Re: tube amp -- should it be with tube phono preamp?

Google cut my posting- presumably because it couldn't handle the "read
more" feature. That's why I'm posting it this time up front.
Mr. Ludvig, I wish to thank you for taking time to explain in a very
accessible fashion some of the tube/transistor merits and demerits. I
can not judgef technicalities but to me you explained them very well
indeed.
It is a rather sad comment on the real interests of some of the most
doctrinaire "scientific" posters that there was no discussion of your
article. But the pointless sniping, no doubt will go on as ever.
Ludovic Mirabel .
--------------------------------------------
Bret Ludwig wrote:
Let's look at this:


Tube Electronics

A caution

Audio high fidelity is a subjective matter, in that one listener's
preference may be to another listeners disliking. This is especially
true of speakers. Also, a given suite of equipment will sound different
in different environments.
A WARNING!

Tube audio equipment can have voltage potentials exceeding 700 volts
AC. If you intend to perform internal maintenance (other than tube
replacements on unplugged equipment) you should learn and follow all
precautions for high voltage electrical work. Most audio equipment will
be safe when unplugged but some may retain high voltages even then.
Tubes can get very hot (especially if the circuit is not operating
correctly) and burns are a hazzard.
Why tubes?

Electron tubes are thought by many to be well suited for high fidelity
audio applications. Technical observers report that when a tube
amplifier is operated near its power limits that the distortion
produced is the addition of even harmonics (even multiples of the
fundamental freqency), while transistor amplifiers produce a distortion
consisting of odd harmonics. Many listeners think that the addition of
even harmonics is acceptable and even pleasant, while finding odd
harmonics are harsh and disturbing. The addition specific proportions
of even harmonics to a pure sine wave will produce a sawtooth wave,
which has a timbre similar to a reed instrument such as a clarinet,
while a similar addition of odd harmonics will produce a square wave,
percieved as a harsh buzz, similar to the sound of a kazoo. Click here
for a diagram of harmonic addition. On loud transients, the current
capacity of the tube and a tube-rectified power supply will limit with
a gradual fall-off, where solid state will "clip", introducing harsh
high frequency components that can even damage speakers. Thus many
solid state amplifiers are overbuilt, with extra capacity to avoid the
introduction of this distortion under conditions rarely encountered.
Tube amplifier watts are said to be "bigger", in that under extreme
conditions a given musical passage will sound better on a tube
amplifier than on a solid state amp of the same wattage. Modern mass
market solid state equipment is now built to meet specific
manufacturing cost targets. (Some think that there was a "golden age"
of Japanese solid state equipment around the 1980's, when the
technology was mastered and engineers rather than accountants still
ruled.) It has been my experience that an old mid priced tube amp
sounds much better than modern mid priced solid state equipment (using
the same speakers and source), especially in the way that instruments
in a symphony orchestra's string section will retain their individual
identities, rather than being muddled together.

There is modern production of tubes and tube equipment and there are
shops around capable of servicing both old and new units.

Modern replacements for many of the more common tubes are readily
available at reasonable prices. At the time that tube electronics
dominated high end audio, speakers with both high fidelity and high
efficiency were rare, and so audiophiles felt the need for power, with
mid range (and mid price) equipment not getting the respect now
deserved when driving modern high efficiency speakers. Now, old
equipment of modest wattage can produce much more quality sound than
was typical in its time.
Disadvantages

Tube equipment was replaced with solid state because solid state
answered the following disadvantages of tubes, most of which are
critical in military and industrial applications:

Tubes require a warm-up time, typically 20 to 40 seconds before useful
output is obtained and up to twenty minutes before circuits reach a
steady state.

Tubes are sensitive to shock and vibration, which can affect both
durability and performance.

The high voltages used require use of larger and more expensive
capacitors and adds stress to the winding insulation of power supply
and output transformers.

Tubes produce considerable heat which can shorten the life of other
components in the device.

Designing for disposal of the heat produced restricted the design of
equipment enclosures, requiring bulky box shapes for equipment. This
heat leads to low efficiency in terms of audio watts produced for wall
plug watts consumed. Tube equipment efficiency is especially bad at low
levels of output since cathode heaters consume constant power
regardless of the device's output.

Tubes have a limited life. Several thousand hours of use is typical.
Many on and off cycles will further shorten tube life, thus a tube set
may be left on when not in use, further degrading overall efficiency.

Tube equipment, particulary power amplifiers, can have deadly high
voltages and high stored energy (even when unpluged, in some cases),
and should be worked on only with knowledge and use of safety
procedures.

