power supple for valve pre-amp

[cr0wl3y]

Hi there,

Been looking around for ideas on building a pre-amp and while looking into power supplies, I noticed that on a couple of designs, a 220V AC supply is "turned" into 250V DC using a network of diodes, a choke and some smoothing capacitors. One example is the one shown in this site:

OBTAINING 250vDC & 6.3vAC FOR VALVES by Harry Lythall

Does this also imply that you can essentially power a valve amplifier (excluding the heaters) using European mains and the aforementioned diodes-choke-caps circuit? Is it adviseable?

Thank you,
Nikos

 

[wakibaki]

Yes. No.

My guess, nobody really wants to get into this because there are loads of safety issues and no-one really wants to encourage you because your post is a bit glib. We don't like glib where mains power is involved. There are legal issues too. All-in-all too much to go into into with someone with a bare grasp of the basics. 240VAC will give you plenty of DC to operate a valve but in general you should not operate any device other than a simple resistive load direct from the mains without an isolating transformer.

w

 

[Steve Dunlap]

Yes. No.

My guess, nobody really wants to get into this because there are loads of safety issues and no-one really wants to encourage you because your post is a bit glib. We don't like glib where mains power is involved. There are legal issues too. All-in-all too much to go into into with someone with a bare grasp of the basics. 240VAC will give you plenty of DC to operate a valve but in general you should not operate any device other than a simple resistive load direct from the mains without an isolating transformer.

w

If you check the link he posted, you will see he does use a transformer.

 

[leadbelly]

If you check the link he posted, you will see he does use a transformer.

But if you read his post, you will see that he is asking if he can leave it out.

It must be stated even more emphatically than wakibaki did that this is a no go, an isolating transformer must be used for safety.

 

[Steve Dunlap]

But if you read his post, you will see that he is asking if he can leave it out.

It must be stated even more emphatically than wakibaki did that this is a no go, an isolating transformer must be used for safety.

I missed that part. You are absolutely correct.

 

[cr0wl3y]

Thanks for the advice - transformer it is!

For the record, what does "glib" mean?

 

[Salas]

Offhand, superficial, it means.

 

[cr0wl3y]

One more question, if I may:

The schematic posted before (it's actually been mover to a new server, link posted below) starts with 220V AC, which is then rectified and smoothed to power the pre-amp. Assuming I have 230V AC instead, will I need to re-think the amp circuit?

The new link: OBTAINING 250vDC & 6.3vAC FOR VALVES by Harry Lythall

Thanks,
Nikos

 

[wakibaki]

No, the difference is not significant in this case. Lots of components used in valve circuits have tolerances of 5%. 1-in-22 is less than 5%. Depending on the design your last requirement may be to tweak some values for best performance once things are running, almost certainly you will want to check what quiescent currents you have ended up with.

w