[[email protected]]

Except from the price, I´ll notice a big difference between the 8B and
the Dynaco ST70?

Thanks

[Peter Wieck]

On Jan 30, 3:51 pm, " wrote:
Except from the price, I´ll notice a big difference between the 8B and
the Dynaco ST70?

There are significant differences. Whether you notice them or not
would be a function of other factors including your ears, speakers,
source material and so forth. "Big" is in the ears of the beholder.

Now, there are other advantages favoring the 8B on the design end, and
those advantages are significant, all other things being equal. As you
noted, they are not.

Peter Wieck
Wyncote, PA

[Peter Wieck]

On Jan 30, 4:17 pm, "Bret Ludwig" wrote:
If you buy one right you can resell at about what you paid.

Ignore the little man in the corner....

With apologies to the Wizard of Oz (the film).

Bret is not much more than a minor can of worms with some VERY strong
prejudices. Were he at all rational about said prejudices, he might be
a reasonable person. But he is not.

Peter Wieck
Wyncote, PA

[Michael L. Squires]

On Jan 30, 3:51 pm, " wrote:
Except from the price, I´ll notice a big difference between the 8B and
the Dynaco ST70?


In a listening test in the late 1970's I ran a rebuilt 8B, repaired Audio
Research D76, and a slightly modified but fully functional Eico HF-89 in
an informal listening test. Speakers were double KLH 9's, all amps were
a bit underpowered for the job. I preferred the HF-89 to them all.

(The slight modification was a stiff power supply to replace the HF-89's
voltage doubler supply, and the removal of most of the HF rolloff caps.
I saw no signs of instability, and I did look at the output with a scope
(Tektronix 555 (!).)

The HF-89 may not be a practical amp for today, since it ran the 6CA7's
glowing red in order to get 50wpc output.

The 8B and D76 were serviced by "The Audiophile" store in Gaithersburg,
which was one of the few places it was safe to send things like a REL
Precedent or Marantz 10B tuner.

The two best amps I've ever heard driving the KLH 9's was the D150 (Audio
Research) and the solid-state dB Systems DB-6.

Mike Squires

[Jon Yaeger]

in article , Bret Ludwig
at wrote on 1/30/07 5:30 PM:


On Jan 30, 4:22 pm, (Michael L. Squires) wrote:
On Jan 30, 3:51 pm, " wrote:
Except from the price, I´ll notice a big difference between the 8B and
the Dynaco ST70?

In a listening test in the late 1970's I ran a rebuilt 8B, repaired Audio
Research D76, and a slightly modified but fully functional Eico HF-89 in
an informal listening test. Speakers were double KLH 9's, all amps were
a bit underpowered for the job. I preferred the HF-89 to them all.

(The slight modification was a stiff power supply to replace the HF-89's
voltage doubler supply, and the removal of most of the HF rolloff caps.
I saw no signs of instability, and I did look at the output with a scope
(Tektronix 555 (!).)

Not so slight. The voltage doubler supply is a terrible sounding
thing. It's what keeps most Mc amps from being really good sounding.


*** I disagree. In fact, the opposite may be more the case -- maybe there
is a sonic benefit to the degree of isolation offered by the doubler
arrangement. In any case, the Eico HF-87 & 89 are wonderful sounding amps,
voltage doubler or not.

The HF-89 may not be a practical amp for today, since it ran the 6CA7's
glowing red in order to get 50wpc output.

It would be a good chassis and opt's to build on.

*** it's just a so-so chassis to build on.

The 8B and D76 were serviced by "The Audiophile" store in Gaithersburg,
which was one of the few places it was safe to send things like a REL
Precedent or Marantz 10B tuner.

The two best amps I've ever heard driving the KLH 9's was the D150 (Audio
Research) and the solid-state dB Systems DB-6.

The early ARC amps sounded pretty good, but were troublesome. Later
ones were cheapened in construction and do not sound as good. This is
true of VTL/Manley as well.

[Ned Carlson]

wrote:
Except from the price, I´ll notice a big difference between the 8B and
the Dynaco ST70?

Thanks


When I had a chance to listen to both (both restored, the
ST70 had a replacement board using an EF86)
the main difference to me was on the bottom end, which
I'd expect, given the larger output transformer.

