double check the math

tenderland · 26th March 2006, 10:54 PM

Hello Im building the attached amp in a mono mode and the B+ will be
300 v instead of 350. to keep the preamp voltages and currents the same I calculated the the 27K feed resistor to be now 3333 ohms
Does this seem kosher ?

Thanks Jeff

arnoldc · 26th March 2006, 11:08 PM

The voltage difference then is 350-293 = 57V, with 27000 dropping resistor, the current is 2mA.

Now you want to drop 7V (300-293) at 2mA, the resistor is 3500 ohms.

Close.

richwalters · 27th March 2006, 04:24 PM

Use switchmode caps for cathode decoupling stages...they make a worthwhile improvement in sound quality. Choose 105°C low ESR types. Soundwise, I find them just as good a tants, esp for 1st stage.

richj

Giaime · 27th March 2006, 04:48 PM

Quote:

Originally posted by richwalters
Soundwise, I find them just as good a tants, esp for 1st stage.

richj

Do you really like tants?

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26th March 2006, 11:08 PM	#2
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	The voltage difference then is 350-293 = 57V, with 27000 dropping resistor, the current is 2mA. Now you want to drop 7V (300-293) at 2mA, the resistor is 3500 ohms. Close.

27th March 2006, 04:24 PM	#3
richwalters diyAudio Member Join Date: Sep 2003 Location: Alps:Tube amp designs over 150W, SMPS guru.	Use switchmode caps for cathode decoupling stages...they make a worthwhile improvement in sound quality. Choose 105°C low ESR types. Soundwise, I find them just as good a tants, esp for 1st stage. richj

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