cheap silicon
rectifiers and large electrolytic capacitors makes capacitor-input filters
more economical to build than choke- input filters"? My observation is
that chokes of any sort, "swinging" or filter, were gone from Hi-Fi amps
even before the use of silicon rectifiers became common, and also long
before large electrolytic capacitors came on the scene, which appear to
have come later than silicon rectifiers.

You're the hi-fi historian, so I won't disagree. Most of the commercial
hi-fi designs I'm familiar with used a tube rectifier, smallish electrolytic
capacitors, and a small smoothing choke in the main B+ supply. Some,
like the Marantz 8, used solid-state diodes but still retained the choke.

Choke input filters, I think, were always costly. Regardless of the
economics of power supply design during the interim period you refer
to, in the present day the cost advantage of capacitor-input filters is
clear. This ignores any ostensible performance advantages of the
choke-input power supply.

-Henry

To a large degree the swinging choke was found in power supplies used with Class B, PP modulators as seen in
the 30's & 40's. They were probably used in public address systems with Class B amplifiers as well. Fidelity
was not a concern in those applications. Just lots of audio without too much demand on the power supply.

Cheers, John Stewart

I agree. Swinger chokes were used to get a lot out of a rectifier tube with with better regulation
than a cap input filter.
The whole idea of the swinger was to get less B+, variation, ie, better natural regulation,
something very desirable in a class B modulator or class C RF amp.
Fidelity with a class B amp can be quite fair.
Klangfilm built 300 watt theatre amps using a sixpack of EL34; I once rebuilt a 400 watter with 8 EL34,
and with pentode mode, I used only 12dB NFB; the guy used it for PA at a hall with 300 ppl, it was the most
wondrous warm beautiful sound from "PA" that I had heard; it didn't measure like the best but it did the business
ok.
The screen voltage was well regged, that was the secret.

Patrick Turner.

"Patrick Turner" wrote in message ...
I have built a lot of PS in my time even with 500V at 650mA for my 300
watt amps there is *no* problem with PS hash... if someone cannot prevent
rectifier noise getting into the signal they are a power supply novice...

I also find that using fast recovery diodes isn't any quieter than plain slow
old cheap Si diodes...

But I am a careful with PS, prefering to have a mild steel sheet enclosure
around the PS to stop magnetic fields and electrostatic fields interfering.

I know that diode switching artifacts are real and measurable, and I know
there are ways to minimize them. This is even true with a choke input filter.
Jones' book shows how to properly snub a filter choke and backs it up
with actual scope traces.

I think if you have the right measuring equipment it is pretty easy to prove
that power supply switching noise makes it to the output of the signal
circuitry. The noise is much harder to filter out than it is to prevent in the
first place. There is a lot of objective as well as anecdotal evidence that
proper use of common-mode chokes and effective bypassing can improve
the performance of audio equipment.

The results will vary a lot depending on the circuit, the wiring layout, chassis
design, and of course the sensitivity of the listener and his state of mind. I
think this is an area where you can legitimately probe deeper and deeper
and deeper, and at each level open up a new realm of cost and complexity.
If you are trying to build a neutrino detector, the cost is probably justified.
The question is how good is good enough for consumer audio work?

Well ya gotta know what you buy, or don't buy it; I wind all mine.

It would be more cost effective for me to pay you to wind chokes for me
than for me to wind them myself. But -- oh my god -- I would probably
have Michael do the work, if only because he's closer.

The second concern is that the choke has to be made well enough that it
can withstand the added stress due to magnetostriction and core heating.
Hammond, which is the biggest supplier of affordable chokes in North
America, specifically states that their chokes are not rated for use in
choke-input filters. I don't know exactly what they mean by this.

Well, you can work it all out for a given choke. RDH4 has Hanna's method,
supposed to be good for filter chokes only with low ac across them.

That's fine, but it tells us nothing about the quality of the construction of
off-the-shelf parts. If Hammond says their chokes aren't intended for
choke-input service, could that mean they are cutting corners on
mechanical robustness, or does it just mean that they don't want the
hassle of dealing with hobbyists who don't properly derate the chokes
for that application?

I should keep my arse in a large steel bucket to prevent bruising eh....

If you intend to accuse me of child molestation, yes, you should plan to
armor-plate your backside.

-Henry

In article , "Henry Pasternack"
wrote:

"John Byrns" wrote in message
...
This question is not meant as criticism of your general comments on
"swinging chokes". Are you sure that it is true that "The reason swinging
chokes are so rare nowadays is that the availability of cheap silicon
rectifiers and large electrolytic capacitors makes capacitor-input filters
more economical to build than choke- input filters"? My observation is
that chokes of any sort, "swinging" or filter, were gone from Hi-Fi amps
even before the use of silicon rectifiers became common, and also long
before large electrolytic capacitors came on the scene, which appear to
have come later than silicon rectifiers.

You're the hi-fi historian, so I won't disagree. Most of the commercial
hi-fi designs I'm familiar with used a tube rectifier, smallish electrolytic
capacitors, and a small smoothing choke in the main B+ supply. Some,
like the Marantz 8, used solid-state diodes but still retained the choke.

Choke input filters, I think, were always costly. Regardless of the
economics of power supply design during the interim period you refer
to, in the present day the cost advantage of capacitor-input filters is
clear. This ignores any ostensible performance advantages of the
choke-input power supply.

Hi Henry,

You are of course correct that some Hi-Fi amplifiers did use filter chokes
as part of a capacitor input filter, among them as you point out was the
Marantz 8B, and there were also others such McIntosh and some Dynaco
models. I should have known this, and actually did know it, as I have
owned the Marantz 8B and several Dynaco Stereo 70s. I am not sure how I
ended up saying "that chokes of any sort, "swinging" or filter, were gone
from Hi-Fi amps even before the use of silicon rectifiers became common",
specifically how the word "filter" got in there. Well I sort of know how
it got in there, I had originally typed the words "swinging or other" to
indicate that the input choke might either be a so called "swinging"
choke, or it might simply be an ordinary sort of choke. I remember
changing the word "other", because it somehow didn't seem right, but what
I might have been thinking to replace it with the word "filter" I haven't
a clue. I have noticed before that sometimes when I go back and change a
few words in isolation, to some that sound better, it is possible to
grossly change the meaning of the whole paragraph unless I remember to go
back and proof read the entire paragraph after making the change.

Also while I don't believe that the coming of silicon rectifiers had
anything to do with the disappearance of choke input filters from domestic
Hi-Fi amplifiers, your basic thesis is probably correct in a broad sense.
For example Mercury Vapor rectifiers, which were once common in higher
power equipment, almost universally used choke input filters, as using
capacitor input filters with mercury vapor rectifiers required including
special protective circuits which probably weren't any less expensive than
the choke they eliminated, and which also would introduce a new failure
point reducing reliability. Silicon rectifiers made it possible to use
capacitor input filters without special protective circuits. Personally
the thing I like about choke input filters is that they reduce the stress
on the rectifiers and power transformer, and so should result in a more
reliable amplifier.

When speaking of "large electrolytic capacitors" it is not clear that we
are talking about the same thing, what do you consider to be a "large
electrolytic capacitor"? I suspect that what you are referring to as a
"large electrolytic capacitor" may be what I would call a "medium sized
electrolytic capacitor".


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article .com,
" wrote:

That he has made actionable accusations against Mr. Pasternack (and
others, apparently) should make him glad that he is some thousands of
miles away and has done nothing for which he might be extradited. That
he sticks by them despite your attempt to show him otherwise
demonstrates his irrationality as well as his lack of skill.

It is possible that the reason Andre sticks by his story is because he may
be talking about a different pornography incident than the one I know
about, so even though the common thread was presumably an attempt to
discredit Andre by sending out pornography under his name, the
perpetrator(s) could have been different in the two cases. The case I am
talking about occurred in late 1998 IIRC, and Andre appears to be talking
about an incident that occurred in early 2001.

