Understand that inside a typical computer switching power supply there
is a higher multi kilohertz voltage (350v RMS????) produced by the
switching action of the rectified 115 or 230 volt AC input?

This high freq AC through various usually toroidal step down
transforner windings is then rectified to provided the plus and minus
5, 12 volt outputs etc. Correct?

We recently modified such a power supply to get a single 12 volt DC
output at about 20 amps for a particular, amateur radio application.
In order to do so we had to load one of the 5 volt ouputs with a
couple of amps in order to get the unit to work; but that's normal.

Question: Is it possible to get at that higher AC voltage inside and
directly rectify it as a B+ supply for tube equipment? While also
possibly tiddling one or more of the 5 volt DC outputs closer to 6.3
volts for tube heaters?

Rectified 10 or 20 kilohertz wouldn't need much filtering compared to
60 or 120 DC ripple of a conventiaonl power supply? Recall building a
number of conventional 50 and 60 hertz power supplies many years ago
with heavy chokes and large capacitors. But now have a number of
slightly older ex computer power supplies of various wattages around.

Or is the idea completly off base?

You're pretty much on base with some some slight adjustments.

The switching frequency is about ten times higher about
100KHz or so. The high voltage might be full wave
rectified, doubled or boosted by a power factor corrector
.... but 300V is close.

The step down transformer is usually an E-E core or ETD
core. The toroids are output inductors. An additional
inductor is used for 3.3V in some supplies as a magnetic
amplifier, which lops off some pulse width from the +5V
output.

It's possible to modify a PC supply and add a B+ output
but you'd have to re-wind the transformer and output
inductor(s).

Usually the outputs are cross-regulated. That is the +5V
is the regulated channel and the other outputs track due to
the transformer turns ratios (sometimes with help from
weighted-sum voltage sensing.) That's why the 5V output has
to be loaded to get any output from the +12V.

If the 6.3VDC output was most of the power it would make sense
to use the 5V channel for this, strip off the other outputs and
wind a new secondary for your B+ in their place.

You're right, the transformer and filter components would be
much, much smaller. Though you'll need room for additional
EMI filtering... even so it's still much smaller. Some newer
PC supplies spread the clock frequency (frequency modulate it
with pseudo random noise) which can help.



Understand that inside a typical computer switching power supply there
is a higher multi kilohertz voltage (350v RMS????) produced by the
switching action of the rectified 115 or 230 volt AC input?

This high freq AC through various usually toroidal step down
transforner windings is then rectified to provided the plus and minus
5, 12 volt outputs etc. Correct?

We recently modified such a power supply to get a single 12 volt DC
output at about 20 amps for a particular, amateur radio application.
In order to do so we had to load one of the 5 volt ouputs with a
couple of amps in order to get the unit to work; but that's normal.

Question: Is it possible to get at that higher AC voltage inside and
directly rectify it as a B+ supply for tube equipment? While also
possibly tiddling one or more of the 5 volt DC outputs closer to 6.3
volts for tube heaters?

Rectified 10 or 20 kilohertz wouldn't need much filtering compared to
60 or 120 DC ripple of a conventiaonl power supply? Recall building a
number of conventional 50 and 60 hertz power supplies many years ago
with heavy chokes and large capacitors. But now have a number of
slightly older ex computer power supplies of various wattages around.

Or is the idea completly off base?

terry wrote:
Understand that inside a typical computer switching power supply there
is a higher multi kilohertz voltage (350v RMS????) produced by the
switching action of the rectified 115 or 230 volt AC input?

This high freq AC through various usually toroidal step down
transforner windings is then rectified to provided the plus and minus
5, 12 volt outputs etc. Correct?

We recently modified such a power supply to get a single 12 volt DC
output at about 20 amps for a particular, amateur radio application.
In order to do so we had to load one of the 5 volt ouputs with a
couple of amps in order to get the unit to work; but that's normal.

Question: Is it possible to get at that higher AC voltage inside and
directly rectify it as a B+ supply for tube equipment? While also
possibly tiddling one or more of the 5 volt DC outputs closer to 6.3
volts for tube heaters?

Rectified 10 or 20 kilohertz wouldn't need much filtering compared to
60 or 120 DC ripple of a conventiaonl power supply? Recall building a
number of conventional 50 and 60 hertz power supplies many years ago
with heavy chokes and large capacitors. But now have a number of
slightly older ex computer power supplies of various wattages around.

Or is the idea completly off base?

The "higher voltage" is usually on the line side of the isolation
transformer. You would create a safety hazard by accessing that voltage.

A thought might be to use the non-rectified low voltage side to drive a
small high frequency step up transformer or use a diode voltage
multiplier circuit or a combination of transformer and voltage multiplier.

There is a company that builds high voltage switchers for amateur radio
amplifiers, and there have been construction articles to build these.
(Check QEX magazine).

Building from a surplus PC power supply would have a cost advantage.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

"RFI-EMI-GUY" wrote in message
g.com...
terry wrote:
Understand that inside a typical computer switching power supply there
is a higher multi kilohertz voltage (350v RMS????) produced by the
switching action of the rectified 115 or 230 volt AC input?

