Pelle Post Q13????
Hi Sam
You may want to check out a recent post regarding this amp Q13 in Holton's n-channel amp
Apparently, there's some confusion as to which mosfet is the Vbe multiplier. According to JasonL's pictures, there is a MJE340 legend with a preset beside it. Check the tracing underneath to confirm if indeed this is the Vbe transistor. If it is, jump 3 wires and connect it to the main heatsink. That should prevent the amp from thermal runaway. Cheers.
Hi Sam
You may want to check out a recent post regarding this amp Q13 in Holton's n-channel amp
Apparently, there's some confusion as to which mosfet is the Vbe multiplier. According to JasonL's pictures, there is a MJE340 legend with a preset beside it. Check the tracing underneath to confirm if indeed this is the Vbe transistor. If it is, jump 3 wires and connect it to the main heatsink. That should prevent the amp from thermal runaway. Cheers.
My main complaint about the irf devices is that they tend to be unstable in CFP configuration. In spite of the fact that their input capacitance isn't really that much bigger than the Hitachis.
Once you get them in a EF-like set-up, they are fine stability wise.
Once you get them in a EF-like set-up, they are fine stability wise.
I think the susceptibility to thermal runaway increases significantly with the bias current, especially since one or two Mosfets start hogging current more as you increase it. The IRF Vbe multiplier would be great, if the thermal coupling was perfect. With imperfect coupling I found the bias would just increase all the time.
I would try the BJT at a lower bias and watch the current through the hottest output device very carefully. If you play loud music for awhile then check the current again after stopping it, the current should be the same or slightly less (not much less).
I would try the BJT at a lower bias and watch the current through the hottest output device very carefully. If you play loud music for awhile then check the current again after stopping it, the current should be the same or slightly less (not much less).
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