| Author |
Message |
Pooh Bear
Guest
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 Posted:
Sat Oct 22, 2005 5:46 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
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Fred Bartoli wrote:
| Quote: | "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> a écrit dans le message
de news:435973D6.D4F4E4C3@hotmail.com...
Spehro Pefhany wrote:
On Fri, 21 Oct 2005 17:43:36 -0500, the renowned John Fields
jfields@austininstruments.com> wrote:
On 21 Oct 2005 15:05:41 -0700, Winfield Hill
Winfield_member@newsguy.com> wrote:
Peter Andersen wrote...
I would very much like to have some ideas, schematics, tips on how
to design a lab power supply for experimenting with tube designs.
The specifications could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i just
design it like a normal low voltage PSU? like a opamp,
voltagedivider,
a BU508 as seriesregulator, and a couple of high voltage caps.??
One problem in designing such a power supply is the short-circuit
current-limiting aspect of the design. BJT's have a horrible 2nd-
breakdown effect that will greatly exacerbate your design problems.
To get an idea of the problem, study the BU508's SOA curves. Ouch!
For example, at 40 volts, you're allowed 120 watts of dissipation,
but at 400V you're allowed only a wimpy 36 watts!!! These are 25C
values, which have to be derated as the transistor's case heats up.
^^^^
junctions
I recommend that you use high-voltage MOSFETs as pass elements, and
avoid the issue.
Cat got your tongue?
It puzzled me too at first
Look for the up arrows under the word case ( although it may have moved
now on
account of the fixed/proportional spacing issue )
Plus it's plain wrong. The max power dissipation depends on the case
temperature. If the junction was at 25°C there will be no power limit.
|
It depends which way you care to calculate it.
Either way it's actually the die temp that ultimately matters. Case temp simply
factors in the junction to case thermal resistance making the calculation easier
for the novice. If an insulating washer is used then you need to go back to die
temp and add the washer's resistance in the thermal circuit.
Graham
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Pooh Bear
Guest
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| Posted:
Sat Oct 22, 2005 5:52 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
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Pooh Bear wrote:
| Quote: | Fred Bartoli wrote:
"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> a écrit dans le message
de news:435973D6.D4F4E4C3@hotmail.com...
Spehro Pefhany wrote:
On Fri, 21 Oct 2005 17:43:36 -0500, the renowned John Fields
jfields@austininstruments.com> wrote:
On 21 Oct 2005 15:05:41 -0700, Winfield Hill
Winfield_member@newsguy.com> wrote:
Peter Andersen wrote...
I would very much like to have some ideas, schematics, tips on how
to design a lab power supply for experimenting with tube designs.
The specifications could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i just
design it like a normal low voltage PSU? like a opamp,
voltagedivider,
a BU508 as seriesregulator, and a couple of high voltage caps.??
One problem in designing such a power supply is the short-circuit
current-limiting aspect of the design. BJT's have a horrible 2nd-
breakdown effect that will greatly exacerbate your design problems.
To get an idea of the problem, study the BU508's SOA curves. Ouch!
For example, at 40 volts, you're allowed 120 watts of dissipation,
but at 400V you're allowed only a wimpy 36 watts!!! These are 25C
values, which have to be derated as the transistor's case heats up.
^^^^
junctions
I recommend that you use high-voltage MOSFETs as pass elements, and
avoid the issue.
Cat got your tongue?
It puzzled me too at first
Look for the up arrows under the word case ( although it may have moved
now on
account of the fixed/proportional spacing issue )
Plus it's plain wrong. The max power dissipation depends on the case
temperature. If the junction was at 25°C there will be no power limit.
It depends which way you care to calculate it.
Either way it's actually the die temp that ultimately matters. Case temp simply
factors in the junction to case thermal resistance making the calculation easier
for the novice. If an insulating washer is used then you need to go back to die
temp and add the washer's resistance in the thermal circuit.
|
I forgot to say ----- because it's not very practical to measure case temp directly.
Heatsink temp is the way it's done in practice.
Graham |
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Jon Yaeger
Guest
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| Posted:
Sat Oct 22, 2005 5:57 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
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in article Onl6f.165430$xl6.149633@tornado.tampabay.rr.com, west at
westley@tampabay.rr.com wrote on 10/22/05 2:55 AM:
| Quote: | "Jon Yaeger" <jono_1@bellsouth.net> wrote in message
news:BF7EDAD7.3C46C%jono_1@bellsouth.net...
in article 43596055$0$171$edfadb0f@dtext02.news.tele.dk, Peter Andersen at
peterandersen@mespilus.dk wrote on 10/21/05 5:40 PM:
Hi
I would very much like to have some ideas, schematics, tips on how to
design
a lab power supply for experimenting with tube designs. The
specifications
could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i just design
it
like a normal low voltage PSU? like a opamp, voltagedivider, a BU508 as
seriesregulator, and a couple of high voltage caps.??
