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Old 11-22-2010, 07:12 AM   #101
Cathbard
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Quote:
Originally Posted by Kanthras
I was not ever this stupid, you silly troll.
Perhaps a touch antagonistic, but hey, I learned to take the chill pill every now and then.

And I really hope you're not speaking of the whole "talkback debacle". I'm not getting into it, but I still think it's a stupid term.

I really don't know what's so stupid about it. It's just a description of dynamics that describes a behaviour in relation to the player in a poetic way. You're not into poetry maybe? I think it paints a perfect picture of what is happening in artistic terms which is better than trying to describe it in a clynical fashion. Why not use an artistic description for an artistic phenomenon?
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Old 11-22-2010, 07:35 AM   #102
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Originally Posted by farmosh203
The supply voltage of the active electronics doesn't matter unless the signal is coming close to the positive rail of the power supply. The only reason to increase the voltage supply of an amplifier would be to prevent the signal from clipping if it was coming close. The gain is set by the feedback resistors, not the voltage supply.


My mistake, I intended to say increase the headroom.

But this begs the question of why you were wondering about the purpose of the 18v mod if you understood it in the first place.
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Old 11-22-2010, 07:54 AM   #103
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I had to call in sick at work today from the headache this thread gave me, reading it as I did over my morning coffee.
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Old 11-22-2010, 09:39 AM   #104
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Quote:
Originally Posted by Cathbard
I really don't know what's so stupid about it. It's just a description of dynamics that describes a behaviour in relation to the player in a poetic way. You're not into poetry maybe? I think it paints a perfect picture of what is happening in artistic terms which is better than trying to describe it in a clynical fashion. Why not use an artistic description for an artistic phenomenon?
I guess I'm not too big on poetry. But when you put it that way, I can see how it's a good term to describe talkback. Perhaps it is appropriate that something subjective is described by a vague term.
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I had to call in sick at work today from the headache this thread gave me, reading it as I did over my morning coffee.
I can imagine.
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Old 11-22-2010, 10:42 AM   #105
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Originally Posted by farmosh203
My whole point of this thread was that an amplifier is more of an impedance matching device rather than amplifying the signal by a lot.


I disagree. There is impedance matching that goes on, obviously, but you can't say it's "more" for that when it does, indeed, amplify by so much.
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Old 11-22-2010, 10:50 AM   #106
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This is this thread.
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one of the best, educated and logical posts I've ever seen on UG in the Pit. Well done good sir.
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Old 11-22-2010, 12:00 PM   #107
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Originally Posted by farmosh203
....So if you're driving an 8 ohm speaker at 30Vrms, your output power is 112.5Watts.

Assuming 100% efficiency in the power supply, your current coming from the wall would be 120*current = 112.5Watts, which would mean your input current is 112.5W/120V = 0.9375Amps.

What was the current at the output? Well 112.5W / 300V = 0.375Amps.

Can we all agree on this?
No. The output current is 30/8.
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Old 11-22-2010, 12:38 PM   #108
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i knew this was going to deliver.
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Old 11-22-2010, 12:40 PM   #109
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This thread is win. Even if it didn't set out to be.

Also: If that's the case, then I need a warmer output transformer.
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Old 11-22-2010, 12:47 PM   #110
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Tube amps are not supposed to be warm... Wait...
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Old 11-22-2010, 02:09 PM   #111
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no. the end.
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Old 11-22-2010, 02:33 PM   #112
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One of the most confusing albeit amazing threads ever
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Old 11-22-2010, 11:10 PM   #113
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Quote:
Originally Posted by Wesbanez
I had to call in sick at work today from the headache this thread gave me, reading it as I did over my morning coffee.