I would also expect that you, as his friend, amanuensis and sycophant
would hasten to help him come up with a proper series of designs rather
than letting him spring his half-baked bunk (to quote Mr. Stewart) onto
an unsuspecting public. Given your expertise, history and experience,
that should be an easy thing for you, it would certainly have saved
MANY threads of needless vituperation... and given your general
self-effacing character, I am sure you would have been happy for Mr.
McCoy to actually bask in adulation (for your design) for well-executed
designs rather than having vultures picking over the dead corpse of his
design(s). Certainly, Mr. McCoy would be happy to take your design
whole-cloth... you may wait a considerable time before public
acknowledgement, however.=20

I don't think this is a reasonable suggestion because Andre's and my
design tastes and styles are completely different, although perhaps both a
little offbeat. One of my designs just wouldn't look right under Andre's
name, just as one of his designs wouldn't look right under my name. In
the instant case I attribute much of the apparent weirdness of Andre's
KISS amp to its heritage, that is that it is descended from his ill fated
book attempt, and the fact that he has a large box of Lundahl transformers
left over from that project that he wants to make use of. While the
premise of his book was interesting, I thought that he was overreaching
when he first brought it up back in 1998, and IIRC I told him so at the
time. The idea of the book as I remember it was to build a series of
amplifiers each of higher quality than the previous one, and always
recycling the iron from the old amplifier into the new amplifier with the
addition of additional transformers and chokes. This idea makes some
sense for a series of two or possibly three different amplifiers, but I
felt that Andre pushed the idea too far, IIRC to something like a half a
dozen different amplifier designs, and the result was that some of them
required a few very grotesque design details to be able to use the same
iron as the rest of the series. I felt he would have done better to
concentrate on maybe three amplifiers at the most, of increasing price and
performance.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

"John Byrns" wrote in message ...
Personally the thing I like about choke input filters is that they reduce
the stress on the rectifiers and power transformer, and so should result
in a more reliable amplifier.

I agree with that.

When speaking of "large electrolytic capacitors" it is not clear that we
are talking about the same thing, what do you consider to be a "large
electrolytic capacitor"? I suspect that what you are referring to as a
"large electrolytic capacitor" may be what I would call a "medium sized
electrolytic capacitor".

I mean "large" in the sense that you don't have to think twice about putting
enough capacitance in to give your cap-input power supply stiff DC
regulation. I don't mean, for instance, 1000uF or greater.

-Henry

John Byrns wrote:
I don't think this is a reasonable suggestion because Andre's and my
design tastes and styles are completely different, although perhaps both a
little offbeat. One of my designs just wouldn't look right under Andre's
name, just as one of his designs wouldn't look right under my name.

Much Snipped


John, with all due respect, that is most likely true. Were Mr. McCoy to
put forth a design that actually worked 'out of the box', we all would
know instantly that he had nothing to do with it. And at the same time,
were you to put out a half-baked bit of semi-deadly and unreliable
bunk, we would also know that it was not yours... at least not yours
when sober.

You are playing your role to the hilt, however, and adding that of
'Apologist'... which is truly beneath you. Let Mr. McCoy manage his
explanations. You would not get tarred with the same brush aiming for
him.... something that you really do not deserve.

Do you actually believe that any sane individual or group would let him
design Bicycles!? That they would sell to the public? Did you note his
artful implication without actually stating that he had such a
commission? That is the bred-to-the-bone pretentious pathology that
you are defending. A simple consideration of the necessities of Product
Liability would expose his pretense for the lie that it is without
further proof being necessary.

Peter Wieck
Wyncote, PA

Andre Jute wrote:

My original long reply seem to have gone missing in the ether. Here's a
condensed recreation.

John Stewart wrote:
Andre Jute wrote:

choke input .....
is traditionally built with two sections, meaning two chokes.

Not traditionally built in two sections at all.

RDH p1192ff. 1954 is traditional enough for me.

Better take another look at your reference in RDH4. That is two seperate chokes,
their cores in no way connected as they are in the Lundahl chokes.

I will post a reference later, probably on the weekend in regard to choke caused
problems when the choke is included in the PS return leg.

BTW, our company today was part of an industry exhibit to the local customer base.
I spent some time with Fred Hammond & some of his staff as well as other industry
associates.

Cheers, John Stewart

Never let a fact get in the way of a good story...

You should know better, John!

Peter Wieck
Wyncote, PA

Mark S wrote:

"Henry Pasternack" wrote in message
...
"Patrick Turner" wrote in message
...
Well, Si diodes and high value cap input filters are better regulated
than any
tubed choke input filter. Gone is the series resistance of choke and
tube.
The choke input allowed the tube rectifier to conduct throughout the
cycle;
there is no peak charging that had limits with tubes.

It seems to be a strong concensus among subjective-minded hobbyists that
choke-input filters sound better because a lot less RF hash is generated
by
diode switching. Even Morgan Jones, who's a pretty no-nonsense guy and
not at all afraid of silicon, thinks so. The argument makes sense to me.

This doesn't mean, though, that a given amplifier built with a cap-input
power supply will sound bad. There are many counter-examples.

Well if the choke is simply able to comply with RL / 1,100 where RL is
the Edc / Idc and Idc is considered at 10% of that normally drawn, the
choke is probably ok for choke input with a higher V ac HT winding
to produce the same B+.

There are a couple of concerns. The first is that the choke should have a
high enough current rating that it won't saturate with the large AC
currents
flowing through it in this application. Manufacturers don't spec their
chokes
for choke-input service and don't publish detailed design information, so
you have to make educated guesses.

The second concern is that the choke has to be made well enough that it
can withstand the added stress due to magnetostriction and core heating.
Hammond, which is the biggest supplier of affordable chokes in North
America, specifically states that their chokes are not rated for use in
choke-input filters. I don't know exactly what they mean by this. I have
a pair of Hammond 10H @ 300mA, 60 Ohm, chokes that run absolutely
cool and quiet as input chokes with a 1000VCT power transformer and
200mA DC load current.

Hi Henry,
Interesting experience with the Hammond chokes. I tried their 5H 500 mA
choke with a 1250 VCT trans @~250mA years ago in a choke input config and
while it was a very stiff supply, the choke buzzed like nuts. I actually
called Hammond about this and they said they would have to specially "dip" a
choke for this app.

1,250V with CT means you'd have 550Vdc and at 50mA dc RL = 11k, and the
L-critical required
is 11k/1,100 = 10H, and you have only 5H.
When max Idc occurs, RL = 1.1k, and L needn't be so much, so L is allowed to
fall a bit, ie, swing, due to dc current,
so the swing is fine, methinks you didn't have enough L, therefore causing weird
wave forms with a switching
content as the choke saturated partially and therefore hummed.
Sure the chokes may also have needed another "dip", ie, it needed to be properly
impregnated with varnish
and your sample is a typical reason why I won;'t let anyone else wind anything
for me.
Having two chokes in series may have fixed the hum problem.




This was about 1992 so things may have changed since

then. I know the 1650 outputs went through a redesign since as my 100 w 1650
OPT's are significantly heavier / larger then the current offering. This
was also when I learned about critical inductance in a choke input filter.
Good thing I did have 1000v of caps in place when I first fired up that
supply. Sowter also has a separate series of chokes for choke input filters.

625 Vrms will soar to +881V without a bleeder. A pair of 450V rated electros in
series is barely enough rating.

Patrick Turner.



MarkS


Nobody is perfectly competent. I do not post with purpose to point out
mainly the incompetence of others, but more to offer an alternative which
may or may not appear to be truer than what else may have been said, or
to augment what has been said already.
I found teachers who came at me to primarily kick my butt of ignorance
to be rude.

Sometimes there is no choice but to kick the ass of a disruptive student.

-Henry

Andre Jute wrote:

My original long reply seem to have gone missing in the ether. Here's a
condensed recreation.

John Stewart wrote:
Andre Jute wrote:

choke input .....
is traditionally built with two sections, meaning two chokes.

Not traditionally built in two sections at all.

RDH p1192ff. 1954 is traditional enough for me.

Presumably you're now on the right circuit:
http://members.lycos.co.uk/fiultra/T...trafi-crct.jpg

That is a special case.

Not at all. Rectifiers have spec limits on the value of capacitance
that may be applied in different power filters. The only way to get the
LC values desired is by using two sections. Many committed builders of
SETs use several sections: LCLCLCLC is not uncommon. Don't throw a
thrombie over the cost, John. If you're tonedeaf, before you start
dancing you should ask what the tune is. This tune has buggerall to do
with cost-engineering.

If you think I will give up square-rooting the noise left after one LC
section merely to save an additional LC section costing around a
hundred bucks, you should raise your head from your cheap junkbox amps
and smell the rich air of the 21st century.

