tubes and seasoned age

[DrWho]

I tried to find a few pictures readily available online, but these two will have to suffice:

http://www.mitedu.freeserve.co.uk/Theory/inzoz.htm

http://www.bcae1.com/outptimp.htm

If you need more info, I can probably find a way to get my course notes posted. All you're going to need is a voltmeter and a resistor of known impedance. A signal generater of some sort will be needed too, but you could get by with a test tone on a CD.

[Deang]

I posted the link earlier that explains how to do it -- below is the text from the link.

Output impedance is easy to calculate. Lets look at three types of amplifiers, single-end tubes amplifiers, push-pull tube amplifiers, and OTL amplifiers. Solid-state amplifiers are similar to OTLs.

Single-Ended
The first step is to calculate the impedances of the output devices. One 300B has a plate impedance of 700 ohms. If there were more than one tube, we simply divide the plate impedance by the number of tubes. Two 300B tubes would then have a net impedance of 350 ohms.

Next we calculate the impedance ratio between the primary and secondary windings of the output transformer. If the primary were 3000 ohms and the secondary were 8 ohms, the ratio is then 3000 ÷ 8 = 375. The output impedance is then the tube plate impedance divided by this number or 700 ÷ 375 = 2.13 ohms. Thats it! Negative feedback can be applied to reduce the impedance further.

Push-Pull
Lets use a pair of 6550s with a transformer with a 5000 ohm primary. Two 6550s in push-pull have a combined plate impedance of about 10,000 ohms in pentode mode. The transformer has an impedance ratio of 5000 ÷ 8 = 625. The output impedance is then 10,000 ÷ 625 = 16 ohms. In this case it is absolutely essential to employ negative feedback to get the output impedance down. Amplifiers of this nature typically require about 25 dB of negative feedback to get the output impedance down to 0.8 ohms. (25 dB of feedback reduces output impedance 18 times)

OTL
Lets look at the Transcendent T8 as an example. It uses 8, EL509 tubes in push-pull. Each 509 has a plate impedance of about 150 ohms. 150 ÷8 = 18.75 ohms. This is unacceptable. Negative feedback is employed to achieve proper performance. The amplifier uses 33 dB of negative feedback which reduces the output impedance to 0.4 ohm thereby achieving outstanding woofer control and the ability to drive 4 ohm speakers. This specification was verified by Stereophile when they reviewed the amplifier.

Different tubes will provide similar results. The configuration of the OTL output stage does not matter whether it is series connected push-pull or balanced. The controlling factors here are the number of output devices and the plate impedance of the devices. A 6AS7G is a dual triode with a plate impedance of 280 ohms. An amplifier that uses 8 such tubes will have an output impedance of 280 ÷ 16 = 17.5 ohms. A fourteen tube amplifier will have an output impedance of 10 ohms.

[jackpod]

output impedance is only stable with a single frequency and a resistive load. Funny I have always considered my tube gear to be smoother, more mellow, more warmer and lifelike than SS. My autoformered McIntosh has almost the same "tube" sound, not like standard SS, so there might be a correlation with impedance, but i don't see where age has anything to do with it other than maturity and wisdom

Knowledge is good, knowledge is being booksmart....

practical application and experience, it takes years to gain experience and that equals WISDOM

[HarryO]

Doc,

You're gonna make a great engineer.

HarryO

[Deang]

There's nothing wrong with trying to figure out why things sound the way they do or different from each other -- and there's certainly nothing wrong with believing that the differences can be quantified with measurements.

[DrWho]

Thanks Dean []

You get your new fancy tripath amp yet?

[NOSValves]

You're right - I'm never going to get it until someone starts posting quantifiable data instead of all these fancy descriptors subjective to psychoacoustics

========================

Amp 1

Sensitivity (volts RMS) for full rated power at

4 ohms: 1.25 V.

Frequency Response (at 1 watt) 22 Hz to

20 kHz: +0 dB, 1 dB.

