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I am building an amp using 3 stages:

1st stage-ECC99 direct coupled ---> 2nd stage ECC99 ---> RC coupled 300B

But my OPT 2nd winding show this strange look.(attached picture)

Question:

(1) What is cause for those Spike, (short spike pluse, they generate Deeeeee sound, I use AC HT

(2) When direct couple ECC99 for 2nd stage, do I have to elevate the HT voltage by using votalge divider and a hum bypass cap. Right now I only short one leg of the AC HT on ground.

(3) When ground short the 1st stage ECC99, the noise from 2nd winding seem OK, but when it was left open (with 100K grid leak R to ground for 1st stage ECC99). There is a huge oscillcation problem on the ECC99'grid (around 5mV high freq oscillation).

The (3) is the major problem, any clue you may suggest to look into ?

Regards,


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