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Trevor Wilson[_3_] Trevor Wilson[_3_] is offline
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Default Introducing a New Horse to the Stable

On 10/09/2019 9:54 pm, Peter Wieck wrote:
OK, OK, I will bite! Minor rant to follow:

Tube vs. Solid State on reliability:

There are not so very many 60-year old components in operation these days unmodified since-new. My oldest tube item turned 100 this year and likely works better than when it was new based on a better understanding of antenna systems, optimum tube voltages and so forth. Other than moving parts (CD player), the newest component in my office system was made in 1963. The system runs 9 hours per day, 5 days per week. Oh, and the tubes are original as well.

On the other hand, and given my hobby, I see a large number of SS components that have blown transistors, exploded capacitors and much worse, irrespective of age and source. The well made, well designed stuff is serviceable, distinguishing it from the rest of the garbage out there.


**Sure. That has been my observation. I see a lot of junk across my
bench, though I tend to reject many products nowadays. Not worth my
time. FWIW: I have 70 year old radio coming in next week. Obviously,
it's not really worthwhile, but it is a family heirloom, so the client
will spend whatever is necessary. I expect it will be an electrolytic
cap swap. Maybe a valve. We'll see.


I would make a fairly apt comparison: A tube amplifier is much like a mid-last-century Mercedes or VW - few things were self-adjusting, and they required regular and attentive care-and-feeding. With such, they were good for several hundred thousand miles of reliable service. A contemporary Ford, Cadillac, Plymouth would be considered remarkable were it to survive 100,000 miles without heroic measures. Might run very nicely when running, but that would be your basic solid-state device in comparison.


**That would be a poor comparison. Having owned a number of vehicles
over the past 50 years, I can assure you that, in general, modern cars
are VASTLY superior in most areas. Ignition systems and fuel handling
systems are the big ones. Before modern EFI, I grappled with
carburettors, that required constant adjustment and let's not even get
into the standard Kettering ignition systems. Such systems require
constant and careful adjustments. As for the body of the vehicle, shall
we discuss the impact of rust? Most (all?) modern cars utilise some kind
of rust prevention at manufacture. Older cars rely on paint. My two
present cars are thoroughly modern vehicles (one is 2 years old and one
is almost 20). Both are perfectly reliable and offer excellent levels of
safety, fuel economy and performance. Both demonstrate the kind of
performance which would be associated with race cars from the 1960s
(though both could manage a tight, twisty race track more quickly, due
to their all wheel drive ability). Without the unreliability.

Anyway, that's all a bit off-topic.

I service equipment from all generations. Older equipment almost always
require replacement of electrolytic caps and carbon composition
resistors (where used). That may be valve or SS.


Put simply, they are different beasts designed with different things in mind, but for the same basic purpose. That one is or is not "BETTER" than the other is not relevant to the purpose in either case.

Now, when I here things like "Zero global NFB" and "Critically matched components", I can smell the snake-oil from a great distance, even the 10,000 miles from here to Australia. I am sure that process also contains descriptives of "interconnects" rolled on the thighs of virgins on Walpurgis Night...


**I did not mention "interconnects". However, you may care to
investigate the possible reasons why many listeners prefer the sound of
valve amps. Consider the amount of global NFB used in typical valve
products. Compared to SS gear, that NFB is either very low, or
non-existent. Consider the action of valve amps under the conditions of
Voltage limiting (clipping) and current limiting. Most SS amps do not
cope with such conditions well, whereas most valve amps clip and current
limit in a benign fashion. SS camps can be designed to act similarly,
but few are. As for the matched components, it's a necessity in the
design I cited. Without matched components, it is impossible to achieve
high reliability, low distortion and zero global NFB. Cumbersome? Sure.

Further and for the record: I have subjected myself to many double blind
tests over the years to verify my preference is uncoloured by vision.



Note that even "critically matched" solid-state components drift after a very short period of time in-service. All of them, such that that "less than 1%" is meaningful for perhaps 12 hours or so.


**The solid state devices are matched at the operational temperature of
the amplifier (60 degrees C) of course. The amplifiers use a demand
responsive fan (infinitely variable speed), which maintains the heat
sink temperatures at 60 degrees C (+/- 3 degrees) at all times. A short
(20 mins) warm-up time is necessary for optimal performance.



Being as this is a hobby for me, I get to try things that are otherwise unproductive, unprofitable or impractical. Such as shotgunning a device with single-value capacitors and then comparing it to the same device with carefully screened and matched caps. Or matching driver and output transistors and comparing to a similar device with disparate values. Guys and gals - you would be seriously shocked to discover how little difference some things make that the ALL-SEEING, ALL-KNOWING gurus will tell you are critical. Often no difference at all.


**Well, that has not been my experience. It depends on the design. A
standard, high global NFB amp, which has been designed to cope with off
the shelf devices will likely show zero difference when fitted with
critically matched devices. HOWEVER, in a past life, I was service
manager for Marantz Australia for several years. During the late 1960s
and 1970s I noted that most Marantz models (even some of the Japanese
built stuff) was specified to use closely matched output and driver
devices (roughly 30% HFE match). I vividly recall the time when, for a
short time, stocks of output devices for the Model 240 (250, 250M, 1200,
1200B) were depleted. I decided to try using unmatched devices in one
repair. Distortion approached 0.5% (rated distortion was 0.1%, but I
would typically measure 0.01%). Clearly a most unacceptable result. I
explained to the customer that they would need to wait for Marantz to
supply the correct devices.

So, matched devices are not as uncommon as you might imagine.


--
Trevor Wilson
www.rageaudio.com.au

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