PT rectifier centre as B+

[pdf64]

Are you saying that your PT 5V winding for the rectifier heater has a centre tap (ie so it's 2.5-0-2.5)?
If so just leave the CT not connected, ie sleeved off.
If your B+ is connected to pin 8 of the rectifier, then there's no interaction between the rectifier heater 5V, and the B+. The B+ just acts as a dc reference for the 5Vac.
But if the B+ is taken from pin 2, then the 5V would be a ripple on the B+ (because the rectified B+ current would be flowing along the heater).
Peter.

[Steve Conner]

But that's the whole point of a directly heated rectifier. The heater is also the cathode, so the HT current is emitted by it, and hence flows in it alongside the filament current.

So the centre tap on the heater winding helps directly heated rectifiers run completely balanced. Without the center tap, one side of the rectifier works a little harder than the other.

With indirectly heated rectifiers like the GZ34 it does the opposite, unbalancing them.

In all cases the difference is probably hardly worth bothering about, but this is the internet where we take trivia to new levels of pedantry.

[Philr228]

Thanks Steve and MWJB with this one. I think the answer is yes then but, and I realised this the extra voltage is pretty insignificant.

From what you all indicate I think going for a 5V4 instead of a 5Y3 and using my rectifier supply centre tap ( I like balance - always have done!) is the way to go - but of course I could change my mind, 'specially if you suggest something else, hehe!

Thanks again.

Phil

[tubeswell]

For directly heated rectifiers, running the B+ off the CT of the 5V winding (if it has one) is supposedly quieter, but I've never been sufficiently annoyed to be bothered finding out. FWIW Merlin B has a schematic at the bottom of this page

The Valve Wizard

[pdf64]

'But that's the whole point of a directly heated rectifier. The heater is also the cathode, so the HT current is emitted by it, and hence flows in it alongside the filament current.'

I don't see how the HT current should flow alongside the heater current.
The HT and heater both happen to share pin 8, but there's no circuit between them.
Because the heater current flows between the cathode (pin 8) and pin 2. And the HT current flows from the cathode. The HT will only get 'corrupted' by the rectifier heater supply if the HT is taken from pin 2, the other end of the heater.
I acknowledge that my analysis seems to differ from everyone else's, but I can't see where I'm going wrong.
A 5V4 will give a 'harder' tone with more power output, than a (NOS) 5Y3.
Peter.

[Steve Conner]

I don't see how the HT current should flow alongside the heater current.
The HT and heater both happen to share pin 8, but there's no circuit between them.

That would be true in an indirectly heated rectifier. But in a directly heated tube, both of the filament pins are also cathode connections. The electrons pushed through the filament to heat it are the same ones that boil off it to produce the HT current, and they come from whichever filament pin has the most favourable voltage at that instant in time.

[pdf64]

Thanks for your patience - I've now got my head around directly heated cathodes, ie the cathode is the heater. Peter.

[Philr228]

Well, certainly a lot info buzzing about, I may give a Sovtek 5Y3 not a NOS 5Y3 a go once I've measured the output from the transformer and wire the B+ from the centre tap of the rectifier supply.

Thanks again for all the discussion and help.

Phil