Tube amplifiers
 

Arny Krueger wrote:

"Jim Lesurf" wrote in message


FWIW My recollection is that when we had valve TVs years ago, that
calls to the repair man were more common. Mainly to replace valves.
Indeed, we used to have nearby high street shops that did this. Such
things vanished later on as with SS units many shops contracted any
repair work back to the makers or a central agent as it wasn't worth
their while to keep a repairman employed any more just for the shop.

When all we had were valve-based electronics in the US, many
consumer-oriented stores including hardware stores and drug stores had tube
checkers. Repair shops for home electronics proliferated to the point where
just about every commercial strip had at least one. Electronics stores were
dominated by shelf after shelf of replacment valves.

Today, shops that repair consumer electronics are regional businesses. In
1960 there were three within a mile of my current residence. Today the
nearest one is about 5 miles away.

The most easily blameable and replaceable thing in tube electronics
was the valve.

But I have a US book written in 1960 about the reliability of electronics
especially in the military.
In 1955, about 1/3 of Naval electronics was out of action at anyone time.
If we'd had a 3rd world war then, we'd have had only 2/3 of a war because of
electronics failures.
In the book many tables are shown of reasons why gear failed and tube
instigated failures were lower than
those caused by R or C or L failures, all of which were mostly caused by
inadequate design
by dopey engineers wanting to screw the last drop of performance from all the
gear.
A US aircaft carrier had 12,500 tubes on board with 250 guys to service/use the
gear.
Nowdays twice that number of blokes are used but they look after a much more
reliable
10 million+ transistors in a a range of complex gear that needs constant
maintenance, but it does more.


Tubes could never be blamed for all the troubles we had with TVs or radios.

It was so easy for a service guy to tell a householder "Gee, this tube went,
see here..."
when it really was a 10c capacitor. Thus householders subsidised the costs
of new tubes that didn't need replacing.

The repair industry was riddled and infested with shonky dishonest repair
people
trying to make a quid like the car repair ppl, house repair ppl, pest
exterminators,
plumbers, electricians, dentists, doctors, lawyers, real estate agents,
undertakers etc, etc, etc.
and the whole bloody lot of them.

Patrick Turner.

Tube amplifiers
 

In article ,
Patrick Turner wrote:
Tubes could never be blamed for all the troubles we had with TVs or
radios.

They certainly could. I had an early colour TV (UK) which was a hybrid
design. Needed all the line output stage bottles changed about every two
years - and they were expensive. Frame output lasted longer.
It also drifted, requiring registration and grey scale balance pretty
often.

Good while it worked, though. The solid state replacement has never needed
*any* repairs, and is still working although not the main set anymore.
It's about 20 years old. ;-)

--
*Geeks shall inherit the earth *

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

Tube amplifiers
 

On Wed, 22 Dec 2004 03:08:55 +1100, Patrick Turner
wrote:

Stewart Pinkerton wrote:

On Sun, 19 Dec 2004 19:39:02 +0200, "Iain M Churches"
wrote:

"Patrick Turner" wrote in message
...
Even if the Ro of the open loop amp is infinite,
series voltage NFB converts it into a voltage source.
It doesn't take much NFB to get a DF of 10.

Jim Lesurf wrote
The snag is that my impression is that some valve designs with output
transformers only use a modest amount of feedback. As a result they can
have output impedance of the order of 0.5 Ohms. (e.g. the amp Iain
mentioned in another thread recently). This level of output impedance
allows for quite audible changes in the response with loudspeakers whose
input impedance varies with frequency.

Rubbish, imho.

Hmm. Now this has really become confusing:-)) I sent Jim's post as an
e-mail to a pal of mine ex BBC engineering, who replied in *exactly*
the same terms as Patrick.

Your Beeb pal might like to consider that many modern speakers have
impedances which dip to 3 ohms or so, somewhere around the crossover
frequency, which is often in the region where the ear is most
sensitive. A difference in Ro of 0.5 ohms will give a change of volume
of about 1.5dB in the area of that dip, which most speaker engineers
would consider very likely to be audible.

