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Old 7th July 2006, 01:12 PM   #1
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Question How do I design minimum current for 35W PP AMP

Now I need a circuit with low current : EL34 35W PP amplifier !!!
But general designer often used 30-60 mA for bias them, I get some idea from Berning Tube Amplifier EA-230 which used 3 mA each power tube (6JN6)

If possibly with EL34, How do I ?

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Old 7th July 2006, 01:59 PM   #2
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The Berning amp uses sweep tubes and screen grid drive. It also runs right at the edge of class B, hence the low idle current. The peak current will still be as high as a conventional class AB amp. I have tried this with other sweep tubes (6AV5's) and it works quite well. Screen grid drive requires a tube with a sensitive screen grid. This can often be determined by the maximum screen grid voltage, the lower the better. An EL-34 won't work here.

To get a low idle current, you must operate close to class B , this requires a tube that is linear at very low currents. I haven't tried it, but again I don't think that an EL-34 will work here.
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Old 7th July 2006, 02:07 PM   #3
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Quote:
I haven't tried it, but again I don't think that an EL-34 will work here.
I have. It doesn't.

On the bright side, suitable sweep tubes like the 6JN6 that Berning used are cheaper than good EL34s and readily available. I just got a few dozen of them for $5 each, new in box.
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Old 7th July 2006, 06:57 PM   #4
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Question OK, I need some suggestion about sgreen grid drive

Thanks SY for your reply, I look at Berning EA-2100 they used 6LF6 for tube power but I need some help if I use EL509 instead of 6LF6, How do I set current bias and How many watts does it has ? (250V Plate, 10mA bias)

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Old 9th July 2006, 02:18 PM   #5
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Wink Nobody here?

I searching a lot of EL509's link, but I can't understand different of control grid drive & sgreen grid drive.

Please me some link if you known.

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Old 9th July 2006, 02:21 PM   #6
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6LF6 are unobtanium these days. Take a look at the EA2101 schematic where Berning used paralleled 6JN6.

His schematics are a great tutorial on how to do screen drive. Optimal idle currents vary with load impedance, particular tube used, plate voltage and the like. You'll need to determine it experimentally. Figure it will be between 2 and 10mA.
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Old 12th July 2006, 05:27 AM   #7
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Lightbulb Someone suggest me, please

I decide to use EL519 for amplifier project in stead of 6LF6 of Berning EA-2100 but I have something wrong, It used 10mA each power tube !!! 100WRMS ?!?

How do I design OPT ?
: 700V Plate, 10mA bias, 100WRMS ?
: K of OPT?
: Henry of Primary & Secondary ?
: Wire size, Turn ratio ?

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Old 14th July 2006, 04:38 AM   #8
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Question Please me

Does anyone have EL509/519 6LF6 on hand ?
I need 4 tubes and sockets, my car tube amplifier coming soon with screen drive circuit.

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Old 14th July 2006, 02:32 PM   #9
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How much power do you want in your car amp. I used the 6AV5 in a screen drive amp that delivered 80 watts RMS at clip and 3% distortion at 50 watts with no feedback anywhere in the amp. 6AV5's are under $5 each in most tube stores and they fit an octal socket. There is a 12 volt version the 12AV5. They are available on Ebay for $1.50 each!

The amplifier runs at a B+ level of 550 volts and uses a 6600 ohm output transformer. The idle current is low, about 10 mA per tube I think. Just remember that the amp will draw about 200 mA per channel at full crank. Your power supply should be able to supply this much on signal peaks.

My amp is still in the prototype stage, but can be seen here. It is at the bottom of the page.

http://www.tubelab.com/6AV5.htm
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Old 16th July 2006, 07:22 PM   #10
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Thumbs up Thanks Mr.Tubelab.com

I need more 50 WRMS for drive my Dynaudio MW150 5.75" midbass,

Quote:
I used the 6AV5 in a screen drive amp that delivered 80 watts RMS at clip and 3% distortion at 50 watts with no feedback anywhere in the amp
How do I design 80W with 6AV5 PP in screen grid drive ?
1.Schematic ?
2.Voltage ?
3.Bias ?
4.OPT ?

Thanks very much
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