CJ Tube Preamp PS Diode Upgrade?

[Guest]

Archived from groups: rec.audio.tech (More info?)

Hi, All,

I have a Conrad Johnson Premier Three "classic" tube preamp that I
really love. I am very happy with the sound, but I am curious about
whether I should consider upgrading the power supply diodes to
high-speed soft-recovery diodes...

I have performed this modification on other components myself (solid
state preamp, CD player), and the diodes in my McCormack DNA-1 power
amp were upgraded when the amp was modified to "Revision A Gold" level
by Steve McCormack.

I have noticed an improvement in the general sound of my system
following the diode replacement, but I have been hesitant to replace
the diodes in my CJ preamp for two reasons:

I am reluctant to alter what is definitely a "classic" preamp design
(although the modification could be easily undone), but the main reason
is that I don't know if the diode upgrade would be as effective in tube
equipment.

It seems that over the last 10 years it has become generally accepted
that high-speed soft-recovery diodes are the way to go when designing
and modifying "high end" components, but I have never seen any specific
advice pertaining to TUBE equipment.

My questions:

Does the substitution of high-speed soft-recovery diodes have a
beneficial effect in tube components?

Should the diodes be replaced in both the high voltage supply and the
heater supply as well?

Thanks for any thoughts, wisdom or advice!

Ken

 

[Guest]

Archived from groups: rec.audio.tech (More info?)

<spampup@aol.com> wrote ...
> Does the substitution of high-speed soft-recovery diodes have a
> beneficial effect in tube components?

Use of high-speed, soft-recovery diodes has no beneficial effect
for ANY mains-frequency (50-60Hz) power supply. Unless you
believe in magic. In fact, they make the power supply even MORE
efficient at passing through any HF noise from the power line.
Most people would view this is a negative effect.

The whole purpose of high-speed, fast-recovery diodes was for use
in high-frequency Switching power supplies (SMPS) that run at
super-sonic frequencies. (30, 50, 100, 150 KHz, etc.)

The use of high-speed diodes for mains-frequency power supplies is
snake-oil of the first order. It is the belief that more expensive diodes
must be "better" somehow even if you don't undestand HOW. Yes,
they are "better" for high frequency use, but a waste of money for
low-frequency use.

>
> Should the diodes be replaced in both the high voltage supply and the
> heater supply as well?

Note that replacing vacuum tube rectifiers (or selenium stacks) with
solid-state rectifiers (whether conventional or high-speed) will
significantly raise the power supply output voltage. It may even exceed
the rating of the existing filter capacitors. I have seen people use high-
power resistors in series with the diodes to simulate the voltage drop
of the tube/selenium rectifier.

I certainly would NOT replace a tube or selenium rectifier with any
kind of solid-state diode without accounting for the lower equivalent
series resistance and the accompanying rise in voltage. And certainly
not on any kind of classic equipment that has any resale value. You
have a very real potential of damaging the downstream components.

On the practical side, you should NOT replace tube rectifiers (or
selenium stacks, etc.) with silicon diodes without comprehending the
significant difference in voltage drop.

On the "magical" side, you are wasting your money on "high-speed"
diodes for 50-60Hz mains linear supplies. Certainly there are those
who believe in this sort of thing, but this is the wrong newsgroup for
such magical beliefs.

 

[Guest]

Archived from groups: rec.audio.tech (More info?)

You might get some benefit from redesigning the power supply, but you
may also damage the rest of the tubes in the circuit. Tubes may be
damaged by having a B+ voltage applied before the filaments are hot and
working. Replacing a power supply tube with diodes will put B+ voltage
on the rest of the tubes before their filaments are functional unless
you add some type of delayed turn on.