Viewing 7 posts - 1 through 7 (of 7 total)
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  • #10701
    Bruce Hamilton
    Forum Participant

    My 1947 deForest has a couple of electrolytic capacitors that don’t seem to be standard any more, a 25mfd 25 volt and an 8mfd 150V. Can i substitute an 22 mfd and a 10 mfd for these and expect them to work reasonably well? Are there some general rules for substituting components that are available somewhere? As you can tell I am a raw rookie at this and need all the help I can get.
    Bruce

    #10702
    Alistair Thomson
    Forum Participant

    Absolutely. Most electrolytics are quoted with a tolerance of +/- 20%, and the circuits they are installed in aren’t tuned circuits, with the possible exception of power supply filters where the choice of the choke is related to the value of the capacitors, and even then, a 20% error is insignificant. And I’m pretty sure that the tolerance of early caps weren’t as close as 20%!

    Regarding a rule for choice, I’d suggest that given two caps which might be a candidate for replacing a bad one, choose the higher value, and always choose a higher voltage too.

    #10712
    Bruce Hamilton
    Forum Participant

    Thanks a bunch. Now i can get going on my project

    #10713
    Don Henschel
    Forum Participant

    These values aren’t overly hard to find if you look at “the usual suspects” as venders are usually known as on the vintage auto forums I belong to. I just placed a large order to this gentleman a month ago including an assortment of high&low voltage axial and radial electrolytics. Also it isn’t mentioned what “flavor” IE Polyolester, Polypropylene, and my inquiry was answered with polypropylene for 95% of the values I ordered. His (Sal Brisindi) prices are lower than our Canadian supplier in Eastern Canada AND out of protest for being charged US prices and currency from a Canadian seller to a fellow Canadian I might add.
    http://www.tuberadios.com/capacitors/
    My order was large of the axial “yellow fellows” of great quality and electrolytics and he mentioned what were very common high use and not so, low use so we adjusted accordingly. Oh and shipping was also free because I placed a large order but reasonable amounts most likely will qualify. Other than that I find the little green, brown red etc. Mylar Polypropolyne style are usually dirt cheap with excellent selection, quantity, and voltage from eeevilPay with free shipping from some of the Chinese suppliers. Quantities over 100 for $4-$8 These will work good in my block capacitors found in my Philco 444
    Anyway enough of that and on to the values and substitutions………….
    Correct me if I’m wrong? I was warned about sizes of electrolytics in the power supply possibly from this forum? I used to think bigger was better especially reducing hum and this can be true but the larger capacitors when totally discharged can be too large of a load during recharging at startup on the rectifier tube and in automotive can also be a strain on the vibrator and transformer. Apparently some of the very old rectifier tubes can possibly become damaged from the momentary current spike as the capacitors charge up. Let’s see what other members know about this if I’m wrong in some areas.

    #10723
    Dan Walker
    CVRS Member

    Don, I agree with you about this charging US dollars in Canada to a Fellow Canadian.
    There ought to be a law.
    I am going to check with Sal and see what he has to offer.
    I usually replace the electrolytic caps with the closest value upwards, only because I was told that was the way to go, but as you say the %
    of tolerance might make a difference
    Dan in Calgary.

    #10749
    Don Henschel
    Forum Participant

    Dan if you want a laugh on some American forums they complain about the higher prices the “usual suspect” in Canada charges but they have a dollar worth something compared to our worthless Canuckastan Beaver Pelts. Now if he was listing Canuck currency they would have an advantage.

    #11055
    Don Henschel
    Forum Participant

    Since I’m presently dealing with my Philco 444 from 1936 which uses a type 80 rectifier tube earlier we were discussing the size of capacitors in the power supply. My power supply using the 80 only has a pair of 8uf at 450v. From what the opinion is on these based on past experience from others dealing with them is keep fairly close to the smaller values and it was mentioned this direct heated rectifier was prone to arcing and damage if pushed too hard. In my case I have 4.7, 10, and 15 so I will replace them with a pair of 10’s. Also what was mentioned is if you venture into larger capacitors, at least place a smaller or same value as original in the reservoir or primary capacitor and the larger after the filtering choke if used or in the case of this vintage the speaker coil being used as a filter or smoothing choke. Another determination is the type of rectifier tube used as a number of the newer types have much larger current handling capabilities.

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