Circuitwise, the main differences are the power supply
(8B uses diodes and a bigger transformer), the larger output
transformers, and the phase splitter (cathode coupled vs.
split load). I would've kept the 8B but for the difference
in the price I could get. One could biamp with solid-state,
to make up for the bottom end response, altho that kind
of thing typically doesn't hold its value like an 8B will.


--
Ned Carlson
SW side of Chicago, USA
www.tubezone.net

[John Byrns]

In article .com,
"Bret Ludwig" wrote:

On Jan 30, 8:29 pm, Ned Carlson wrote:
wrote:
Except from the price, I´ll notice a big difference between the 8B and
the Dynaco ST70?

Thanks

When I had a chance to listen to both (both restored, the
ST70 had a replacement board using an EF86)
the main difference to me was on the bottom end, which
I'd expect, given the larger output transformer.

Circuitwise, the main differences are the power supply
(8B uses diodes and a bigger transformer), the larger output
transformers, and the phase splitter (cathode coupled vs.
split load). I would've kept the 8B but for the difference
in the price I could get. One could biamp with solid-state,
to make up for the bottom end response, altho that kind
of thing typically doesn't hold its value like an 8B will.

Now we are getting somewhere.

My idea is that if we are going to the trouble of building a vacuum
tube box in 2007, we ought to not screw around with half-ass measures
but go the distance and do it right. The description you give is
pretty well enough: the Marantz has an adequate power supply (though
more is always more, improvements are asymptotic and there isn't much
more we can do short of going to a outboard choke filtered supply) and
a pair of output transformers that are also very adequate. The circuit
of the Marantz is also way better, although I prefer all triode front
ends.

The Marantz 8B already has an all triode front end, and it also has a
choke filtered power supply. I have owned an 8B as well as a couple of
ST-70s, the problem with the 8B from an audiophile perspective is that
it has a voltage doubler power supply.


Regards,

John Byrns

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

[Jon Yaeger]

in article , John
Byrns at wrote on 1/31/07 8:13 AM:

In article .com,
"Bret Ludwig" wrote:

On Jan 30, 8:29 pm, Ned Carlson wrote:
wrote:
Except from the price, I´ll notice a big difference between the 8B and
the Dynaco ST70?

Thanks

When I had a chance to listen to both (both restored, the
ST70 had a replacement board using an EF86)
the main difference to me was on the bottom end, which
I'd expect, given the larger output transformer.

Circuitwise, the main differences are the power supply
(8B uses diodes and a bigger transformer), the larger output
transformers, and the phase splitter (cathode coupled vs.
split load). I would've kept the 8B but for the difference
in the price I could get. One could biamp with solid-state,
to make up for the bottom end response, altho that kind
of thing typically doesn't hold its value like an 8B will.

Now we are getting somewhere.

My idea is that if we are going to the trouble of building a vacuum
tube box in 2007, we ought to not screw around with half-ass measures
but go the distance and do it right. The description you give is
pretty well enough: the Marantz has an adequate power supply (though
more is always more, improvements are asymptotic and there isn't much
more we can do short of going to a outboard choke filtered supply) and
a pair of output transformers that are also very adequate. The circuit
of the Marantz is also way better, although I prefer all triode front
ends.

The Marantz 8B already has an all triode front end, and it also has a
choke filtered power supply. I have owned an 8B as well as a couple of
ST-70s, the problem with the 8B from an audiophile perspective is that
it has a voltage doubler power supply.


Regards,

John Byrns


John,

What is the audiophiles problem with a doubling supply?

[John Byrns]

In article ,
Jon Yaeger wrote:

in article , John
Byrns at wrote on 1/31/07 8:13 AM:

In article .com,
"Bret Ludwig" wrote:

On Jan 30, 8:29 pm, Ned Carlson wrote:
wrote:
Except from the price, I´ll notice a big difference between the 8B and
the Dynaco ST70?

Thanks

When I had a chance to listen to both (both restored, the
ST70 had a replacement board using an EF86)
the main difference to me was on the bottom end, which
I'd expect, given the larger output transformer.