I like to supply an OPT with dc at say 400V @ 150mA which has only mV of ripple.
Same goes for any SE amp, where lack of ripple is far more important because the
ripple
is across the OPT and with SET the Ra is lower than RL so nearly all the ripple
appears across the OPT primary.
I explained in a previous lengthy post where I cited the reactance values needed
for good ripple reduction.
If you have low C values and a tube rectifier and high dc, chokes are necessary,
and preferably CLCLC, or LCLC at least.

Quad II got away with having a perfectly lousy power supply with 16uF to anchor
down the CT and ripple
was 17Vms. While in class A, a PP amp obstructs virtually all ripple current flow
from the CT;
the ripple appears at both ends of the OPT and same phase, so no ripple flow in
the primary.
In class AB the common mode rejection stops, and the hum becomes in series with
the tube that is conducting.
Most guitar amps have lousy filtering of their PS in the same way as Quad II and
operate in low class A and almost classB. Musos like the growl in the background
of loud notes due to hum.
Quad used a 20H choke + 16uF to filter the screen voltage though. It only reduces
the 17Vrms hum at the CT to
0.14vrms. 1H and 330uF would be just as good a filter, but because Idc for the
screens is low
you could get away with 470 ohms and 470uF.

Quad II PS caused artifacts are about equal to the THD measurement.

With a well done PS the PS artifacts are difficult to measure.

The better idea for building good hi-fi amps as one off articles is to always
exceed the lowest common denominator
of the status quo mass market junk product.

Patrick Turner.






If
you put one section in the -ve lead & the other in the +ve lead the common
mode voltages if they are present will be stopped.

I do it anyway, because I can. Everest; Hillary: "Because it is there."
Ultrafi; KISS; Jute: "Screw the cost engineers."

But then you need to be
aware of other possible problems!

List those "possible problems!", John, and then we'll compare them with
the known disadvantages (!) of the standard engineering method (cheap
single-coil choke on the positive lead) and with the extensive
advantages (!) of my screw-the-cost-engineers method of a split choke
with one section on the negative lead and one section on the positive
lead.

Good luck with dual winding chokes.

I don't see the need for myself; my amps are complex and difficult to make already
and I don't like adding to all that.
I often just have CLC with the choke in the ground so there is no HV from winding
to
earthy core. Noise is never a problem in anything I build.



When it comes to protecting the rectifier(s) from excessive peak currents as
seen in cap input filters a single section choke of at least the critical
inductance will do just fine. No need at all for that 2nd
winding.

You haven't got it, pal. If the rectifier has to live dangerously and
be sacrificed occasionally in the service of better sound, I'd gladly
do. But in this amp the sonic imperatives dictate topologies that tend
to conservative use and protection of the rectifier. The second choke,
whatever its effect may be on the security of the rectifier, by
intention has buggerall to do with protecting the rectifier. From the
blank sheet, this amp was intended, cost no object, to drive noise into
the basement. That is what the second choke and cap do. It also
contributes to some other desirable features of the amp. Production is
not contemplated; it is a DIY amp; cost is immaterial.



You might ask what the design objectives are before you start
pontificating from the burning bush: "This is The Great P'Eng. Second
filter sections are an ostentatious abomination before my face. You
will burn in Hell for double-coil chokes, double filter sections, and
expensive tubes, because I am The P'Eng of The Cheap Junkbox." Sheesh,
man, what did they teach you at engineering school about determining
purpose as the first step? Or did you go only to cost-accounting
school?

JLS

Thanks for your thoughts. Let's hear some more about the "possible
problems!" of common mode rejection.

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

Henry Pasternack wrote:

"Patrick Turner" wrote in message ...
I have built a lot of PS in my time even with 500V at 650mA for my 300
watt amps there is *no* problem with PS hash... if someone cannot prevent
rectifier noise getting into the signal they are a power supply novice...

I also find that using fast recovery diodes isn't any quieter than plain slow
old cheap Si diodes...

But I am a careful with PS, prefering to have a mild steel sheet enclosure
around the PS to stop magnetic fields and electrostatic fields interfering.

I know that diode switching artifacts are real and measurable, and I know
there are ways to minimize them. This is even true with a choke input filter.
Jones' book shows how to properly snub a filter choke and backs it up
with actual scope traces.

Its all too easy to have an input lead or a feedback lead close to a mains or other power supply lead
which has switching noise within it.



I think if you have the right measuring equipment it is pretty easy to prove
that power supply switching noise makes it to the output of the signal
circuitry.

The CRO can see it. If I set it for its mosrt sensitve range, and hums and switch spikes are less than
0.3mV,
I am usually happy.

The noise is much harder to filter out than it is to prevent in the
first place. There is a lot of objective as well as anecdotal evidence that
proper use of common-mode chokes and effective bypassing can improve
the performance of audio equipment.

common mode chokes are used to effect in IEC shielded/filered mains input sockets
but I have not used any in a CLC supply and I don't see the need.
There's no free lunch in a common mode choke in a LF CLC.
Nothing much in RDH4 about them.


The results will vary a lot depending on the circuit, the wiring layout, chassis
design, and of course the sensitivity of the listener and his state of mind. I
think this is an area where you can legitimately probe deeper and deeper
and deeper, and at each level open up a new realm of cost and complexity.
If you are trying to build a neutrino detector, the cost is probably justified.
The question is how good is good enough for consumer audio work?

Quad II got away with murder in their PS. I make mine with 60 dB less noise at the CT.
This does not mean that listeners will gain a 60dB improvement in listeing pleasure.
Just what does give such an improvement? What makes something 1,000 times better?

But making a PS 1,000 times quieter than Quad II places thatv PS beyond blame, into the land of angelic
power supplies, ie, like HV batteries.
Angelic power supplies can be built at low cost. ( Wings are the most expensive parts, since not many spare
feathers
are available ).



Well ya gotta know what you buy, or don't buy it; I wind all mine.

It would be more cost effective for me to pay you to wind chokes for me
than for me to wind them myself.

No, I charge like then light brigade. Buy them from Hammond,
they have costs because of mass production far cheaper than mine, and just use CLC.


But -- oh my god -- I would probably
have Michael do the work, if only because he's closer.

Arch Angel Micheal should be able to provide angelic power supply components.
Pray harder.



The second concern is that the choke has to be made well enough that it
can withstand the added stress due to magnetostriction and core heating.
Hammond, which is the biggest supplier of affordable chokes in North
America, specifically states that their chokes are not rated for use in
choke-input filters. I don't know exactly what they mean by this.

Well, you can work it all out for a given choke. RDH4 has Hanna's method,
supposed to be good for filter chokes only with low ac across them.

That's fine, but it tells us nothing about the quality of the construction of
off-the-shelf parts. If Hammond says their chokes aren't intended for
choke-input service, could that mean they are cutting corners on
mechanical robustness, or does it just mean that they don't want the
hassle of dealing with hobbyists who don't properly derate the chokes
for that application?

To really know, ya gotta buy a choke; they are dirt cheap, and a choke is cheaper than
couple of big Macs with the lot. Big value caps are even cheaper.



I should keep my arse in a large steel bucket to prevent bruising eh....

If you intend to accuse me of child molestation, yes, you should plan to
armor-plate your backside.

I have never accused anyone of such nefariousness. What folks do with other folks organs isn't my business.

I'd even discuss tubes with George Bush if he was interested, and he's ****ing a whole country
in the middle east.

All I can say to George is that there is no accounting for taste.

Patrick Turner.



-Henry

John Byrns wrote:

In article , "Henry Pasternack"
wrote:

"John Byrns" wrote in message
...
This question is not meant as criticism of your general comments on
"swinging chokes". Are you sure that it is true that "The reason swinging
chokes are so rare nowadays is that the availability of cheap silicon
rectifiers and large electrolytic capacitors makes capacitor-input filters
more economical to build than choke- input filters"? My observation is
that chokes of any sort, "swinging" or filter, were gone from Hi-Fi amps
even before the use of silicon rectifiers became common, and also long
before large electrolytic capacitors came on the scene, which appear to
have come later than silicon rectifiers.

You're the hi-fi historian, so I won't disagree. Most of the commercial
hi-fi designs I'm familiar with used a tube rectifier, smallish electrolytic
capacitors, and a small smoothing choke in the main B+ supply. Some,
like the Marantz 8, used solid-state diodes but still retained the choke.

Choke input filters, I think, were always costly. Regardless of the
economics of power supply design during the interim period you refer
to, in the present day the cost advantage of capacitor-input filters is
clear. This ignores any ostensible performance advantages of the
choke-input power supply.

