Viewing 7 posts - 1 through 7 (of 7 total)
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  • #7142
    Bob Cuthbert
    Forum Participant

    First post, new member to CVRS, and doing a repair/restore of a Marconi 181 AA5 radio and looking for supplier who sells capacitors, resistors and tubes etc. in Canada.

    thanks

    Bob Cuthbert

    #7143
    Rick D
    Forum Participant

    Hello Bob
    I am from Hamilton Ontario,I get all my capacitors and resistors from
    Dave at justradios.com he is in Scarborough Ontario,he has every thing
    in the line of caps and resistors that you will need,great price and they
    will be there in about two days.I get all of my tubes from Gary at
    playthingsofthepast he is in the U.S. but the price is right,where are you
    from Bob,all the best, I am sure some of the fellows will let you know
    where they get tubes from,all the best Rick

    #7164
    Bob Cuthbert
    Forum Participant

    Thanks Rick D, did send an email to JustRadios.com a few days ago and had not heard back, likely they just out for the weekend. So good to know they are a good company to deal with. I live in Prince Rupert BC, just south of the Alaskan Pan Handle, pretty much the edge of nowhere.

    Cheers

    Bob

    #7165
    Bob Cuthbert
    Forum Participant

    Continued story about replacing capacitors on my 1940 AC/DC Marconi 181 30 Volt AM radio (AAFive) Untouched and in good shape internally, just really old.

    I have started my list of capacitor replacements and have a couple of questions. Info from the web site for JustRadios.com https://www.justradios.com/orderform.html is great very informative. They cannot fill custom orders but this is actually a good thing as it forces me to read and learn.

    Radio is AA5 Marconi 181, have the spec sheet for all the capacitors.
    Questions:
    1) The largest capacitor, the electrolytic capacitor is 2 in 1 (C-18 and C-19) The schematics shows 25Mfd and 50Mfd both 150 DCWV with a Max S’G.E.V. of 200. There is a negative end with one black wire and the other end has a green and red wire going to separate tubes. Inside my radio the writing on the electorlytic capacitor indicates it is 20 Mfd and 40 Mfd, something to do with it being a Canadian manufuture. On the order form from “JustRadios.com” should I choose 250V 22uF and 250V 40uF or should I go with the schematics and get 250V 33uF and 50uF?

    2) Is 250V the correct voltage for this EC? (I don’t know what Max S’G.E.V. means)

    3) I am replacing the appropriate paper capacitors that are recommended to be replaced with “Safety Capacitors” (again ref to JustRadios.com). Having determined which ones are “Line to Ground” (X-2) and “Across the Line” (Y-2) capacitors I am trying to select the right size. It is easy to see that C-20 is the “Across the Line” and is 0.03Mfd with 125V 900 V Test Rolled Paper on the 1940’s schematics. So on the “JustRadios.com” order list I believe I select the X-2 0.047uF 275VAC for Cap 20 replacement (that is the closest without going under). Where I get some what lost is for the “Line to Ground” capacitors, there are 3, C-11, C-21 and C-22. These are recommended to be replaced with Y-2 type safety capacitors. However, they are 0.2 Mfd, 0.002 Mfd and 0.2 Mfd respectfully. and “JustRadios.com” does not have Y-2 in those sizes. They do have a 0.0047uF @ 250VAC (film) would that be ok for the C-21 (0.002Mfd)? or would it be better to go with their combined X1/Y2 Safety Cap @250 VACin 0.0022 size? As for the 0.2 Mfd in Y2 the biggest they have on their order sheet is 0.1 uF. What do I do about replacing these 0.2 Mfd with Safety Caps?

    Thanks inadvance for any assistance, in the mean time I will keep on reading!

    BTW, will post pics of the refinished Walnut case of the 181, it was painted white. T

    Attachments:
    #7167
    Peter Heembrock
    Forum Participant

    Hi Bob,

    Try to stay close to 20uF for the first electrolytic cap since gong any higher may cause issues with the rectifier tube. SGEV or PV means peak voltage…which is higher than the working voltage ( WV ). 250 volts should be more than adequate in this case. You should only need an X2 cap for C20. I recommend installing a polarized power cord and fuse and moving the AC switch contact to the hot lead which would go to the filaments of the tubes. This would also allow you to use standard 630 volt orange drop or yellow capacitors for C11, C21 and C22.

    Let me know if you have any more questions about the rewiring of the AC mains power cord and switch. Changing to a polarized cord and moving the switch and adding a fuse will make this a safer radio.

    PH

    #7168
    Bob Cuthbert
    Forum Participant

    Thanks Peter,

    This helps me with understanding what to consider when placing my order. I will be replacing the cord with a polarized power cord and found on the web instructions to rewire so the chassis is not “hot”. Just one question, what size of fuse would you add and where? Thanks again.

    Bob

    #7173
    Peter Heembrock
    Forum Participant

    Hi Bob,

    For a fuse size I always use a 1 amp slow blow due to the heater current inrush…
    The fuse should always be the first item connected to the hot lead of the power cord before the switch ( in case of a switch failure ).

    I do all of my AA5 radios like this…electrical safety standards were still evolving in the 40’s and 50’s.

    PH

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