This high freq AC through various usually toroidal step down
transforner windings is then rectified to provided the plus and minus
5, 12 volt outputs etc. Correct?

We recently modified such a power supply to get a single 12 volt DC
output at about 20 amps for a particular, amateur radio application.
In order to do so we had to load one of the 5 volt ouputs with a
couple of amps in order to get the unit to work; but that's normal.

Question: Is it possible to get at that higher AC voltage inside and
directly rectify it as a B+ supply for tube equipment? While also
possibly tiddling one or more of the 5 volt DC outputs closer to 6.3
volts for tube heaters?

Rectified 10 or 20 kilohertz wouldn't need much filtering compared to
60 or 120 DC ripple of a conventiaonl power supply? Recall building a
number of conventional 50 and 60 hertz power supplies many years ago
with heavy chokes and large capacitors. But now have a number of
slightly older ex computer power supplies of various wattages around.

Or is the idea completly off base?

The "higher voltage" is usually on the line side of the isolation transformer.
You would create a safety hazard by accessing that voltage.

A thought might be to use the non-rectified low voltage side to drive a small
high frequency step up transformer or use a diode voltage multiplier circuit
or a combination of transformer and voltage multiplier.

There is a company that builds high voltage switchers for amateur radio
amplifiers, and there have been construction articles to build these. (Check
QEX magazine).

Building from a surplus PC power supply would have a cost advantage.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©




There's a schematic of a typical (although a bit dated) ATX power supply that
shows the concept of a PC power supply design at
http://www.pavouk.org/hw/en_atxps.html. Current models might use different
components but the basic design will be the same.
Here, you can easily see the building blocks of the supply and how the various
voltages are generated.
There's also a link on that page (http://www.webx.dk/oz2cpu/radios/psu-pc1.htm)
that demonstrates a way to modify a power supply for high current +13.8V output.

Modification for HV output would obviously involve rewinding the switching
transformer to give it a HV winding.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster
it goes.

RFI-EMI-GUY wrote:

There is a company that builds high voltage switchers for amateur radio
amplifiers, and there have been construction articles to build these.
(Check QEX magazine).

Regrettably the author of the key article, and owner of the company
"Watts Unlimited", died a few years ago.

The commercial unit followed some years after the QEX article. It
contained a number of important improvements but schematics were never
published. The big unanswered question is why that design had no voltage
feedback, and therefore had quite poor output regulation? (We can only
speculate that a feedback loop must surely have been tried, but proved
unworkable... and then wonder why that should be?)

An example application for the commercial unit:
http://www.gare.co.uk/k5and/8877.htm

Building from a surplus PC power supply would have a cost advantage.

These days, tube RF amplifiers only begin to show a clear advantage over
solid-state at 500-1000W RF output, ie 1-2kW DC input. That is way
beyond the capabilities of PC power supplies.

A small-scale project based on a PC supply would be a good way to begin
to understand the problems, at relatively little cost, but it would be
another big step to build (or modify) a much larger SMPS for a serious
tube amplifier.


--

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek

The "higher voltage" is usually on the line side of the isolation
transformer. You would create a safety hazard by accessing that voltage.

Joe Leikhim K4SAT
"The RFI-EMI-GUY"©
,

Pshaw

I used to make a living fixing TV sets that ran off of the mains wit
no isolation. Needless to say there were millions of these TV's back
in the day, The trick was to use half wave rectification.
You can do the same thing with a PC supply. Instead of using an AC
input you would half wave rectify the AC and and a suitible filter
capacitor to make up for the frequency change. Also you has to use the
neutral as ground, and use a polarized plug in the USA, Now it's true
if the wall outlet got wired the wrong way you could be in for a treat
of epic proportions. So a GFI would be in there somewheres to protect
you. Then your HV DC ground will be at neutral. At which point you
could use a Voltage multiplier to get close to any whole number
multiple of the mains voltage.

Now it's true you you may not get away with this trick on 3 phase or
split phase 220 mains, because then where is the neutral?


73 OM

n8zu

On Oct 1, 12:55*pm, terry wrote:


We recently modified such a power supply to get a single 12 volt DC
output at about 20 amps for a particular, amateur radio application.
In order to do so we had to load one of the 5 volt ouputs with a
couple of amps in order to get the unit to work; but that's normal.

Hey terry

I did that very same thing loaded the 5volt with 5ohm at 5 watt.
Ran my TenTec 526 off the 12 volt side of the PC power supply.
I thought it was the sweetest thing since sliced bread. Then
people started telling me I had this strange background noise.
They asked me what was going on in my shack. I had this strange
eerie noise in my shack, so they thought. Wasn't in my shack per
say but it was the PC power supply. Nobody knew I was running
a PC supply to power my rig.

