Subject: Re: [drakelist] AC-4 Cap values
From: k5vkl{at}juno.com

on 
> the bias supply.  Oh yes, as usual nowadays, the 650 is really closer
to 
> 700, and the  250  is about  290.  When the power supply is switched 
> on, it thunks a bit harder than it used to, due to the lack of leaky 
> caps and the increased cap values.  The supply is much stiffer than 
> before. Very little sag and absolutely no detectable hum.
> 
> I guess this demonstrates that with brute force, we don't need no 
> steenkin regulators!
> >
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> On Behalf of Carl Strode 
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Carl,
 
Now might be a good time to review some slow-start feature design=20
reviews,
looking forward to incorporating one into the turn-on function of the=
=20
power
supply.  When you have a "thump" from turning
on a power supply, =
it=20

generally is indicative of too great of a surge current going=20
into the filter 
capacitors and stressing them unnecessarily.  
It doesn't =
help=20
the rectifiers,
either.  Also, I'm not sure that it is a
"leaky" capacitor that =
causes=20
the
"thump" you heard at power supply turn-on....I've
always been led to <=
/DIV>
believe that the "thump" was from the large flow of
current into an
uncharged capacitor, although I've never had it proven to me that=20
this
was the actual cause.
You could, however, benefit the power supply considerably, by =
inserting=20
a
resistor of the proper resistance and wattage, into the 650 volt =
output,=20

between D2 and the connection to R1.  This would also serve to =
bring=20
your 
650 volt HV (now approx. 700 volts, as you indicated) back down nearer=
 to=20

the correct 650 volt value.
Your could also do the similar action with a resistor added between D5=
=20
and
the connection to C3, and also reduce the 290 volts down to the=20
original
design value of 250 volts.   
Possibly, the original design of this power was=20
slighted somewhat, by not 
including a choke in each of the two points I noted
above. &=
nbsp;=20
That would 
have produced a significant reduction in the capacitor surge=20
current at 
turn-on.   Chokes would also have
been more effective =
in=20
reducing the 
ripple you originally saw on the outputs.   
I'm naturally assuming, of course, that you do
intend to =
reduce=20
power 
supply outputs down to their specified voltage
levels. 
I haven't intended to sound critical of your modification efforts here=
,=20
Carl.
Moreso, I am critical that Drake didn't put choke filtered =
supplies in=20
this
equipment.   I would sure have liked my
T-4XB/R-4B's AC-4 to=
 have=20
been
choke filtered.   (Guess they figured the cost
of the choke,=
 a=20
place to put it,

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