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Old 3rd March 2009, 11:31 AM   #1
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Default 12aY 7 preamp out

this what my scope shows when i connect a 10khz squarewave @200mv in the input of my preamplifier

do you think that this correct ????

should i post a schematic of the preamp ????
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Old 3rd March 2009, 11:36 AM   #2
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It looks like you have yourself an oscillation.
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Old 3rd March 2009, 12:07 PM   #3
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Default VERY WELL ....

here is the schematic with what i am working with

your opinion about corners is getting rounded is because of oscillation ????
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Old 3rd March 2009, 12:11 PM   #4
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Default quick posting

very quick posting
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Old 3rd March 2009, 12:17 PM   #5
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No, the rounding of the square wave is normal- it means that your bandwidth doesn't go to RF. It's the fuzzy tops and bottoms that show the oscillation.

edit: if you really have a 100k resistor at the input, that's what's causing the HF rolloff. But really, do you need half a megahertz bandwidth?
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Old 3rd March 2009, 04:19 PM   #6
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Here's the same 10Khz square wave from my hyperfly preamp with -3dB 100Khz using EF184's as triodes. Tone controls flat. The EF184 is my tube of the month.
I will do anything to avoid using the 12AU7 series unless there is a darned good reason for doing so.

richy
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Old 4th March 2009, 10:40 AM   #7
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Default after

a lot of effort we come up with this design that lloks tha performs very fine for at least 20 KHZ square wave

any opinion will be very welcome thank you very much
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Old 4th March 2009, 03:04 PM   #8
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Default i apologize

it seems that i had some error in my schematic ....

here is the correct one
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Old 4th March 2009, 05:59 PM   #9
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Default The fuzzy top is probably due to 50-60hx hum

...or you are close to an AC EMI field like flouriescent lites. Cascading two sections doubles the transconductance and halves the plate resistance. Ray
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