HV benchtop power supply, help on opamp setup

[jackinnj]

Anatoliy -- I am shocked -- the BC348 was the first receiver I ever bought -- it cost about $80 from Fair Radio Sales in Lima OH. I had been using a Knight Star Spanner prior to that.

These were the days when you could get an AN/ART-13 for about $200.

[Wavebourn]

Originally posted by jackinnj
Anatoliy -- I am shocked -- the BC348 was the first receiver I ever bought -- it cost about $80 from Fair Radio Sales in Lima OH. I had been using a Knight Star Spanner prior to that.

These were the days when you could get an AN/ART-13 for about $200.

Sorry for off-topic...

I still use mine that I bought for $45 + shipment.
I take IF through a capacitive divider and feed it to a modified AM/FM radio that uses Japanese chip. The AM is hard tuned to 915 KHz (It would be great to find a 1370 KHz crystal, but I still had no chance...).
The set outperformed well serviced Collins R-392/URR that I kept in my bedroom so I sold it on ePay.

[gootee]

Originally posted by panos29

<snipped>
On the other hand, is it possible to setup a common opamp driving a fet of bipolar to extend its output from about 20v to be able to swing about 100 that it is needed for the grid of the tube?

Yes. See the following application notes:


- AN-272 at http://www.national.com ,

and

- AN18 at http://www.linear.com .


I hope that those are helpful.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html

[panos29]

Thanks everybody for the interest and help. Afer alot of experimentation and one or two dead 741s, I decided that driving the grids of a 6C33 through a tinny opamp is simply impossible, at least considering my knowledge level of SS chips. Thus I am abandoning this project and I will work on my working prototype based on 6AU6 and 5651.

Thanks again,

Panos

[GK]

Originally posted by panos29
Thanks everybody for the interest and help. Afer alot of experimentation and one or two dead 741s, I decided that driving the grids of a 6C33 through a tinny opamp is simply impossible, at least considering my knowledge level of SS chips. Thus I am abandoning this project and I will work on my working prototype based on 6AU6 and 5651.

Thanks again,

Panos

Just reference the opamp to ground and use a high voltage transistor (such as a TIP50) as a common emitter amplifier (with, say, a 470k collector resistor) to drive the series pass tube grid.
The opamp can be configured as an intergrator, with a overly large time constant to ensure stability just to get a prototype working.

[Wavebourn]

Originally posted by panos29
Thanks everybody for the interest and help. Afer alot of experimentation and one or two dead 741s, I decided that driving the grids of a 6C33 through a tinny opamp is simply impossible, at least considering my knowledge level of SS chips. Thus I am abandoning this project and I will work on my working prototype based on 6AU6 and 5651.

Thanks again,

Panos

You don't need to kill 741'th, just use one high voltage transistor on output of the opamp, like somebody advised already. Or use a transistor only without any opamp as on the link I've posted.

[panos29]

After months of experimenting and trial and error I finally managed to arrive at a working prototype. It is based on a new HV opamp made by texas OPA454. The prototype is capable of 1 A, yes 1A at 220V with less than 1,5mV ripple fully loaded, which is more like random noise on my scope. One problem I noticed is that when the speed-up capacitor (68n) is out of the circuit the power suplly is unstable producing a steady 5-6KHz oscillation. Otherwise the circuit is very stable and there is no measurable drop in output voltage from no load to full load.
Any comments or suggestions are very welcome.

[panos29]

Allright, please disregard the previous schematic, as I made a mistake, the opamp inputs are the other way around. I enclose the corrected schematic with some small changes at the values of the speed up capacitor from 68n to 470n and the output capacitor, from 10u to 68u. These changes are really needed for the correction of the HF frequency responce of the regulator. Any proposals concerning the correction or upgrade of the schematic are very much appreciated.