Hi Henry,

You are of course correct that some Hi-Fi amplifiers did use filter chokes
as part of a capacitor input filter, among them as you point out was the
Marantz 8B, and there were also others such McIntosh and some Dynaco
models. I should have known this, and actually did know it, as I have
owned the Marantz 8B and several Dynaco Stereo 70s. I am not sure how I
ended up saying "that chokes of any sort, "swinging" or filter, were gone
from Hi-Fi amps even before the use of silicon rectifiers became common",
specifically how the word "filter" got in there. Well I sort of know how
it got in there, I had originally typed the words "swinging or other" to
indicate that the input choke might either be a so called "swinging"
choke, or it might simply be an ordinary sort of choke. I remember
changing the word "other", because it somehow didn't seem right, but what
I might have been thinking to replace it with the word "filter" I haven't
a clue. I have noticed before that sometimes when I go back and change a
few words in isolation, to some that sound better, it is possible to
grossly change the meaning of the whole paragraph unless I remember to go
back and proof read the entire paragraph after making the change.

Also while I don't believe that the coming of silicon rectifiers had
anything to do with the disappearance of choke input filters from domestic
Hi-Fi amplifiers, your basic thesis is probably correct in a broad sense.
For example Mercury Vapor rectifiers, which were once common in higher
power equipment, almost universally used choke input filters, as using
capacitor input filters with mercury vapor rectifiers required including
special protective circuits which probably weren't any less expensive than
the choke they eliminated, and which also would introduce a new failure
point reducing reliability. Silicon rectifiers made it possible to use
capacitor input filters without special protective circuits. Personally
the thing I like about choke input filters is that they reduce the stress
on the rectifiers and power transformer, and so should result in a more
reliable amplifier.

When speaking of "large electrolytic capacitors" it is not clear that we
are talking about the same thing, what do you consider to be a "large
electrolytic capacitor"? I suspect that what you are referring to as a
"large electrolytic capacitor" may be what I would call a "medium sized
electrolytic capacitor".

You are right about all that John. Cap inputs are rare in industrial apps.
They still are.

A "large electro" is 470uF/450v rated or more as opposed to the puny values of
16uF used in the 1950s.

I put 1,500uF/450V electros into a pair of 100 watt mono ampos I made, 150mm tall,
75mm dia, screw terminals,
probably 20A ripple rating. They were taken out of little used university research
equipment that was junked in the 1980s, so cost me only $25 each.
Not much stinking ripple in those amps.

Patrick Turner.



Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

On Wed, 5 Apr 2006 16:29:46 -0400, "Henry Pasternack"
wrote:

I'd be interested in knowing what an RF vector network
analyzer *was*. Been too far outa the loop lately, obviously.

A device that that allows you to make very accurate complex impedance
and transmission measurements (magnitude and phase) of RF networks
over a wide range of frequencies.

Info he http://www.n2pk.com

A Smith chart generated by DSP. Now I've seen everything and can
pass easily. Very cool, indeed; thanks.




Makes me think I should do it with transistors and be done with it.

Oh, sorry; you're using vacuum valves? Don't know why I'd
assumed you'd gone over to the Dark Side (like I have, because
I so often need to drive an A/D converter, and because I
need to include gain trim controls and metering).


Another design that is 180 degrees opposite from your approach,
yet still very interesting, is the Pass Pearl phono preamp. Single-
ended, zero feedback FETs. It's supposed to be pretty good.

Doubtless true, but it's ag'in my religious beliefs.

In the pure, no-extreme-loading world of vacuum-valves-
only, you might be interested in a topology like Dick
Burwen's from 1948, two triodes cascaded with the first
stage run wide open and the second with EQ in the "anode
follower" feedback. Still haven't found better, IMO, for
use into very light loading.

Thanks, as always,

Chris Hornbeck

On Thu, 06 Apr 2006 06:57:21 +0100, Stewart Pinkerton
wrote:

Here's an alternative, using *lots* of tiny transistors! :-)

http://www.lurcher.org/ukra/stewart_p/stewart_p.html

A very interesting topology, instrumentation input stage
run flat, feeding 75 muS passive rolloff; then the lower frequency
corners in the second stage's feedback. But why the third stage?
Is the DC servo easier to implement?

My only really cogent comment is: Great Photography!
Really nice light. And don't blame the camera; if you
get beautiful light, it's the photographer's fault.

Thanks, as always,

Chris Hornbeck

"Patrick Turner" wrote in message
...


Mark S wrote:

"Henry Pasternack" wrote in message
...
"Patrick Turner" wrote in message
...
Well, Si diodes and high value cap input filters are better regulated
than any
tubed choke input filter. Gone is the series resistance of choke and
tube.
The choke input allowed the tube rectifier to conduct throughout the
cycle;
there is no peak charging that had limits with tubes.

It seems to be a strong concensus among subjective-minded hobbyists
that
choke-input filters sound better because a lot less RF hash is
generated
by
diode switching. Even Morgan Jones, who's a pretty no-nonsense guy
and
not at all afraid of silicon, thinks so. The argument makes sense to
me.

This doesn't mean, though, that a given amplifier built with a
cap-input
power supply will sound bad. There are many counter-examples.

Well if the choke is simply able to comply with RL / 1,100 where RL
is
the Edc / Idc and Idc is considered at 10% of that normally drawn,
the
choke is probably ok for choke input with a higher V ac HT winding
to produce the same B+.

There are a couple of concerns. The first is that the choke should
have a
high enough current rating that it won't saturate with the large AC
currents
flowing through it in this application. Manufacturers don't spec
their
chokes
for choke-input service and don't publish detailed design information,
so
you have to make educated guesses.

The second concern is that the choke has to be made well enough that
it
can withstand the added stress due to magnetostriction and core
heating.
Hammond, which is the biggest supplier of affordable chokes in North
America, specifically states that their chokes are not rated for use
in
choke-input filters. I don't know exactly what they mean by this. I
have
a pair of Hammond 10H @ 300mA, 60 Ohm, chokes that run absolutely
cool and quiet as input chokes with a 1000VCT power transformer and
200mA DC load current.

Hi Henry,
Interesting experience with the Hammond chokes. I tried their 5H 500 mA
choke with a 1250 VCT trans @~250mA years ago in a choke input config
and
while it was a very stiff supply, the choke buzzed like nuts. I actually
called Hammond about this and they said they would have to specially
"dip" a
choke for this app.

1,250V with CT means you'd have 550Vdc and at 50mA dc RL = 11k, and the
L-critical required
is 11k/1,100 = 10H, and you have only 5H.
When max Idc occurs, RL = 1.1k, and L needn't be so much, so L is allowed
to
fall a bit, ie, swing, due to dc current,
so the swing is fine, methinks you didn't have enough L, therefore causing
weird
wave forms with a switching
content as the choke saturated partially and therefore hummed.
Sure the chokes may also have needed another "dip", ie, it needed to be
properly
impregnated with varnish
and your sample is a typical reason why I won;'t let anyone else wind
anything
for me.
Having two chokes in series may have fixed the hum problem.

Hi Patrick,
Maybe the 10 H choke might have been a better choice but it was the 27 ohm
DCR of this choke that caught my eye. Seems as though there are quite a few
NOS potted chokes showing up on ebay these days. I replicated this supply
with a potted UTC choke and that choke was dead silent.althought the DCR was
a little higher, 50 ohms.



This was about 1992 so things may have changed since

then. I know the 1650 outputs went through a redesign since as my 100 w
1650
OPT's are significantly heavier / larger then the current offering.
This
was also when I learned about critical inductance in a choke input
filter.
Good thing I did have 1000v of caps in place when I first fired up that
supply. Sowter also has a separate series of chokes for choke input
filters.

625 Vrms will soar to +881V without a bleeder. A pair of 450V rated
electros in
series is barely enough rating.

I had a pair of 500's in place. I determined the bleed resistor emperically
as the critical inductance constants are a little conservative. 10K would
knock the start voltage down to around 600v until the output tubes warmed
up.
I think I am going to revisit this type supply soon with the UTC choke and
damper diodes for rectifiers. I'll post the results but I can't see getting
to it til the fall.

Best Regards,
MarkS


Patrick Turner.



MarkS


Nobody is perfectly competent. I do not post with purpose to point
out
mainly the incompetence of others, but more to offer an alternative
which
may or may not appear to be truer than what else may have been said,
or
to augment what has been said already.
I found teachers who came at me to primarily kick my butt of
ignorance
to be rude.

