407A/B Preamp

[philajoe73]

New to diyAudio. Been looking to build a preamp around some 407B tubes I have and have seen a few schematics that look interesting. My question is how do I power the filament on these tubes @20-40v when all I see is transformers that have 6.3 and 5V windings? Why did Western use these particular voltages? Was it to work with 48-52VDC talk battery in the central office? Are there transformers that provide 7.5, 10, etc.?

 

[madisonjam85]

Use a separate transformer to power the filaments.

Hammond 166 series transformers are available with a 20V secondary.

 

[philajoe73]

Seperate transformer

Thanks, Madison. Is there any benefit to using DC over AC for the filament?

 

[dsavitsk]

Or use a 5670/2C51/396A which is the same tube with a 6.3V heater.

DC will probably be quieter.

 

[CiroMarzio]

5670/396A are easy to find and very affordable. And you can use the power transformer for other tubes in case you change your mind

 

[astouffer]

I committed heresy and used a small 24 volt switching supply with a 3 terminal regulator.

 

[philajoe73]

Trying to keep things all Western. I'd like to make a phono preamp that could work with my WE KS-16617-L1 monoblocks. The other possibility is somehow reworking the Low-Gain side to do the same (all in one package). The Low Gain isn't used and it uses 6BA6/12AT7s. I am trying to learn this as a hobbyist, while not ruining my amps. (Which sound splendid!!!!)

Just noticed you listed the 396A, really should wear my readers more!

 

[philajoe73]

My goal is to start using my old turntable (MC/no-pre-amp).

 

[mach1]

If you already have 407b use them.

 

[andypap]

If you already have 407b use them.

Hi, maybe a bit old thread but is there any schematics with 407A in
kathode follower configuration? I want to build an output stage for my dac
thanks