Please mail me any kind of schematics and give me some help and hints
about
this project...
Peter
Save yourself a lot of grief and buy a used Heath SP-17A power supply. I
saw one for sale for $50 here:
http://www-stlg.remote.arrl.org/RadiosOnline/ads.html?ordby=&wanted_category
=Power+Supplies
Or do the eBay thing.
Jon
Jon,
Do you think a 100ma HT supply will be adequate?
west
|
Not for many power amps under some conditions. No problem for preamps or
low wattage stuff. |
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Fred Bartoli
Guest
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| Posted:
Sat Oct 22, 2005 6:30 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
|
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"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> a écrit dans le message
de news:435A35FD.EA4281CB@hotmail.com...
| Quote: |
Pooh Bear wrote:
Fred Bartoli wrote:
"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> a écrit dans le
message
de news:435973D6.D4F4E4C3@hotmail.com...
Spehro Pefhany wrote:
On Fri, 21 Oct 2005 17:43:36 -0500, the renowned John Fields
jfields@austininstruments.com> wrote:
On 21 Oct 2005 15:05:41 -0700, Winfield Hill
Winfield_member@newsguy.com> wrote:
Peter Andersen wrote...
I would very much like to have some ideas, schematics, tips on
how
to design a lab power supply for experimenting with tube
designs.
The specifications could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i
just
design it like a normal low voltage PSU? like a opamp,
voltagedivider,
a BU508 as seriesregulator, and a couple of high voltage
caps.??
One problem in designing such a power supply is the
short-circuit
current-limiting aspect of the design. BJT's have a horrible
2nd-
breakdown effect that will greatly exacerbate your design
problems.
To get an idea of the problem, study the BU508's SOA curves.
Ouch!
For example, at 40 volts, you're allowed 120 watts of
dissipation,
but at 400V you're allowed only a wimpy 36 watts!!! These are
25C
values, which have to be derated as the transistor's case heats
up.
^^^^
junctions
I recommend that you use high-voltage MOSFETs as pass elements,
and
avoid the issue.
Cat got your tongue?
It puzzled me too at first
Look for the up arrows under the word case ( although it may have
moved
now on
account of the fixed/proportional spacing issue )
Plus it's plain wrong. The max power dissipation depends on the case
temperature. If the junction was at 25°C there will be no power limit.
It depends which way you care to calculate it.
|
???
You know this: maximum power dissipation is given at TJ=max and Tcase=25.
You have to derate the power with increasing Tcase. TJ is already at max and
stays there.
How can this depends on the way you calculate it?
| Quote: | Either way it's actually the die temp that ultimately matters. Case temp
simply
factors in the junction to case thermal resistance making the
calculation easier
for the novice. If an insulating washer is used then you need to go back
to die
temp and add the washer's resistance in the thermal circuit.
|
Indeed, but that wasn't the point.
| Quote: | I forgot to say ----- because it's not very practical to measure case temp
directly.
Heatsink temp is the way it's done in practice.
|
--
Thanks,
Fred. |
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John Stewart
Guest
|
| Posted:
Sat Oct 22, 2005 9:57 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
|
|
Peter Andersen wrote:
| Quote: | Hi
I would very much like to have some ideas, schematics, tips on how to design
a lab power supply for experimenting with tube designs. The specifications
could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i just design it
like a normal low voltage PSU? like a opamp, voltagedivider, a BU508 as
seriesregulator, and a couple of high voltage caps.??
Please mail me any kind of schematics and give me some help and hints about
this project...
Peter
|
Does the PS need to be SS? There are many bullet proof tubed designs.
And why go down to zero volts? That really complicates things & many practical
regulated PS's are not that stable, zero to 100 volts. My own preference would
be two supplies.
That would be a zero to 150 SS & a 150 to 500 volt tubed version. That way one
can do the biasing while the other handles the B+.
My thoughts, anyway. John Stewart |
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Patrick Turner
Guest
|
| Posted:
Sat Oct 22, 2005 10:24 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
|
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John Stewart wrote:
| Quote: | Peter Andersen wrote:
Hi
I would very much like to have some ideas, schematics, tips on how to design
a lab power supply for experimenting with tube designs. The specifications
could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i just design it
like a normal low voltage PSU? like a opamp, voltagedivider, a BU508 as
seriesregulator, and a couple of high voltage caps.??
Please mail me any kind of schematics and give me some help and hints about
this project...
Peter
Does the PS need to be SS? There are many bullet proof tubed designs.
And why go down to zero volts? That really complicates things & many practical
regulated PS's are not that stable, zero to 100 volts. My own preference would
be two supplies.
