If anyone can help me confirm or deny what I'm about to tell you I would be grateful. So would a lot of other owners, I suspect.
My Roadster lags badly when it's hot. I played what amounted to an outdoor gig in Texas last weekend & got 3-5 second lag after the first set.
So I bought a heat gun.
If I point the heat gun at the mute circuit bits I can get the collector voltage of the driving transistor (6426P) to drop from 11-12V down to 1V even while the base of the transistor is pulled down with the 10K resistor. Somewhere around 4-5V the muting will kick in. I pulled all the pieces around the transistor & tested them for heat stability. They are all good so I'm left with the transistor.
What I think is happening is that as the transistor gets hot it pulls more collector current & gets the collector voltage dangerously close to the 5V threshold. Once the mute is triggered & then released back to "cutoff" there is not enough voltage available on the collector to release the jfets until one or more of the caps in the muting circuit charge back up. Interestingly, there is a 2uf2 cap charging through a 2M2 resistor that should take about 4.8 seconds to charge. This corresponds nicely with how long my mute lag lasts.
Is there a better transistor to use? (I am not an EE...)
I'm going to find a heatsink to fit onto the transistor & see if that will be enough to stabilize it. Failing that, I'm going to devise some kind of venting. Maybe a grill in the bottom of the case or something.
Anyway, if anyone wants to help me out in establishing the root cause that would be great.
thanks.
Dave