OK had a stab at re-creating the schematic. It's screwed together from essentially 3 bits:
[1] The full-wave doubler giving some 136V DC .and 68V DC
[2] A string of zeners to set the o/p voltage of the pass transistor.
[3] A 10mA current limiter, 0-20mA meter and a switch to discharge the cap.
NB
In accordance with my lifelong habit of not getting anything error free, the transistors are
MJE 13005, not
MJ 13005.
The 2 resistors with *** may need small changes as the load regulation of the transformer may give a higher o/p voltage.
If anyone builds it,
[1] Do the doubler first and check the volts are fairly near, although they won't be precisely the same.
[2] Make the Zener circuit, then set VR1 for 20V on the 16V range. [ you'll see why in a bit ]. Measure from Q1 emitter to 0V. Check the other voltages, make sure you ain't got a cranky Zener. They should all read about 4V high.
[3] Make the rest. Put a short circuit instead of the cap. and set VR2 to give 10mA on the meter.
[4] With a 10R resistor instead of cap. tweak VR1 again to read 16V from the -ve to +ve test terminals on the 16V range. Then check the other ranges.
The -ve test terminal actually sits at some +4V because of the Q2 limiter action, hence the 4 extra volts in [2].
Poke a
GOOD biggish cap. in and set up. [ Not in that order ]
![:thumbup:](https://madmodder.net/Smileys/default/happy0034.gif)
The meter should whip up to 10mA and stay there. When the cap's charged up it will swiftly drop to zero.
As this contraption is sort-of linear you can make a fair stab at finding out what a cap. really is.
CV = It ...
![:thumbup:](https://madmodder.net/Smileys/default/happy0034.gif)
Capacitance x Volts = Amps. x Seconds
Or:
C = ( I x t ) / V
So:
Suppose we have 25V, Amps. = 0.01, time to when the needle starts to drop, 6 seconds.
We have (6 x 0.01) / 25 = about 2400uF.
Have done this with caps. marked 56,000 uF, 25V and then with my Peak capacitance meter and it's pretty accurate.
D.
EDIT S1 is a 1P 12W rotary switch, stopped off @ posn. 8 ..
S2 on mine is a ON [ON] 2P 2W just flick it to discharge the cap.
![:thumbup:](https://madmodder.net/Smileys/default/happy0034.gif)
DVM should drop to 0V, then cycle cap. again if it's not been used for a long time. The 'slow' drop from 10ma to 0 gets sharper as cap. improves.