P
Pooh Bear
- Jan 1, 1970
- 0
Phil said:"Pooh Bear"
** But like most things - it did not sink in ??
I was hoping you might elaborate. And you did - cheers.
** Yawn - shows how far out of touch you are.
** Same size and design as all MJ15003/4s sold up till the late 1990s.
** Die size is not a reliable guide to power rating or overall quality.
It certainly plays a part ( in power rating ) though. Simple thermal resistance
assures that. In the same way that a copper slug in a TO-3 can helps power
rating too.
I have a collection of 2N3055s where the variation in area spans a range of
5:1. The smallest is the Motorola one - known to be a good example of the
beast.
Interesting. Do you have the dims ?
** Quite possible - IME.
There was a big change in the MJ15024/25 chips a few years back -
Motorola initially used the new number, MJ21193/4 for the revised design.
Then, as they often do, reverted back to the familiar number. You can buy
both numbers now - exactly the same insides however. MJ21193/4s will cost
you more though.
The MJ21193/4 chip are identical to the ones inside the plastic
JL21193/4s - plastic packs cannot normally use chips designed for TO3
packs - that is how the new design came about. Now, one size fits all
Yes - that issue caught my eye. More interestingly On's 'indicative pricing' for
the higher dissipation rated TO-3 is significantly less than the TO-3P. At least
it was when I last looked.
Kinda blows a colleauge's theory that " *everyone* want plastic 'cos it's
cheaper " out of the water !
Over the last 20 years, Motorola has sold the MJ15003 device badged as a
2N3773, MJ 802 and others. Similarly the MJ15003 has be badged as an MJ4502
and several others - with a price hike attached !!
Seems Motorola figure that any device that equals or exceeds the basic
specs of another can be sold as that other !! Plays havoc with trying to
match up new and old devices in parallel sets - "your problem" says
Motorola.
Had similar issues with RCA devices in 1980.
Genuine MJ802/4502 pairs will give lower THD figures in amps than the later
MJ15003/4s - or if the rebadged ones are fitted. Lots of traps for the
innocent.
All interesting stuff. Thanks for that Phil.
BTW
If you follow EW magazine, you will be aware of Doug Self's " blameless "
amplifier design that nobody who has tried can duplicate the same
vanishingly low THD figures.
How vanishing btw ? I admit I haven't seen it.
I've a ( mosfet ) design ( from 1990 ) that measures 0.0008% THD+N @ 1 kHz @
600W / 4 ohms ( AP residual is 0.0007% ! ). And yes the decimal point's in the
right place - i.e. -102dB SINAD - better if you discount the test set residual.
In the fine print of the article, Doug says he used devices from his
private stash of old (and therefore genuine) MJ802/4502s in the prototypes.
QED.
I've heard that Doug has a high opinion of himself too.... Most of the stuff
I've seen of his is basically 'old hat' dressed up so he can look important.
Incidentally we both interviewed ( amongst others ) for a position as Graham
Blyth's 'sidekick' at Soundcraft many years ago ( I didn't know the other guy
was Doug until someone told me yrs later ). He got the position by blagging that
he *knew* microprocessors so I've been told. I took my time a little more before
adopting them for practical designs.
Graham