Help design a Small 250VDC PSU for tube preamp

[dealio55]

Apparently it needs 330V 4mA, 6.3V 1.1A.

So you'll want the first transformere to be 9VA or more, but the second can be 6VA (or maybe even 3VA, although the loasses may be too great with such a tiny transformer). I suspect you may only get 250Vdc or so, at the output though.

So what do you recommend?

 

[Koifarm]

You can use schematic below with some adjustments.

Do not use the kbl10 rectifier but schottky diodes(uf4007). Use for secundairy 46 windings.
Input capacitor can smaller from 2200uf to 1000uf, Output capacitor also smaller from 470uf to 100uf. You can draw 10mA at 330v.

 

[Koifarm]

Example of transformer.

 

[nigelwright7557]

On my valve mixer I used two small transformers back to back.
The first one drops mains to 12VAC for the series connected heaters.
The second transformer is 18VAC wired backwards to give about 230VDC.
A couple of 10VA transformers will do the job.

 

[Koifarm]

I have done that in several designs.
But for (phono)preamps you still have to deal with the humm.
SMPS schematic works with 100khz no humm.

 

[dealio55]

You can use schematic below with some adjustments.

Do not use the kbl10 rectifier but schottky diodes(uf4007). Use for secundairy 46 windings.
Input capacitor can smaller from 2200uf to 1000uf, Output capacitor also smaller from 470uf to 100uf. You can draw 10mA at 330v.

I might give that a try 😉 thanks

 

[willanth]

I've done a DC-DC boost SEPIC PSU for my next amp project, a render of which is attached. It operates from 12-48VDC and is good for 150mA at 300VDC or so. It's a prototype so I plan on tuning the feedback values to get the right B+ value. It's based off of a Texas Instruments switch-mode controller. I got the idea from Pete Millett, and as he says in some of his designs noise at 100 or 500kHz is a lot easier to filter to the desired level than noise at 50-100Hz. If you already have a source of mains isolation (laptop or other power supply to give DC) this may be a good way to go.

I also echo the caution, dangerous voltage ahead.

Cheers
Will

 

[jazbo8]

Ready-made...

An advantage of the 12VDC external plugpack, and either including the 12/270V DC/DC in the control unit, or in a small attached housing, is that the mains AC can be kept away from the control unit, and can be handled by a commercial power unit (ie. not diy).

Mains hum is removed, both from heater and HT entry paths. The heater and HT supplies may well have a minute level of smps ripple, but I suggest that is a red herring and if paranoia sets in then some judicious hf filtering can get anything down to below your oscilloscope optic nerve.

A mains input smps may well generate noise in to the audio spectrum if not well managed in the smps and allowed to couple over, due to the mains 2f energy within.

But a dc/dc smps (such as 12VDC to 300VDC) does not intrinsically have the same noise structure in the audible range as there is no 100/120Hz component.

Read it all here.

 

[dealio55]

I've done a DC-DC boost SEPIC PSU for my next amp project, a render of which is attached. It operates from 12-48VDC and is good for 150mA at 300VDC or so. It's a prototype so I plan on tuning the feedback values to get the right B+ value. It's based off of a Texas Instruments switch-mode controller. I got the idea from Pete Millett, and as he says in some of his designs noise at 100 or 500kHz is a lot easier to filter to the desired level than noise at 50-100Hz. If you already have a source of mains isolation (laptop or other power supply to give DC) this may be a good way to go.

I also echo the caution, dangerous voltage ahead.

Cheers
Will

Any schematic? 😀

 

[wa2ise]

I think it would be too bulky, whereas OP prefer to reduce iron weight.

Use a 12V AC wall wart. Power the heaters, and use a backwards 12V transformer to make the B+.

 

[stocktrader200]

there is a 5 Va AMveco 9,12 or 15 volt secondaries. Get one of those and a 12 volt 1 amp wall wart and feed the heaters and Torroid with the 12 volt output.
The pre probably only uses 10 ma at 200 volts. (2 watts)