[R-390] OT: Pass Transistor Question

[2002tii]

Jon wrote:

>Thanks for the info on the MJ15003s.  I've already purchased a 
>handful or 2N3773s since they were cheap and available so I'll give 
>them a shot first.  They are Brand X by the way.  Could be one of 
>the thousands of processes Motorala must of spun off to the 2nd line 
>fab houses.  If I end up with flight at/near current limit I won't 
>be too concerned since I don't plan to run the amp anywhere near 
>there anyway.  And yes I am the curious type.  Sounds like this 
>could turn into an interesting exercise.
>
>So how did Crown Audio get the kind of recognition they 
>received?  Given the parts available at the time, dealing with basic 
>design problems is one thing.  The packaging  however is such a 
>disappointment.  I think I could have done better in my garage.

2N3773s are an unfortunate choice -- they are much slower than the 
originals and you will probably never get the amp stable.  The 
datasheets I can find on the web do not specify the transition 
frequency, so I'm assuming it's horrible just like it always 
was.  Motorola didn't make 2N3773s, I don't believe -- they were 
originally RCA parts.

Just so you know, "It's OK if it does something strange near clipping 
[or current limiting] -- I'll never get it there" are the famous last 
words of people who are about to need both their amps and speakers 
repaired.  Designers and service techs always laugh when we hear 
someone say it.

Crown was pretty much the first company to make readily-available 
high-power (i.e., greater than 25 watt) solid-state amplifiers, so 
they were really the only game in town for several years.  And their 
first competitors' amps were even more unreliable (Phase Linear comes 
to mind).  Anyone with an ear used one of the better tube amplifiers 
(McIntosh, mostly) in their home system through the late '70s or 
early '80s, but touring sound companies needed SS amps for sound 
reinforcement work because tube amplifiers are heavy and do not 
travel well.  They lived with the horrible sound and unreliability.

I have no idea why Crown used that mechanical design, although it is 
possible they already had the extrusions for some other product they 
made that had much simpler drive circuitry (DC power supplies, 
possibly, with all of the power transistors in parallel).  Crown 
(Techron) manufactured primarily industrial electronics up until the mid-'70s.

Best regards,

Don