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 dgta 14th November 2012 04:40 AM

Rectifier characteristics

Typical voltage drop in a tube rectifier is shown on graphs as a (more or less) 3/2 law curve. As you would expect.

Yet many data sheets state an "effective plate impedance" or "effective plate resistance", for example 50 ohms per plate for a 5Y3. But that 50 ohms is nowhere near dV/dI at any point on the curve. More like an order of magnitude off.

So what exactly is that "effective plate impedance" ?

 Miles Prower 14th November 2012 07:26 AM

Quote:
 Originally Posted by dgta (http://www.diyaudio.com/forums/tubes-valves/223545-rectifier-characteristics-post3240828.html#post3240828) Yet many data sheets state an "effective plate impedance" or "effective plate resistance", for example 50 ohms per plate for a 5Y3. But that 50 ohms is nowhere near dV/dI at any point on the curve. More like an order of magnitude off. So what exactly is that "effective plate impedance" ?
Bad choice of words, that's what. It refers to the resistance of the HV windings. The 5Y3 needs about 50R in series with the plate to help reduce the Isurge when used with a C-input type ripple filter. Most PTXs have at least that much, but if you find one that doesn't, you may need to add additional resistance in series with the plates.

 DF96 14th November 2012 10:10 AM

They probably use 'effective' as a clue that you have to include the reflected primary resistance too.

 dgta 14th November 2012 03:48 PM

Aha! Thank you gents.

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