Signal-to-Noise Ratio (20 Hz to 20 kHz, inputs

terminated)

A-weighted, below rated power: > 100 dB.

No weighting, below rated power: > 95 dB.

Total Harmonic Distortion (THD): < 0.5%.

Intermodulation Distortion (IMD):

(60 Hz and 7 kHz at 4:1) from full rated output

to 40 dB: < 0.3%.

Damping Factor (8 ohm) 10 Hz to 400 Hz: >200.

Crosstalk (below rated power)

at 1 kHz: 75 dB.

at 20 kHz: 59 dB.

Input Impedance (nominal): 20 kilohms balanced,

10 kilohms unbalanced.

Amp 2.

Distortion< 0.005% from 20Hz to 20kHz at rated output into 8 Ohms

IM or THD+noise< 0.007% from 20Hz to 20kHz at rated output into 4 Ohms

Noise (Measured with input shorted; 20Hz. to 20kHz.)>110dB below rated output

@ 29dB gain (-75dBu)>113dB below rated output

Slew rateGreater than 60 volts per microsecond

Power bandwidthFrom less than 1 Hz to over 100 kHz

Damping factorOver 300 at 20 Hz, ref. 8 Ohms

Input Impedance50k Ohms single-ended, 20k Ohms balanced (10k each leg)

I think Amp 2 is better than Amp 1. What do you think?

Now that is funny....

[NOSValves]

output impedance is only stable with a single frequency and a resistive load. Funny I have always considered my tube gear to be smoother, more mellow, more warmer and lifelike than SS. My autoformered McIntosh has almost the same "tube" sound, not like standard SS, so there might be a correlation with impedance, but i don't see where age has anything to do with it other than maturity and wisdom

Knowledge is good, knowledge is being booksmart....

practical application and experience, it takes years to gain experience and that equals WISDOM

Excellent!! READ THIS CAREFULLY YOUNG JEDI........

[Deang]

Funny I have always considered my tube gear to be smoother, more mellow, more warmer and lifelike than SS.

How does smoother, mellower, and warmer translate into being more "lifelike". I've heard a lot of live music in my time, both amplified and not -- and it never sounds smooth, mellow, or warm.

[DrWho]

Of course not....These are just different aesthetic philosophies one might adopt. There is no right one or wrong one.

Sometimes I wish I could put all my philosophies about music into a single sentence...I am very much one that prefers the emotional impact of the music, and could care less about the technical proficiency. Nevertheless, I think there is an important distinction to be made about the analogies you provided...

You provided analogies that involve the process of creation/expression. Music playback in our homes is supposed to be a process of reproduction. Maybe I'm nitpicking, but I think the philosophy involved arrives at slightly different conclusions.

And just for clarity, lets not confuse the art of creating equipment with the process of music reproduction.

[meagain]

Funny I have always considered my tube gear to be smoother, more mellow, more warmer and lifelike than SS.

How does smoother, mellower, and warmer translate into being more "lifelike". I've heard a lot of live music in my time, both amplified and not -- and it never sounds smooth, mellow, or warm.

This is exactly what I don't get. These types of statements (warm, mellow, smooth) are precisely that made me balk at the concept of tubes in the first place. I don't see those words as being a good thing.

[DrWho]

And just for clarity, lets not confuse the art of creating equipment with the process of music reproduction.

================

I don't confuse the two at all. "Music reproduction" occurs when a musician sits down and plays music which has been played before...

It's quite annoying when someone chooses to redefine the words of another to try and change what they were saying...

And your new definitions of music and xerox copies and all of your analogies are a bunch of [bs] Sorry to be blunt, but fancy words do not equate to wisdom.

[Cal Blacksmith]

Mark,

[DrWho]

I could sit down and contradict all your claims and point out the

shortcomings of your analogies, but I honestly believe it wouldn't

achieve anything. I would expect you to resort to using your old age as

a justification to discredit any claim I might make. The crazy thing is

I am far more aware of the limitations of my experience than any of you

lecturing old guys try to imply. And far be it for this young guy to

return the same lecture back to the old guys that pretend to know

everything about everything (but will say otherwise in their wisdom).