That would be a zero to 150 SS & a 150 to 500 volt tubed version. That way one
can do the biasing while the other handles the B+.
My thoughts, anyway. John Stewart
|
My own bench top HT supply was built around an old
tranny I found which has a few heater windings and 425-0-425
HT, good for nearly 600V at low current.
I have the output voltage adjustable in 50V steps and regulated through
a pair of 6AS7 triodes for a max of 400mA with a 6BX6
acting as the gain element to control the regul pass tubes.
I did try SS with BU208A etc, but after fusing several i gave up
and I have since never had a problem with the tube regulation.
I don't have to worry about the supply ever wearing out because
its not used much, or for long, but I do have a fan in the box, and
the supply is switchable from full wave cap input to choke input,
allowing the input voltage to be reduced to avoid unecessary dissipation in the
triode pass elements.
I do have a series R at the output with a little circuit with an scr which
reacts to the voltage across this R to that if current exceeds a certain amount
a relay turns off the power.
This often happens when changing something on a rig being tested, but
resetting is done by just turning the PS off, then on again.
If I was doing a supply now I would just wind a huge transformer
rated at 1 kW, and with very low losses, then have taps to switch to change the
voltage.
The regulation with such a tranny with SS rectifiers will be quite OK for
mosts tests on class AB amps.
Alternatively, a pile of 5 smaller trannies each making
+100V at say 1 amp, will do ok, and then you can switch down the stack of DC
voltages.
So cheap SS PTs ( toroidals ) with 2 x 35Vrms windings will give
+50V and +100V, and fairly high current.
Patrick Turner. |
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John Larkin
Guest
|
| Posted:
Sat Oct 22, 2005 10:28 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
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On Fri, 21 Oct 2005 17:50:15 -0400, Jon Yaeger <jono_1@bellsouth.net>
wrote:
| Quote: |
in article 43596055$0$171$edfadb0f@dtext02.news.tele.dk, Peter Andersen at
peterandersen@mespilus.dk wrote on 10/21/05 5:40 PM:
Hi
I would very much like to have some ideas, schematics, tips on how to design
a lab power supply for experimenting with tube designs. The specifications
could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i just design it
like a normal low voltage PSU? like a opamp, voltagedivider, a BU508 as
seriesregulator, and a couple of high voltage caps.??
Please mail me any kind of schematics and give me some help and hints about
this project...
Peter
Save yourself a lot of grief and buy a used Heath SP-17A power supply. I
saw one for sale for $50 here:
http://www-stlg.remote.arrl.org/RadiosOnline/ads.html?ordby=&wanted_category
=Power+Supplies
Or do the eBay thing.
Jon
|
Is that the one with the off/standby/on switch on the front? If so,
never use it with transistor circuits. When you switch from standby to
on, it overshoots about 80 volts!
John |
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Bret Ludwig
Guest
|
| Posted:
Sun Oct 23, 2005 12:08 am Post subject:
Re: Designing a lab power supply for tube experimenting |
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west wrote:
<<snip>>
| Quote: | Me too, Bret. Do you recall the year & month of that Glass Audio article?
west
No, but I bet Bruce does. I think he has a web site. |
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bill ramsay
Guest
|
| Posted:
Sun Oct 23, 2005 2:46 am Post subject:
Re: Designing a lab power supply for tube experimenting |
|
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On Fri, 21 Oct 2005 23:40:42 +0200, "Peter Andersen"
<peterandersen@mespilus.dk> wrote:
| Quote: | Hi
I would very much like to have some ideas, schematics, tips on how to design
a lab power supply for experimenting with tube designs. The specifications
could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i just design it
like a normal low voltage PSU? like a opamp, voltagedivider, a BU508 as
seriesregulator, and a couple of high voltage caps.??
Please mail me any kind of schematics and give me some help and hints about
this project...
Peter
I built the one that is in Bruce Rozenblits book. Actually i made it |
dual channel as I had a humungous transformer to hand
I also incorporated his current sense tip cct as well, except that I
put in a couple of current sense resistors that can be switched in and
out. THis means tha I have two current sense levels.
Actually this came in pretty handy once, i couldn't work out why the
power supply kept tripping, I had inadvertantly connected the scope
earth side to something that was not ground. eek.