Sometimes there is no choice but to kick the ass of a disruptive
student.

-Henry

On Fri, 07 Apr 2006 05:21:09 GMT, Chris Hornbeck
wrote:

On Thu, 06 Apr 2006 06:57:21 +0100, Stewart Pinkerton
wrote:

Here's an alternative, using *lots* of tiny transistors! :-)

http://www.lurcher.org/ukra/stewart_p/stewart_p.html

A very interesting topology, instrumentation input stage
run flat, feeding 75 muS passive rolloff; then the lower frequency
corners in the second stage's feedback. But why the third stage?
Is the DC servo easier to implement?

The third stage is simply there to ensure that the 20Hz IEC rolloff
formed by C10-14 and R15 is not deranged by a low-impedance load, and
hence to provide a controlled and very low output impedance. The phono
stage sits within a foot of the arm base, so might have to drive quite
a long interconnect. The passive treble rolloff avoids any possibility
of scratch overload causing momentary latchup, and maintains the
correct rolloff even after the opamp would level it off to unity gain
in an active configuration. The nice thing about the input stage is of
course that it's differential, so it rejects any common-mode hum and
hash the cartridge and the arm leads might pick up. It's what Andre
would call a very 'silent' amplifier.

My only really cogent comment is: Great Photography!
Really nice light. And don't blame the camera; if you
get beautiful light, it's the photographer's fault.

Thanks, but it's just the available daylight in the room, which has a
pair of 6-foot windows spaced along each of the 25 foot long walls.
Taken with a Sony DSC-S85, a great little camera now replaced by an
absolutely superb Sony DSC-R1. I've done A2 sized prints off this new
beauty and they are clean and crisp edge to edge, sharp as a tack with
200dpi resolution. I've even taken it up to A0 just for fun, and from
a 3-foot viewing distance they appear flawless.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Patrick Turner" wrote in message ...
I'll send you the schematic of the amp, and if you like the look of it, I
can send you the other 4 sheets. In each channel it uses one 2SK369,
1 x 6DJ8, 1 x 12AT7, 1 x 6CG7. These are paralleled so each tube
socket has just one triode each.

Thank you for sending me the schematic. It seems to be a defensible
design. For my purposes, I would want to get a selected input FET
with Idss suitable for running with the source resistor connected to
ground. This is the way Allen Wright does it, and it avoids the need
for the -6V bias supply.

I'm also surprised you doubled up the tubes on the SRPP stage, but
I guess you wanted to have a very robust output drive capability.
The same for the 6DJ8, but if you hadn't paralleled it you'd have had
an extra section lying around. I assume you don't believe in sharing
tube halves between channels in a purist design.

I still haven't decided what phono circuit to build, but I'm getting
closer. One that intrigues me is this:

http://www.pacifier.com/~gpimm/phono.htm

The 6GK5 and 6ER5 are really hot tubes, but not very linear for
large signals, I think.

I received a new pulley for my turntable yesterday, to convert it from
string drive to 1/2" tape drive. If I can find suitable splicing tape, this
evening I will sacrifice one of my gay pornography videos to make a
new drive belt. Hopefully there will be no more speed variations and
that "hump, hump", I mean "thump, thump", every time the knot goes
around will be gone.

-Henry

John Byrns wrote:

I attribute much of the apparent weirdness of Andre's
KISS amp

There's no weirdness to my KISS amps (plural, there are two of them);
they are exceedingly conservative (except for a few details to trip up
the clowns, of course!). Those two nice clean designs are he
http://members.lycos.co.uk/fiultra/T...trafi-crct.jpg
http://members.lycos.co.uk/fiultra/T44bis-'Populaire'-crct.jpg
and are fully described he
http://members.lycos.co.uk/fiultra/T...mp%20INDEX.htm

Any "apparent weirdness" is the result of:
a) the resident scum resolutely looking at the wrong circuit and
screeching about it and
b) a few noise-reducing measures, like split-wound chokes on the same
cores used for common mode noise reduction, beyond the understanding of
the cost-engineers.

to its heritage, that is that it is descended from his ill fated
book attempt,

Oh, that baby was not only born but is a lusty, screaming infant. You
may remember that the sociopath Michael LeFevre of Magnequest publicly
threatened that if I published the book he would organize a campaign of
denigration. I could not under those circumstances take the publisher's
money, so I returned the advance and found other ways to take the money
out of the skin of LeFevre and his gang of bullyboys. (I made a
six-figure sum out of the self-immolation of Frank Deutschmann, for
instance. In your face, scum, and in my bank account! LOL.) But the
book isn't dead. It merely morphed into my KISS netsite, for which the
Magnequest scum has paid far, far more handsomely than the original
publisher's advance.

and the fact that he has a large box of Lundahl transformers
left over from that project

I wish. No, those Lundahls have long since walked out of the door and
been replaced, several times over. The truth is that the Lundahls are
simply the most suitable at any price for my KISS amps; I don't see the
point of paying more than Lundahls cost for transformers which are
usually no better and very often inferior. There are no dropper
resistors in the right circuits. As I said, the screeching scum whining
about ballasts were (probably deliberately) looking at the wrong
schematic, for a proofing knockup intended to last only a couple of
days to prove the driver stage of the T39. (It was kept after that as a
potato amp because it sounded so sweet... The circuit is here
http://members.lycos.co.uk/fiultra/t...17acircuit.jpg
for builders of my T39 KISS amp who want temporarily to experiment with
a potato amp on the fullblown KISS experience.)

While the
premise of his book was interesting, I thought that he was overreaching
when he first brought it up back in 1998, and IIRC I told him so at the
time.

I should have listened... Oh, well, like Edith Piaf sang, No time for
regrets now.

The idea of the book as I remember it was to build a series of
amplifiers each of higher quality than the previous one, and always
recycling the iron from the old amplifier into the new amplifier with the
addition of additional transformers and chokes. This idea makes some
sense for a series of two or possibly three different amplifiers, but I
felt that Andre pushed the idea too far, IIRC to something like a half a
dozen different amplifier designs, and the result was that some of them
required a few very grotesque design details to be able to use the same
iron as the rest of the series. I felt he would have done better to
concentrate on maybe three amplifiers at the most, of increasing price and
performance.

Nah, the most interesting amps in my Modular series were the ones that
were also most controversial. I fondly remember the absolute base amp
which used photoflash caps, and which no one except me built because
everyone else thought that if you were spending for 300B anyway
photoflash caps were a whole mile of cheapies too far. And the one with
the two power transformers operating each as a halfwave circuit to
output fullwave rectified DC beyond the two tube rectifiers, while it
is true that the usual scum screeched for months about it on RAT,
earned me a lot of interest off-list from real engineers who wanted to
know me -- precisely because I had the brains and the balls to
resurrect that forgotten topology.

Anyway, the second-cheapest amp in that Modular Series 300B, the T44,
which you picked as your fave because of the silicon rectifier, was the
one most people built, to my distress, because I thought then and still
that a tube rectifier is A Good Idea. So I took a hint and morphed it
into a stereo amp as the other KISS amp, the T44bis. An intelligent
designer -- and intelligent artist, an intelligent human for that
matter -- wastes nothing.

Regards,
John Byrns
Surf my web pages at, http://users.rcn.com/jbyrns/

I enjoyed that trip down memory lane. ZNFB. Zweirdness. Zregrets.

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

Henry Pasternack wrote:

"Patrick Turner" wrote in message ...
I'll send you the schematic of the amp, and if you like the look of it, I
can send you the other 4 sheets. In each channel it uses one 2SK369,
1 x 6DJ8, 1 x 12AT7, 1 x 6CG7. These are paralleled so each tube
socket has just one triode each.

Thank you for sending me the schematic. It seems to be a defensible
design. For my purposes, I would want to get a selected input FET
with Idss suitable for running with the source resistor connected to
ground. This is the way Allen Wright does it, and it avoids the need
for the -6V bias supply.

The Allen Wright FVP just has the gate biased by 47k to 0V and an 18 ohm source R to 0V for
source biasing just like having a cathode R to bias tube.
Other versions of his amps have a CCS tail for a j-fet LTP which I tried but it was noiser
than the SE version I sent you. The -6V supply is no problem in itself with the network of resistors
which can be varied with a link to set the gain so that in the highest gain setting there is effectively 30
ohms from the source, R6&R7 with a link to R3, 10 ohms to 0V. The original FVP had no adjustment for gain.

