[sdiy] High Voltage Opamps ?

[John L Marshall]

Good answer. Think of the tube as a big, hot FET.

----- Original Message -----
From: <jhaible at debitel.net>
To: Michael Buchstaller <buchi at takeonetech.de>;
<synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, January 29, 2002 5:17 AM
Subject: Re: [sdiy] High Voltage Opamps ?


> Add a Tube output stage to your opamp !
> The tube will add some gain, so you can drive the grid with a few volts
from a standard
> opamp. Tube must be included in feedback loop of opamp. (Choose divider
ratios to
> keep the voltages at the opamp inputs in the opamp's common mode range.)
> You will need some extra compensation of the opamp because of the extra
gain of
> the tube stage.
> I've seen headphone amps like this. While I wouldn't really want an opamp
in a tube
> HP amp, it should be ok for static and low frequency measurements.
>
> JH.
>
>
> Michael Buchstaller <buchi at takeonetech.de> schrieb:
> > Hello group,
> >
> > a friend asked me to build him a computer controlled tube curve tracer.
He
> > is one of these strange audiophiles who wants to konw every silly stuff
about the
> > old tubes.
> >
> > So, the conversion from the measured voltage levels via a voltage
divider and feeding that
> > into an ADC seems to be no problem.
> >
> > I will have to build a regulated DC heater, but with it´s low voltages
(1...15V) that will be no problem
> > for any Opamp with a transistor follower in the regulated loop.
> >
> > But, how will i create the high voltage levels ? Ordinary DAC´s output
0...2.5V or so, How do i convert that
> > to 0...600V ? Are there Opamps for high voltages that i could use, or
can i use some clever trick to
> > work with low voltages on the controlling side ?
> > Any hints of leads to suitable application notes would be more than
welcome.
> >
> > Thank you all !
> >
> >
> > -Michael Buchstaller