"Patrick Turner" wrote in message

Jim Lesurf wrote:

In article , Patrick Turner
wrote:

[snip]

A known tube amp hater pointed you in the terrible direction of one
of the the worst designs ever to be seen at

http://members.aol.com/aria3/output.htm

This type of audio amp uses tubes to be directly connected to the
load, and it is called an OTL, or output transformerless amplifier.
They are notoriously unreliable. But some sound excellent while
working.

I assume you are referring to Trevor above.

Nope, never assume anything while I am around; it was arny who gave
the references.

Agreed. However, I bumped into them following posts made by supposed
tube-lovers on URA.

I don't have direct experience of the valve amps he quoted, but my
(perhaps unreliable) recollection is
that they have had good reviews in magazines from reviewers that
like/prefer valve amps.

OTL tube amps have appalling load matches to the tubes.

Only when people go cheap on the tube count. It does take an apalling number
of tubes to adequately drive a reasonable-worst-case speaker that dips just
below 4 ohms.

It'd be like using a couple of bjts to drive 0.2 ohms.

This cab work, its just a matter of picking your implementation.


Tube amps with output transformers are able to achieve a better
match between the load and the tubes so the matching of tubes is
relatively unimportant, and the reliablity is far better, so that
5,000 hrs can be expected from an output tube such as a 6550.

It is probably correct that the power efficiency tends to be better
using transformers.

Far better.

Not an absolute rule, but one that is well-rooted in practicality.

However I'd avoid using 'match' here as speakers tend to be
designed assuming the power amp is a low-impedance voltage source.

NFB normally converts any current source into a voltage source.

There are few if any perfect voltage or current sources in the real world.
Furthermore, there are such things as amplifiers that use NFB to produce a
more ideal current source.

If you listen 2 hrs per day, 365 days per year, you get 6.8 yrs out
of an output tube. Whilst some solid state gear might last that long
without a service, a lot do not,

No idea what percentage of what commercial designs you call "a lot".
Perhaps you could specify?

It's partially a matter of how much degradation you are willing to tolerate.
For the inveterate tube, egregious amounts of distortion are apparently
considered to be a feature, not a bug. For those of us who were into sonic
accuracy, it was kind of depressing to see our amps with EL-34 output pairs
lose 10-20% of their clean output capability within 6 months.

Enough to keep me busy repairing the darn things.

It's a business! ;-)

And I am only one of maybe 50 repair blokes in a town of 300,000 ppl.

Says something good about the actual reliability of modern electronic
components.

FWIW most of the amps I use are 20+ years old, and from personal
experience, and working in the field in the past I'd say most of the
SS amps I know about survive quite well for well over 6.8 years with
no necessity for any service. Don't have any reason to assume that
the designs I knew were unusual. Hence I would not have said "a lot"
as you do above. I might have said "a few", but I don't know what
percentage, designs, etc, you have evidence on.

A well-built SS amp will run continuously for a decade or two. You don't
wanna know how may tubes it would take to keep a tube amp within 90% of spec
for the same period of time.

That said, I assume that you'd regard this as irrelevant as the OP
was asking for a valve amp recommendation, not a comparison of
opinions on reliability and long term service costs: valve versus
transistor. :-)

and the cost of a fix for a high end SS amp may well be more than
the cost of re-tubing in say 6 years.

The cost of buying a good new SS amp can be less than the cost of re-tubing.

SS amps go phut as often as a TV.

Balderdash, not that I see a lot of dead TVs, either.

Mine has had 3 failures since 1982.

Bragging or complaining?

My TV is up-to-date enough that it probably couldn't have existed in 1982.

Its been parked for 6 years since then, and since the last Olympics
when it went bung, and I decided TV was a bad influence anyway....

The less TV the better, agreed.

The 1975 SS AM/FM receiver with 30 watt amps in it has had two
services before I parked it in a cupboard.

Bragging or complaining?

So I have spent my hundreds fixing modern "reliable" appliances....

I've been through a lot more electric coffee pots and vacuum cleaners than
amps.

If you listen 2 hrs per day, 365 days per year, you get 6.8 yrs out
of an output tube. Whilst some solid state gear might last that long
without a service, a lot do not,

No idea what percentage of what commercial designs you call "a lot".
Perhaps you could specify?

It's partially a matter of how much degradation you are willing to tolerate.
For the inveterate tube, egregious amounts of distortion are apparently
considered to be a feature, not a bug. For those of us who were into sonic
accuracy, it was kind of depressing to see our amps with EL-34 output pairs
lose 10-20% of their clean output capability within 6 months.

What an outright lie this guy tells!.

I have an amp with a pair of Sylvania EL34 that are at least 35 years old,
and it gets used every other day in my workshop for testing client's speakers,
and where I need a
low impedance source for testing crossovers.