Circuitwise, the main differences are the power supply
(8B uses diodes and a bigger transformer), the larger output
transformers, and the phase splitter (cathode coupled vs.
split load). I would've kept the 8B but for the difference
in the price I could get. One could biamp with solid-state,
to make up for the bottom end response, altho that kind
of thing typically doesn't hold its value like an 8B will.

Now we are getting somewhere.

My idea is that if we are going to the trouble of building a vacuum
tube box in 2007, we ought to not screw around with half-ass measures
but go the distance and do it right. The description you give is
pretty well enough: the Marantz has an adequate power supply (though
more is always more, improvements are asymptotic and there isn't much
more we can do short of going to a outboard choke filtered supply) and
a pair of output transformers that are also very adequate. The circuit
of the Marantz is also way better, although I prefer all triode front
ends.

The Marantz 8B already has an all triode front end, and it also has a
choke filtered power supply. I have owned an 8B as well as a couple of
ST-70s, the problem with the 8B from an audiophile perspective is that
it has a voltage doubler power supply.


Regards,

John Byrns


John,

What is the audiophiles problem with a doubling supply?

This quote from Bret Ludwig sums up the audiophile attitude, "The
voltage doubler supply is a terrible sounding thing."


Regards,

John Byrns

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

[west]

"Jon Yaeger" wrote in message
...
in article , Bret
Ludwig
at wrote on 1/30/07 5:30 PM:


On Jan 30, 4:22 pm, (Michael L. Squires) wrote:
On Jan 30, 3:51 pm, " wrote:
Except from the price, I´ll notice a big difference between the 8B
and
the Dynaco ST70?

In a listening test in the late 1970's I ran a rebuilt 8B, repaired
Audio
Research D76, and a slightly modified but fully functional Eico HF-89
in
an informal listening test. Speakers were double KLH 9's, all amps
were
a bit underpowered for the job. I preferred the HF-89 to them all.

(The slight modification was a stiff power supply to replace the
HF-89's
voltage doubler supply, and the removal of most of the HF rolloff caps.
I saw no signs of instability, and I did look at the output with a
scope
(Tektronix 555 (!).)

Not so slight. The voltage doubler supply is a terrible sounding
thing. It's what keeps most Mc amps from being really good sounding.


*** I disagree. In fact, the opposite may be more the case -- maybe
there
is a sonic benefit to the degree of isolation offered by the doubler
arrangement. In any case, the Eico HF-87 & 89 are wonderful sounding
amps,
voltage doubler or not.

Jon ... What do you mean by a voltage doubler giving better isolation?
Please expand on "isolation." Thanks,

west

snip

[John Byrns]

In article .com,
"Bret Ludwig" wrote:

If you'll draw out a VD supply you'll see, but the result is a very
"bouncy" supply. it has a high impedance and poor regulation and,
depending on the ESR and other characteristics of the caps, all sort
of things happen. That said if you follow it up with linear regulation
or a choke and enough capacitance it's a valid option for Class A
circuits where the transformer isn't loaded much at all.

That's not an explanation; it's just a bunch buzzwords strung together
to sound impressive to the uninformed. Can you provide a real
explanation?

Can you explain why the VD is "a very bouncy supply" and what that means?

Can you explain why the VD has "high impedance", and with respect to
what?

Can you explain why the VD has "poor regulation", and with respect to
what?

Can you explain why the transformer must not be "loaded much at all",
with respect to other options, for the VD to be a "valid option"?


Regards,

John Byrns

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

[west]

"Bret Ludwig" wrote in message
oups.com...
On Jan 30, 2:51 pm, " wrote:
Except from the price, I´ll notice a big difference between the 8B and
the Dynaco ST70?


If both are stone stock, oh yes, huge. The 8B is within a ballpark of
being as good a tube amp as you can build or buy at that power level,
whereas the stock ST70 is a dismal affair. In fact it makes a better
musical instrument amp for applications that want the sound only
crapped up a little (Leslie, steel guitar, etc.) than a hi-fi amp
except that in such service something will fail pretty soon. If the
stock ST70 is run with continuous power much above its Class A power
point, it will let out some magic smoke. The people who defend it are
playing it intermittently, or at low volume or through efficient
speakers or all three. Not running it flat out where it will crap
out.

