5670 Soul Sister C4S

[calsaint]

Hey hey !
Been a while for this formerly pretty active poster. Hope everyone's doing great.

So I built a 5670 Soul Sister as posted in the Valve archive and have a question about the plate voltage.
I've got series 0D3 feeding the C4S 300v , 330R rk
The schematic suggests I should have 150v at the plate, but I'm getting like 230v. Is this just something I can expect to be a little up in the air given the 5670 I happen to have in the socket ?
Pre sounds great, it was fun to build something again.
 
Thx gang as always
-Steve

[vetmed]

A link to the schematic would be very helpful

[Paul Birkeland]

100 Ohms as your C4S R1 with HLMP-6000's will give just under 9mA.  9mA through the 332 Ohm cathode resistor will give you roughly 3V of bias. 3V of bias and 9mA gives you a plate voltage closer to 200V than 150V.

Take out the 332 Ohm cathode resistor and install an HLMP-6000 on each channel (stripe to ground) and you should be between 140 and 160V on the plate, you'll get a little more gain, and I bet the preamp will even sound a bit better.

-PB

(PS - welcome back!)

[Paul Joppa]

The spec sheet lists the operating point as 8.2mA, 150v, with 240 ohm cathode resistor (2v bias). The original schemo (VALVE 1998 v5n4) has some errors. Just some FYI.

[calsaint]

good stuff here PB and PJ.
many thanks as always - the BH team is really the primary reason I have a cool system and a cool hobby.

-Steve