solid state Vs Tube Rectification

[sandy]

Hello,

I've build couple of Tube Preamp (one with 12AX7 and another with 6SN7)...with good results. In both these projects, i've only used solid state rectification with Chokes smoothen those curves..

I've never tried tube/valve based power supply before. Currently i'm thinking of trying out a power supply with tube recitification (5U4G). Before spending more money...i was wondering if the forum members would provide feedback on thier experience....what would be the impact on the sonic qualities.

Also, please recommend some good tubes for the rectification circuit.....got one 5U4G (NOS NEC, Made in Japan).

Cheers
Sandy.

 

[ray_moth]

If you use a tube rectifier, the results should be:

- lower noise (unless you're using Schottky diodes);

- slow turn-on, which will be kinder to the tubes in your preamp;

- higher impedance, which will give a lower output voltage.

The high impedance of a tube rectifier can cause "sag" with a variable load, such as a class AB1 amp, but not with a class A preamp.

If you change to a tube rectifier, I think you'd be better off with an indirectly-heated one, such as EZ81 (6.3v heater) or 5V4 (5v heater), because of the slower turn-on of about 15-20 secs. Your directly-heated 5U4 will deliver full voltage in only a couple of secs.

 

[rcavictim]

If you drill a hole in the amp chassis and install a vacuum tube rectifier, as a first priority place it as far away a physical layout will allow from the low level audio tubes and circuitry. Second priority is to move it as far as you can from the ouptut tube(s). Often parking it on the opposite side of a steel shielding object like a transformer is a good option.

The recifier tube can capacitively radiate mains hum noise to other tubes through the air and the wiring to the recifier tube plates on the socket underneath the chassis can also couple capacitively to low level circuit wiring.

 

[SHiFTY]

Depends on your power transformer. for a 5 volt rectifier(5U4, 5V4), you need a separate 5 V 3A winding. For a 6 Volt rectifier (EZ80, EZ81) you can power it off the same filament winding as the rest of the valves, as long as the total current draw is not higher than the windings rating.

Your power transformer will also need a centre tap in the high voltage secondary. This centre tap is connected to ground.

I would prefer a GZ32/5V4 or the EZ80 or EZ81 as these all have a nice slow warm up. However there is no problem with using a 5U4, they will be just coasting along with a preamp. And if you already have one then why not!