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Old 26th February 2010, 12:27 PM   #1
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Default Regulated tubelab SE

So, my tubelab SE is almost completed. I installed the Hasimoto OPT. I don't think I have gifted hears, but there is a big difference compared to the James.

I'll post a picture as soon as I get the covering plate (It has a funny cabinet :-) )

Going to business, I am using a separate power supply, feeding the amp with B+ , B- and AC 6.3V.
At the moment nothing is special in the unregulated PSU, just using good component.
I would like to try to put the Salas shunt regulator in the middle, and see what will happen. I wanted to do it with the 300B, but maybe I'll try first with the 45.

I drafted current and voltage requirements, and I would like to know if you think they are correct:

300B
400V (Could be a bit less)
190mA Idle 250 mA peak

45
275V
90mA idle
140 mA peak.

George, I remember a post where you were speaking about the benefit of regulated DC. Did you try this ?


Thanks,

Davide
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Old 27th February 2010, 10:51 AM   #2
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By the way, forgot to say, this machine is unbelievable. I don't have big expedience, but I love the sound, different planet compared to KT88.

Can't wait to try the 45.

D.
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Old 2nd March 2010, 03:11 AM   #3
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Davide,

I design and develop all of my amplifiers using lab type regulated power supplies, including the Tubelab SE. After the amplifier is working to my satisfaction, I try to design a power supply to result in similar performance. It is difficult to design a non regulated power supply with the same performance as a fully regulated power supply, so some compromises are usually involved.

In order to create a power supply for the Tubelab SE that works better than the on board uint some considerable complexity will be involved. In order to stabilize the output tubes, if the B+ is regulated the negative bias supply must be regulated too. If you are going this far, it would be good to provide another positive supply in the +50 to +150 volt range for the PowerDrive mosfets. Running the mosfet drains on a lower voltage than the B+ will allow the current through them to be increased without excessive heat generation. This supply doesn't need to be regulated, but should be clean.

You asked for B+ voltage recommendations, so I will offer mine, but you may have different preferences with different tubes and transformers. For 300B's I usually like 360 to 380 volts with about 75 to 80 mA through each tube. I usually use cheap tubes (Shuguang or Sovtek) and I have seen tendency toward runaway in older Sovteks when you get too close to 400 volts in some tubes. If I was designing the power supply (see below) I would make it adjustable from 350 to say 420 volts. Then you could find the sweet spot for your tubes.

On the 45 I tend to use 300 to 320 volts. Yes this is over spec, but I have never seen a tube that complains about it. I don't have any rare or expensive 45's though. I run the current at 25 to 30 mA per tube. Again, an adjustment range of 275 to 325 volts should work with most tubes.

I have not tried a shunt regulator. They tend to be a little more specific in their setup since the voltage is not usually adjustable. I have been working on a "universal regulated power supply" for use with vacuum tube amps. I will eventually make a board for one of these designs for use with the Tubelab SE and other amps. I have 3 different designs currently, 2 solid state and 1 tube. It's too soon to know when anything will be ready since I haven't had time to work on them.
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Old 2nd March 2010, 08:18 AM   #4
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George,

Thank you very much for your reply. The current you indicated are the idle currents. What should I consider as peak ? from my calculations with 75mA for each tube (300B) I get aroung 105 mA peak. The driver should stay at 17 mA as it has the CCS. So the total peak current should be 240mA. Am I correct ? something in the range of +30%.

For 45 (biased at 25ma) I should a total peak of 100mA.

By the way great amp, I am playing with it more to learn things that for a real improvement :-). I have a separate PSU as I do not want to spend lot of money on power transformer, as I will change country and voltage in few years. I asked to have a custom made transformer for the tubelab SE with double primary, and they asked me 270 $ !!!

D.
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Old 3rd March 2010, 10:17 AM   #5
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Few more questions:
What will be the current requirements for the negative rail and for the PSU of the power drive ?
Additionally, how does the amp sound if I "fry" the mosfet ? IS it obvious ?
Does replacing the IXYS CCS with the DN2540 need changes in other components ?



Thanks,

D.
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Old 5th May 2010, 04:05 AM   #6
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I made some experience with the salas regulator for another project, and I think I made up my mind on how to test them.
The dissipation of the shunt are very high for current over 100mA, so I will use one b+ regulator per channel, between the board and opt, with the 10 ohm resistor after the regulator. B- will be regulated with the Morgan Jones, mpsa92 based regulator. As George suggested a separate psu for the power drive will be provided.
The onboard psu will be used as a hv source for the regulators.
What I did not address yet is the b+ for the drivers. Is it i
important to have it regulated with the ccs? In case should i also separate one regulator per channel ?

I'll test first with the 45, then I'll raise the current.

Like this all the voltages will be adjustable.

BR,

Davide
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