GE J-664 filter cap ? - Printable Version
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GE J-664 filter cap ? - Eric - 07-24-2014
This radio calls for a 50 & 60uf at 160vdc can I safely use 2 - 50's? Other wise I have to hunt down a 60uf
http://www.nostalgiaair.org/Resources/109/M0008109.htm
Eric
RE: GE J-664 filter cap ? - Steve Davis - 07-24-2014
I think 50uf would be OK. It would probably fall within the tolerance of the 60uf. But, since this is the output filter, going a little higher, say up to 100uf wouldn't hurt anything.
Steve
RE: GE J-664 filter cap ? - Eric - 07-24-2014
I do have a 100 uf but thought it to be to high because it is more then the 50% of the value called for. I will tomorrow take a run over to Fry's and see what they have I would like it to be closer.
RE: GE J-664 filter cap ? - Arran - 07-24-2014
I've seen the values of filter caps for AC/DC sets all over the map, some are 30/50, others 40/40, 40/50, 50/50, and even 80/100, I don't think it makes as much difference as people think. Almost all of these AC/DC sets use half wave rectification, with a pi filter, so they can probably use as much filtering as you can stuff in there.
I know that the tube manuals suggest certain values as an input, but I've used photoflash capacitors in AC/DC sets, such as 150-160 uf at 330 vdc, for years of use and never noticed the sets eating rectifier tubes. Maybe in the old days the filter caps had a much higher ESR then the modern caps do so the high value caps were harder on rectifiers? Maybe it's because these were photoflash capacitors, designed to charge and discharge rapidly? Who knows?
Regards
Arran
RE: GE J-664 filter cap ? - Mondial - 07-24-2014
While there may be limitations on the capacitance of the input cap after the rectifier due to peak rectifier current concerns, the second filter cap after R14 is not so limited. In fact the larger the value of the second cap the better as it provides increased filtering.
Most likely, the original limitation was cost and size, and manufacturers used the largest values that they could afford in the design which would also physically fit under the chassis. Today we are not so limited, as larger value caps are both cheap and physically tiny.
I would have absolutely no concerns about using 100uf for the second cap after R14, and as an added bonus, you will experience a lower hum level.
In general, I try to stick to the original value of the input cap after the rectifier, but routinely oversize the caps after the first stage of filtering. This results in better dynamic supply regulation and a uniformly lower hum level.
RE: GE J-664 filter cap ? - Eric - 07-25-2014
Mondial, Arran, Steve
Thanks for the info. This is a relatively small chassis and the original filter cap pretty much takes up all the depth of the chassis I doubt they could have put a higher value cap in there but with today's caps I should have no problem using a 100uf.
Eric
RE: GE J-664 filter cap ? - codefox1 - 07-25-2014
Agre, but thing being what they are, I'd use 400 VDC rating replacements. Only pennies more.