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Post subject: Re: Tube Knowledge
Posted: Tue Sep 03, 2013 10:01 pm
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bluesky636 wrote:
1969spacecowboy wrote:
Sure! The question was general knowledge.... As far as 12AX7's, I've experienced various gain rates from 40% to 100%. Typically 12AX7's are the highest gain preamp tube. I've found that different company's design there 12AX7's differently, there for, one 12AX7 will function and sound different then another. And of course you could find several that function and sound the same. My experiences have taught me not all 12AX7's are created equally. I'm more of a power tube snob, but do take preamp tubes serious for they effect the power tube sound. I prefer power tube break up vs. pre amp break up. In conclusion, theory vs. reality always leaves the discussion with so many unanswered ????????'s! So, for me I'll find and dial in my own tube recipes while making great music.


Again, "gain factor" is unit-less. There is no percentage of anything related to it.


AGAIN! "The gain Factor" of a tube simply measures how much it amplifies the input signal!
This unit-less theory of yours is bogus!

For example, the common 12AX7 tube has a gain factor of 100, while a 5751 tube (which is often used in place of a 12 AX7) has a gain factor of 70. This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain. Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up.


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Post subject: Re: Tube Knowledge
Posted: Tue Sep 03, 2013 10:47 pm
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1969spacecowboy wrote:
AGAIN! "The gain Factor" of a tube simply measures how much it amplifies the input signal!
This unit-less theory of yours is bogus!

For example, the common 12AX7 tube has a gain factor of 100, while a 5751 tube (which is often used in place of a 12 AX7) has a gain factor of 70. This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain. Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up.


I suggest you do a little research into the definition of "gain factor" or "mu", because you are totally clueless as to what it represents.

And no, using lower gain tubes in an amp will not cause the power tubes to be driven harder when you turn it up to the same control setting as used with a higher gain tube. Again, do some research.

And yes, it is true that an amp will be quieter with a lower gain tube. Score one for you.

This forum is populated with people who are true experts in vacuum tube amp design. If you expect to be taken seriously here, you better know what you are talking about. So far, you do not.

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Post subject: Re: Tube Knowledge
Posted: Tue Sep 03, 2013 10:50 pm
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Dang it bluesky636, you beat me again! :lol: I had this all typed out so I'll post anyway.

I think that what bluesky636 is pointing out is that these "gain factor" numbers are not a "measure" of anything, and are meaningless except to compare to other tube types in a general way. A 12AX7 does not have a gain of 100 or anywhere near 100. The numbers used on the chart indicating gain factor are just used for comparison between tubes to get an idea of which tubes could amplify the most under ideal conditions. Once the tubes are in an amp, these numbers do not directly relate to gain at all, as the circuit, and the tube strength, determines the actual gain of the tube. Measuring various 12AX7 types on my tube tester can show that the strength can vary anywhere from 80% to 140% (still in the "good range"). But again, these numbers are basically just for comparison as they aren't any accepted standard of measure except for this particular tube tester manufacturer, but can show stronger vs weaker tubes.

Looking at the schematic for the HRDlx for example, it looks like the 12AX7s in the preamp actually have gains in the neighborhood of approximately 20 to 25, so it takes a few stages to get the very high gain.

Hint:
You can't argue with Engineers, especially when they are right. :wink:

bluesky636 wrote:
...using lower gain tubes in an amp will not cause the power tubes to be driven harder when you turn it up to the same control setting as used with a higher gain tube...


+1

Lower gain preamp tubes will drive the power tubes less than higher gain preamp tubes. It seems simple, and I'm not sure why this is misunderstood so much.

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Post subject: Re: Tube Knowledge
Posted: Tue Sep 03, 2013 11:14 pm
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shimmilou wrote:
Dang it bluesky636, you beat me again! :lol: I had this all typed out so I'll post anyway.

I think that what bluesky636 is pointing out is that these "gain factor" numbers are not a "measure" of anything, and are meaningless except to compare to other tube types in a general way. A 12AX7 does not have a gain of 100 or anywhere near 100. The numbers used on the chart indicating gain factor are just used for comparison between tubes to get an idea of which tubes could amplify the most under ideal conditions. Once the tubes are in an amp, these numbers do not directly relate to gain at all, as the circuit, and the tube strength, determines the actual gain of the tube. Measuring various 12AX7 types on my tube tester can show that the strength can vary anywhere from 80% to 140% (still in the "good range"). But again, these numbers are basically just for comparison as they aren't any accepted standard of measure except for this particular tube tester manufacturer, but can show stronger vs weaker tubes.