Tube characteristics change with use and in some equipment this change
should be periodically compensated for by adjustments for best
fidelity, efficiency, and component life. Adjustment may be required
when certain tubes are replaced, while some lower power amplifiers
require no such adjustment. Adjustment requires the use of at least
simple test equipment and elementary knowlege. Radio tuning circuits
will require adjustment using specialized equipment and knowlege when
certain tubes are replaced.

Older equipment may use components that are difficult to obtain. This
can usually be compensated for by modifying circuits to use more
readily obtainable parts.

Tubes are bulky compared to transistors.

You can't make an integrated circuit using conventional tube
technology, although there have been experimental efforts to design and
construct microstructure cold-cathode vacuum devices that would be
suitable for operating in high radiation environments that can damage
solid state devices. These microstructures are produced using the
lithographic deposition and etching techniques developed for the
manufacture of integrated circuits.
Recent History

Electron tubes have an interesting recent history. Tubes (what the
speakers of British English call "valves") were for an extended period
were the only economical means of amplifying analog electrical signals
(and thus useful in radios and high fidelity amplifiers). They were
thought obsolete in the West when their functions could be efectively
done by transistors. The Soviet Union, however, continued to use them
in military electronics. This was thought by western analysts to be due
to an inability to produce transistors and integrated circuits of the
quality necessary for such application, but in reality their use by the
Soviet Union was based on the fact that electron tubes are
radiation-hard, becoming fully functional seconds after a nuclear
blast. The high currents induced by the magnetic pulse produced by an
atomic blast and ionizing radiation can permanently destroy transistors
and integrated circuits.

As a consequence of this recent use of these devices, modern factories
within the former Soviet Union, China, and Eastern Europe continue to
produce tubes and are a primary source of electron tubes for
replacement and use in newly manufactured audio equipment. The quality
and durability of tubes is said to vary, however, with some countries
having a far better reputation than others. Caches of "New Old Stock"
(NOS) tubes are sometimes found as old electronic shops change hands
and some brands are treasured by tube audiophiles, but sometimes modern
low quality tubes are remarked or repackaged to look like NOS. Also,
some cheap rectifier tubes are "pin compatable" with original tubes and
are labled with the same designation but are not the same internally
and can damage the amplifier. These lack a cathode envelope around the
heater and thus warm up too fast, shocking other components with high
voltage befor they are warmed up and causing "cathode stripping" and
other problems. (BEWARE!)

Modern tube audio equipment of new manufacture is now a specialty shop
item. Some retailers sell only tube equipment. Modern amplifiers are
now styled to show off their tubes and transformers whereas older
equipment kept such things "under the hood". To obtain, refurbish, and
maintain old tube audio equipment can be either a major hassle or an
enjoyable and rewarding hobby - it all depends upon your outlook,
interests, and skills. Price of older equipment will vary greatly,
being dependent on brand, condition (particulary cosmetics), factory vs
kit built, and the knowlege and interest of the buyer and seller.
Thrift shops and garage and estate sales can sometimes reward the
careful and persistant shoper with a real bargain, but such equipment
usually requires careful initial warm up and often extensive
replacement of components.

Some professional equipment builders produce new designs while using
the power and output transformers from older equipment. The
transformers are the most expensive components of tube equipment. This
is a particularly effective way to recycle obsolete integrated
monophonic equipment into single channel amplifiers (monoblock) or
stereo or multichannel integrated units.

Other than bad tubes, typical problems with old used equipment will be
overheated resistors and wiring due to operation excessive current from
tube operation out of the proper bias range. This is often due to
(electrically) leaking coupling capacitors. If you cannot adjust the
tube current to the proper level or if your equipment is self biasing
but the output tubes run hot, you probably have leaking coupling
capacitors. These can easily be replaced with a little knowlege and the
usual safety precautions. When replacing interstage coupling
capacitors, always use the same capacitance, but a higher voltage
rating will not hurt. Often resistors are out of specification and
performance can be greatly improved by replacement, particularly in the
phase splitter circuit that drives the final amplifier tubes. Leaky
capacitors in intermediate stages can also cause plate and cathode
resistors to run hot and go out of specifications.

If old equipment (tube or transistor) has not been operated for a long
time, operation can cause catastrophic failure of electrolytic
capacitors. Such equipment should be brought into operation at low
voltage using a variac (variable A/C transformer), warming up gradually
over a 20 to 30 minute period.

For long life, keep your equipment clean and dust free and at least
once a year perform any required adjustments. Many units require a bias
adjustment to preserve tube life, reduce heat, and keep the best sound
reproduction. This will usually require modest test equipment, knowlege
of the equipment in question, and the usual safety precautions. <<

.

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