Sanyo FBET process

[xmitterengineer]

I doubt youll get any performance benefit from the swap. What you should be looking at is a higher early voltage transistor and with less Cob. Something like 2sa1208/2sc2910 or 2sa1370/2sc3467, now those will lift performance by a fair margin.

Thanks for that information. The curves for the devices you mention do look impressive.
One of the things I was looking for was devices with a larger surface area, therefore better thermal performance. The original cascode devices in both channels ran uncomfortably hot. I associate the elevated temperature with the failure.

Good Day.

Rickey.

 

[homemodder]

Thanks for that information. The curves for the devices you mention do look impressive.
One of the things I was looking for was devices with a larger surface area, therefore better thermal performance. The original cascode devices in both channels ran uncomfortably hot. I associate the elevated temperature with the failure.

Good Day.

Rickey.

Mmm, ok I was not aware of this problem as I dont know the design but use these instead then 2sa1209/2sc2911 or rather these as they are far easier to come by 2sa1381/2sc3503 or their Fairchild equivalents ksa1381/ksc3503. These can be found at nearly all electronic vendors like mouser, digikey etc.

 

[xmitterengineer]

Mmm, ok I was not aware of this problem as I dont know the design but use these instead then 2sa1209/2sc2911 or rather these as they are far easier to come by 2sa1381/2sc3503 or their Fairchild equivalents ksa1381/ksc3503. These can be found at nearly all electronic vendors like mouser, digikey etc.

I'll probably "try" the 2SA1403/2SC3597 pairs in the cascode just to see if it will work as I have these parts on hand.
They exceed the MPSA06/MPSA56 devices in almost every way.
Of course the devices you suggest look even better.
I'm thinking that cascode minimizes miller effect, making low capacitance less but still important?

This particular P3000 was a fairly "nice sounding" amp prior to the crispy crunchy sound setting in on the right channel. I was quick on the power off at the first sign of trouble.

Subsequent testing revealed that tapping one of the cascode transistors with a plastic alignment tool produces crunchy sounds in the speaker but mostly only when cold. Therefore my diagnosis.

In a previous lifetime I repaired Hi Fi equipment for a living. 30 years ago I experimented with the use of video output transistors in the VAS with favorable results. In those days we would bulk order 100 of each type output, driver, etc. Then I would measure DC gain at some appropriate single operating point. The gain figure was then marked on each transistors case so that crude matches could be selected. Ahhh the good old days.

I will update this thread when I finish (or before).

Now I wish I had access to proper distortion measuring equipment. The best I can hope to do is an A/B null on a dual trace oscilloscope.

Thanks for the advice.

Rickey.

 

[xmitterengineer]

http://www.diyaudio.com/forums/solid-state/208738-hafler-p300-repair-modification.html