[Amps] ps caps

[Will Matney]

Vic,

Does that mean you believe in using equalizing resistors across the HV rectifiers also? Electrolytic capacitors actually have a semiconductor function to them. No other capacitor does though that is non-polarized. The diode action of an electro cap is due to the anodized anode foil and the electrolyte being the other plate. Actually the cathode is the electrolyte and the other strip of aluminum is used to make contact with it and serves no other function. That's why polarized caps go BOOM when connected backwards, same as connecting a diode backwards. Kirchoffs law comes into play here. If the capacitances were way off from one to another, then you'd have unequal voltages, but I've never seen that in new products. Capacitors out of the same run and lot, I have never found to be a difference. Everything is controlled in their manufacture right down to the lengths of the foil, and the mixture of the electrolyte. The only way I'd see some might be different would be mixing some made a years apart or so which they dont do. The distributors sells so many and buys by lot runs, I highly doubt ever buying new would cause a problem. I personally think Alphas comments is a bunch of malarky and or horse kaka. Just my opinion of course.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 8/22/05 at 9:23 AM Vic K2VCO wrote:

>Actually, it's quite possible that they are matched.  The voltage across 
>series capacitors will divide unequally depending on the capacity and 
>the leakage resistance.  If there are 20% tolerances, this can be a big 
>difference.
>
>Part of the function of the equalizing resistors is to swamp out these 
>voltage differences (they also serve as bleeders).  If the capacitors 
>are not matched, the resistors across the ones with lower capacity 
>and/or higher leakage resistance will run hotter than the others.
>
>If the amp is designed to use capacitors that are matched to within, 
>say, 5% for leakage and capacitance, then they could use higher value 
>resistors which would be less effective in swamping the voltage 
>differences.  This would cause some of the capacitors to operate at 
>higher voltage than others.
>
>I would believe what Alpha is telling you.  I doubt that a large part of 
>their revenue comes from selling replacement capacitors!
>
>Gary Smith wrote:
>> Sounds to me they want to match their profit on each capacitor they
>> sell. 73
>
>> Gary...wa6fgi
>
>> Will Matney wrote:
>
>>> Do what?
>>> 
>>> They buy those like any other manufacturer by the case or how many
>>> they need. I'll guarantee they don't take the time to grab each
>>> capacitor and check it for capacitance, ESR, and leakage on an
>>> assembly line, then try to match them up! The ones at Mouser are
>>> just as good no matter what anyone tells you, period.
>>> 
>>> I thought I'd heard the BS before from manufacturers, but that
>>> claim reminds me of those audio amp manufacturers. Ask Alpha if
>>> that means your audio will sound any better, LOL!!!
>>> 
>>> Best,
>>> 
>>> Will
>
>>> *********** REPLY SEPARATOR  ***********
>
>>> On 8/21/05 at 4:20 PM hcawthra at sbcglobal.net wrote:
>>> 
>>> 
>>> 
>>>> I need a opinion. I want to replace the filter caps in my Alpha
>>>> 78 amp. Alpha wants $30 ea for the caps mouser wants $16.40 ea
>>>> for the exact same part number. Alpha claims caps are matched.
>>>> Any ideas. 73 Howard KA6IOB
>
>-- 
>73,
>Vic, K2VCO
>Fresno CA
>http://www.qsl.net/k2vco
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