Now modified ST70s are a different story. The only question is how
much modification is needed. The problem is that if you buy a working
ST70 at market price now, you are paying a lot of money to throw out
big chunks of it and its value won't go up at all. Probably will go
down. If you are paying someone else to do this you are a three-way
girl, because you are getting every input plugged. Even if you are
DIYing it still makes more sense to unload the beast.

How good can a modified ST70 be? Well, very good. The limiting factor
is the stock output transformers, which are simply not as good as the
Marantz's. None the less you can get quite good performance from them.
The stock power transformer is too small, which means the fix involves
replacing it, or getting two ST70s and running each as a single
channel going. The stock center driver board should be removed and
with the 7199s set aside, destroyed and thrown in the board recycle
bin. You now have a chassis, two opt's and the power supply and can
build any of several circuits, either on a new quality PCB or
pointwired.

The Marantz is overpriced as are all collectible tube boxes for pure
listening, but there was a reissue that may be more reasonable than
the originals, and unlike the crappy MC275 reissue is spot on. If you
buy one right you can resell at about what you paid.

Bret ... if the stock power xfr is too small, would a separate filament xfr
help? What part of the stock is too small?

west

[Ned Carlson]

Bret Ludwig wrote:

Because then load regulation _gets even worse_. You have the copper
losses and the doubler losses and given the frequency of the load
variation some strange resonances, more work to figure out than my
small brain can handle, arise.

The copper losses on a FWVD are actually less than either
a FW bridge or FWCT circuit. They have to be on principle
simply because there's fewer turns on the secondary.

The main issue with the doubler is that how well the thing
performs is going to be dependent on the capacitors used.
Doublers are hard on the capacitors used in the capacitor
side of the doubling circuit as they have to handle all the
AC current used, not merely ground ripple current.

There were tests done back in the day showing that a well done
voltage doubler actually regulated better than either
the bridge or CT circuit, at least given the components
used then. Not everyone agreed that doublers were such a great
idea, (Dynaco for one never used doublers) but I don't think
Harmon Kardon and Marantz used doublers on their most expensive
amplifiers just to save a few bucks on the power transformer,
either.


A good application for the voltage doubler can be, for example, in
the bias circuits of some guitar amplifiers where tube swaps may need
more negative voltage than the stock bias tap may provide. Rather than
put in another transformer, a doubler off the extant bias winding may
give enough voltage, but filtering and shielding needs close
attention.

I've done that to put 6550's in place of 8417's, but unless there's
a completely separate bias winding, you can't put a voltage
doubler in a bias circuit.



--
Ned Carlson
SW side of Chicago, USA
www.tubezone.net

[Arny Krueger]

"John Byrns" wrote in message

In article
.com,
"Bret Ludwig" wrote:

If you'll draw out a VD supply you'll see, but the
result is a very "bouncy" supply. it has a high
impedance and poor regulation and, depending on the ESR
and other characteristics of the caps, all sort of
things happen. That said if you follow it up with linear
regulation or a choke and enough capacitance it's a
valid option for Class A circuits where the transformer
isn't loaded much at all.

That's not an explanation; it's just a bunch buzzwords
strung together to sound impressive to the uninformed.
Can you provide a real explanation?

Good point, and as usual Bret failed to rise to the occasion.

Ned Carlson's explanation is pretty much the one that I learned in the day
of.

A VD necessarily passes AC through some extra capacitors. If they have high
enough capacitance and low enough ESR, then the regulation will be about as
good as anything.

VDs weren't very practical until solid state rectifiers became readily
available.

[Arny Krueger]

"west" wrote in message
news:l8cwh.37888$uC6.11034@trnddc02

If the stock ST70 is run with continuous power much above its
Class A power point, it will let out some magic smoke.
The people who defend it are playing it intermittently,
or at low volume or through efficient
speakers or all three. Not running it flat out where it
will crap out.

Nonsense. I used to do rock-and-roll DJ duty in the days of tubes, using a
pair of ST70s driving a pair of JBL 01 systems, driven by a pair of
turntables hooked to a pair of PAS-3s, mixed via a simple resistive mixer.
We ran the ST70s just below clipping for 3-4 hours at a whack, once or twice
a week.

