[R-390] OT: Pass Transistor Question

[ews265]

Don,

I see what you mean.  The MJ15003 has an Ft of 2 MHz whereas a listing 
in an old Motorola catalog shows 200 kHz to the 2N3773 plus the MJ15003 
has another 100 watts of dissipation, I think.  Looks like it IS the 
"Hot" setup.

JS

2002tii wrote:
> 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
>
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