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Old 30th December 2012, 08:16 AM   #71
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Make it 2 separate 6.3V windings that way you got more options.

Parallel/series and you can run them at different potentials.
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Old 30th December 2012, 12:31 PM   #72
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Quote:
Originally Posted by flatheadmurre View Post
Make it 2 separate 6.3V windings that way you got more options.

Parallel/series and you can run them at different potentials.
thanx, that is a good idea.

300-0-300v, 100mA
0-6.3 - 4A
0-6.3 - 4A
0-5 - 4A
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Old 30th December 2012, 01:29 PM   #73
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I think the heater windings are a bit on the big side.

With only 100mA HT its a medium amp transformer.

Keep the 0-5-6.3V rectifier winding, 3A will be enough for most aplications.

For the 6.3V windings you need 2-3A not more.
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Old 12th March 2015, 12:20 PM   #74
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Its been a long time and i havent done anything yet with tubes, but the good thing is that I have learned a lot of things since I tried it last. I want to make this preamp this time.

I plan to use an ecc88 (I've got max variants for this and its a nice tube) and since most of my sources have plenty of output voltage, will go for a unity gain buffer with a ring of two ccs. I got the best sim numbers with about 55-60v plate voltage and about 15ma current.

I have a 12-0-12 transformer that I can use to generate about -12v for the ccs using lm337. The other winding I plan to use to generate +6.3v using lm317. Both trafos are EI.

For HT, I have a 22-0-22 transformer that will give me about 61v dc after ditching the center tap. I also have +-35 trafo at hand If I want to go for a higher voltage for B+. Inductors are expensive and a headache to get, so I will go with a crc or crcrc filtering.

One potential issue I see with this is that the Vgk is varying from -140mv to -340mv (with a 2V RMS sinewave signal), is it too close to 0v. If I use a 95v B+, then it varies from about -1.3 to 1.5v. Is this even an issue.

How do I go about grounding the two supplies together, and what about the Protective chassis earth point. I plan to make a pcb for pre and psu, but I would probably breadboard it before trying the pcb.
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Old 12th March 2015, 01:04 PM   #75
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Quote:
Originally Posted by doors666
One potential issue I see with this is that the Vgk is varying from -140mv to -340mv (with a 2V RMS sinewave signal), is it too close to 0v. If I use a 95v B+, then it varies from about -1.3 to 1.5v. Is this even an issue.
It could be an issue. If it gets too close to 0V then you get grid current. Some valves start this from about -1V - but it varies from sample to sample and may change with age. Grid current will introduce distortion and noise unless you can always feed it from a low impedance source - but then you would not need a cathode follower at all!

A good valve model will include realistic grid current. Try simulating with a resistor in series with the signal source. If the distortion varies as you vary the resistor then you have grid current in the model.
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Old 13th March 2015, 08:26 AM   #76
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I tried what you suggested, the distortion varies when i put a resistor before c1 and change its value from 1k to 100k. The model I am using is ayumi model for ecc88. I see about 28nA peak sine wave for grid current.
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Old 14th March 2015, 06:46 AM   #77
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I have attached a rough supply diagram. For grounding, do I short A with C or B with D. I think its the latter, but would like to confirm. Any issues if I later switch 22-0-22 with a 0-45 transformer.
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Old 14th March 2015, 08:23 AM   #78
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I don't dare to suggest anything before you have given more detailed diagram.
Are LM317/337 connected to transformer without any rectification ?
Where are ground pins of LM's connected ?
etc.
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Old 14th March 2015, 10:19 AM   #79
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Quote:
Originally Posted by aeandm View Post
(...) the output
any power transformers (220) rated at 10 watts, with
output voltage of about 10 volts.
The power transformer capacity of at least 20 watts (...)
An average quality power transformer used as an output transformer?
IMHO that is NOT a good idea.

It could be acceptable if all you want is playing with tubes.
Not if you are seriously interested in listening good music.

By the way, an average quality power transformer is not suited for audio even when you use it as power transformer.

An audio grade power transformer is a totally different beast:
different core
used in a different point of magnetizing curve
different winding design
different winding tension
different winding structure
different insulation materials
different impregnating material.

Different Sound.

Last edited by CiroMarzio; 14th March 2015 at 10:21 AM.
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Old 14th March 2015, 11:39 AM   #80
DF96 is online now DF96  England
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Quote:
Originally Posted by doors666
For grounding, do I short A with C or B with D.
B to D.
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