Total Newb cops a design

[martianbanshee]

Can somebody who knows what they're doing take a look at this and tell me whether I will power my tube preamp or electrocute myself and set my house on fire (or both)?

Many thanks.

[nicoverduin]

It will work. Personally I would use a DPDT switch for the mains. As for the diodes, I assume you checked the rating. And what is de voltage AC out of the transformer?

[martianbanshee]

Thank you very much Nico. The diodes are rated at 400V, the transformer voltage is 230VAC (tube B+ from US110VAC mains). I think regulation would be a good idea, but don't know of a regulator IC to do the job, and I don't know anything about using zener diodes (which I suspect might work). My only engineering training is mechanical or manufacturing process oriented, so I know how to build it, but not how to design it.

[sawreyrw]

400 volt diodes are not adequate. C4 will charge to the peak transformer voltage (230*1.414=325 volts) and the minimum voltage at the diode anodes will be -325. So the diodes will see a peak reverse voltage of 650 volts. You should have some additional margin for voltage spikes, so a 1000 volt diode would be a good choice.

[Mooly]

If you are thinking about adding regulation etc a couple of important details are...
1. What is the final voltage you want to end up with.
2. What current do you wish to draw from the supply.

[ChrisA]

Originally Posted by martianbanshee

Can somebody who knows what they're doing take a look at this and tell me whether I will power my tube preamp or electrocute myself and set my house on fire (or both)?

Many thanks.

I can't read some of the numbers but here are comments anyways

1) You can loose those resisors between the transformaer and diodes. the transformers itself likey has internal resistance. Diodes are rated and designed to handle in-rush current.

2) Why not use 1n4007 diodes? They are cheap and rated for 1KV. If you want to bypass the diodes with caps they needs a high voltage rating

3) Did I see a _milli_ henry value on L1? That is way to small. Typical values used in this application as 5 to 15 henrys. It will be hard to buy a power supply choke smaller then that. Also they need to be rated for the high voltage.

4) why is there a "plus" symbol on the diode bypass caps? They would not be electrolytic

5) Typical values for the caps in the filter section would be 47 uf on each side. these would be electrolytic. You might want to bypass them with .47 film caps.

6) Very important -- add a "bleeder" resistor from the B+ to ground to the filters caps will discharge when the power is switched off

7) how many gain stages are in the preamp? If more then two you will need another filter section. Stages that are in phase must be powered from de-coupled supplies. But hifi amps rarely need more then two. Guitar preamps can have quite a few stages.

8) place another cap, from B+ to ground physically near the load.