The emission is down about 15% over new tubes but the amp still measures 0.15%
at 25 watts.

I have measured it several times since i built it 6 years ago using the second
hand tubes
I aquired cheaply, and which are expendable if they fail.
None of the claimed degradation
in the cleanliness of the power output has occured.
Many other amps that I have built and sold and serviced year later for
occasional nopisy pots, or to allow some upgrade have shown no audible or
measurable
reduction of power or increase in thd.



Enough to keep me busy repairing the darn things.

It's a business! ;-)

And I am only one of maybe 50 repair blokes in a town of 300,000 ppl.

Says something good about the actual reliability of modern electronic
components.

There shouldn't be a single failure of an SS amp in my town in any given year.

But maybe thousands of failures occur.

There is no point in arguing with Arny.

Patrick Turner.

In article , Patrick Turner
wrote:



And I am only one of maybe 50 repair blokes in a town of 300,000 ppl.

Says something good about the actual reliability of modern electronic
components.

There shouldn't be a single failure of an SS amp in my town in any given
year.

How many commercial valve amp designs can you quote reliability statistics
for that show failure rates of 1:300,000 or less per working year?

Or are you simply wishing that no SS were in use? :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"Jim Lesurf" wrote in message

In article , Patrick Turner
wrote:



And I am only one of maybe 50 repair blokes in a town of 300,000
ppl.

Says something good about the actual reliability of modern
electronic components.

There shouldn't be a single failure of an SS amp in my town in any
given year.

How many commercial valve amp designs can you quote reliability
statistics for that show failure rates of 1:300,000 or less per
working year?

The other half of the story is the genesis of the missile defense system
that I worked on in the Vietnam era. Interesting because it is still in
service today. An apples-to-apples comparison is possible. When I worked on
it, a Hawk system was composed of about 10 major functional units, each
barely small enough for highway travel. It was powered by about 8 45 KW
diesel generators. With full complement of staff it took about 100 men and
35 duce-and-a-half trucks to move. At least 5 of the 10 functional units had
MTBFs on the order of a day or less. Each was tuned and thoroughly checked
several times a day. The rest were only a bit more reliable. Three of them
had about 400 tubes each. Just the cables required to tie this system
together weighed over a ton.

Today, the fire control system fits on the back of a Humvee which also
powers it. It has about 5 times the range. None of the equipment is
routinely maintained in the same sense. Components basically run until they
break (rare) or are fired, and then they are replaced.

Really and truely the only difference is solid state technology and other
technological changes that it enabled.

"Arny Krueger" wrote in message
...
"Jim Lesurf" wrote in message

In article , Patrick Turner
wrote:



And I am only one of maybe 50 repair blokes in a town of 300,000
ppl.

Says something good about the actual reliability of modern
electronic components.

There shouldn't be a single failure of an SS amp in my town in any
given year.

How many commercial valve amp designs can you quote reliability
statistics for that show failure rates of 1:300,000 or less per
working year?

The other half of the story is the genesis of the missile defense system
that I worked on in the Vietnam era. Interesting because it is still in
service today. An apples-to-apples comparison is possible. When I worked
on it, a Hawk system was composed of about 10 major functional units, each
barely small enough for highway travel. It was powered by about 8 45 KW
diesel generators. With full complement of staff it took about 100 men and
35 duce-and-a-half trucks to move. At least 5 of the 10 functional units
had MTBFs on the order of a day or less. Each was tuned and thoroughly
checked several times a day. The rest were only a bit more reliable. Three
of them had about 400 tubes each. Just the cables required to tie this
system together weighed over a ton.

The Hawk missile batteries were only deployed & never actually used in the
Vietnam conflict. Kept personnel busy though.....


Today, the fire control system fits on the back of a Humvee which also
powers it. It has about 5 times the range. None of the equipment is
routinely maintained in the same sense. Components basically run until
they break (rare) or are fired, and then they are replaced.

Really and truely the only difference is solid state technology and other
technological changes that it enabled.


........and it fits into your top pocket now ;-)

"Mike Gilmour" wrote in message

"Arny Krueger" wrote in message
...
"Jim Lesurf" wrote in message

In article , Patrick Turner
wrote:



And I am only one of maybe 50 repair blokes in a town of 300,000
ppl.

Says something good about the actual reliability of modern
electronic components.

There shouldn't be a single failure of an SS amp in my town in any
given year.

How many commercial valve amp designs can you quote reliability
statistics for that show failure rates of 1:300,000 or less per
working year?

