DH Diode Valve Bridge Rectification

[Andrew]

-- Gents,

I was thinking about using this as one way to get more B+ from the same mains TX, of course, a diode bridge might be even more efficient, but wouldn't look at all nice.

So I drew it out, it looked OK, then I added the cathode heaters and boy did I get confused. The heaters seems to cross with the HT. So I did the heaters first then added the HT and got even more confused.

Assuming, dual diodes, say a 5Y3, for the sake of argument, which of the two rectifiers should be used for what position in the bridge?

Combo's I can think of are....

One rectifier the left two diodes, one for the right.

One for the bottom, one for the top.

Opposite diagonals.

Is there a known way to do this?

Help....

-- Andrew

[James D]

It's known as a Hybrid Graetz Bridge, the link shows the schematic.

James

[Andrew]

Hi James,

I know that one...in fact it was you who kindly pointed me to it before, just wondering if it can be down with two rectifiers.

Oh your link's not right somehow tho'?

cheers,

-- Andrew

[James D]

Sorry! That's what happens when you speed read the post and don't do it properly.. You mean using two dual rectifiers (rectifiers mean valves, diodes mean ss when I speed read...wrong assumption! my fault.) It isn't possible to make an all valve bride from dual dht rectifiers - the best ones to use for a valve bridge are boost diodes such as EY500 or PY500 or 6D22S and the usual american ones that L.O. etc. uses.

Hope that helps!

James

[Andrew]

-- Hi James,

So it would work with a couple of EZ81, i.e non-dh, or I have to use single rectifiers. I wonder why Duncamp's PSU Designer offers the 5Y3 option for Bridge Rectification, programming error perhaps?

thanks,

-- Andrew

[slowmotion]

I'm a bit confused now, but anyway;
you need one double and two single valve rectifiers.
Or four singles. I use a 3B28 bridge, 4 valves, one high tension transformer and three filament transformers.

The Hybrid Graetz Bridge seems to be a simpler solution.

[Andrew]

Originally Posted by slowmotion

I'm a bit confused now, but anyway;

That's what got me, try drawing it out and you're fine when you just have the heaters or just the HT, but having the two togther did me 'ed in...perhaps it was just a Friday night...but it seemed to me that you ended up with the mains TX in parallel with the heaters.....didn't seem right to me...

cheers,

-- Andrew

[Tony Moore]

You need a pint of Witham Wobbler...

[Andrew]

Hi Tony,

Witham Wobbler's much better at doing me 'ed in.....you seen the h'evidence ;-)

Martin we need another excuse to visit Witham ;-) and have a Wobble.....

cheers,

-- Andrew

[John Caswell]

Hi Andrew,
Bridge rectifiers made from valves are a messy way to go but can be done.
The main problem is that not many, if any, rectifier valves were made with two cathodes and a common anode, which is what you require for one side of the bridge, so the simplest way is to use single diodes such as 6D22s, EY 81/84/88, PY81/84/88, or for low volts for bias EB91/6AL5. They will also require, for safety's sake, separate heater supplies for each valve. The separate heaters are not absolutely essential but make life easier as it means that you do not have to worry about heater cathode insulation breakdown.
I will scribble out a cct and put it up here later today I hope.

John aka Dr John