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Hi again guys ,
Speaking of 5Y3GT , until I find a NOS , I'm gonna use a new production that I've already got ( SOVTEK) . I'm completely confused about the pin layout : seems like DC comes out through one of the filament pins (#8) , how come? .
I know new 5Y3 are different to NOS , does this happen with its pins too? I'm asking because on the amp layouts , I can see 4 pins being used (2,4,6,8 ) but my tube has also a pin at 1 .
Sorry if these questions are dumb , but I've been scratchin' my head the whole day .
Thanks once more .
SUSO

Pin 1 doesn't do anything ... it's just there to help hold the tube in the
socket. DC does come from the filament/cathode pin.

Here is a link to tube data where you can see how it works:

http://tdsl.duncanamps.com/

Thanks Tom . By the way , being AC and DC at the same pin , what should I do with my 5V center tap ... ground it , leave it unconnected ?
Cheers

Don't ground it ! You'd short the high voltage to ground and blow the tube pretty quickly !

Some designs use the center tap as the DC output, but most of the time you just cap it off and carefully tuck it away. You can use small wirenuts or a layer or two of heatshrink tubing, or even solder it to an unused tie strip point if you have one.

Thanks Tom . You saved me a lot of trouble .
SUSO

Using pin 8 as the cathode / DC takeoff point also makes the circuit 5AR4 / GZ34 plug-in compatible.

As above, don't ground or use the 5VAC CT, just carefully cap it off so it doesn't short to ground or any other point in the circuit.

/ed B