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Kenwood bias information

68.7.93.11
Posted on October 28, 2009 at 21:28:03
manoteal
Audiophile

Posts: 2
Location: So. Cal
Joined: October 28, 2009
 Hi Gang,
I used to post here but I couldn't get in with my 'old' information, so I am back. I might be remembered as deafelectromark- my eBay name.
I have a Kenwood power amplifier Basic 2A that needs the bias adjusted. Some of the transistors were running hotter than others and I resolved most of the problem by re-soldering the .22 ohm twin bias measuring resistors onto the circuitboard. They were intermittent and the bias would go from 2-22mV on one of them and from 0 t0 44mV on the other. There are tiny trimmers near those resistors (VR3 and VR4) and on the outside board there are larger controls that are named VR1 and VR2.
The off set is only 45mV at start up and reduces close to 0mV when warmed up. The bias changes as it warms up, so I need to know what to set the voltage on the pins of those resistors to get the correct amount. And since there are 4 controls, I imagine the outer two are for DC offset?
Any help will be appreciated,
Mark
Music is subjective
RE: Kenwood bias information, posted on October 28, 2009 at 23:49:40
djk
Manufacturer

Posts: 3888
Joined: June 17, 2000
 VR1, VR2 are DC off-set; VR3, VR4 are bias.

The bias voltages are not listed on the scematic, I would use 10mV across one of the 0R22 emitter resistors.

Re-adjust DC and bias after a one hour warm up.

RE: Kenwood bias information, posted on October 29, 2009 at 23:21:22
manoteal
Audiophile

Posts: 2
Location: So. Cal
Joined: October 28, 2009
 Thanks for your help. I will give that a try and see how if balances the temperature of the output transistors. Creepy looking things with 5 leads and only negative voltages going to them (-95 and -52 VDC) I don't know what they are doing with this one!\
Mark
Music is subjective

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