[Peter Wieck]

Bret:

You forget, conveniently ignore or deny a few simple truths, being in
part but not limited to:

a) the overall survival rate of the ST-70. Were it as crapped out,
overstressed and limited a design as you maintain, and given its (at
best) spotty assembly history, for the most part they have survived
and pretty well at that. What's more is that most have survived as
"stock". This includes even those with the original phenolic boards...
something even I understand is *now* pretty risky. For a design that
first hit the streets well over 40 years ago, that is not half-bad.

b) most every person peripherally or seriously interested in tube
audio has had one at one time or another. What's more is that at least
a fair plurality maintains one to this day. Some maintain several.

c) apart from hard-core-from-scratch DIY, as you do state the 70 is a
design that invites modification, experimentation and general
tweaking. As a learning platform, it is very nearly perfect. What's
more is that its near-childish simplicity (some would suggest
limitations) allows a "return to stock" at about any point in the
process.

d) even at a 'typical' price of around $300 these days it is a bargain
for an operating (relatively) high-wattage tube amp that will give at-
least adequate service at a high level of reliability with just
minimum (but competent) care. Even better, the level of competence
required is not much above the most basic common-sense level.

When you get off on these rants against something that *never was*
meant to be the be-all and end-all of Audiophilia, but no more than a
reasonably reliable entry-level power amp, you so far miss the point
as to be taken as a babbling fool. Something that at least you believe
that you are not. A simple analogy: I doubt that (Insert 5-star
restaurant name here) will ever serve a Hostess Snow Ball as their
dessert of the month, but Hostess sure sells a lot of Snow Balls.
Ranting after Hostess for the quality of their items is a fool's game
as you so effortlessly prove.

Peter Wieck
Wyncote, PA

[John Byrns]

In article om,
"Bret Ludwig" wrote:

John, you're a bright guy. You know as well as I do that a high
impedance supply in this context means that with changing loads, its
voltage output will vary a great deal, and in that sense has poor
regulation, specifically load regulation.

That is true by definition.

The VD is high impedance
compared to conventional bridge or "bi-phase half wave" (what we here
call full wave with center tap) C-L-C or C-R-C networks because it has
the ESR of the caps "in the loop".

How is the "VD" any different than the conventional bridge or "bi-phase
half wave" in this regard? They all have the ESR of the caps "in the
loop". The only difference is that with the "VD" you have the ESR of
two caps in series, but that simply means that the ESR of each of the
two caps in the "VD circuit must each have half the ESR of the cap used
in the other circuits. For equivalent performance the capacitance of
each capacitor must also be twice the capacitance of the capacitor in
the other circuits.

One advantage of the VD is that the ripple currents are at twice line
frequency,

How is this any different than the conventional bridge or "bi-phase half
wave", the ripple voltage for both of those circuits is also twice the
line frequency.

and with triplers and further iterations-the voltage
multiplier principle can go to fairly high multiples-the frequency
goes up with the multiplication, making filtering easier.

Are you sure about this? While I have to admit I have never played with
anything beyond various doubler circuits, I am having a very hard time
imagining how voltage multipliers with higher multiplication ratios than
the doubler could have ripple frequencies higher than twice the line
frequency. Can you give an example of a circuit with a ripple frequency
of say four times the line frequency, I get the feeling that you don't
know what you are talking about here? Also keep in mind that the ripple
frequency of a half wave voltage doubler is the same as the line
frequency.


Regards,

John Byrns

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

[John Byrns]

In article ,
Ned Carlson wrote:

Bret Ludwig wrote:

Because then load regulation _gets even worse_. You have the copper
losses and the doubler losses and given the frequency of the load
variation some strange resonances, more work to figure out than my
small brain can handle, arise.

The copper losses on a FWVD are actually less than either
a FW bridge or FWCT circuit. They have to be on principle
simply because there's fewer turns on the secondary.

I agree that the copper losses for a "FWVD" are less than for a "FWCT"
circuit, but I would expect the copper losses of the "FWVD" and the "FW
bridge" to be the same. While it is true that there are fewer secondary
turns with the "FWVD" the current is also higher, so it all comes out in
the wash. Agreed that the traditional "FWCT" is the pits.

