Question about power consumption Hagerman Cornet Octal

[jev]

Hi all,

I am about to rebuild the Hagerman phono stage Cornet Octal. My previous version had too much humm and not enough space in the chassis.

I have two chokes lying around. They are rated 50mA. This is enough I hope? Does anyone know how much current the Hagerman Cornet Octal consumes (two halves of 6sl7 and one gain stage of a halve of a 6sn7)? I use this http://www.hagtech.com/pdf/cornetoctal.pdf .

Thanks. Jeroen

 

[Miles Prower]

I have two chokes lying around. They are rated 50mA. This is enough I hope?

More than enough. A "50mA" rating for a ripple choke doesn't refer to the max current capability of the wire. It's the current that will guarantee that the choke will have the specified inductance. (The very definition of inductance assumes a linear realtionship between current and magnetic flux, and that applies to air coils only. The relationship is very nonlinear when ferromagnetics are involved.) If pulling less current, the inductance will be somewhat higher than rated, and that'll help increase ripple attenuation. Paralleling a hollow state power supply with a single capacitor really is horribly inadequate. You can't get that capacitor large enough without seriously compromising the service life of the diode, and you'll have too much ripple if you keep that capacitor low enough not to ruin the diodes. It's not like solid state where you can just hook up a huge capacitor and be done with it. You'll need additional filtration: LC filter, RC filter, active decoupler.

Still, I question whether it's worth it. 100K plate loads for a 6SL7 look too small. This triode has an r(p) of around 70K (nominal) and really should work into a load of 144K or better for the best linearity.

 

[jev]

Is there a better circuit?

I was satisfied with the Cornet circuit. But since you mention a weak spot in the design. Is there a better circuit you know of using 6sl7 and 6sn7?

 

[Palustris]

You probably should measure the resistance of your choke and then reduce the 3.3k resistor by that amount. You will then want to add another 47uF to 100uF capacitor at the junction of the existing resistor and the new choke.

 

[jev]

Ah thanks yes that is a good suggestion. I will do that.