73 OM

n7zu

On Oct 2, 4:29*am, raypsi wrote:
On Oct 1, 12:55*pm, terry wrote:



We recently modified such a power supply to get a single 12 volt DC
output at about 20 amps for a particular, amateur radio application.
In order to do so we had to load one of the 5 volt ouputs with a
couple of amps in order to get the unit to work; but that's normal.

Hey terry

I did that very same thing loaded the 5volt with 5ohm at 5 watt.
Ran my TenTec 526 off the 12 volt side of the PC power supply.
I thought it was the sweetest thing since sliced bread. Then
people started telling me I had this strange background noise.
They asked me what was going on in my shack. I had this strange
eerie noise in my shack, so they thought. Wasn't in my shack per
say but it was the PC power supply. Nobody knew I was running
a PC supply to power my rig.

73 OM

n7zu

I also use a modified PC power supply with no problems. I did add a
filter removed
from a commercial computer SMPS. I dont know the values of the
components but its a Pi filter
and the inductor is wound on what looks like a ferrite rod. The caps
are some pretty big disk
that had the writing rubbed off of them a long time ago. As Grumpy put
it. I like to "Frankenstien"
some of my projects.

I have been giving some thought as to what it would take to modify a
PC power supply for HV use.
I have been thinking along two lines,

1 Connect a second step-up transformer before the rectifiers.
2 Replace the transformer with one with a HV windingputting a 5volt
winding on the new
transformer for loading and feedback.

Jimmie

On Oct 2, 11:37*am, wrote:
On Oct 2, 4:29*am, raypsi wrote:





On Oct 1, 12:55*pm, terry wrote:

We recently modified such a power supply to get a single 12 volt DC
output at about 20 amps for a particular, amateur radio application.
In order to do so we had to load one of the 5 volt outputs with a
couple of amps in order to get the unit to work; but that's normal.

Hey terry

I did that very same thing loaded the 5volt with 5ohm at 5 watt.
Ran my TenTec 526 off the 12 volt side of the PC power supply.
I thought it was the sweetest thing since sliced bread. Then
people started telling me I had this strange background noise.
They asked me what was going on in my shack. I had this strange
eerie noise in my shack, so they thought. Wasn't in my shack per
say but it was the PC power supply. Nobody knew I was running
a PC supply to power my rig.

73 OM

n7zu

I also use a modified PC power supply with no problems. I did add a
filter removed
from a commercial computer SMPS. I don't know the values of the
components but its a Pi filter
and the inductor is wound on what looks like a ferrite rod. The caps
are some pretty big disk
that had the writing rubbed off of them a long time ago. As Grumpy put
it. I like to "Frankenstien"
some of my projects.

I have been giving some thought as to what it would take to modify a
PC power supply for HV use.
I have been thinking along two lines,

1 Connect a second step-up transformer before the rectifiers.
2 Replace the transformer with one with a HV winding putting a 5volt
winding on the new
transformer for loading and feedback.

Jimmie- Hide quoted text -

- Show quoted text -

Great info: Thanks for all the ideas and especially about the warning
that the HV would be on the line side (input) from115/230 volt mains.
Unless a 60 hertz full isolation transformer were used; the weight and
size of which sort of negates the idea of using a lighter weight SPS!

I too used to fix TVs without power transformers, using selenium
rectifiers (boy could they stink!) and voltage doubler circuits to
provide B+. That was back in the mid late 1950s. I also made up a
little B+ power supply in a box clipped in during house calls to show
a customer that the problem was indeed inside the chassis and it had
to be taken away for a 'bench job'!

By that and means of never charging for a house call if I didn't fix
the set in situ; built up a reputation for straightforward dealing
which, despite the slightly funny accent of a British immigrant to
Canada, some 15 years later, may have helped me become elected to the
areas first town council? And that in a day and age when TV repairmen
didn't have the best reputation in the world (well at least around
here) for ethical dealings!

These days customers are a lot more cynical and questioning; and
rightly so!

BTW first heard about SPS in the telephone industry, before PC were
common; when power supplier representatives started telling us about
'rectifier/power supplies' that had efficiencies of over 80%.

Ian White GM3SEK wrote:
RFI-EMI-GUY wrote:

There is a company that builds high voltage switchers for amateur
radio amplifiers, and there have been construction articles to build
these. (Check QEX magazine).

Regrettably the author of the key article, and owner of the company
"Watts Unlimited", died a few years ago.

The commercial unit followed some years after the QEX article. It
contained a number of important improvements but schematics were never
published. The big unanswered question is why that design had no voltage
feedback, and therefore had quite poor output regulation? (We can only
speculate that a feedback loop must surely have been tried, but proved
unworkable... and then wonder why that should be?)
(snip)

I worked on a 13.8 Volt SMPS made by TODD for Motorola as an OEM without
any documentation. There was a large stud mounted 13.8 Volt zener on the
output to clamp the voltage and some op amp circuitry to sense if the
output voltage fell below 13.8V it would start increasing the PWM to
charge the filter caps. This PS apparently never worked right because
the transformer leads were never soldered and then were plastered in
conformal coating.


--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P