7 Feb
2025
7 Feb
'25
2:44 p.m.
Looking at this circuit, it occurred to me that 41 volts is about what you would expect to
see if the 2n6045 was just shorted, E to C (center to right). I checked with the diode
tester in my meter and it looked bad. This 2n6045 was out of a box of random unused
transistors that I've had around forever. I looked through the box again, and through
a couple of other boxes but no luck for a 2n6045 or equivalent. I did have a new pack of
2n6043s. The only difference I can see is that the 45 is rated for 100V and the 43 is
only 60. Since the circuit seems to be running at 41, I decided to try a 43. Now I have
a nice clean 24 volts. I wondering whether it will go bad under heavy load, but I think
I'm willing to very quickly test the FD400 in it. Will report results.
-----Original Message-----
From: William Sudbrink [mailto:wh.sudbrink@verizon.net]
Sent: Friday, February 07, 2025 4:12 PM
To: 'General Discussion: On-Topic and Off-Topic Posts'
<cctalk(a)classiccmp.org>
Cc: 'Tony Duell' <ard.p850ug1(a)gmail.com>
Subject: RE: [cctalk] Re: Use (abuse?) of a 7924 in a +24 PS...
Hi Tony,
Thanks for the reply. This is what it looks like to me (I hope this comes out):
AC--- + ---------------------------------------------------FD400 +24
| |
| | ----------------
|+ left| |right |
BR2 C4 2200uf 50V 7924 |
|- |center |
| | |
| B |
AC--- - ----------------------E 2n6045 C--------------FD400 common
2n6045 E/B/C are according to the silkscreen. The actual physical pins are: B-left,
C-center, E-right.
Left, right, center designations are with the tab up for both devices. As far as I can
tell, there are no other components (capacitors, resistors, diodes) involved in the
circuit. I'm measuring a smooth +41 volts at the FD400 connector with some 24volt
automotive bulbs as load.
In case the above is illegible, Circuit is: AC to bridge rectifier. BR+ goes straight to
FD400 +24. BR- goes to 2n6045 right pin. BR +/- connected with a 2200uf 50V electrolytic
cap. 7924 left pin goes to BR+.
7924 center pin goes to 2n6045 left pin. 7924 right pin goes to FD400 common. 2n6045
center pin goes to
FD400 common.
Maybe I'm not loading it enough? I'm very hesitant to reattach the FD400 until I
understand this. By the way, plus and minus five volts are fine.
Bill
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