Dumb series/12.6V heater questions

[Zozobra]

I want to play round with a ZVS DC DC booster again in the near future, only this time I want to run it straight from a 12V SMPS. For simplicity I want to run the heaters at 12V from the SMPS without having to mess around with dropping to 6.3V via a regulator or buck. I've never had the pleasure of running preamp heaters at 12V before, partly because all my Pxs have 6.3V taps ands partly because I've never quite understood 12.6V series heater chains, so thus here come the dumb questions

If I were to run the heaters of multiple 12ax7s in series with each other then I need to provide N x 12.6V? e.g., 3 12ax7s all connected in series would need a 37.8V supply?

Can I run each heater in series for 12.6V operation, but then chain them in parallel thus the supply only need be 12.6V? e.g., all the pin 4s are tied together to +12.6VDC and the pin 5s are tied together to ground? I've never quite found this information spelled out clearly for the slow readers as I can only assume that it's so obvious it shouldn't need explaining or there is some magic trick that I'm oblivious too which I can't find with google

[alexradium]

I want to play round with a ZVS DC DC booster again in the near future, only this time I want to run it straight from a 12V SMPS. For simplicity I want to run the heaters at 12V from the SMPS without having to mess around with dropping to 6.3V via a regulator or buck. I've never had the pleasure of running preamp heaters at 12V before, partly because all my Pxs have 6.3V taps ands partly because I've never quite understood 12.6V series heater chains, so thus here come the dumb questions

If I were to run the heaters of multiple 12ax7s in series with each other then I need to provide N x 12.6V? e.g., 3 12ax7s all connected in series would need a 37.8V supply?

Can I run each heater in series for 12.6V operation, but then chain them in parallel thus the supply only need be 12.6V? e.g., all the pin 4s are tied together to +12.6VDC and the pin 5s are tied together to ground? I've never quite found this information spelled out clearly for the slow readers as I can only assume that it's so obvious it shouldn't need explaining or there is some magic trick that I'm oblivious too which I can't find with google

the last one,i did it myself with a GTO,i used a normal 12V/2A external brick to the jack on the box,internally connection direct to the heaters in parallel and to the HV boost converter,It works very good,no noise.

[Zozobra]

the last one,i did it myself with a GTO,i used a normal 12V/2A external brick to the jack on the box,internally connection direct to the heaters in parallel and to the HV boost converter,It works very good,no noise.

Great, that's exactly what I wanted to hear

I may also go down the external PSU brick route too. I know that I need the type which has the negative terminal bonded to the earth pin for safety and noise reasons but I can't for the life of me remember what class that is at the moment.

[tubeswell]

... and here's the picture

[tubeswell]

And yes, you can run heaters in series or parallel. 3 x 12.6Vac haters in series requires a 37.8VAC supply. Each 12.6Vac filament draws 0.15A, but since they are in series, the same current goes through one, then the next one, then the next one, so the overall draw on the winding is still only 0.15A.

But if you ran the same 3 x 12.6VAC filaments in parallel, you'd need a 12.6Vac supply, and the total current draw for the three filaments combined would be 0.45A (because each filament is drawing 0.15A from the winding through its own separate circuit, so the current draw sums)

[Zozobra]

Thanks folks. This has cleared up things immensely and will make my impending foray into rack preamps much simpler and cheaper