Re: Amplifone +/- 24v regulation

Zonn,

I wanted to thank you for taking the time to respond so thoroughly to my
question regarding the Amplifone current regulation. That was really
awesome to see a schematic accompany the reply!!!

If I may be so bold .. what does the complementary circuit look like for
the 7924/2N3716? I have this vision of swapping some combination of the
transistor leads incorrectly. As you can tell, analog circuit design is
not my area of expertise. :-) I mean, umm, given that this email is
getting archived, shouldn't we have the circuit drawn out, just for the
record? You know, just in case some other misguided soul tries to get
rock solid performance out of his Amplifone this weekend? Yeah ..
that's it.

Thanks!
Joel-

Zonn wrote:
>
> The unregulated voltage is not dropping too low, so bigger caps won't help (and
> if that were the case, better regulation wouldn't help either). What happens is
> that the 7x24's can't supply enough current. You could lower the value of the
> 50 ohm pass resistor, but that will reduce the 7x24's ability to regulate and
> the vectors will not be as stable. The thing to do is add pass transistors that
> beef up the current capacities of the 7824/7924.
>
> The new pass transistors must be heatsinked (so you'll have to find a heatsink
> to mount the transistors to). The ideal transistors would be the standard
> 2N3716 and 2N3792 already used in the WG for this. Just leave the 7x24s where
> they are, remove the 50 ohm power resistors, and connect the base and collector
> of the pass transistors in place of the 50 ohm resistors. (The base goes to the
> input of the regulator, and the collector goes to the output.)
>
> Cut a trace in the PCB just in front of the input of the 7824/7924 and jumper
> the cut with a 5 ~ 7 ohm 1/2 resistor. Connect the emitter of the pass
> transistor to the side of the cut that's not connected to the regulator, and
> walla, a mucho beefed up regulator.
>
> ASCII art:
>
> (Old Circuit)
> 50 ohm
> +-----/\/\/----+
> | |
> | ------- |
> +unreg ----------+----|7824 |---+---- +24v reg
> -------
> |
> |
> ---
> -
>
> (New Circuit)
>
> +------------+--- ----------+
> | \ / |
> | V / 2N3792 |
> | 6 ohm 1/2 watt ----- |
> | +--/\/\/---+ | |
> | | | | ------- |
> +unreg ---+--+---X X----+-----+----|7824 |---+---- +24v reg
> ^ -------
> Cut trace here |
> |
> ---
> -
>
> Do the same thing with the 7924 side, but use the 2N3716 as the pass transistor.
>
> I haven't done this to an Amplifone, but the circuit is right out of the
> National Voltage Handbook. (I have used this circuit before, and it works
> great, I just haven't done this to an Amplifone yet.)
>
> -Zonn
>
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>
> ------ ___ Member of A.A.C.S.:
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Received on Fri Jul 10 07:58:21 1998