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Old 19th May 2008, 11:42 PM   #1
nhuwar is online now nhuwar  United States
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Default tube voltage regulator error amp

What kind of mu do you need for an error amp in a tube voltage regulator. Is anything over 100 good?

Thanks,
Nick
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Old 19th May 2008, 11:48 PM   #2
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Pentodes are ideal here. The higher the amplification, the better. Take a look at some of the regulators that Tek used to use.
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Old 19th May 2008, 11:52 PM   #3
nhuwar is online now nhuwar  United States
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Is a triode with a mu of 100 good, my problem is the voltage around 1 to 1.5 kv.

I have found a few triodes that will do this but no pentodes so far.

How do you compare the amp factor of a pentode to a triode, if it's even listed for the pentode.
All the ones I have looked at to are very low like a mu of 6 to 10 for pentodes.


I will take a look at some old Tek schematics but if memory serves they did some funky stuff with the high voltage or nothing at all.

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Nick
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Old 20th May 2008, 01:22 AM   #4
nhuwar is online now nhuwar  United States
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SY I looked at a few TEK tube scope schematic for reference as you said.

Out of the 2 I looked at all the error amp tubes were 6au6's and it's mu is 36.


The question I have is can I use a triode for this application if it has a high mu say 100 or 150?




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Nick
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Old 20th May 2008, 01:52 AM   #5
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Quote:
Originally posted by nhuwar
How do you compare the amp factor of a pentode to a triode, if it's even listed for the pentode.
u= gm X rp for all devices

Example: 6CB6:

rp= 280K
gm= 8.0mA/V

u= (280E3)(8E-3)= 2240

They don't list it for pents or solid state since it's not very useful for anything but triodes since only triodes exhibit significant Ip change with varying Vpk. Calculations for devices other than triodes use gm. (You can also use gm with triodes as well, if you so desired.)


Quote:
All the ones I have looked at to are very low like a mu of 6 to 10 for pentodes.
That would be for trioded operation (screen in parallel with plate). For most pentodes, u should be several hundred to several thousand.
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Old 20th May 2008, 02:12 AM   #6
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Quote:
Originally posted by nhuwar


The question I have is can I use a triode for this application if it has a high mu say 100 or 150?
Yes you can. The old Kepco tube supplies did it all the time. Actually they used a dual triode (12AX7) in differential mode with one side as the reference and the other as the error amp.

Victor
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Old 20th May 2008, 04:39 AM   #7
SY is offline SY  United States
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nhuwar, a 6AU6 will give a gain MUCH higher than 36, since they use it as a pentode, not a triode. At 4-5mA/V transconductance, a 100k plate load resistor will give a gain of 400-500.
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Old 20th May 2008, 06:19 AM   #8
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A tube super regulator can be found here Mr. Bob Pease has dig up something from the stone age.
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Old 20th May 2008, 06:20 AM   #9
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Hi,

6CB6A's are great for this. Can be had really cheap too.

Here's a decent performing reg using a high-mu triode/pentode:
http://geek.scorpiorising.ca/GeeK_Zo...p?topic=3665.0

Steve Bench has great examples too.

Cheers!
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Old 20th May 2008, 06:39 AM   #10
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Keep in mind the stability of the closed loop system.... You need to calculate the compensation values to maintain a safe and stable loop.... You can plot your POLES and ZEROS on a BODE plot if you prefer graphical representation....
The objective is stay above 60 degrees of Phase Margin at your cross-over frequency... and better than 15 degrees of Gain Margin..

Chris
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