Designing a lab power supply for tube experimenting

"Pooh Bear" a écrit dans le message de news: snipped-for-privacy@hotmail.com...

message

how

designs.

just

caps.??

short-circuit

2nd-

problems.

Ouch!

dissipation,

25C

up.

and

moved

??? 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?

simply

calculation easier

to die

Indeed, but that wasn't the point.

directly.

--
Thanks,
Fred.

Hey, I remember tubes! Something like this...?

+unreg | __|__ +---------+------ | ___ | | | | | | r1

In article , Winfield Hill wrote: [....]

A type 861 triode doesn't have a 2nd breakdown problem.

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--!+/

--
--
kensmith@rahul.net   forging knowledge

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.

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.

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

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

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

West. You can find it in Vol.2 No.2 1990

Iain

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.

>

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: