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The Sound of Rectifier

Posted on October 1, 2012
by tubemaze

Some of you might have been asking the same questions as I did – Does tube
rectifier change sound? How effect does it have on a sound?

To test this, I put together an amp that takes 5U4 rectifier, but could be
easily be replaced with 5Y3, 5Z3, 5AR4 and of course solid state rectifier.

Ones and for all, I proved to myself at lest that RECTIFIERS DO CHANGE SOUND!
Keep in mind that I was one of the biggest doubters.

What?! How?!?! Why?!?!?!

It appears that the main reason, but not the only one, is voltage drop for
different rectifiers, so your amp works at different operating point; thus,
sound changes.

5U4G (44v drop) has a smaller voltage drop compared to 5U4GB (50v drop), so
you amp is running at higher voltage. But the effects on the sound is that the
amp sounds softer – the sharpness on the top is less audible.

5R4 rectifier (67v drop) in the same circuit produced more transparency on
the top and tighter bass.

5AR4 rectifier (17v drop), Mullard especially, has one of the smallest drops
in voltage, which lead to tighter sound, but also more transparency and more
speed, but warmth was sacrificed – with type 45 and 2A3 tubes that was not a
desired effect.

In some cases, changes were huge (e.g., 5AR4 vs 5u4G); in some case, changes
were practically none. In cases like 5Y3GT (60v drop), sharpness in the sound
was quite obvious, moving to 5Y3G didn’t change much, so it’s not about the
shape
Using, 5Z4G (20v drop) made sound more dynamic – the same as with 5AR4.

How do different manufacturers affect sound? I couldn’t hear any difference
from different brands of the same type of the tube. GE vs RCA – same
results.

Solid Stage rectifier changed sound quite a lot making it much sharper on the
top, the desired tubiness decreased.

So there you go. Different circuits will behave differently with different
rectifiers, but you will likely hear a change

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This entry was posted in Guides,
Vacuum
Tubes by tubemaze.
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4 thoughts on “The Sound of
Rectifier”

eicoeico on October 5, 2012 at 11:46 AM
said:

You have touched on several important points re: tube rectifier sonic
differences, and offered some great real-world, practical and useful
information about the VERY confusing issue of “rectifier sound”. Sonic
differences in rectifiers has always fascinated me, and I have figured SOME of
it out (but not all by any means!) The first huge variable as to how different
rectifiers have a unique sonic signature from each other is basic construction
type. Common tube rectifiers developed in the 1930s and 1940s such as USA
types 5U4, 5R4, 5V3, WECO 274B etc, and U.K. / European rectifiers such as the
legendary U52 are all what is known as “filamentary cathode” or “directly
heated” types. Just like the legendary audio triodes like type 45 and type
300B, the directly heated/filamentary cathode rectifiers (5U4 etc) use a
thoriated tungsten cathode that is ALSO the heater for the tube. When heater
voltage is applied to a directly heated/filamentary cathode rectifier, it is
able to produce DC voltage almost immediately. More about that issue later.
The other main type of rectifier is the Indirectly Heated type such as
GZ34/5AR4, 5V4, GZ37, 6X5 etc etc. These rectifier tubes have a heater and a
cathode that are two separate units in the tube, electrically speaking. They
use a traditional sleeved cathode just like KT88 etc; the cathode sleeve is a
metal tube with a heating element, or filament, inside and a coating on the
outside of that cathode sleeve comprised of various oxides of barium, along
with small amounts of other metallic and semi-metallic elements that all have
thermionic emissive properties, meaning that when heated they release huge
amounts of electrons. The electrical differences between these two types of
rectifiers, directly heated (5U4, 5R4) or indirectly heated cathodes (GZ34
etc), are the largest by far reason the two types sound vastly different.
Also, the ability to release vast amount of electrons at light speed, internal
plate to plate impedance, and other factors like how each type handles
internal stray capacitance make these two types sound so different. IMHO,
directly heated rectifiers like 5U4 have a “faster” more “transparent” sound
with a lot of punch, speed, and dynamics as compared to a Mullard GZ34. The
legendary GZ34, though, has a much more refined, more “hifi” sound with
smoother treble, warm detailed mids, and less edgy sonics than directly heated
types like 5U4. I tend to favor the indirectly heated rectifiers not just
sonically, but for the “cathode stripping” issue that I’ll cover in part 2. As
far as sonic differences within the indirectly-heated filament type rectifiers
like GZ34: The various formulas for these barium-based, cathode
coating/electron-emitting emulsions were the most closely guarded secrets of
tube manufactures in the golden age of tubes (1940s to 1970s) The exact
formula and more importantly the way it was applied to the cathode sleeve
(i.e. emulsion applied all at once, or in layers with drying time in between
coatings, for example) were largely responsible for the different sound/sonic
signature of the different cathode-sleeve/indirectly heated rectifiers.
Likewise, the manner in which the thoriated tungsten melt was done for
directly heated rectifiers causes huge sonic differences. As for voltage drop–
voltage drop is an EFFECT, caused by the electrical nature of a specific
rectifier, mostly internal impedances between the tube elements. The internal
impedances between the tungsten filament and the plate, the small stray
capacitances inside the tube (the top mica of a rectifier tube basically acts
like a small mica capacitor in circuit; the mica itself and the various DC
voltages that stray from the tube elements that are anchored by the mica
create capacitance).. these factors combine to create the voltage drop, but
more importantly they hugely affect the tubes in circuit performance. Internal
impedance relationships inside a rectifier are the single largest variable in
sonic signature, with the second most important being manufacturing techniques
and quality control. Whew! Part 2 will look at peak inverse voltage,
capacitor/choke issues, and go a little deeper on the “why” of rectifier sonic
differences.

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eicoeico on October 5, 2012 at 12:59 PM
said:

Sorry to create a bit of confusion in the first post about rectifier tubes–
stray capacitance doesn’t have much (if anything) to do with creating voltage
drop itself but this stray capacitance (and how the rectifier tube deals with
it in-circuit) is HUGE as far as affecting the overall sound of various
rectifiers. I mixed the two concepts of voltage drop and stray capacitance by
trying to tackle both at once…Voltage drop is almost exclusively a direct
result of internal, inter-electrode impedance within a rectifier tube. This
voltage drop is not caused by stray capacitance… Stray capacitance has much
more subtle effects on the way a rectifier behaves under real-world audio
applications in a tube amp. I didn’t mean to mix the two concepts and just
wanted to clarify. Later today I’ll go into such things as WHY there is no
modern GZ34 tube that can compare with a vintage Mullard… Also, we can examine
the cathode stripping issue on input and output tubes– that is, gradual
cathode stripping/degrading in audio signal tubes resulting from using solid
state diode rectifiers as well as directly heated rectifiers like 5U4 in a
power supply…. And most importantly for the real world we will take a look at
how to build a power supply that minimizes the sonic differences present in
different rectifier tubes. Sorry for any confusion in the above post; I
over-reached a bit! Thanks very much.

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eicoeico on October 6, 2012 at 10:29 AM
said:

A problem caused by directly heated or filamentary cathode rectifiers is
known as cathode stripping. Cathode stripping is a highly technical issue, but
the basics of it are this: Filamentary Cathode rectifier tubes like 5R4, 5U4,
274B etc can deliver full DC levels only FIVE seconds after powering up an amp
in which they are installed. In contrast, it takes TWELVE seconds, more or
less, for the input tubes (12AX7, 12AU7, 6SN7 etc) and the output tubes (KT88,
EL34 etc) to even BEGIN conducting this DC voltage.. so there are about 7
seconds where full DC levels are applied to the power supply capacitors and
the audio input and output tubes… and these tubes are not ready to use/conduct
this DC voltage. Thus, when the audio tubes do begin to conduct current at ca.
twelve seconds after the amplifier is turned on, the 5U4/5R4 type rectifiers
have already been charging the entire circuit with full DC current/voltage
levels for 6-7 seconds. This difference in warm-up time causes a huge
transient surge of current and electron emission in the cathodes of the input
and output tubes as these audio tubes begin emitting electrons and thus
conducting current— The audio tubes essentially are “slammed” by the full DC
levels that have been present for several seconds before they were able to
conduct current. These extreme transient currents and emission levels at the
moment when the audio tubes begin to emit electrons and thus conduct current
causes cumulative damage to the cathode. This cumulative damage gradually
begins “stripping” precious cathode emulsion away as small amounts of the
cathode emulsion are literally boiled off the cathode during the brief but
intense current spike as the audio tubes first reach operating temperature
some 7 seconds later than a filamentary cathode rectifier reaches operating
temperature. The damage is rather small each time, but over the course of
hundreds of turn-on cycles when the amplifier is powered up it cumulatively
contributes to an early death for expensive audio tubes. Cathode Stripping is
NOT an issue with triode output tubes like type 45, 2A3, 300B, 6B4G etc
because these early triodes are filamentary cathode/directly heated tubes just
like 5U4/5R4 etc.. these early triode output tubes reach operating temperature
at the same exact time a 5U4 or 5R4 will. To eliminate cathode stripping,
indirectly heated/cathode sleeve-type rectifiers like 5V4, 5Z4, GZ30, GZ34,
GZ37, 6X5 and many others were developed by tube designers. These tubes, being
indirectly heated, take 12 seconds to even begin delivering DC
voltage/current, and are only able to deliver maximum DC voltage and current
levels to the audio tubes after 18-20 seconds. This is known as a “slow ramp
up” of the DC voltage applied to the circuit by a rectifier, and this
characteristic of delayed delivery of DC voltage to the audio tubes in an
amplifier eliminates the intense current spikes that can stress power supply
capacitors and cause cathode stripping in audio tubes. This is why indirectly
heated rectifiers such as the legendary Mullard GZ34 are so much in demand.
Slow ramp-up of the DC avoids huge transient current spikes, and thus prolongs
the life not just of the expensive audio amplifying tubes but also the power
supply capacitors and the power transformer itself. In the next section, I’ll
go deeper into the indirectly heated rectifiers like GZ34/5V4/5Z4 etc,
comparing and contrasting their electrical parameters, and referencing these
abstract electrical data to real-world performance Finally, a large percentage
of modern tube equipment uses solid state diodes to rectify DC; a diode can
deliver full voltage and current in less than a second after turn-on.
Well-designed modern tube equipment uses a variety of methods to delay the
instantaneous voltage/current delivery of these diodes and thus it is not
generally a problem. Likewise, there are delay devices available that allow
slow ramp-up of DC levels with filamentray cathode rectifiers like 5U4 for
audiophiles who prefer the sound of the directly heated type
rectifiers.

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