Apex

Sure, for one-offs. Last one I used was in about 1989, as the output stage of a piezo driver for a prototype atomic force microscope. IIRC it was a PA85, which was a beefier replacement for the Burr-Brown

3584--higher voltage (450V vs 300V) and much faster (1 kV/us vs 150 V/us).

The Apex parts were very noisy, iirc, but since it was the output stage, I didn't care very much.

I really doubt I'd use one in any design that was going to be replicated more than 20 times. OTOH the quickish slew rate is worth a fair amount sometimes.

Cheers

Phil Hobbs

Did you look at the price on that heat sink?

Even boring heat sinks are priced at kilobucks these days.

Well, it's $3k, but they have none in stock and the lead time is 22 weeks. That's less than $140 per week on layaway. What's not to like?

(I have some 8-pin TO-3 heat sinks I bought for use with LH0063s and LH4009s. They'd fit.)

Cheers

Phil Hobbs

Free shipping though!

I'd read that as Aavid has decided to drop that product, but for $3K, they will pull the tooling out of storage and make a run. Once going, they will make many, and sell you the first.

Joe Gwinn

Might well be. Drilling a few more holes in a TO-3 heatsink is pretty simple--that $3k is more of a stupidity tax. ;)

Distributor prices for heatsinks are pretty high in general. (Not usually as high as that, of course.)

Cheers

Phil Hobbs

I'd hate to pay shipping for parts that are out of stock.

I see insane pricing on some parts, factors of 10 and sometimes 100x reasonable.

The pricing on these opamps may be insane but so are the parts, I never knew things like that were on offer (2.5kV peak to peak output!). I have not done more than 200V peak to peak, was some 10 years ago, I did it with discrete parts though. The project could not have afforded opamps like these anyway.

We designed our own box to replace the ugly awkward Hammond things. We designed a custom extrusion and had a bunch extruded and machined and anodized, and still saved money.

Commercial heat sinks cost crazy multiples of the cost of extruding aluminum.

You can make your own kilovolt-level opamps pretty easily. There are some nice HV mosfets like IXTY02N120 and 2SK4177 and the IXTT02N450HV. If you optocouple up into the fets, it avoids all sorts of ugly level shifting.

Well I have never needed that sort of thing so I never thought of it really, my HV experiences are by just making HV sources (up to 5kV) which only need HV diodes at the HV side apart from caps etc. (I got some really good - fast, small etc. - HV diodes on ebay, can you believe it). The opto-level shifting is an interesting idea indeed, one could easily overlook it and go into that "ugly level shifting", I had not thought of it. I did "normal" level shifting on that +/- 100V thing back then but it was not too ugly, getting the thing stable with optocouplers might have been a challenge (unless one can get decent spice models, never looked for any). But even without models one can manage it with some trial and error of course.

Slow HV isn't too hard, if you don't mind a few watts' quiescent dissipation. You can put HV transistors in series, for instance, with a resistive voltage divider driving the bases.

Fast HV is another thing. Last time I needed to do that, I used an

811A. (It was about 1990.)

Cheers

Phil Hobbs

Here are some opto-coupled HV things. As Phil says, slow HV isn't hard.

Well obviously the slower the easier :-). My 200V p-p output stage (I think it did up to 100 mA, it was for a one-off thing for a plasma-physics lab) did something like 2300V/s which is not too fast for a 200V peak to peak (and it needed much less than that). They wanted to drive the voltage and monitor the current IIRC. Then 200V really is not HV, just the highest V I have designed some driver for. What is this 811A, is it the valve which I kept finding?

Class B has an undeserved bad reputation.

Yup.

Cheers

Phil Hobbs

It can be done well, for sure, but usually isn't IME.

Cheers

Phil Hobbs

I did some fun stuff with a TV HV rectifier tube, 1B3 I think, as an amplifier, with the input going into the filament. Voltage gain around

50K, bandwidth not so good.

It's amazing that I survived childhood.

One of the instructors[1] that taught my 15yo to fly gliders flew pointy nosed jets in the 1950s. He once told me, w.r.t. my daughter, that "you expect to lose a few". I just grinned.

[1] her favourite, since he let her continue when other instructors would have taken control :)