A tube amp designed for 8 ohms with Ro = 0.5 ohms has a good DF.

So use 8 ohms, eh.

You're from Ontario, eh? :-)

OK, name half a dozen top-quality speakers whose impedance doesn't
drop below 7 ohms.

If the designer has any brains, he will have provided alternatively
arranged secondaries on the OPT so that the turn ratio can be reduced
by a factor of 0.67, ( two windings of N turns instead of three windings of N
turns in series )

If the NFB applied is the same, the load match is then to 3.6 ohms,
and Ro falls to 0.22 ohms.

And the output voltage has also gone down by 3dB.

Any other way could be poor engineering.

Indeed....................... :-)

It's called a SET amplifier.

Then if you connect the 8 ohm speakers to your 3.6 ohm outlet, the classA %
of the total AB power increases, and thd is halved, DF is obviously so much
better,
all at the cost of slightly less maximum power.

Slightly less? you mean 3dB, *half* the power.

With any decent SS amp, this problem simply doesn't occur.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Tube amplifiers
 

On Tue, 21 Dec 2004 18:00:36 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Patrick Turner wrote:
Tubes could never be blamed for all the troubles we had with TVs or
radios.

They certainly could. I had an early colour TV (UK) which was a hybrid
design. Needed all the line output stage bottles changed about every two
years - and they were expensive. Frame output lasted longer.
It also drifted, requiring registration and grey scale balance pretty
often.

Good while it worked, though. The solid state replacement has never needed
*any* repairs, and is still working although not the main set anymore.
It's about 20 years old. ;-)

The best thing about that telly would have been the phosphors (I'm
assuming it was a delta, not a PIL). Unlike the current high-luminance
ones, they gave really convincing skin tones. Present phosphors render
everything in shades of purple - nasty.

d

Pearce Consulting
http://www.pearce.uk.com

Tube amplifiers
 

"Patrick Turner" wrote in message
...


A tube amp designed for 8 ohms with Ro = 0.5 ohms has a good DF.

Stewart has misquoted my figure which was Ro=0.4 Ohms, so DF=20
I have been given to understand by others that this is a good figure,
and that increases above DF 12 do not seem to yield audible
improvement.

Iain

Tube amplifiers
 

In article ,
Don Pearce wrote:
Good while it worked, though. The solid state replacement has never
needed *any* repairs, and is still working although not the main set
anymore. It's about 20 years old. ;-)

The best thing about that telly would have been the phosphors (I'm
assuming it was a delta, not a PIL).

Yup. However, some later TVs after the advent of VHS had deliberately
restricted definition so the comparison wasn't so marked - early PIL ones,
for example. Don't think I ever saw 5.5 megs on one of those.

Unlike the current high-luminance
ones, they gave really convincing skin tones. Present phosphors render
everything in shades of purple - nasty.

It's mainly the reds which are wrong - too orange, so everyone looks like
Des O'Connor...

--
*No radio - Already stolen.

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

Tube amplifiers
 

In article , Patrick Turner
wrote:


Rubbish, imho.

99% of ppl would remain totally unaware if a 1 ohm resistor was
placed betwen their speakers and a low Ro amp.

Regarding SS reliablity, all I know is that there are many failures,
and mainly due to shorted speaker leads.

Patrick Turner.




I've just tried it with a 1.2 Ohm resistor on a marantz PM44SE and it
is very noticeable! The bass becomes more flabby.

Not with all speakers.

I agree. But probably audible with rather more than 1% of speakers. :-)

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

Tube amplifiers
 

In article , Patrick Turner
wrote:


Fleetie wrote:

"Patrick Turner" wrote
Regarding SS reliablity, all I know is that there are many failures,
and mainly due to shorted speaker leads.