SO when the el34s warmed up, suddenly they were passing a lot more
current that they wanted to.
my 2c worth. |
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Bret Ludwig
Guest
|
| Posted:
Sun Oct 23, 2005 4:42 am Post subject:
Re: Designing a lab power supply for tube experimenting |
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Bret Ludwig wrote:
| Quote: | west wrote:
snip
Me too, Bret. Do you recall the year & month of that Glass Audio article?
west
No, but I bet Bruce does. I think he has a web site.
|
http://www.transcendentsound.com/contact.htm |
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Chris Jones
Guest
|
| Posted:
Sun Oct 23, 2005 6:35 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
|
|
Peter Andersen wrote:
| Quote: | Hi
I would very much like to have some ideas, schematics, tips on how to
design
a lab power supply for experimenting with tube designs. The
specifications could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i just design
it like a normal low voltage PSU? like a opamp, voltagedivider, a BU508 as
seriesregulator, and a couple of high voltage caps.??
Please mail me any kind of schematics and give me some help and hints
about this project...
Peter
|
Although it isn't really in the spirit of valve audio, one way to make a
cheap and robust HV supply might be to get two low voltage power mosfets
and a SMPS IC and make a push-pull inverter using the transformer out of an
old PC power supply but in reverse, i.e. drive the low voltage winding,
rectify and LC filter the HV winding. By using a SMPS IC which takes
feedback from the output of the supply, it should be possible to achieve
good regulation and excellent efficiency. Some sort of post-regulation
could be added if very low ripple is necessary.
As a source of DC to power the thing, another PC power supply could be used.
The main disadvantage I can see to this approach is that it would be
unsuitable for use in servicing radio receivers because it would interfere
with them.
Chris |
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Peter Andersen
Guest
|
| Posted:
Sun Oct 23, 2005 7:19 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
|
|
bill ramsay wrote:
| Quote: |
I built the one that is in Bruce Rozenblits book. Actually i made it
dual channel as I had a humungous transformer to hand
I also incorporated his current sense tip cct as well, except that I
put in a couple of current sense resistors that can be switched in and
out. THis means tha I have two current sense levels.
Actually this came in pretty handy once, i couldn't work out why the
power supply kept tripping, I had inadvertantly connected the scope
earth side to something that was not ground. eek.
SO when the el34s warmed up, suddenly they were passing a lot more
current that they wanted to.
my 2c worth.
|
Thanx. Is it possible for you or anybody to make a scan of the those pages
in that book and email it to me? I would be very happy.
--
vh. Peter Andersen
www.mespilus.dk |
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bill ramsay
Guest
|
| Posted:
Mon Oct 24, 2005 4:43 am Post subject:
Re: Designing a lab power supply for tube experimenting |
|
|
On Sun, 23 Oct 2005 16:19:41 +0200, "Peter Andersen"
<peterandersen@mespilus.dk> wrote:
| Quote: | bill ramsay wrote:
I built the one that is in Bruce Rozenblits book. Actually i made it
dual channel as I had a humungous transformer to hand
I also incorporated his current sense tip cct as well, except that I
put in a couple of current sense resistors that can be switched in and
out. THis means tha I have two current sense levels.
Actually this came in pretty handy once, i couldn't work out why the
power supply kept tripping, I had inadvertantly connected the scope
earth side to something that was not ground. eek.
SO when the el34s warmed up, suddenly they were passing a lot more
current that they wanted to.
my 2c worth.
Thanx. Is it possible for you or anybody to make a scan of the those pages
in that book and email it to me? I would be very happy.
|
sure,
email me at my work on ramsay dot bill aht ubix dot co dot nz
reverse the my two names to get to me.
and I will send you the scans.
bill |
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Peter Andersen
Guest
|
| Posted:
Mon Oct 24, 2005 7:46 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
|
|
bill ramsay wrote:
| Quote: | sure,
email me at my work on ramsay dot bill aht ubix dot co dot nz
reverse the my two names to get to me.
and I will send you the scans.
bill
|
I have mailed you - and hopes i got the adress right :-))
Otherwise just sent it to my mailadress used in this group - have only the
same.
--
vh. Peter Andersen
www.mespilus.dk |
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Iain M Churches
Guest
|
| Posted:
Mon Oct 24, 2005 8:00 pm Post subject:
Re: Designing a lab power supply for tube experimenting |
|
|
"west" <westley@tampabay.rr.com> wrote in message
news:tjl6f.165429$xl6.14601@tornado.tampabay.rr.com...
| Quote: | "Bret Ludwig" <bretldwig@yahoo.com> wrote in message
news:1129942897.929549.93690@o13g2000cwo.googlegroups.com...
Peter Andersen wrote:
Bret Ludwig wrote:
The Heathkit supply is nowhere near the quality of the Lambda and
Kepco supplies that are available just as cheaply. However, with
refurbishment, the Heathkit will do okay.
Glass Audio ran an article by Bruce Rozenblit on a very nice bench
supply you can build some time ago.
Do you have a link, pdf, scan..? I would like to read it.
Me too, Bret. Do you recall the year & month of that Glass Audio article?
west
West. You can find it in Vol.2 No.2 1990 |
Iain |
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