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    Building, troubleshooting and testing of these amplifiers should only be
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Output tube generates pitch tone

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hi there

I am testing my 2nd DIY amp. 6SN7 drives KT66 at triode mode.

Gain looks fine when testing with a signal gen and a 8 ohm resistor load.
The problem is when I increase the input frequency from 1kHz to higher, the output tube generates significant pitch tone directly(there is no speaker connected). Tone varies with input frequency changes until 15kHz that my ears are not able to hear them anymore!

Do you guys have any idea!
thanks.

amp.png
 
hi fullrangeman

ah, that makes sense and I could not identify the source of the noise tone actually, I just hear and not sure where they from!

choke and opt are all with full metal cap. the only thing is i left the "earth" pin open on opt, the hashimoto one. I am going to check...

cheers
 
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