Re: Ampliphone HV FAQ is done!!!

On Mon, 7 Jun 1999 11:59:15 -0700 , you wrote:

>> Yet the insulator serves no purpose here. On the HV board I looked at
>> (a beige board) the heat sink was rivetted and solder to gnd. Since
>> the tab of a 7824 is connected directly to it's pin 2, and pin 2 is
>> also solder to ground, there is nothing to insulate, they're already
>> electrically connected! If you remove the 7824 from the heat sink and
>> let if float, then connect an ohmmeter to the heat sink and the body
>> of the 7824 you'll get zero ohms of resistance. This being the case,
>> what does the insulator accomplish (besides cutting down on heat
>> transfer)?
>>
>Sometimes hardware manufacturer's do stuff like this simply for
>"consistency". If I have one part the blows up in a shower of sparks if its
>uninsulated, and another more or less identical looking part that doesn't--
>do I really want to trust the first-year technician-guy to remember which
>one *has* to be insulated?
>
>"Remember to replace the insulators on the little transistor thingys" is
>easier for the unexperienced to remember than "remember to replace the
>insulator on the 7924, but not on the 7824, they look the same so check the
>numbers and look it up in the book if you forget which is which".
>
>(Plus, If it's running so close to the thermal shutdown that the difference
>in heat transfer an insulator would make causes it to fail it probably
>deserves a fan or something in the first place... )

I agree with you completely Clay, but the original FAQ was to go
through the trouble of *adding* an insulator to an already
uninsulated, working, 7824 regulator.

I'm not even saying it makes that much difference, it just seemed
unnecessary to take a perfectly working HV board, and add an insulator
between two ground points, when its only effect is to lower the heat
transfer from the 7824 to the heatsink -- nothing else is changed.

To belabor your "unexperienced" point, it seems less likely a
first-year technician would do any damage by doing "nothing" (if it
works, don't fix it) than by adding an insulator. ("Oops, a pin
broke". "A nut dropped between the pins that I didn't see before I
turned it on", "I think I stripped the nut / cracked the case / broke
a diode", etc.)

On the other hand if you're repairing a broken board and cannot
remember which part needs to be insulated, you could certainly add
insulators to both parts with not much effect -- but if your reading
this excellent FAQ, and adding diodes / resistors, changing caps, all
because your want everything to be absolutely optimal, it would seem
strange that you would want your regulator to be running slightly
hotter than it optimally could be. Make sure you get your caps and
diodes pointing the right way, and make sure you place the insulator
on the reg that needs it. Not really all that difficult for someone
undertaking the recommendations of this FAQ, considering the other
tasks called for.

I don't believe Michael's original intent was to "make things simple",
but was to "make things a best as they can be", which is the only
reason I brought up the insulator in an, email to him, in the first
place.

-Zonn
Received on Mon Jun 7 15:42:26 1999