Looking at the schematic for the HRDlx for example, it looks like the 12AX7s in the preamp actually have gains in the neighborhood of approximately 20 to 25, so it takes a few stages to get the very high gain.

Hint:
You can't argue with Engineers, especially when they are right. :wink:

bluesky636 wrote:
...using lower gain tubes in an amp will not cause the power tubes to be driven harder when you turn it up to the same control setting as used with a higher gain tube...


+1

Lower gain preamp tubes will drive the power tubes less than higher gain preamp tubes. It seems simple, and I'm not sure why this is misunderstood so much.


Actually, the first and second gain stages of the HRD (V1A and V1B) each have unloaded voltage gains of about 62 (36 dB) since they are both have fully bypassed cathode resistor. No "percent", just "62". Their gains would be about 32 (30 dB) if the cathodes were not fully bypassed.

For some strange reason, people seem to think that if they turn a low gain preamp stage up higher, they are driving the power tubes harder. If it take 10 volts to drive a power stage to full power with a 12AX7, it still takes 10 volts to drive the power stage to full power with a 5751 (or 12AT7, 12AY7, ....). You have to turn the lower gain stage up more to get that 10 volts, but it still takes 10 volts.

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Post subject: Re: Tube Knowledge
Posted: Tue Sep 03, 2013 11:57 pm
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Yeah, I have heard the bogus claim before that the lower gain tubes drive the output tubes harder......strange. :roll:

As for the gain stages in the HRDlx, I just went by the TP voltage in at the grid vs the TP voltage out at the Plate. I can calculate the gain for an op-amp circuit, but for a tube circuit I have to measure. :oops:

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Post subject: Re: Tube Knowledge
Posted: Wed Sep 04, 2013 12:16 am
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" For example, the common 12AX7 tube has a gain factor of 100, while a 5751 tube (which is often used in place of a 12 AX7) has a gain factor of 70. This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain. Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up. "


1969spacecowboy, I think you are still thinking of the mu-factor as the most important part of a gain stage. It's a factor. But, not the only one. Mu-factor is calculated with the tube alone, not in situ. You can design a gain stage that can swing the most demanding tubes (like a 6550 or 7027A) with lower mu-factor tubes. You just need more of them. Many amps use 6SN7 or 5687 stages to push big output tubes.

More important is subbing various tubes into an amp effect things downstream. In other words the whole thing is much more complex than simple tube changes.


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Post subject: Re: Tube Knowledge
Posted: Wed Sep 04, 2013 12:48 am
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shimmilou wrote:
Yeah, I have heard the bogus claim before that the lower gain tubes drive the output tubes harder......strange. :roll:

As for the gain stages in the HRDlx, I just went by the TP voltage in at the grid vs the TP voltage out at the Plate. I can calculate the gain for an op-amp circuit, but for a tube circuit I have to measure. :oops:


Gives you loaded voltage gain:

http://ampbooks.com/home/amplifier-calc ... capacitor/

Gives you unloaded voltage gain:

http://ampbooks.com/home/amplifier-calc ... impedance/

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Post subject: Re: Tube Knowledge
Posted: Wed Sep 04, 2013 6:29 am
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bluesky636 wrote:
1969spacecowboy wrote:
AGAIN! "The gain Factor" of a tube simply measures how much it amplifies the input signal!
This unit-less theory of yours is bogus!

For example, the common 12AX7 tube has a gain factor of 100, while a 5751 tube (which is often used in place of a 12 AX7) has a gain factor of 70. This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain. Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up.


I suggest you do a little research into the definition of "gain factor" or "mu", because you are totally clueless as to what it represents.

And no, using lower gain tubes in an amp will not cause the power tubes to be driven harder when you turn it up to the same control setting as used with a higher gain tube. Again, do some research.

And yes, it is true that an amp will be quieter with a lower gain tube. Score one for you.

This forum is populated with people who are true experts in vacuum tube amp design. If you expect to be taken seriously here, you better know what you are talking about. So far, you do not.


Thanks for the advice, but I didn't know this forum was for experts in vacuum tube design. What I mean is, "How many amp builders does it take to build and understand a great amp?" Answer! One and a room full of other amp builders to tell him how to build and understand it!

No pun taken though!

Maybe you could explain to the world how preamp tubes work and what their purpose is.
Have you watched or studied Randall Smiths studies just on preamps? Do you know anything about multi gain staging in a pre amp? Are you familiar with Randall Smiths designs? How about Mike Zaite designs?


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Post subject: Re: Tube Knowledge
Posted: Wed Sep 04, 2013 7:21 am
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1969spacecowboy wrote:
bluesky636 wrote:
1969spacecowboy wrote:
AGAIN! "The gain Factor" of a tube simply measures how much it amplifies the input signal!
This unit-less theory of yours is bogus!

