Aleph 5 source resistor voltages

[Keith Marrison]

I recently completed an Aleph 5 using Kristians boards which was sounding great until there was a flash from inside the amp! this turned out to be due to my not isolating the power supply caps stud from the chassis(red face s all round). I ended up changing 3 of the IRFP240's but now have have source resistor voltages as follows:- 3 @ o.775V; 1 @ 0.958V & 2 @ 0.630V ! All other voltages are within a fraction of what they should be. And yes I did match the Mosfets to better than 0.1V. Any advice would be a
appreciated.Thanks in advance.
Keith

 

[Nelson Pass]

So they're a little off spec. I don't think they'll break otherwise.
Have you checked the Source resistors? Some of them might
have gotten burned a little and be off value - that would do it.

Since 3 of them seem to be averaging out at .7, I would bet
that the .958V one is the burned one.

 

[Keith Marrison]

WOW; my first post and a reply from the ONE AND ONLY!! My hands shaking. Thanks Nelson; it would appear tp be the source resistors; I have swapped IRFP240;s again and the main culprit's voltage dropped from above 1V to just below. Allsource resistors measure 1.1 ohm whemn measured cold and in circuit; can they be drifting when warm? I will swap them anyway.
May I say abig thank you to you; as I have enjoyed good sound from my system having built A40;s and for the past few years been the happy user of a Zen and Boz. Could not believe how loud 10 watts would go!! Once again many thanks.
Cheers; keith

 

[Nelson Pass]

Looks like it was the Mosfets after all.