Re: Maybe I am just being unbiased...



DH82C wrote:

On Mar 31, 10:20 am, J.P. <jpas...@xxxxxxxxxxx> wrote:
On Mon, 31 Mar 2008 04:36:40 -0500, Rich Koerner <ri...@xxxxxxxxxxxxx>
wrote:







DH82C wrote:

Ok.. more bias questions.
When I was young and impressionable I read the "right" way to bias a
pushpull amp was to use a signal generator and an oscilloscope. Look
for crossover distortion, the most negative grid voltage that didnt
have crossover distortion was the ideal. You could run with less neg
voltage on the grids if you liked the tone but at the expense of tube
life. But that was many many moons ago before Al Gore invented the
internet. Now I see there are more than one way to skin a cat than
just fu*ing it to death.

Question: Does anyone actually use an oscilloscope to bias their amps

Every day.

The only way to SEE what those free electrons are doing is to use a scope.

The scope is the single most important piece of test gear you could have on the workbench.

or do you all use Bias probe/1ohm cathode resistors/

Oh, you mean the paint by numbers method?

Where'd that number come from for the tube that really sit in the amp in front of you?

Some web site with the clairvoyance to tell everyone that... that their *one* number also fits YOUR
tube exactly.

BS!

Shunt Method ?

Never use it.

I am thkinking of buying an oscilloscope (used 150$)
1 Ohm resistors are .50$ ea. (i.e. much cheaper than a silly scope)
Shunt method is free (I have a decent DMM already)

I would love to know what y"all think.

You are blind without a scope.

You are blind without a scope playing the numbers game on one ohm resistors.

You are blind setting output tube bias, when you have no awareness of it's effect on the dynamic
energy flow to the load.

The only bias method mentioned in this thread that addresses the individual tube sitting in front of
you
is the DARKROOM METHOD. Which tells only of the individual tube's current limit. The method is
incomplete as a stand alone bias method. It's just another quick bias method's shot in the dark.

Without the observation of the dynamic transfer of electrical energy though the amplifier to the
load, you are in the darkroom with your bias setting toys.

Dynamic operation comparisons of different output tubes are not possible with the limited
information these bias methods require.

So, as long as a single idle adjustment gets the motor to run, you can get to the store and back.

But, if you want to take it out on the highway..... well?

Now, look at that amplifier, and think about stepping down on it's gas pedal as you are about to hit
highway Rt. #66 with your foot on the floor.

It is unreasonable to think that a single bias adjustment, and/or bias method... will unify all the
variables between the current crop polished turds for tubes, and make any one of them INDIVIDUALIZED
for YOUR amplifier's *maximum* performance.

Your amp's performance level can only be as good as the tubes put in it, and the man who knows how
to get the most out of them.

Regards,

Rich Koerner,
Time Electronics.
http://www.timeelect.com

Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers

How come some people are running from oscilloscopes? They are really a
neat piece of test equipment. And is a BIG part of bench test
equipment. They do look daunting with all of those knobs but the "How
to use a Scope" DVD explains it very well. And a few questions on the
scope Yahoo groups and here can direct you to what to get so you are
not wasting $$.


I have not seen that DVD, but would guess it's a good thing to have for better understanding scope
applications.

An old vacuum tube Tektronix of HP scope is great for the beginner exploring vacuum tube land.

It's hard to snap out the front end input circuits of vacuum tube scopes.

The more modern scopes of today have a lower input voltage rating, and require high voltage probes
to protect their inputs.

A little more caution is required.


As far as spending $$...if you cannot find the $$ for a scope then
you likely don't need to pursue electronics as a career..maybe a
hobby. But, if a $250 scope helps save a set of $250 tubes, then the
money is well spent. And being able to see the waves comping from your
amp stages is an educating experience also.- Hide quoted text -

- Show quoted text -

I am not looking for a career in electronics. I do enjoy tweaking and
restoring my amps tho.
Rich and JPs comments pretty much sold me one getting one (but not
necessarily for biasing).

Good man.


I have been thumbing my books at home and the one that seemed most
comprehensive was the
book by (Dan?) Torres. He shoots down the oscillocope method by saying
you are putting the amp in
an atypical state (1KHz sine wave with the amps volume turned short of
clipping and into a dummy load)
and expecting it to perfom the same way when you have a reactiv load
(speaker) and and a
signal source that produces a range of frequencys at the same time.I
am not knowledgable enough
yet to agree or disagree.


As you learn more of the basic characteristics of DC and AC circuits, the better your understanding
becomes with the test gear to verify the text book circuit theory. There is the theory classroom,
and the laboratory to verify the theory you studied.

It's never ending, and fun for the right individuals.

Think of it a visiting the universe of sub particles of the physical world around you.

You don't have to be a musician to get into that mini universe that exists.



I get the impression that biasing isnt exact anyway. Tubes are never
perfectly matched.
Static dissapation (?) can vary as components heat up. As long as the
tube
is running hot enough to not have any crossover distortion (for push
pull amp for example) but not so hot to
fry the tubes you are fine. Someone once said "Let your ears be the
judge" (I have to work on that too lol)

As you go along, you will gain an understanding of what is going on in your amp, and will become
aware of the "absolutes" and "variables" that exists in your amplifier's circuits. You will begin
to SEE the bigger picture of the dynamic characteristics that are involved.

You WILL come to discover that, what you thought before.. isn't, there are really "absolutes" in the
equation... where you thought there was none, and the devil is always found looking you right in the
eye.... most often deep in the details of the "variables".

This is true of any issue that has appeared with great controversy here in AGA.

You will come to SEE and understand the world of vacuum tube Polished Turds as I do, and come to
find the work-arounds that others can't see.

You'll SEE right through the BS.

And,... it will freak you out, because other fail to SEE what you see, and follow blindly.

When this happens to you, you are on your way to becoming the real deal.

Just remember one thing. The same rule applies in both the theory classroom and the electronics
laboratory.


Always measure with respect to ground, and always keep one hand in your pocket when standing in
front of the blackboard with the chalk in the other hand.


Does that make sense?

LOL,... sometimes I don't make sense to me, and that is a sign of a lost ground in thinking.

Imagine, if you took that other hand out of your pocket while thinking.

Now, you're in deep ***, in your thinking on NOW.... more than one subject.

Remember, always keep one hand in your pocket, and resolve one issue at a time.

Keep your mental focus.


Thanks for your comments Rich, I have seen you
often in the forums and find your
posts enlightening.

Thanks, for the kind words.

I know I can be a little difficult to understand at times, and have been told I'm not wired like
most people.

I just try hard doing my thing.

You just do the same thing, have fun, explore the world around you, fu_k the BS, and those selling
it.



Regards,

Rich Koerner,
Time Electronics.
http://www.timeelect.com

Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers
.