That is not really the fault of the amplifier. If it wasn't designed
to withstand the shorted output condition, you can't fault it for
blowing up if your short the output. That is not a matter of
"reliability".

I agree basically but makers have ensured the steady early deathrate in
much consumer SS amps by installing springloaded speaker terminals which
are 12 mm apart instead of 50mm.

Well, I have eight power amps of various 'vintages'. None of them use
springloaded speaker terminals.

Makers don't want amps to last, they want to sell as many as possible.

Sweeping claims again... :-)

Basically I agree, but the humans cause the blow ups. Something that
tells an SS amp to switch itself off if the load falls below 3 ohms at
any level should be legislated for in Parliment.

I'm not sure that all speaker makers and users would be happy with that.
:-)

Slainte,

--
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

Tube amplifiers
 

In article , Patrick Turner
wrote:


Jim Lesurf wrote:

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,

Lemme see now.

I do about 40 amps per year, nearly all SS. I am a very low volume
repairist, and if 50 of us have an average of 60 per year that's 3,000
SS amps per year need an average fix of $80 each. There are 120,000
households for 300,000 ppl, and with an average of 1 amp per household.
So 2.5% fail each year, with many failing before the warranty period
expires. Ppl replace all their electronics about every 7 years on
average.

Your idea of a one in 300,000 failure rate p.a. is just **** and wind.

I'm afraid that the "idea" you refer to here is one you incorrectly
ascribe to me. :-) If you read what I wrote, I think you will find
that I did not say that the failure rate of *any* amp either was "one in
300,000" nor did I say that it "should be" so. :-)

Now please look again at what *you* wrote, and the *actual* question I
asked - not one you imagine I asked. :-)

1) Your statement was that "There shouldn't be a single failure of an SS
amp in my town in any given year."

2) My question was to ask how many *valve* amps you knew of that met this
standard which *you* seek to impose in your statement.

Are you able to answer the question I asked?

If not, can you explain why you want to impose a standard for SS amps that
you can't show that valve amps already meet?

If you analyse the values of electronics spare part $ values being
imported into your country, you will see I ain't wrong.

Depends if "wrong" includes failing to deal with the actual question asked.
Also you might feel it was "wrong" for you to assume that I have introduced
an "idea" which I have not, and which seems to actually come from your
own statement (1) above. :-)

My point was that *you* were introducing the "idea" that SS amps "should"
have failure rates of this low level. If so, it seems reasonable to me
to try and find out if you apply the same standards and requirement
to valve amps - and if so, what evidence you have for thinking such
a standard is appropriate in *both* cases.

I appreciate that you may find it emotionally satisfying to resort to
personal abuse or dismissive "**** and wind" statements. But I think
you will find that people will take your views more seriously if you
focus on the actual issues and questions that are relevant.

However if you really wish to argue in "**** and wind" terms then you
may care to note that in this case what you object to seems have its
source in your statement (1), not in my following question (2). :-)

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

Tube amplifiers
 

"Stewart Pinkerton" wrote in message
...
Your Beeb pal might like to consider that many modern speakers have
impedances which dip to 3 ohms or so, somewhere around the crossover
frequency, which is often in the region where the ear is most
sensitive.

Please refer to the AES recommendations for speaker impedances
(which are followed by reputable manufacturers) They do not allow
a speaker of nominal impedance of 8 Ohms to fall to 3 Ohms.

Or were you talking about a 4 Ohm speaker?
You did not say so.

A difference in Ro of 0.5 ohms will give a change of volume
of about 1.5dB in the area of that dip, which most speaker engineers
would consider very likely to be audible.

I don't know from where you got the "difference of 0.5 Ohms". We were
originally talking about a amplifier with an Ro of 0.4 Ohms. So the
difference is perhaps 0.3 Ohms.

So your "change of volume of about 1.5dB" is no longer valid,
being reduced to a value which could possibly be perceived
on sweep tones (this will be an interesting thing to test in
the New year) but probably not with music.

Iain