u67 c9 cap voltage rating

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salomonander

Well-known member
Joined
Aug 28, 2011
Messages
913
hey there,
im sorry if this has been asked before.
im wondering about the voltage rating of the c9 coupling cap in a u67. i have two schematics.... one says 1uf/450v, the other 0.5uf/250v.
i was asked to mod a u67 clone. in there its a 0.47uf/160v. now the original caps are really hard to find. but if 160v are enough it would make it a lot easier. anyone have some knowledge of this? whats the lowest voltage i can get away with?
thanks a lot
jakob
 
At least the U67 schematic i have (with the 0.5uF / 250v cap) says the plate voltage is "approx 75v", so 160v should be safe enough, i'd reckon.

That being said, for "ultimate safety" (ie. the tube blows so bad that it's out of circuit), you'd want 250v, so it's above the 210v coming from the power supply.
 
C9 sees aprox. 75VCC but could see much more at startup (no regulation on HT) if you hotplug the mic ( never do that...)
i would say that 160v is enough for a film cap (mkp or mkt) , and even with a solid tantalum
1uF will perform better at very low end frequencies and could make the mic more sensitive to rumble
0,5uF is enough, anyway not a big difference...
 
one more question if you dont mind.
say i find two 1uf 100v ones and use them in series.... should be 0.5 with 200v right?

cheers
 

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