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Old 30th December 2012, 03:57 PM   #11
Ketje is offline Ketje  Belgium
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Quote:
Originally Posted by denny9167 View Post
So I should probably stick with the transistor,and only use half of the 12AT7,and use separate windings? I won't need to worry about lifting my heaters either?
Yes you can do that,or use any other triode with 5mA/V (more or less).
The heaters can be left floating but some prefer connecting them to the cathode.
Don't forget,you need a neg.tension (stable) as a reference voltage.
The neg.out in the original is wrong,is connected to the base of the transistor,has to be the emitter.
Mona
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Old 30th December 2012, 05:29 PM   #12
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I don't really need the negative bias supply, as I will
Be just using this for a general bench power supply.
I could go ahead and add it for testing power amp curcuits using fixed bias.
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Old 31st December 2012, 12:44 AM   #13
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I think I've decided to go a different route,I found an article in AudioXpress on regulated supplies and found one that's a better performer,and has been tested. I've re-drawn the schematic for expresspcb. The author didn't mention lifting the heater on the pass tube,so I will do that if it's needed.
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Old 31st December 2012, 03:40 AM   #14
tomchr is offline tomchr  United States
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In the original schematic, it looks like V2 (EC92) is supposed to work as the error amplifier. However, it doesn't have any voltage reference and will always operate with a positive Vgk. Not what you want...

The 0~-70 V output isn't regulated either. I honestly don't see the point of the emitter follower T2. Why would you take the supply output off the base but run the meter off of the lower impedance emitter?

There are better ways to build tube power supplies. Have a look at Designing Power Supplies for Tube Amplifiers by Blencowe for example.

You can also look at this thread: High Voltage Regulators (Maida or zener)
I went through quite a few regulator topologies before landing on the two I have on my website.

For a variable supply, I use a high-voltage transformer fed from a variac. Works great. No thermals to worry about. No regulation either, but good enough for most experiments.

~Tom
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Last edited by tomchr; 31st December 2012 at 03:45 AM.
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Old 31st December 2012, 03:51 AM   #15
tomchr is offline tomchr  United States
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Sorry... Didn't see Post #13 until I after I'd written my post above.

Quote:
Originally Posted by denny9167 View Post
I think I've decided to go a different route,I found an article in AudioXpress on regulated supplies and found one that's a better performer,and has been tested.
With the dual differential pair, it's a very "semiconductor" approach to a tube regulator. I don't see any reason it shouldn't work, though.

Quote:
Originally Posted by denny9167 View Post
I've re-drawn the schematic for expresspcb. The author didn't mention lifting the heater on the pass tube,so I will do that if it's needed.
You'll need to check the data sheet for your pass tube of choice to figure that out. You'll have to select a voltage that ensures the pass tube doesn't have its Vhk violated at any output voltage.

~Tom
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Old 31st December 2012, 07:54 AM   #16
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To use the 12AT7 at 6.3V you need to connect Pins 4&5, not 4&9. In your schematic half of the heater is shorted.
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Old 31st December 2012, 11:34 AM   #17
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Originally Posted by grommeteer View Post
To use the 12AT7 at 6.3V you need to connect Pins 4&5, not 4&9. In your schematic half of the heater is shorted.
I've worked on several Dynaco Fm3's and it has a mixture of
6 and 12volt tubes, this is I believe a parallel connection.
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Old 31st December 2012, 11:43 AM   #18
SY is offline SY  United States
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Pin 4 and 5 short together, 6V between 4/5 and pin 9.
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Old 31st December 2012, 11:46 AM   #19
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Quote:
Originally Posted by tomchr View Post
In the original schematic, it looks like V2 (EC92) is supposed to work as the error amplifier. However, it doesn't have any voltage reference and will always operate with a positive Vgk. Not what you want...

The 0~-70 V output isn't regulated either. I honestly don't see the point of the emitter follower T2. Why would you take the supply output off the base but run the meter off of the lower impedance emitter?

There are better ways to build tube power supplies. Have a look at Designing Power Supplies for Tube Amplifiers by Blencowe for example.

You can also look at this thread: High Voltage Regulators (Maida or zener)
I went through quite a few regulator topologies before landing on the two I have on my website.

For a variable supply, I use a high-voltage transformer fed from a variac. Works great. No thermals to worry about. No regulation either, but good enough for most experiments.

~Tom
Thanks for the suggestions, I'm glad you mentioned the book, I bought that
Book a few months back for my iBooks app, I haven't finished it yet
But it is a marvelously well written book, as soon as I get my new iPad I will try and finish it, it's hard to read on an iPhone!! I also have Morgan Jones' book.
On Kindle that is an in depth read.
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Old 31st December 2012, 11:53 AM   #20
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In the later schematic it says 6V3 heater for both double triodes and the tubes are in parallel. That's ok. But connecting pin 4&9 on each tube is not ok. Pins 4&5 connected together are one pole of the 6V3 heater, pin9 is the other.
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