[sdiy] Integral scope on VCO

[Theo]

?? Assuming you got some (12V?) AC hanging around,
won't a simple diode/capacitor cascade do the trick??

Theo



----- Original Message -----
From: Thomas Dunker <dunker at invalid.ed.ntnu.no>
To: Tony Clark <clark at andrews.edu>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, April 14, 2004 1:07 AM
Subject: Re: [sdiy] Integral scope on VCO


> On Tue, 13 Apr 2004, Tony Clark wrote:
>
> >    It's quite possible to make very tiny high voltage supplies for your
> > application.  I just finished designing just such a thing for a product
> > my company is making.  I was able to come up with a design that
> > will generate a good 1200V DC (approximately) and fit in a 2x2x0.5
> > space.  It runs on 12V at 120mA and the best part is the total parts
> > cost is less than $10.00 (in quantity, probably about $15.00 for a
1-off)
> >    Don't know what kind of current the CRT requires, but the power
supply
> > will definately give you a good zap!
>
>  As far as I can tell from the data sheets on the CRT, the beam current is
> virtually in the microamps range, but I also need a reasonably high
> voltage supply for the deflection amplifiers (need about 250V pk-pk for
> full deflection on either axis) and it seems most realistic to get the
> supply voltage for these amp stages from the same supply. The deflection
> amps can be high impedance things so don't really need to take a lot of
> current. I just emailed a Norwegian ham who built a scope module with this
CRT,
> so it'll be interesting to find out how he did the deflection amps. I
thought
> about using diff stages with 12AX7 type tubes which work fine at 0.5mA per
> section, so two diff stages would typically draw about 2mA. But for the
> sake of saving space it would be nice if I could use transistors in the
> deflection amps. I don't know precisely how that would work out in terms
> of current consumption. I may have to sink some current into a voltage
divider
> and some pots and things on the same supply, unless I can get a HV
> transformer with sectioned secondary and make a stacked supply. In any
> case I will be needing something like -50V, 0V, 500V and 800V taps.
>
>  It's not like I don't have high voltage transformers in my stash, but
> they do take up a lot of space (relatively) and so do high voltage filter
> caps when they have to take care of 100Hz ripple current. It's cool when
> it's a classic tube amp for the stereo where size and weight doesn't
> matter (to me, anyway) and one can liberally build pi filters with 10
henry
> iron core chokes and that sort of thing, but this is a little different...
>
>  I was looking at some high output voltage DC-DC converters in Farnell's
> catalog, but they were far too wimpy on the current for my purpose. We're
> probably looking at a 10-20W supply, whereas the module available from
> Farnell was good for 1 watt...
>
>  A buddy at work says I'd probably have to use a flyback type converter if
> I want to go that way. I'm just a total idiot when it comes to switched
> power supplies, since I've always avoided them in audio apps, but for the
> scope they'd sure come in handy. It would be a good excuse to learn a
> little more about them... I guess if I need multiple voltage taps I could
> feed like three separate ferrite core transformers from the same switcher
> thing? Oh, and it would definitely be most convenient for me to make an
> AC/DC supply with 230VAC input at this kind of power, otherwise I'd eat
> away at the synth's low voltage supply's available current real fast.
>
>  Can you say a little more about the type PSU you had in mind?
>
> Thomas
>