EH 12ay7 pre - phantom problem

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buschfsu

Well-known member
Joined
Dec 31, 2004
Messages
760
Location
jacksonville FL
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phantom is at 104v right now. i checked at R37 and its 220V  at R3/D1 and its 104.  my first thought is replace the zeners. (actually order them wait 6 days then replace)  i could just cut phantom for this pre but the 18v is used to bias the tubes so i want to make it right.  btw x y and z are a switch and pM goes through a LED to ground

does that sound like the most probable culprit?

thanks
 
Check the top of D1(you did and have 104VDC)
Check D1 D5 node VDC
This will help tell if the zeners are bad or if you have bad solder connections

Next powered down and all power supply caps discharged and checked.
Check the solder side of the board solder connections to the zeners.  Check the diodes with a DMM diode check setting.

Is the circuit fragment shown a known good schematic?
 

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