Re: [drakelist] AC-4 Cap values

[k5vkl]

Carl,   Now might be a good time to review some slow-start feature design reviews, looking forward to incorporating one into the turn-on function of the power supply.  When you have a "thump" from turning on a power supply, it generally is indicative of too great of a surge current going into the filter capacitors and stressing them unnecessarily.   It doesn't help the rectifiers, either.  Also, I'm not sure that it is a "leaky" capacitor that causes the "thump" you heard at power supply turn-on....I've always been led to 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 this was the actual cause. You could, however, benefit the power supply considerably, by inserting a resistor of the proper resistance and wattage, into the 650 volt output, between D2 and the connection to R1.  This would also serve to bring your 650 volt HV (now approx. 700 volts, as you indicated) back down nearer to the correct 650 volt value. Your could also do the similar action with a resistor added between D5 and the connection to C3, and also reduce the 290 volts down to the original design value of 250 volts.    Possibly, the original design of this power was slighted somewhat, by not including a choke in each of the two points I noted above.   That would have produced a significant reduction in the capacitor surge current at turn-on.   Chokes would also have been more effective in reducing the ripple you originally saw on the outputs.   I'm naturally assuming, of course, that you do intend to reduce power supply outputs down to their specified voltage levels.  I haven't intended to sound critical of your modification efforts here, Carl. Moreso, I am critical that Drake didn't put choke filtered supplies in this equipment.   I would sure have liked my T-4XB/R-4B's AC-4 to have been choke filtered.   (Guess they figured the cost of the choke, a place to put it, and also a slight change in the secondary output winding in the power transformer secondaries would cost too much to add into the equipment price.   Anyhow, and Meanwhile, back at the Ranch (as "they" say, somewhere) keep up the good work, and keep us posted.   Bill Flowers   K5VKL         _______________________   On Wed, 02 Mar 2005 20:37:21 -0800 Carl Strode <[EMAIL PROTECTED]> writes: > > Carl Strode <[EMAIL PROTECTED]> made an utterence to the > drakelist gang > ---------------------------------------------------------------------- > 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 > ____________                   __________________                  ________________  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! > > ---------------------------------------------------------------------- > On Behalf of Carl Strode <[EMAIL PROTECTED]> > Submissions:        drakelist@www.zerobeat.net > Unsubscribe:        [EMAIL PROTECTED] - unsubscribe > drakelist in body > Hopelessly Lost:    [EMAIL PROTECTED] - help in body of > message > Zerobeat Web Page:  http://www.zerobeat.net > Brought to you courtesy of TLCHost.net  http://www.tlchost.net/ > ---------------------------------------------------------------------- > >