For example, the common 12AX7 tube has a gain factor of 100, while a 5751 tube (which is often used in place of a 12 AX7) has a gain factor of 70. This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain. Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up.


I suggest you do a little research into the definition of "gain factor" or "mu", because you are totally clueless as to what it represents.

And no, using lower gain tubes in an amp will not cause the power tubes to be driven harder when you turn it up to the same control setting as used with a higher gain tube. Again, do some research.

And yes, it is true that an amp will be quieter with a lower gain tube. Score one for you.

This forum is populated with people who are true experts in vacuum tube amp design. If you expect to be taken seriously here, you better know what you are talking about. So far, you do not.


Thanks for the advice, but I didn't know this forum was for experts in vacuum tube design. What I mean is, "How many amp builders does it take to build and understand a great amp?" Answer! One and a room full of other amp builders to tell him how to build and understand it!

No pun taken though!

Maybe you could explain to the world how preamp tubes work and what their purpose is.
Have you watched or studied Randall Smiths studies just on preamps? Do you know anything about multi gain staging in a pre amp? Are you familiar with Randall Smiths designs? How about Mike Zaite designs?


I hold a degree in electrical engineering earned back when tubes were part of the curriculum. I design and build amps as a hobby. Others who have contributed to this thread, design, build, and repair amps as a profession. We know what we are talking about and gladly explain things to people who are interested in learning.

To answer your last four questions: Yes; yes; yes; and yes.

As the saying goes, in a battle of wits, I refuse to fight with an unarmed person. You continuue to prove your lack of understanding on this subject and your unwillingness to listen to what others are telling you. Welcome to my ignore list. Buh-bye.

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Post subject: Re: Tube Knowledge
Posted: Wed Sep 04, 2013 8:28 am
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Stunning entry into the forum, Maurice.

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Post subject: Re: Tube Knowledge
Posted: Wed Sep 04, 2013 9:34 am
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Ok, this link KINDA explains how voltage, bias, plate load parameters affect a triode gain stage. Remember, these examples do not include global feedback constraints.

Ready to polish up the old math? :lol:

http://www.tpub.com/neets/book6/20k.htm


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Post subject: Re: Tube Knowledge
Posted: Wed Sep 04, 2013 9:54 am
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BMW2002Ti wrote:
Ready to polish up the old math?


Whew!

:shock:

Glad I still have my old TI engineering calculator!

:lol:

Arjay

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Post subject: Re: Tube Knowledge
Posted: Fri Sep 06, 2013 7:04 am
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shimmilou wrote:
Yeah, I have heard the bogus claim before that the lower gain tubes drive the output tubes harder......strange. :roll:

As for the gain stages in the HRDlx, I just went by the TP voltage in at the grid vs the TP voltage out at the Plate. I can calculate the gain for an op-amp circuit, but for a tube circuit I have to measure. :oops:


And you beat me to it also,because I was going to ask how in the world could you drive power tubes harder with lower gain preamp tubes? I don't see how that is possible! :?: I find reading about electronics,...especially when you're dealing with tubes,...very interesting
whether you're dealing with guitar amps,or amateur radio gear. So much to learn about both ham radio and tube guitar amps,...and it's a LOT of fun. I'm beginning to get a better understanding of how tube amps operate,tube characteristics,etc. just from this site,my radio related books,and a two of my books on tube amps. Only book I don't have and need is an RCA Receiving Tube Manual! :) BTW,...where can a get a schematic for my HRD III amp? I'm curious to learn more about how that baby operates by tracing the signal path,etc.

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Post subject: Re: Tube Knowledge
Posted: Fri Sep 06, 2013 8:02 am
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KC9SYJ wrote:
BTW,...where can a get a schematic for my HRD III amp? I'm curious to learn more about how that baby operates by tracing the signal path,etc.


Fender website > Support > Amplifier Schematics > Hot Rod Deluxe III Schematic

http://support.fender.com/schematics/gu ... _Rev-B.pdf

Amazing, eh? :wink: :D

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Post subject: Re: Tube Knowledge
Posted: Fri Sep 06, 2013 9:17 am
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bluesky636 wrote:
KC9SYJ wrote:
BTW,...where can a get a schematic for my HRD III amp? I'm curious to learn more about how that baby operates by tracing the signal path,etc.


Fender website > Support > Amplifier Schematics > Hot Rod Deluxe III Schematic

http://support.fender.com/schematics/gu ... _Rev-B.pdf

Amazing, eh? :wink: :D


Thanks,Bill,...I'll be checking that out! :)

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