The main issue with the doubler is that how well the thing
performs is going to be dependent on the capacitors used.
Doublers are hard on the capacitors used in the capacitor
side of the doubling circuit as they have to handle all the
AC current used, not merely ground ripple current.

Agreed that the doubler is harder on capacitors, although I don't know
what you mean by "ground ripple current"?

There were tests done back in the day showing that a well done
voltage doubler actually regulated better than either
the bridge or CT circuit, at least given the components
used then.

I agree that a well done voltage doubler will regulate better than a CT
circuit, but the bridge should have regulation equal to that of the
doubler, given that equal amounts of copper are used in all three cases.

Not everyone agreed that doublers were such a great
idea, (Dynaco for one never used doublers) but I don't think
Harmon Kardon and Marantz used doublers on their most expensive
amplifiers just to save a few bucks on the power transformer,
either.

I suspect that the Dynaco situation was simply the flip side of the
Marantz, Mcintosh, and Harmon Kardon situation, namely Dynaco was able
to build a "FWCT" power supply for less money than the higher performing
voltage doubler circuit used by the high end manufacturers.

A good application for the voltage doubler can be, for example, in
the bias circuits of some guitar amplifiers where tube swaps may need
more negative voltage than the stock bias tap may provide. Rather than
put in another transformer, a doubler off the extant bias winding may
give enough voltage, but filtering and shielding needs close
attention.

I've done that to put 6550's in place of 8417's, but unless there's
a completely separate bias winding, you can't put a voltage
doubler in a bias circuit.

Sure you can, you simply use a "HWVD", I've done it without a problem.


Regards,

John Byrns

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

[Arny Krueger]

"Bret Ludwig" wrote in message
ups.com
Because then load regulation _gets even worse_. You
have the copper losses and the doubler losses and
given the frequency of the load variation some strange
resonances, more work to figure out than my small
brain can handle, arise.

The copper losses on a FWVD are actually less than
either
a FW bridge or FWCT circuit. They have to be on
principle
simply because there's fewer turns on the secondary.

i went back to "the source", the blue and white Audio
Cyclopedia. It does cover voltage doublers but does not
talk about advantages and disadvantages.

That's because the advantages and disadvantages are not inherent, but depend
on the implementation.

I was always tauught that the essential problem with
voltage doublers was that capacitors by their nature had
no DC path

Wrong - that fact is one reason why doubler work at all.

and all their issues such as dielectric absorption,

Irrelevant in low-impedance circuits like just about any circuit used in
analog audio.

ESR

Largely a solved problem, but moreso now than back in the days of tubes.

and "bounceback"-ie, memory, the
discharged cap that comes back and zaps

That's just an effect of DA which I just explained why it is irrelevant.


Now, I am not a EE and don't claim to be one. So my
education isn't perfect. But....A LOT OF EE MAJORS THESE
DAYS KNOW LESS THAN I DO!

Well they could well know less about analog audio based on obsolete
thermionic technology.

You can't get a classical EE education anymore,

Because it would be practically obsolete.

it's too broad a field and there is
too much emphasis on Spice, VHDL, and the other
computational packages they use,

Welcome to the 21st century.

and too much of math
which was once the domain of math and physics majors.

Nahh, EE has been math-intensive for at least 50-80 years. It's the nature
of the beast.

EEs in the semiconductor industry are glorified computer
applications operators.

Computers are just tools. Since computers are among the most general purpose
of all tools, you can't really make any reasonable judgements at all based
on the fact that someone uses one.

Both the most repetitive and the most creative of jobs can involve the use
of computers, so you can't tell how creative a person's job is based on just
the fact that they use a computer.

So all I can say with authority is, "The voltage doubler
has a terrible reputation with audiophile

(read amateur, as in often untrained or poorly-educated)

builders,
because amplifiers using it mostly sound pretty bad."
This I can attest to.

So what?

I agree that the copper losses for a "FWVD" are less
than for a "FWCT" circuit, but I would expect the copper
losses of the "FWVD" and the "FW bridge" to be the same.
While it is true that there are fewer secondary turns
with the "FWVD" the current is also higher, so it all
comes out in the wash. Agreed that the traditional
"FWCT" is the pits.