The other half of the story is the genesis of the missile defense
system that I worked on in the Vietnam era. Interesting because it
is still in service today. An apples-to-apples comparison is
possible. When I worked on it, a Hawk system was composed of about
10 major functional units, each barely small enough for highway
travel. It was powered by about 8 45 KW diesel generators. With
full complement of staff it took about 100 men and 35
duce-and-a-half trucks to move. At least 5 of the 10 functional
units had MTBFs on the order of a day or less. Each was tuned and
thoroughly checked several times a day. The rest were only a bit
more reliable. Three of them had about 400 tubes each. Just the
cables required to tie this system together weighed over a ton.

The Hawk missile batteries were only deployed & never actually used
in the Vietnam conflict.

Something about the non-threat posed by the NV Air Force.

Kept personnel busy though.....

You skipped the part where the NVA overran one and sent the parts to Moscow.

Today, the fire control system fits on the back of a Humvee which
also powers it. It has about 5 times the range. None of the
equipment is routinely maintained in the same sense. Components
basically run until they break (rare) or are fired, and then they
are replaced.

Really and truely the only difference is solid state technology and
other technological changes that it enabled.

.......and it fits into your top pocket now ;-)

No, its still pretty much filling up the tail section of a HumVee. The last
major update cut the minimum height of the antenna down to that of smaller
air transport planes than a C5A.

In article ,
Arny Krueger wrote:
Really and truely the only difference is solid state technology and
other technological changes that it enabled.

The other one is the original VRT - the Ampex 1000. Bays of valves. To
make a colour version using valves would have filled the studio it was
meant to serve...

--
*Those who live by the sword get shot by those who don't.

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message

In article ,

Arny Krueger wrote:
Really and truely the only difference is solid state technology and
other technological changes that it enabled.

The other one is the original VRT - the Ampex 1000. Bays of valves. To
make a colour version using valves would have filled the studio it was
meant to serve...

Yeah, talk to old-timers about the MTBF of the first generation color TV
cameras.

In article , Arny Krueger
wrote:
"Jim Lesurf" wrote in message

[snip system details]

Today, the fire control system fits on the back of a Humvee which also
powers it. It has about 5 times the range. None of the equipment is
routinely maintained in the same sense. Components basically run until
they break (rare) or are fired, and then they are replaced.

Really and truely the only difference is solid state technology and
other technological changes that it enabled.

In a parallel vein, when I started developing/using 100-400 GHz receivers
20-30 years ago for astronomy we used to use Klystrons that typically
lasted about 100 Hours each and cost a few thousand pounds each, and BWOs
that cost loads more and lasted a bit longer. More recently we just built
our own Gunn oscillators, which just run until we shove them in the
cupboard until next needed. :-)

(OK, one died when an MSc student insisted on applying double the required
voltage for long enough to kill the protection circuit, and then the
diode.)

The PSU's for the Gunns are loads cheaper and easier as well. Indeed, my
favourite Gunn PSU is the same design as I used to like for use in audio
preamps. :-)

FWIW My experience with domestic audio is that the main reliability
problems [1] are down to things like switches, contacts, etc. e.g.
essentially 'mechanical' in nature. With electrolytic caps wearing out as a
secondary issue.

[1] Ignoring 'hostile action' by the user. 8-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"Jim Lesurf" wrote in message

In article , Arny Krueger
wrote:
"Jim Lesurf" wrote in message

[snip system details]

Today, the fire control system fits on the back of a Humvee which
also powers it. It has about 5 times the range. None of the
equipment is routinely maintained in the same sense. Components
basically run until they break (rare) or are fired, and then they
are replaced.

Really and truely the only difference is solid state technology and
other technological changes that it enabled.

In a parallel vein, when I started developing/using 100-400 GHz
receivers 20-30 years ago for astronomy we used to use Klystrons that
typically lasted about 100 Hours each and cost a few thousand pounds
each, and BWOs that cost loads more and lasted a bit longer. More
recently we just built our own Gunn oscillators, which just run until
we shove them in the cupboard until next needed. :-)

(OK, one died when an MSc student insisted on applying double the
required voltage for long enough to kill the protection circuit, and
then the diode.)

The PSU's for the Gunns are loads cheaper and easier as well. Indeed,
my favourite Gunn PSU is the same design as I used to like for use in
audio preamps. :-)

FWIW My experience with domestic audio is that the main reliability
problems [1] are down to things like switches, contacts, etc. e.g.
essentially 'mechanical' in nature. With electrolytic caps wearing
out as a secondary issue.

[1] Ignoring 'hostile action' by the user. 8-


Yup. The only grasp I get on this tubed amp think is that people are
afllicted with

(1) Excess sentimentality
(2) Desire to fiddle - like vinyl cleaning rituals
(3) Desire for bragging rights - something out of the ordinary even if
backwards