If you have a differential input pair of fets with CCS tail, there can be two source resistors
and there is more scope for varying gain. But that's two more fets than I have....





I'm also surprised you doubled up the tubes on the SRPP stage, but
I guess you wanted to have a very robust output drive capability.
The same for the 6DJ8, but if you hadn't paralleled it you'd have had
an extra section lying around. I assume you don't believe in sharing
tube halves between channels in a purist design.

I'd rather have only one function per bottle. In my own pre which is similar to the
Rocket, I have a 6EJ7 in triode as the first triode; but almost anything will do, and you could have just
one section
of a 6DJ8 if you wanted to since its really unlikely there would be much cross talk betwen channels, so the
tube count could be halved at the expense of slight dynamic range ability.



I still haven't decided what phono circuit to build, but I'm getting
closer. One that intrigues me is this:

http://www.pacifier.com/~gpimm/phono.htm

The 6GK5 and 6ER5 are really hot tubes, but not very linear for
large signals, I think.

6GK5 has µ = 78, Ra = 5.4k, gm = 15mA/V all at Ia = 11.5mA.
At 2.5 mA for ia as shown in the above schema the gm would be maybe only 1/3
but still OK, but about equal maybe to a parallel 6dJ8 at a total of 5mA.

The above circuit is a little confusing since the load for the two triodes are twin circles of a CCS symbol
but with output coming from a line between the circle which is normally the way a controlled CCS is
indicated.
So we are left to assume the guy really has the anode outputs from the anode and there are conventional CCS
dc feeds to the triodes. Nothing wrong with CCS dc supplies with high ac impedance.
There is 475 ohm unbypassed Rk for the 6GK5, so ra effective is about 10k plus 78 x 475 = 47k total.
I doubt the guy factored in the 47k or actual Rout at the anode into his RIAA network because effectively
he has 47k of Ra' + R4,22k in series with the C1, 0.1 & R5, 3k2 for the 3180 and 318 uS time constants.
Well, 47k + 22k = 69k, so with 0.1uF, you have 6,900 uS, not 3,180 uS...l

In my circuit the Ra' is extremely high for the cascode 6DJ8 triode anodes because the fet below it
has a high Rd which is the cathode resistance for the triode, increasing Ra by µ x Rd, so the anode Ra is
virtually a CCS. The Rout from the 6dJ8 is set by the 22k load resistance.




I received a new pulley for my turntable yesterday, to convert it from
string drive to 1/2" tape drive. If I can find suitable splicing tape, this
evening I will sacrifice one of my gay pornography videos to make a
new drive belt. Hopefully there will be no more speed variations and
that "hump, hump", I mean "thump, thump", every time the knot goes
around will be gone.

Its sounding all a bit primitive there Henry. If that fails to work, hold the stylus carefully and run
around the
record on a table at 33.3RPM. One guy here mounted his house on an old merry-go-round
with record on a shaft up through the centre to sit the record on.
His wife got dizzy...

Patrick Turner.



-Henry

I still haven't decided what phono circuit to build, but I'm getting
closer. One that intrigues me is this:

http://www.pacifier.com/~gpimm/phono.htm

The 6GK5 and 6ER5 are really hot tubes, but not very linear for
large signals, I think.

Oh, and BTW, phono signals are tiny, so linearity with *any* triode will be OK
at less than 0.5Vrms output.

Patrick Turner.

"Patrick Turner" wrote in message ...
The Allen Wright FVP just has the gate biased by 47k to 0V and an 18
ohm source R to 0V for source biasing just like having a cathode R to bias
tube. Other versions of his amps have a CCS tail for a j-fet LTP which I
tried but it was noiser than the SE version I sent you.

It should be 3dB noisier due to the two tubes' noise adding (but not
6dB, evidently). Maybe Andre can explain why.

The -6V supply is no problem in itself with the network of resistors
which can be varied with a link to set the gain... The original FVP
had no adjustment for gain.

If you have a differential input pair of fets with CCS tail, there can be
two source resistors and there is more scope for varying gain. But
that's two more fets than I have....

There are several theoretical advantages to the differential design. Allen
swears it's the bee's knees.

The above circuit is a little confusing since the load for the two triodes
are twin circles of a CCS symbol but with output coming from a line
between the circle which is normally the way a controlled CCS is
indicated.

You have to read the documentation for the current sources. The middle
connection is what he calls the "mu" output. Basically, it turns the tube
and the current source into a hybrid SRPP. Around 400 Ohms output
impedance. Supposed to be sonically transparent, and these guys are
*very* particular.

I doubt the guy factored in the 47k or actual Rout at the anode into his
RIAA network...

He's smarter than you think.

I received a new pulley for my turntable yesterday...

Its sounding all a bit primitive there Henry.

I whipped a belt together quickly. It's not as nice as I'd like, but there's
time to learn to make them better. There's no noise when the splice
goes over the pulley.

Here's a picture.

http://users.rcn.com/hpasternack/teres/belt.jpg

-Henry

Go over to alt.binaries.pictures.radio to read of a problem arising when a choke input
filter is connected in the return leg of a rectifier circuit.

The page is taken from the Electrical Engineering Series, John D Ryder, Author.

Cheers, John Stewart

Henry Pasternack wrote:

"Patrick Turner" wrote in message ...
The Allen Wright FVP just has the gate biased by 47k to 0V and an 18
ohm source R to 0V for source biasing just like having a cathode R to bias
tube. Other versions of his amps have a CCS tail for a j-fet LTP which I
tried but it was noiser than the SE version I sent you.

It should be 3dB noisier due to the two tubes' noise adding (but not
6dB, evidently). Maybe Andre can explain why.

The noise problem wasn't the fet noise; it was mainly hum, but after examining all the figures
and taking into account the fact I only wanted an unbalanced output there was no point in having balanced
input and following balanced gain stage with all the extra bits. Simplicity won, complexity lost, music
gained....



The -6V supply is no problem in itself with the network of resistors
which can be varied with a link to set the gain... The original FVP
had no adjustment for gain.

If you have a differential input pair of fets with CCS tail, there can be
two source resistors and there is more scope for varying gain. But
that's two more fets than I have....

There are several theoretical advantages to the differential design. Allen
swears it's the bee's knees.

I know, he would, most folks do, but I got excellent low noise with the circuit i gave you although it is
hum prone near magnetic fields when using MC carts.
If you have 0.4mV at 1kHz to make the full output, low level hum signals can cause
problems because bass signal sensitivity is higher.



The above circuit is a little confusing since the load for the two triodes
are twin circles of a CCS symbol but with output coming from a line
between the circle which is normally the way a controlled CCS is
indicated.

You have to read the documentation for the current sources. The middle
connection is what he calls the "mu" output. Basically, it turns the tube
and the current source into a hybrid SRPP. Around 400 Ohms output
impedance. Supposed to be sonically transparent, and these guys are
*very* particular.

Yes you are right, the there is a mu follower output which has low Rout
see http://www.pacifier.com/~gpimm/Activ...t_control.html

I'd prefer a fully tubed µ follower...

A tubed µ follower with 6DJ8 can have a low Rout, and the bottom gain tube sees a high RL.
A fet can be still used in cascode with the bottom gain triode.

The overall gain of the fet plus gain tube + load in the anode circuit of the tube
is simply fet gm x tube RL, so in my circuit gain without the source resistors under the fet
the gain = gm x RL = 0.04 x 22k = 880.
Now if the 22k RL was replaced with a bootstrapped follower with say 10k between
bottom triode anode and top triode cathode then the load the gain triode sees is about 300k,
so the overall gain would be huge, maybe 12,000, and way too much and unmanagable, and most likely
to oscillate at RF badly.



I doubt the guy factored in the 47k or actual Rout at the anode into his
RIAA network...

He's smarter than you think.

I missed the µ follower bit. His tube schematic does not show exactly what is there. With Rout very low,
the
0.1 and 22k give 2,200 uS ???



I received a new pulley for my turntable yesterday...

Its sounding all a bit primitive there Henry.

I whipped a belt together quickly. It's not as nice as I'd like, but there's
time to learn to make them better. There's no noise when the splice
goes over the pulley.

Here's a picture.

http://users.rcn.com/hpasternack/teres/belt.jpg

-Henry

Splice over pulley noise shouldn't be audible because the inertia of the rotating masses would limit any
miniscule platter speed changes.

