On Aug 22, 2005, at 9:51 AM, Will Matney wrote:
> Vic,
>
> Does that mean you believe in using equalizing resistors across the HV
> rectifiers also?
Not unless you enjoy replacing shorted rectifiers.
> 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
... and do they ever!
> 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@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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>
>
>
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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