[finsup]

 What is tube regulation?  What is tube rectification?  Why is it desirable to have one (or both?) as part of an amp's design?

[JohnR]

To power an amp or preamp, the power supply converts the AC ("alternating current") power (from the wall via the power transformer) into DC ("direct current"). The first step in doing so is rectification, which turns the negative "phase" of the AC "upside down" into a positive one (speaking in very general and fuzzy terms).

Rectification can be done with solid state diodes, or with tube diodes. Some say they prefer the sound when tube rectifiers are used; possible reasons for this are that tube rectifiers have a higher internal impedance than solid state ones and thus cause some "sag" in the power supply which might interact in a beneficial way with some circuits, and that tube rectifiers "turn off faster" thus reducing high-frequency noise induced into the power supply.

The power is then filtered with capacitors and sometimes inductors to turn the bumpy rectified waveform into a smooth voltage that can be used to power circuits. The "bumpy" part is called "ripple." A voltage regulator can be used to make this even smoother, by using a circuit to "regulate" the supply voltage down to a lower voltage, but one which has even less ripple (and no sag, within limits). Some designers use them, some don't. Why a tube one might or might not be better, I couldn't say.

Do be careful not to make assumptions on the sound of a component from certain parameters of its circuit design. That way lies madness.

[FullRangeMan]

Hope this help:
Tube rectification give a more old fashioned sound to a tube amp, and a SolidState rectification give a more neutral sound.
My 2 cents

Niteshade Audio built custom amps by order with both systems:
http://www.audiocircle.com/index.php?board=172.0

More info on the site: http://sites.google.com/site/niteshadeaudio/Home

[Syrah]

On many of Dan Wright's mods, he offered both a tube and a ss rectifier option.  I moved from the SS to the tubed.  To my ears, and those of every other online commentator I saw, there was no contest by quite a margin - his tubed design was way better.  This is probably not to say it would be better in every implementation.

[avahifi]

Probably the best reason many designers use tube rectifiers for vacuum tube power amplifiers is because they provide a safe and slow and "soft" turn on characteristics.

The tube rectifier starts to conduct slowly bringing up the B+ voltage to the power tubes slowly.  This provides a more benign start up condition for the power tubes.  It also eliminates a substantial voltage overshoot.

With a solid state rectifier, the B+ is up to full capacity instantly, and this puts full voltage on the output tubes before they have warmed up and started to conduct.  This leads to a condition called "cathode stripping".

In addition, since the B+ has come up before the power tubes draw current, this may also lead to a substantial power supply voltage overshoot, putting excess voltage into the circuit before the tubes conduct and pull the voltages down to their normal design values.  Again this could damage power supply capacitors or other parts.

Finally, a tube rectifier is more rugged and less apt to fail from line voltage over-voltage spikes.  When solid state diodes are over-voltaged, they tend to fail instantly, possibly causing more damage downstream.

If you component was designed for a vacuum rectifier, I would not recommend replacing it with diodes unless you have factored in all the considerations above.

Regards,

Frank Van Alstine

[FullRangeMan]

I would say two power swithches is a needed solution too:
1 for Cathode heating, other for Grid and B+.
A power on swith cost under half dollar in China.

[Steve]

I would like to add a couple of more points.

1) The regulator circuit is also designed to address frequencies across the entire audio band while minimizing reactances that the power supply would introduce. But the design is critical.

2) I have scoped the output of SS rectifiers down to the microvolts level and found no increase in noise or other artifacts caused by the diodes vs tubes.

Cheers.

[cheap-Jack]

Hi.

...If you component was designed for a vacuum rectifier, I would not recommend replacing it with diodes unless you have factored in all the considerations above.
Frank Van Alstine

All depends on the circuitry design.

A then very famous Dynaco ST-70 power amp, for example. The GZ-34 tube rectifier once broken down, the manufacturer will replace the rectifier tube with a 2-diode full wave rectifier mounted on a GZ-34 tube socket so that the user can plug the solidstate diode rectifier direct onto the existing GZ-34 socket without need to change anything in the amp.

So far such direct substitution worked fine.

c-J

[cheap-Jack]

Hi.

The tube rectifier starts to conduct slowly bringing up the B+ voltage to the power tubes slowly.  This provides a more benign start up condition for the power tubes.  It also eliminates a substantial voltage overshoot.
With a solid state rectifier, the B+ is up to full capacity instantly, and this puts full voltage on the output tubes before they have warmed up and started to conduct.  This leads to a condition called "cathode stripping".

Yes, this is probably the ONLY reason tube rectfier should be used - to provide a slow starting up HV so as to provide adequate time for the amp tubes to heat up to conduct before HV applied on them.

But we must not neglect the high plate resistance of the rectifier tube which drops down the I/P AC voltage to the rectifier tube plates & the pretty limited current available to the load.

SS diode rectifiers do not have such shortcomings of any tube rectifiers.  Given a simple switch-on time delay for the HV circuit or even a simple manual HV switch (most DIYers prefer such simple manual switching AFTER the tube heated up), SS rectifier is technically superior than a tube rectifier.

c-J

[JohnR]

Has anyone actually measured reduced tube lifetime caused by "cathode stripping"?