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Designing a lab power supply for tube experimenting

K

Ken Smith

Jan 1, 1970
0
Winfield Hill said:
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.


A type 861 triode doesn't have a 2nd breakdown problem.
I recommend that you use high-voltage MOSFETs as pass elements, and
avoid the issue.

With care, you can float all the smarts of the regulator circuit at the
source voltage of the FET. Since this is mains powered, a very small
transformer can be used to make a floating 12V to run the regulator
circuit.

High V
!
!!-
Gate----------!!-
!!-
!
I sense --------+
!
/
\
/
\ Vfloat
------------------------+---------------- To load

----------------------------------------- GND



******************

VRef -/\/\-----+-->!--- overcurrent/
!
!
!
!
GND -/\/\/\/--+-!+\
! >----+-/\/\/-+--- Gate
--!-/ ! !
! ! V
+-/\/\--!!- ---
! !
\ Over Current/
/
\
/
!
Vfloat



*************************


-------+----------- Over current/
!/ c !
ISense ---+---------------! !
! !\ e !
! ! !
! Vref2 !
! -\/\/--!!--------+
! ! !
-/\/\-+--!-\ !
! >-----------
Vref2--!+/
 
P

Patrick Turner

Jan 1, 1970
0
John said:
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.
 
B

Bret Ludwig

Jan 1, 1970
0
west wrote:
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.
 
B

bill ramsay

Jan 1, 1970
0
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.
 
J

John Larkin

Jan 1, 1970
0
Hey, I remember tubes! Something like this...?


+unreg
|
__|__

+---------+------
| ___
| | |
| |
| r1 <optional current limit.. ww pot?
| |
+-----r----+------+----+-----out
| | | |
| pot c r
d | | |
g---+--r--+ | |
s | | | |
| | | gnd gnd
| | r
10v k k 20v |
zeners a a |
| | |
| | |
gnd gnd gnd



But maybe you're supposed to draw a circle somewhere to keep the air
out.

John
 
C

Chris Jones

Jan 1, 1970
0
Peter said:
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
 
P

Peter Andersen

Jan 1, 1970
0
bill said:
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.
 
B

bill ramsay

Jan 1, 1970
0
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
 
P

Peter Andersen

Jan 1, 1970
0
bill said:
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.
 
I

Iain M Churches

Jan 1, 1970
0
west said:
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
 
I

Iain M Churches

Jan 1, 1970
0
Jon Yaeger said:
Not for many power amps under some conditions. No problem for preamps or
low wattage stuff.

Bench supplies at 100mA are usually variable up to 350V.
The Farnell (UK) type E350 is typical.

Even the Rozenblit design (100mA to 400V) cannot drive a
pair of KT88's. I found an old Solatron valve psu (60kilos)
which can supply 600V at 0.5A. I paid Euro 100 for it.
It works perfectly. It seems that no-one wants
junk like that these days:))

Iain

Iain

Iain.
 
1

1234

Jan 1, 1970
0
Years ago, I bought a copy of the white paper
"..Power to the People.." which developed HT
tube power supplies Futterman OTL amps, other
brands of amps and preamps, etc etc etc. I
know I got it around here somewhere, I'll search for it.

JJT



PS: ever changing amp pix & vintage MI paper sale at:

www.jtashjian.com
 
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