Re: Does the power supply limit the actual power of a tube amp?
- From: Rich Koerner <richk@xxxxxxxxxxxxx>
- Date: Tue, 22 Aug 2006 15:46:46 -0400
<original post>
Okay, I've read a bunch of different stuff on this, and it's clear as
mud to me.
Imagine I have a Fender Deluxe Reverb. Now, for grins, imagine I had
pie in the sky amounts of filament current available.
I yank my 6V6 tubes, and toss in some 6L6GC. I rebias the amp (perhaps
yucking with my bias circuit range first).
Now, my common sense tells me I just went about frying my output
transformer. However, Kevin O'Connor, and a few others is telling me:
"You are still only going to get 20 watts out of that pair of tubes...
it's restricted by the load and supply current."
Kevin goes so far in TUT3 to show a Plexi amp that can get the sound of
either a 50 or 100, by using all 4 or only 2 tube sockets, but says the
amp will only ever REALLY produce 50 watts. Assuming I understand why
(and my guess is that the load of the OT primary and the supply current
renders this maximum).
My head is aching... so, can anybody explain this phenomena in detail,
and perhaps apply it to a couple of known amps, like that fender DR?
Thanks!
First, stop looking for the quick detailed answers for general questions.
Detailed questions makes for detailed answers.
ciscochrist@xxxxxxxxx wrote:
I knew the filament current had nothing to do with it, which is why I
labeled it as infinite, so I wouldn't get red herring replies about
"Don't do that, you'll blow your power transformer."
Like those who write books on a general subject, the devil in the details, is usually left out.
Your statement above would be true if, the devil was not in the left out details.
Here's why,......
ALL current from the power transformer's collective secondary windings, MUST be supported by the
COMMON transformer core. Any increase in current draw from ANY one of the secondaries, WILL effect
the other secondaries, due to the way the common core functions.
The secondaries are NOT totally independent of each other. Nor, can they be thought so, when the
secondaries are connected to the common/shared transformer magnetic core.
Since it is true, as O'Connor had stated,
Just because something is found in a book, does not mean it is correct.
I'd trust more in the RCA Radiotron Designers Handbook.
http://www.ermag.com/index.cfm?v_link=product_detail&v_key=92
what I am still hoping for is
the formula that shows the output power of the amplifier, regardless of
tubes.
You can find that for a unit under test on the test load easy enough.
But, if you want "one" equation to predict the output of an amplifier without detailed information,
grab the Magic 8 Ball for your answer.
Example - a hypothetical power transformer can deliver 200ma of B+. So,
At what voltage.
what is the limit in output watts, of this power transformer?
What tubes are being use.
What are their exact operating characteristics.
This is some of the missing details, required to give a fair answer.
<thinking>
It's not that simple.
Amp techs who do not monitor TOTAL line current most often have no idea what actually flows through
the power transformer of what sits on their bench.
The total picture is never seen.
What you ask for escapes the understanding of most, and is not something a few pages of typing in a
newsgroup would satisfy in complete detail.
What you, and everyone else wants is a fast simple "paint by numbers" answers, to avoid the real
labor to detailed understanding of what is before you.
And then, last, but most importantly - if these tubes are biased
correctly, then what behavior do they exhibit, when they cannot draw
enough current to play full output potential?
When the current limit hits, they will clip.
But, at what level.
That,..... REQUIRES the UNDERSTANDING of the DETAILS that are *MISSING* in YOUR equation.
Regards,
Rich Koerner,
Time Electronics.
http://www.timeelect.com
Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers
.
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