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

>>
>>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 >> writes:
>>>
>>>Carl Strode  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 >>
>>>Submissions: drakelist{at}www.zerobeat.net
>>
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>> - unsubscribe
>>>drakelist in body

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