From: Carl Strode 
Subject: Re: [drakelist] AC-4 Cap values


Carl Strode  made an utterence to the drakelist gang
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I have completed re-capping the AC-4.

After looking at the actual caps installed, and comparing it to my 
supply of modern electrolytics, I have replaced the 40 mfd caps (shown 
as 40 mfd on most schematics) with 33 mfd.

The HV filter caps were replaced with 150 mfd 450 volt units.  ( I had a 
bunch of these laying around).

Since my original late model AC-4 had a 100 mfd cap installed at C3 and 
C4a, and an 80 mfd cap installed at  C4b,  I decided to  keep everything 
simple and replace these with 150 mfd caps as well.  I'll save all of my 
82 and 100 mfd caps for some other project.

The 150 mfd caps I have are circuit board mount types, with both leads 
on one end.  This made installation above decks a snap.  I removed the 
old caps, and then reamed out one of the holes used for the old cap 
mounting screws.  I installed a 1-1/4 inch long 6-32 machine screw from 
the bottom so it is sticking straight up near the center of the 
transformer primary winding.  Using nylon tie-wrap, two new caps were 
attached to the .  Just to be safe, I insulated the machine screw with 
some heavy-wall heat-shrink.  This also provided a better grip for the 
tie-wraps.

I soldered the 150K resistors directly across the cap terminals. 

I used a similar technique with the remaining five caps.  Two caps per 
machine screw, and a single one for C4a.

 I mounted C3 and C4b right next to each other, and soldered the big 100 
ohm power resistor right across the terminals.

When I was finished, there was essentially no ripple at all!  only about 
a tenth of a volt on the 650 and the 250 volt, and about 0.2volts 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!

When I started, the HV was only about 450 volts with lotsa AC.

Carl Strode wrote:

>
> Carl Strode  made an utterence to the drakelist 
> gang
> ----------------------------------------------------------------------
> I am about to re-cap one of my AC-4s.
>
> Looking at several schematics, I note that C5a and C5b are shown as 20 
> microfarads.
>
> I have a parts list dated September 1, 1974 that shows both C5s as 40 
> microfarads.
>
> Looking at the AC-4 I see that indeed there are 40 mic caps installed.
>
> What is the scoop here??
>
> Also, I have found a bunch of new electrolytics of larger values that 
> I am planning to use.    I will replace an old 125 with a new 150  
> This is OK, right?
>
> What really has me puzzled is the 20 vs 40 mic caps.  I was planning 
> on using some 33 mic caps I have on hand.
>
> By the way, all of my new caps are 400-450 volt ratings.
>
> Please advise.
>
> Carl
> WA7CS
> R4B, T4XB
>
>
>
> ----------------------------------------------------------------------
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On Behalf of Carl Strode 
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