Maybe the tape won't last forever. Duzzen madder, just rejoin another bit of tape.
But if there's porno on the tapes maybe the music will sound all hot and sweaty...

Patrick Turner.

"Patrick Turner" wrote in message ...
I know, he would, most folks do, but I got excellent low noise with the
circuit i gave you although it is hum prone near magnetic fields when
using MC carts. If you have 0.4mV at 1kHz to make the full output,
low level hum signals can cause problems because bass signal
sensitivity is higher.

My tonearn is unsuitable for MC cartridges, so for better or worse I don't
have to solve that problem. I'm really bummed that Shure has canceled
production of the V15, though. Hopefully they will come out with a
replacement model one of these days.

I'd prefer a fully tubed µ follower...

Gary's current source has extremely high impedance and low noise. It's
a nice example of a design that's been optimized over successive iterations.
A lot of people are reporting very good results using these things.

Now if the 22k RL was replaced with a bootstrapped follower with say 10k
between bottom triode anode and top triode cathode then the load the gain
triode sees is about 300k, so the overall gain would be huge, maybe 12,000,
and way too much and unmanagable, and most likely to oscillate at RF
badly.

Obviously you don't want to load a cascode with a current source...

With Rout very low, the 0.1 and 22k give 2,200 uS

I agree the time constant looks to be off by 50%. Maybe I'll ask him about
it.

-Henry

On Fri, 7 Apr 2006 12:49:12 -0400, "Henry Pasternack"
wrote:

http://www.pacifier.com/~gpimm/phono.htm

Note that C5 and the output transformer are series resonant
at about 50 Hz.

Good fortune,

Chris Hornbeck

On Fri, 07 Apr 2006 23:28:59 GMT, Patrick Turner
wrote:

Oh, and BTW, phono signals are tiny, so linearity with *any* triode will be OK
at less than 0.5Vrms output.

I strongly disagree. FWIW.

Good fortune,

Chris Hornbeck

"Patrick Turner" wrote in message ...
I missed the µ follower bit. His tube schematic does not show exactly
what is there. With Rout very low, the 0.1 and 22k give 2,200 uS ???

There's an RIAA calculator he

http://www.kabusa.com/frameset.htm?/phonpre.htm

It confirms the values in the Pimm schematic. Supposedly, the calculator
is based on math by Stanley Lip****z. I haven't had a chance to check the
calculations, but I suspect it's correct. I guess there's interaction between
the sections that accounts for the seeming discrepancy, although it isn't
intuitively obvious to me why right at this moment.

Gotta get dressed and take the kids to piano lessons.

-Henry

"Henry Pasternack" wrote in message ...
"Patrick Turner" wrote in message ...
I guess there's interaction between the sections that accounts for the
seeming discrepancy, although it isn't intuitively obvious to me why
right at this moment.

The answer is you need to put the two capacitors in parallel when
figuring the 50Hz cutoff.

-Henry

This particular thread is now so contaminated with irrelevant noise,
some of it from transistors and child molesters, that I have opened a
new thread to discuss John Stewart's contribution. It is called "The
KISS AMP: square-rooting the noise: the real work starts" -- AJ

John Stewart wrote:
Go over to alt.binaries.pictures.radio to read of a problem arising when a choke input
filter is connected in the return leg of a rectifier circuit.

The page is taken from the Electrical Engineering Series, John D Ryder, Author.

Cheers, John Stewart

Chris Hornbeck wrote:

On Fri, 07 Apr 2006 23:28:59 GMT, Patrick Turner
wrote:

Oh, and BTW, phono signals are tiny, so linearity with *any* triode will be OK
at less than 0.5Vrms output.

I strongly disagree. FWIW.

Good fortune,

Chris Hornbeck

Hang on a second please.

If you had a fairly non linear triode like a 6J6, 6GK5 whatever, most are capable
of
less than 1% at 10Vrms, resistance loaded. Expect 5% at 50Vrms output.

So at an output of 100mV, expect THD = 0.01%.
Isn't that linear enough?

Now many relatively non linear triodes such as the high gm RF triodes are much more
linear when set up with
a CCS load to buffer them from any R loading effect.
The steeper the RL slope of the RL loadline across the curves, the worse the
distortion.
If the load line is virtually horizontal, distorion is often only 0.1% for 10vrms
output.
i get that with 12AT7 in µ-follower.
So at 0.1Vrms, thd is rather low!

The RCA book curves for 6GK5 show rather non linear curve spacing at 2.5mA of anode
current
but its over a possible 200V p-p V swing.
Over 0.1Vrms, the distortion is the least of our concerns.

I have not seen 6ER8 curves but even if as poor as 6GK5, I suspect thd 0.1% at
500mV output.

I'd never lumber a customer with tubes not being produced now except perhaps the
occasional13E1,
where I have sold a spare to the customer and keep a few more myself. Those guys
will die before i do probably,
and the circuit is alterable to take multiples of 6L6 if the 13E1 is no longer
avaliable.

I have dozens of 6EJ7. It is a fabulous triode.

I don't believe all the curves people have drawn for data curves over the last 60
years.
Many are quite ficticious.

In a recent test of GE6550A in triode I got 1.5% thd with 235Vrms at the anode with
a high value load of
100k with a choke. GE6550A curves show about 3% THD is likely along a horizontal
load line.
at 1Vrms such power tubes have THD noise.
Nearly all the little signal triodes measure better than curves predict; errors
were routinely included with inaccurate
test gear in the 1950s and 1960s when the analog gear was tubed and had worse thd
than the bloomin
tubes they were attempting to measure.

Recent tests of EH6550 and KT90EH show such tubes in triode to be expemplary and
every bit as linear
as a 300B, yet the curves are only an approximation of the linearity, often
incorrect by 2%.
2% is SFA, and not a big deal because from the curves we can still plot valid load
lines
even if they were 5% in error.

A 2SK369 with a 2k RL with Ia = 5mA and with bypassed source has a gain of
80, but you can only get about 6vrms output and THD = about 7%.
Its like a pentode at 60Vrms output.
nevertheless, in cascode with a triode, and with 6dB current FB in the source
circuit,
it has a gain of say 15, and if Vin = 5mV, output = 75mV and thd = about 0.05% max.

with MC and .4mV input, thd falls to 0.01%, and the following tubes don't add
anything extra.

I have much more source degenerative current FB in my fet input stage than Allen
Wright uses in his FVP.

Allen's phono stage and mine are quite linear enough and quiet enough with no loop
NFB, just passive RIAA eq.

A nice phono stage can be built with all fets, take a leaf from the work by Erno
Borbelli...
But triodes are pretty linear at low levels.

The 10 tube preamp I built with a two stage MM phono amp with a pair of µ-followers

but without a fet works great with cart inputs above 2mV, quiet enough, and
certainly linear enough,
and all passive RIAA eq.

My next edition of my website will have all the grimy details of phono amp
developments over the last few years.


Patrick Turner.

Henry Pasternack wrote:

"Patrick Turner" wrote in message ...
I missed the µ follower bit. His tube schematic does not show exactly
what is there. With Rout very low, the 0.1 and 22k give 2,200 uS ???

There's an RIAA calculator he

http://www.kabusa.com/frameset.htm?/phonpre.htm

It confirms the values in the Pimm schematic. Supposedly, the calculator
is based on math by Stanley Lip****z.

I tried using 22k and 47k for R1 in the RIAA calculator and got very different time constant R x C
products. Something is drastically wrong with this online calculator.
Assume it is BS unless you can proove otherwise.


I haven't had a chance to check the
calculations, but I suspect it's correct. I guess there's interaction between
the sections that accounts for the seeming discrepancy, although it isn't
intuitively obvious to me why right at this moment.

Add C1 to C2, and the total should act with R1 to form the 3180uS time constant.
I got strange results.

I prefer my own tested trimmed values for RIAA using a reverse RIAA filter and flat input signal.
You have all the details I sent you.

My RIAA filter has the 75uS filter with a pole added for 50kHz, and has build out R rather than have
the 75uS cap straight across the RC used for 3180 and 318 uS.
There is better isolation and freedom from interaction between the 3 time constants I believe.

Perhaps you'd like to simulate the circuit i sent; and see what BS a program comes up with.
You cannot assume a program is telling you the truth unless you confirm the outcome by measurement.
But the reverse RIAA filter I have has been used to test CJ and ARC and FVP preamps which appeared to have
virtually near perfect responses so I guess my RIAA reverse eq filter values are also perfect enough.


