Pultec high frequency noise after sw/off

[ferrochrome]

I have these two great sounding Pultec clones (Drip)  been using them for a year or so.

These amazing EQP1A clones's has been trouble free, working perfectly since first switch on. For a couple of weeks one of them has been having some issues, I'll call it Pultec1, and the working one : Pultec2. These are inserts on RME ad/da (ADI8) on adat, and Pultec1 behaved similarly while connected to ad/da's on the soundcard (RME UFX).

Problem is noise floor has encreased on Pultec1. Also, when I switch it off a high pitched noise builds up gradually and disappears. When I switch it back on after 5min it buils up again, reaches a peak, falls back and continues with a really high pitched peak.

Before I dive into this, has anybody seen anything like this before? could it be a ground loop? PSU filter cap malfunc?

First picture: Noise floor on working unit (Pultec2)

 

[ferrochrome]

Noise floor Pultec1

 

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Seconds after switching Pultec 1 off

 

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After switching back on

 

[CJ]

try some tube swapping first,

 

[ferrochrome]

try some tube swapping first,

Thanks CJ! I'll try that

 

[ferrochrome]

Thanks CJ, you could't have made a better suggestion. Noise came from a bad JJ ecc82! Problem solved , unit sounds absolutely perfect again!

btw I abolutely recommend these eqp1a builds from Drip Electronics, mine are ver2's, pretty easy builds as well!