I must confess that it is vastly interesting to note the different

kinds of responses when I post these exact same questions in different

places. Those that know far more than myself embrace the exploration of

a young whipper snapper and usually point out any credibility in my

claims and perhaps bounce me off in slightly better directions. And

then there is the Klipsch 2-Channel forum...... Yea, I needn't say any

more - other than I just love posting here for the entertainment []

Perhaps I shouldn't have made the old people jokes? All of my old

people friends would have enjoyed the humor. I'll remember to be more

sensitive to the insecurity on the forum next time. The second you

mention 'age' or 'tubes' in the same sentence with 'possible problem'

and you've got everyone going crazy style. It's just like knocking over

an ant hill []

And what's even more crazy, and people keep glossing over me saying

this - is that sometimes a high output impedance can be a good thing!

But obviously nobody here has any clue about the cool relationships

involved because they got all crazy style defensive...and totally

missed my jokes about smiley face EQ's.

Man, the weather is nice today - I should go outside and play in my sandbox.

[BS Button]

Apart from distortion characteristics (since those have been beat to death), what are the other factors?

Slew rate.

Thanks - sounds like I've got a bit more reading to do.

No, not really Doc. Just more listening. You can't explain everything you hear, hear well or don't hear at all. Now, if you could ever just tell me what treatments I need for that "Slap Ecco" (sp) bay area. What do I need?

I'm confused - are you saying slew rate doesn't matter?

As far as that pingy slapback action - I think a few absorption type panels going along the sides of the parallel walls surrounding the couch would be a good start. Go as thick as you can (like no less than 4" if it'll fit). I'm not exactly sure what kind of aesthetics you're aiming for, but you might consider throwing a heavy curtain that wraps around back there or something crazy like that - it would probably help to cover up that window and the folded shape of the heavy curtain will do a little diffusion as well (provided it's heavy enough - none of this lace stuff...). It would probably also help to throw some stuff along that front wall too, but diffusion is probably the better route there. The absence of side walls will kinda be working to your advantage, but there's some chance that the room is coming back at the listening position all weird too (something easily verified with a few measurements). I suppose it sounds like a lot of work, but it could be done way overkill for under $500. You can work your way down from that to fit a price range and aesthetic impact that you desire.

I'll get my wife on that heavy curtain[]. I could handle the foam on the side walls. Thanks

BS

who gives a crap about slew rates?

BS

[HarryO]

I must confess I am enjoying growing older to many degrees. I've had my hearing checked lately and it passed with flying colors. I am losing some hair and no longer let it grow down to my a$$ anymore. I'm still amazed at the generosity of women. I am thankful that I listen and learn rather than mouth off and pi$$ everyone off around me. Give me a few shots of bad whiskey on top of a few beers and I have a tendency to push my point rather bluntly and show my butt though. Growing older has taught me when to shut up and when to sit down before someone knocks me down. I do have a tendency to push the limit and just start crap when I'm bored too. I don't pick on a bunch of old deaf farts when I want some action though.

Good luck in your education and find a woman to end the boredom. Cheez & rice, that kid has a lot of posts. Maybe I'd better study for my finals.

I'm bored also

HarryO

[colterphoto1]

my cats have been playing in my sandbox [:'(]

[Guest " "]

"Excellent!! READ THIS CAREFULLY YOUNG JEDI........"

He is not a Jedi yet...a Jedi understudy is called a padawan.

To become a Jedi, the padawan must face his inner-most fear....in this case...the padawan needs to get some tubes.

[BEC]

This might be a good place to post what Paul Klipsch had to say about impedance in a speaker being allowed to vary.

Bob Crites

[BEC]

Data mentioned in the last post.

Bob