12aY 7 preamp out

[sakis]

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 ????

[SY]

It looks like you have yourself an oscillation.

[sakis]

here is the schematic with what i am working with

your opinion about corners is getting rounded is because of oscillation ????

[sakis]

very quick posting

[SY]

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?

[richwalters]

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

[sakis]

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

[sakis]

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

here is the correct one

[grhughes]

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