"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.