The main issue with the doubler is that how well the
thing performs is going to be dependent on the
capacitors used.

Doublers are hard on the capacitors used in the
capacitor side of the doubling circuit as they have to handle all
the AC current used, not merely ground ripple current.

Bottom line, a voltage doubler with inadequite caps is going to have more
problems than a more conventional design, because there are more caps in
more different parts of the voltage-doubler's circuit.

Agreed that the doubler is harder on capacitors,
although I don't know what you mean by "ground ripple
current"?

I don't think this is really an issue that is peculiar to voltage doublers.

There were tests done back in the day showing that a
well done voltage doubler actually regulated better
than either
the bridge or CT circuit, at least given the components
used then.

I agree that a well done voltage doubler will regulate
better than a CT circuit, but the bridge should have
regulation equal to that of the doubler, given that
equal amounts of copper are used in all three cases.

Not everyone agreed that doublers were such a great
idea, (Dynaco for one never used doublers) but I don't
think Harmon Kardon and Marantz used doublers on their
most expensive amplifiers just to save a few bucks on
the power transformer, either.

It would be interesting to know what was going through the designer's minds
when they made these choices.

It is easy to see why VDs are used when they eliminate the need for a power
transformer, but that is not the case here.

VD's are not widely used with transformers today, unless they make the
transformer a lot easier to build. For example, a lot of VDs and VTs are
used in very-high voltage applications because small transformers that put
out very high voltages are less practical than high voltage diodes and high
voltage caps.

VDs are also commonly used on the primary side of switchmode power supplies
to facilitate 120/240 volt switching.

I suspect that the Dynaco situation was simply the flip
side of the Marantz, Mcintosh, and Harmon Kardon
situation, namely Dynaco was able to build a "FWCT"
power supply for less money than the higher performing
voltage doubler circuit used by the high end
manufacturers.

It could be as simple as the price structures of their respective
transformer suppliers.

[Arny Krueger]

"Bret Ludwig" wrote in message
oups.com

If the stock ST70 is run with continuous power much
above its Class A power point, it will let out some
magic smoke.
The people who defend it are playing it intermittently,
or at low volume or through efficient
speakers or all three. Not running it flat out where it
will crap out.

Nonsense. I used to do rock-and-roll DJ duty in the days
of tubes, using a pair of ST70s driving a pair of JBL 01
systems, driven by a pair of turntables hooked to a pair
of PAS-3s, mixed via a simple resistive mixer. We ran
the ST70s just below clipping for 3-4 hours at a whack,
once or twice a week.

They were a lot younger then, even if you weren't, Arny.

How would that be relevant?

[Sander deWaal]

"Bret Ludwig" said:


So all I can say with authority is, "The voltage doubler has a
terrible reputation with audiophile builders, because amplifiers using
it mostly sound pretty bad." This I can attest to.


Hogwash.
Electrolytics these days are reliable and of sufficient quality to
build voltage doublers with them that perform well.

--

- Maggies are an addiction for life. -

[Ned Carlson]

John Byrns wrote:
I agree that the copper losses for a "FWVD" are less than for a "FWCT"
circuit, but I would expect the copper losses of the "FWVD" and the "FW
bridge" to be the same. While it is true that there are fewer secondary
turns with the "FWVD" the current is also higher, so it all comes out in
the wash. Agreed that the traditional "FWCT" is the pits.

OK... bear in mind I'm not a magnetics expert... but as the
primary/secondary turns ratio gets lower, the
wire gauge can be made heavier on the secondary,
so the DCR actually drops more percentagewise than
the difference in the secondary turns. It's not a linear
relationship between turns and DCR, so the net effect
is there's less copper loss in the doubler. Make sense?
There's more than one way to skin a transformer cat, too,
so I guess one could build a doubler that's actually worse
than an equivalent bridge, if one was so inclined.


Agreed that the doubler is harder on capacitors, although I don't know
what you mean by "ground ripple current"?

I mean in a FWCT or bridge the capacitors are only passing
the ripple current being filtered out.

