On Aug 20, 10:43*am, "Fred" wrote:
"charles rollo" wrote i
snip for brevity and to save a huge scrolling search....
and BTW, I accidently posted prematurely by pressing the wrong key
here so I repeat a previous post starting the same but with the end
done right......
I've been in the audio business for around 40 years, Charles. *I deal with
customers like you by showing them the door. *You took some risks to save
money and when that backfired, you tried to make it someone else's problem.
If I was Grant and ...
I trade with the general public by occasionally selling custom made
amplifiers, re-designing and re-engineering existing amplifiers, and
repairing other amplifiers. I have placed nearly all the technical
information regarding all that I have built for anyone on line which
is freely available - including lots about active protection measures
which is the best insurance against vacuum tubes which sometimes
sustain BIAS FAILURE or sustain internal arcing within a few months/
hours of use due to bad workmanship during manufacture.
If anyone buys any Chinese made tube amplifier or other amplifier
with
Chinese made output tubes then it is FOOLISH to assume there will
never be any early trouble due to tube failures by internal arcing or
bias failure.
The chinese have yet to conform to tube manufacturing standards which
were established in the 1950s in rich wealthy western nations which
manufactured their own vacuum tubes for domestic consumption, partial
export and for national security reasons.
Now I don't say this just to embarrass the Chinese or goad them into
doing more quality control once they find out what quality control
is. I am just stating what seems obvious to me, and I am a
technician
who has often been called in to clean up the ****ing mess left by
slap
dash Chinese productions. The ameliorating factor to be considered is
that anyone who wanted to by a 211 or 845 in 1955 probably was
someone
who wanted it for a commercial transmitter or for military or
government owned body and the price in terms of a week's pay for an
average bloke was horrendous. Ordinary blokes who saved up out of
their wages for a 211 would have been Radio Amateurs who'd want a 211
for their RF finals.
Nowdays, a Chinese 211 costs around AUD $130 approximately when
average weekly wages in Oz have reached $865.00.
So the price today of a 211 is peanuts compared to the cost in 1955.
The reason the cost of the tubes is so low is the extremely low wages
earned by Chinese workers. If Chinese workers were all paid western
nation wages the price would be horrendous like Western Electric's US
made 300B, which is a much easier tube to build than a 211.
Audiophiles have come to enjoy the sonic benefits of 211 and other
high voltage tubes like 211 and KRT100 et all and they often get good
wages and pay a pittance for these tubes compared to what their
grandad paid in 1955.
Not only should they be so grateful that the Chinese slave away in
conditions and for wages they would never ever tolerate at a place of
work, but they should expect some tube failures because the workers
are under duress and often poorly trained because the brighter
chinese
are attracted to the better jobs desiging/building military hardware
to blow US satellites out of the sky if an international situation
should call fo it.
So finally I say to Charles who is full of whinges with which I can
empathise - Instal active protection measures against shorting
Chinese
tubes and you will save your transformers and you'll become tolerant
of the *"Cracker Tubes"* which are unintentionally sold from poorly
paid Chinese manufactures to us western nation big fat rich boys.
I have a 1957 book written by GE titled 'An approach to Audio
Frequency Amplifier Design, seventeen circuits from 5- to 110-watts'
In the book there are methods given for building circuits to counter
bias failure. Back in 1955 there were no solid state devices but there
were latching relays which could be turned on by current from a
saturated 12AU7 or 12AT7
triode.
But we have SCRs and bjts et all and these are dirt cheap and the
parts of a decent protection circuit including a turn on delay circuit
to prevent excessive inrush current can be purchased for less then the
price of a big hambuger with the lot, or about a 1/4 day's pay for a
Chinese worker - next to nothing.
The GE book shows a class AB amp giving 1,100W and which uses V1505
output tubes which are glass bottle tubes of 93mm dia and 344mm high
and the cost was horrendous back in 1955. The tube data is at
http://tdsl.duncanamps.com/pdf/vm086.pdf
Now the cost of a small 5VA slave transformer to power a 12AU7/12AT7
and suitable supply to work a latching relay would have been a small
fraction of the cost of one output tube. The protection costs less
today because we can make simple and reliable active protection
circuits with a few discrete solid state components.
Patrick Turner.