[bill ramsay]

Evening all.

I'm in the throes of putting together a new amp at the moment, and I
want to regulate the HT.

So I am going to use the LM317 Maida regulator.

thing is, I need 600V at the op. I will have about 650 or so at the
input.

Most of the transistors I have seen have a 500V limit on them for the
pass device.

Any thoughts on a suitable pass device?

look forward to hearing from you.

Bill

[Patrick Turner]

bill ramsay wrote:

Evening all.

I'm in the throes of putting together a new amp at the moment, and I
want to regulate the HT.

So I am going to use the LM317 Maida regulator.

thing is, I need 600V at the op. I will have about 650 or so at the
input.

Most of the transistors I have seen have a 500V limit on them for the
pass device.

Any thoughts on a suitable pass device?

look forward to hearing from you.

Bill

Try BU208A.

Its the best I have ever played with, and takes more abuse than any
mosfet I have played with.
Perhaps a similar voltage bjt but with less Ic rating
will do for darlington connection of a pair which is by far the best
pass device you could have other than a paralleled 6AS7,
which good because it survives trauma very well.
The darlington pair has a high Rin, something necessary for easier base
voltage control.

I most certainly cannot endorse the use of any silly little low voltage
regulator chip
like LM317 floating at +600V and I never use these in any gear with
hundreds of volts present.
One short circuit somewhere, and they are GONE, POOF!.

Always remember to have a series resistor between the B+ unfiltered
supply
and the pass BJT collector so that when I is what you want, there is
about equal Vdc across this R
and across Vc to Ve, so that if a short occurs, maximum I flow is
limited by the R,
and that Pda of the bjt does not exceed SOA, as they expire almost
instantly when this happens.

I dunno why you don't just build a voltage amp using a couple of other
HV signal
bjts as the controller for the base voltage of the pass element.

HV bjts were originally developed for line output amps in TV sets.
Usually a 6CM5 or something similar, 12DQ6 maybe, and these were the
last tubes to be replaced by SS
when SS became reliable and cheap enough to use.
So when you look through the data book, such devices as BU208A are to be
found.
BU108 is also OK but rated for less current.

Patrick Turner.

[[email protected]]

On Mar 10, 9:28 pm, bill ramsay blah@blahdeblah wrote:
Evening all.

I'm in the throes of putting together a new amp at the moment, and I
want to regulate the HT.

So I am going to use the LM317 Maida regulator.

thing is, I need 600V at the op. I will have about 650 or so at the
input.



I have used several LM317's in series to increase the voltage handling
capabilities of the device. If the LM317 only sees a volatge drop of
less than 40 volts then it doesn't care. I used several five watt
resistors in series. One thing to watch for is the load voltage.

Surf my site http://www.retrotech.ca



Most of the transistors I have seen have a 500V limit on them for the
pass device.

Any thoughts on a suitable pass device?

look forward to hearing from you.

Bill