I suspect that the Dynaco situation was simply the flip side of the
Marantz, Mcintosh, and Harmon Kardon situation, namely Dynaco was able
to build a "FWCT" power supply for less money than the higher performing
voltage doubler circuit used by the high end manufacturers.

Good question as to whether this was ecomonics or not, EICO's
sold for about what Dynacos did, but some EICO's had voltage
doublers (eg:HF87), so did some of the cheaper guitar amps
like Danelectro/Silvertone, so did Rockola jukeboxes.



Sure you can, you simply use a "HWVD", I've done it without a problem.

D'oh! Yeah, forgot about that.


--
Ned Carlson
SW side of Chicago, USA
www.tubezone.net

[John Byrns]

In article ,
Ned Carlson wrote:

John Byrns wrote:
I agree that the copper losses for a "FWVD" are less than for a "FWCT"
circuit, but I would expect the copper losses of the "FWVD" and the "FW
bridge" to be the same. While it is true that there are fewer secondary
turns with the "FWVD" the current is also higher, so it all comes out in
the wash. Agreed that the traditional "FWCT" is the pits.

OK... bear in mind I'm not a magnetics expert...

Neither am I, were talking "copper losses" here, you don't have to be a
"magnetics expert" for that.

but as the
primary/secondary turns ratio gets lower, the
wire gauge can be made heavier on the secondary,
so the DCR actually drops more percentagewise than
the difference in the secondary turns.

Correct, I am assuming that the winding for the "FWVD" has one quarter
of the DCR of the winding for the "FW bridge". Think of a single
transformer with two secondary windings, connected in series for the "FW
bridge" and connected in parallel for the "FWVD". Under those
conditions the "copper losses for the "FWVD" and "FW bridge" are equal,
unless I made a mistake pushing the buttons on my calculator.

It's not a linear
relationship between turns and DCR, so the net effect
is there's less copper loss in the doubler. Make sense?

No, the doubler has the same "copper loss" as the bridge when the same
amount of copper is used in the transformers, if you try and chintz on
the amount of copper used in the transformer for the doubler then the
doubler will have more "copper losses" than the bridge.

There's more than one way to skin a transformer cat, too,
so I guess one could build a doubler that's actually worse
than an equivalent bridge, if one was so inclined.

Exactly, see above, with the same amount of copper, the losses of the
two circuits are the same, if you reduce the amount of copper used in
either circuit the "copper losses" will increase, if you are so inclined
you can build a bridge that is actually worse than an equivalent doubler.

Agreed that the doubler is harder on capacitors, although I don't know
what you mean by "ground ripple current"?

I mean in a FWCT or bridge the capacitors are only passing
the ripple current being filtered out.

What additional currents do the capacitors in a "FWVD" have to pass that
are not passed by the capacitor in a "FW bridge"?

I suspect that the Dynaco situation was simply the flip side of the
Marantz, Mcintosh, and Harmon Kardon situation, namely Dynaco was able
to build a "FWCT" power supply for less money than the higher performing
voltage doubler circuit used by the high end manufacturers.

Good question as to whether this was ecomonics or not, EICO's
sold for about what Dynacos did, but some EICO's had voltage
doublers (eg:HF87), so did some of the cheaper guitar amps
like Danelectro/Silvertone, so did Rockola jukeboxes.

I guess that we will have to chalk it up to designer taste then. If it
were me doing the design I would choose the "FW bridge". Note that no
one designing consumer audio equipment during the tube era made that
choice. "FW bridges" were used in professional equipment, broadcast
transmitters, and the like.


Regards,

John Byrns

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

[Ned Carlson]

Arny Krueger wrote:

Nonsense. I used to do rock-and-roll DJ duty in the days of tubes, using a
pair of ST70s driving a pair of JBL 01 systems, driven by a pair of
turntables hooked to a pair of PAS-3s, mixed via a simple resistive mixer.
We ran the ST70s just below clipping for 3-4 hours at a whack, once or twice
a week.

One of Hafler's publicity stunts was to run the entire PA system
of Grand Central Station in NYC off a stack of ST70's.

--
Ned Carlson
SW side of Chicago, USA
www.tubezone.net