Gotta get dressed and take the kids to piano lessons.

Well, Naked dads delivering kiddies to piano lessons are frowned upon here.

Patrick Turner.



-Henry

Henry Pasternack wrote:

"Henry Pasternack" wrote in message ...
"Patrick Turner" wrote in message ...
I guess there's interaction between the sections that accounts for the
seeming discrepancy, although it isn't intuitively obvious to me why
right at this moment.

The answer is you need to put the two capacitors in parallel when
figuring the 50Hz cutoff.

See my other post. Doing the above I still get queer answers.

Patrick Turner.


-Henry

Andre Jute wrote:

This particular thread is now so contaminated with irrelevant noise,
some of it from transistors and child molesters, that I have opened a
new thread to discuss John Stewart's contribution. It is called "The
KISS AMP: square-rooting the noise: the real work starts" -- AJ

John Stewart wrote:
Go over to alt.binaries.pictures.radio to read of a problem arising when a choke input
filter is connected in the return leg of a rectifier circuit.

The page is taken from the Electrical Engineering Series, John D Ryder, Author.

Cheers, John Stewart

Ya gotta watch out from Irrelevanlty Noisy Transelvanian Sisters ( transistors ).

Take garlic in each pocket wherever you go. Be out watching when any said sister tries to
square root you in the misty dawns of the far off mountaines, and if in doubt take a priest
with
stake and mallet in the coach with thee.....

Patrick Turner.

"Patrick Turner" wrote in message ...
See my other post. Doing the above I still get queer answers.

If you put 22,550 Ohms into the calculator (taking into account
the 450 Ohm output impedance of the "mu follower"), you get
3279 Ohms, 0.097uF, and 0.0333uF. So it's evident where
Gary Pimm got his component values.

At low frequencies, the reactance of the capacitors dominates
R5 and R6. The two capacitors are effectively in parallel. If
you figure the corner frequency of 22,500 Ohms in parallel with
0.133uF, you get 53.2 Hz. That's close enough to 50Hz to
serve as a starting point for trimming.

Morgan Jones has the formulas in his book. He says the
numbers are "exact". If R1 is the input resistor, C1 is the
first capacitor, R2 is the resistor in series with C1, and C2
is the second capacitor, then:

R1C1 = 2187uS
R1C2 = 750uS
R2C1 = 318uS
C1/C2 = 2.916

With a low-impedance network like the one in Pimm's design,
afforded by the low output impedance of the first stage, the
effect of stray and interelectrode capacitance is greatly
reduced. I think the design is reasonable and I disagree with
you that the KAB calulator is BS.

-Henry

Henry Pasternack wrote:

"Patrick Turner" wrote in message ...
See my other post. Doing the above I still get queer answers.

If you put 22,550 Ohms into the calculator (taking into account
the 450 Ohm output impedance of the "mu follower"), you get
3279 Ohms, 0.097uF, and 0.0333uF. So it's evident where
Gary Pimm got his component values.

alright, but with 22.55k and 0.13 uf, the product is 2,931 uS, not 3,180 uS.
so -3db is 54.2 Hz.
The two caps together are supposed to begin pulling down the voltage at the output of the 22k
so -3dB is supposed to be 50Hz. I would have though total C should be 0.141uF.
0.141 uF plus 22.55k have -3db at 50Hz and have a product of 3180 uS.

if C2 wasn't there, the attenuation at R1 output should be negligible at 10Hz,
but by 10kHz should be exactly -20dB; you should have poles at 50hz and 500Hz.
so R1 = 9R2, so if R2 = 3.2k, R1 = 28.8k. can you show by first principle reasoning
that I am wrong? I ain't very good with equations with reactive j quanties, vector analysis etc.....
I just measure and trim; its quicker than calculations.
When C2 is added, the response is -20dB down at 1kHz, and -40db down at about 22 kHz.

Everywhere i look around the web there are different relevant values of R&C which are supposed to
give the same error-less outcome, but they are just not all right; and especially RIAA feedback networks.
They all blather on with schematics and calculations, but few measurements.



At low frequencies, the reactance of the capacitors dominates
R5 and R6. The two capacitors are effectively in parallel. If
you figure the corner frequency of 22,500 Ohms in parallel with
0.133uF, you get 53.2 Hz. That's close enough to 50Hz to
serve as a starting point for trimming.

Well that is about true. But trimming should be not necessary when a computer is trying to
see us right; we employ computers to be accurate within 0.1%.




Morgan Jones has the formulas in his book. He says the
numbers are "exact". If R1 is the input resistor, C1 is the
first capacitor, R2 is the resistor in series with C1, and C2
is the second capacitor, then:

R1C1 = 2187uS
R1C2 = 750uS
R2C1 = 318uS
C1/C2 = 2.916

With a low-impedance network like the one in Pimm's design,
afforded by the low output impedance of the first stage, the
effect of stray and interelectrode capacitance is greatly
reduced. I think the design is reasonable and I disagree with
you that the KAB calulator is BS.

Well, BS-ishy a bit imho.

I never trust these things unless they measure right after a good test.

The noise generated by the network after the first gain stage is quite negligible
compared to the noise already in the amp from V1 grid input noise and flicker noise and shot noise.
You could have R1 = 100k, and still the noise and stray C effects are negligible, and especially
since you have a high output MM cart of 2mV input

With my circuit, noise is also very low since stage 1 cascode has a lot of gain, and RC filter components
are
low enough. Problems with filter stray C and noise only arrises if you have R1 = 1M like they used to
use with V1 as say 1/2 a 6SL7, or a damn pentode, a real BS solution imho.







-Henry

"Patrick Turner" wrote in message ...
alright, but with 22.55k and 0.13 uf, the product is 2,931 uS, not
3,180 uS. so -3db is 54.2 Hz.

I neglected to consider the effect of the 3.2K resistor, which adds
to the total series resistance seen by C1. This lowers the corner
frequency.

if C2 wasn't there, the attenuation at R1 output should be negligible
at 10Hz, but by 10kHz should be exactly -20dB; you should have
poles at 50hz and 500Hz. so R1 = 9R2, so if R2 = 3.2k, R1 = 28.8k
can you show by first principle reasoning that I am wrong?

But C2 is there, and the network never hits a flat response of -20dB.
At midband (1000Hz), where RIAA is specified to be -19.911dB, the
reactance of C2 is a non-negligible 4.8K Ohms.

I ain't very good with equations with reactive j quanties, vector
analysis etc. I just measure and trim; its quicker than calculations.

It's certainly quicker if you're no good with equations.

Everywhere i look around the web there are different relevant values
of R&C which are supposed to give the same error-less outcome, but
they are just not all right; and especially RIAA feedback networks.
They all blather on with schematics and calculations, but few
measurements.

If you account for all strays and second-order effects, calculations
will be exact. It's easier to use a reasonable approximation to get
within, say, 0.5dB and trim the network on the bench to get it
spot-on.

Well that is about true. But trimming should be not necessary when
a computer is trying to see us right; we employ computers to be
accurate within 0.1%.

We would have no RIAA curve in the first place without calculations.
I don't deny that you can get good results without math, but in this
case I think your lack of math background causes you to be unduly
suspicious of computers and calculations

The noise generated by the network after the first gain stage is
quite negligible compared to the noise already in the amp from
V1 grid input noise and flicker noise and shot noise.

The 20dB loss introduced by the network adds directly to the noise
figure measured at the input to the second stage. If the first stage
had only 20dB of gain, at midband the signal level at the input to
the second stage would be the same as at the first stage, and so
the second stage noise would be as significant as the first's. There
doesn't seem to be any advantage to degeneration in the cathode
(or source) of the first stage except as required to set the bias
current and to insure sufficient input overload margin. Every dB of
gain in the first stage lessens the effective noise contribution of
the second stage.

-Henry

In article , wrote:

Go over to alt.binaries.pictures.radio to read of a problem arising when
a choke input
filter is connected in the return leg of a rectifier circuit.

The page is taken from the Electrical Engineering Series, John D Ryder,
Author.

While I have seen other references to problems like this with chokes in
the "return leg", I don't remember what the explanation for them is, and
your page from Ryder offers no explanation of how the effect arises, can
you explain it? I also have a vague recollection that there is some
advantage to one location or the other, I forget which, from an
electrolysis point of view. Chokes in the return leg are not unheard of
in high voltage supplies of the types that were often used in old tube
type broadcast transmitters, so presumably they are not all bad.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/