F5 power amplifier

I've got a question....

I've got an F5 here and I'm fixin to break it down into monoblocks using another 4U chassis from the diyaudiostore. Each FET will get it's own heatsink. PLENTY of cooling action.... I'm thinking of raising the bias from about 1.4 amp to maybe 1.5. What I'm wondering is, given the much larger cooling solution on each MOSFET, can I get away lowering the source resistor values from .47R to maybe half that? Will that size heatsink give me the stability to pull that off?
 
Oversized heat sinks. Get warm to the touch. I bought these on ebay. Nelson is right , the heatsink cannot be too big.
 

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I've got a question....

I've got an F5 here and I'm fixin to break it down into monoblocks using another 4U chassis from the diyaudiostore. Each FET will get it's own heatsink. PLENTY of cooling action.... I'm thinking of raising the bias from about 1.4 amp to maybe 1.5. What I'm wondering is, given the much larger cooling solution on each MOSFET, can I get away lowering the source resistor values from .47R to maybe half that? Will that size heatsink give me the stability to pull that off?

I reckon you'd be better off going turbo V1 with that chassis and basis... Just my 2C (undithered).
 
Well, that's not what's gonna happen. I've already got 32V rails going and I have no earthly need for that kind of power. Just looking for some opinions on reducing the source resistance.

Parallel output devices essentially halves the source resistance... Also multiple devices spreads the dissipation better over the heatsink and improves reliability. It's not so much about extra power with the V1, but maybe for some reason you don't want to do it, ok...
 
With a single pair of output devices, you've got no current hogging issues. I would think you could get away with dropping the source resistors entirely.

To optimise it for your speakers though you'd want to balance the current delivery with your rail voltage. If your speakers are nominally 8ohms that probably means something on the order of 0R33 for your 32V rails -- although my brain is math challenged so I'd want to sim it first....
 
I did some sims: 0R27 seems to work nicely with a bias around 2.4A. That's into 8 ohms; you'd want more current into 6 or 4.

That's working those MOSFETs pretty hard, so you'd likely be replacing them more often. But I haven't the foggiest if that reduces their average lifetime from something like 20 years to 8 years, or more like 20 years to 8 months.