+1

But seriously, it's not how big your transformer is....it's how you ....wait...ok.... I'm not going to lie to you.
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Old 11-23-2010, 12:12 AM   #114
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Quote:
Originally Posted by farmosh203
The inside of a tube is an open air gap, right?


no, not free air. free space. a vacuum would be the optimal environment. but close to a vacuum

something simple like a diode would have an anode at one end and a cathode at the other (like your FETS). the cathode would consist of a piece of filament with a coating (called a emulsifier). the idea is to run a current through the fillament (thus heating it) until the emulsifier reaches a 'saturation' temperature and is induced into thermionic emmision.

thermionic emmision is an excess 'cloud' of electrons being emitted from a material. without thermionic emission there wouldn't be enough electrons for sufficient operation.

the anode would then be a relatively positively charged plate that will attract the excess electrons surrounding the cathode. with a simple anode/cathode vacuum tube you can implement a diode. you can rectify AC current with those.

but suppose you wanna great tricky. apply a large direct current to the cathode filament to induce a flow of electrons to the anode plate, but place a 'screen' or 'grid' between the anode and cathode and apply an A/C signal to the 'grid' and you can attract some of the current going from cathode to anode (and thus effective control current flow). that is a basic description of a simple triode (equivalent to your transistors and FETs in ways).

larger vacuum tubes (tetrodes and pentodes) just use optimal distances, more heat resistant materials and extra screens/grids to focus the electron beams.

Quote:
Originally Posted by farmosh203
So you aren't going to get much current (if at all?).


thermionic emission is the key. but tubes are horribly inefficient anyway. the plate voltage are enormous vs. FET's/opamps/transistors.

Quote:
Originally Posted by farmosh203
That's the whole reason you need the output transformer, because the tube can't drive enough current through the speaker.


i thought you needed a transformer because a tube's output impedance was so high that it needed to be 'stepped down' to drive low impedance devices like speakers.

i heard FET's and transistors output impedances were so low you can just run an appropriately large load instead of an output transformer.

this may correlate to what you say, but i am not good enough at electronics to tell.
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Last edited by gumbilicious : 11-23-2010 at 12:15 AM.
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Old 11-23-2010, 01:09 AM   #115
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Quote:
No. The output current is 30/8.


Woops, haha... now why would I use the +rail to find output current? My bad.

Quote:
i thought you needed a transformer because a tube's output impedance was so high that it needed to be 'stepped down' to drive low impedance devices like speakers.


Yup that's correct, but that's the same thing as saying that the tube can't drive enough current through the speaker. It's just a voltage divider where you have Vout = Vin*[Rspeaker]/(Rspeaker+Rsource). A high Rsource means your voltage at the output is low, so you have low current.
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Old 11-23-2010, 01:16 AM   #116
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Quote:
Originally Posted by farmosh203
Woops, haha... now why would I use the +rail to find output current? My bad.



Yup that's correct, but that's the same thing as saying that the tube can't drive enough current through the speaker. It's just a voltage divider where you have Vout = Vin*[Rspeaker]/(Rspeaker+Rsource). A high Rsource means your voltage at the output is low, so you have low current.


well if that is the case, then the reason for such a high Rsource would be the extreme conditions that are a vacuum tubes operational environment. there was no secret they were highly inefficient. they were almost better at radiating heat than they were at amplifying.

speakers are also inefficient, but we still use em anyway.
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Old 11-23-2010, 01:19 AM   #117
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Woops, instead of "Rsource", I should have used the variable "Rout", don't grill me! Ok, I'm done with this thread
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Old 02-04-2013, 11:29 AM   #118
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Here's something we're working on

http://milbert.com/tubes_vs_transformers
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Old 02-04-2013, 11:43 AM   #119
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and regarding this

"I just measured the output of my pedal (the stage going into my amplifier) and it's definitely above 4V peak to peak. Sort of having trouble plucking the note, then quickly grabbing the probes on my oscilloscope to measure the signal though." from page 1 of this thread

there's this

Tubes vs Transistors
http://milbert.com/Files/articles/TvsT/tstxt.pdf
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Old 02-04-2013, 01:25 PM   #120
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This thread isn't any less dumb two years later.
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