Parts exchange

Discussion in 'Homebrew and Kit Projects' started by N8YX, Aug 6, 2008.

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  1. AB8RO

    AB8RO Ham Member QRZ Page

    I agree with you. But, I've offered on several occasions and been refused. I don't know whether the polite thing to do is insist or say thank you but, I've opted for the latter. So, my karma balance needs adjustment and if I offer anyone some parts then I'm going to insist on paying the postage. Please understand that I'm just trying to balance my karma wheel and accept.

    What I like best is to just exchange parts by mail. It costs between $1 and $2 to ship a bubble envelope with a few parts in it so I like to make sure that what I'm swapping is worth a bit more than that so that both ends feel that it's worth doing.
     
  2. WR5AW

    WR5AW Ham Member QRZ Page

    OK, I've searched high and low around the junk pile. I need a .22uF 25v tantalum cap. Anyone willing to drop one in a plain envelope I'll return a qsl and stamp.

    Now a question. I have a schematic that calls for a 500ohm pot for volume and a 25k variable for tone. I have a half dozen pots, some really nice ones out of commercial HTs, but none in the 25k or 500 range. Any suggestions?

    This is what I'm working on:
    [​IMG]

    Yea, I gave up on the sine wave project. Maybe another time. Just need something quick and dirty to go with my Picokeyer.

    Thanks.
     
  3. KL7AJ

    KL7AJ Ham Member QRZ Page

    How bout some free advice that won't even cost a stamp? Replace the tantalum cap with a disc ceramic. They're more frequency stable anyway. (You might have to parallel a few to get that value) Tantalums are only necessary when you need a lot of capacitance in a small space.

    Eric
     
  4. VK2AKG

    VK2AKG Ham Member QRZ Page

    [C1] C1 does not need to be tantalum (eg plain aluminium electros, poly and disk ceramics would also be OK) nor does it need to be 25V (anything over 10V will be fine). The value of C1 is not critical either so it is likely that any _similar_ sized (eg 0.15 uF to say 0.33 uF) cap you have will do just fine in this application.

    [R4] whilst a volume control is a nice feature it is likely you will only ever set it once. If you believe that will be so for you then you can dispense with it entirely by connecting C2 direct to R5 and playing with the value of R5 (by trying a few different value fixed resistors for R5) until you get the volume you desire.

    If you want to understand this circuit then have a look at the chip's application notes here and discover that none of the components (well except for the 555) are critical.

    Good luck,

    Frank vk2akg
     
  5. WA9SVD

    WA9SVD Ham Member QRZ Page

    Don'tget me wrong; unless it's a plate transformer for a legal limit transmitter, I'll send something out, and I won't ask (or heaven forbid, demand) reimbursement, it would (IMHO) be the polite and grateful thing to do to at least offer to pay for the postage. If it's only a couple of postage stamps, it's no big deal, but some parts do take some special packaging and added shipping expense.

    On another vein, while I'll gladly help and provide information on parts or equipment, it's hard to expect someone to absorb the cost of photocopying a 200 page instruction manual and postage. (Currently would cost $18.00-$20.00) Quite frankly, the manuals can be purchased from dealers for less. And it's ludicrous to think someone could e-mail such a manual. (OK, daily for about four or five months...) Many of us have ISP's with daily e-mail limitations, and it's hardly realistic to expect that limit to be used up with pages and pages of manuals, at the possible loss of personal e-mail.
     
  6. KC0ZJZ

    KC0ZJZ Ham Member QRZ Page

    part for qrp dummy load

    I bought a bunch of 2.40K 1% 1/4 watt smt resistors awhile back intending to make one of these:
    http://www.norcalqrp.org/ncdummyload.htm

    But changed my mind and got a 30 watt 50.0 ohm resistor in TO-220 part number MP930-50.0-1% datasheet: http://www.caddock.com/Online_catalog/Mrktg_Lit/MP9000_Series.pdf instead. 10 nano-henry inductance typ. $3.51 ea from digi-key.

    So now I have 200 new 2.40K resistors, enough for 4 dummy loads, if anyone is interested.

    Also I have a couple of sa612 mixer/osc in DIP left over, and a small handfull of MPF102 jfets in TO-92 that I doubt I'll use.

    Roger
    .
     
  7. KE7AQL

    KE7AQL Ham Member QRZ Page

    Mrf102

    I need a couple JFETs for a transverter that in part-gathering stage.
    Email me at ke7aql@gmail.com

    Thanks
     
  8. AC0FP

    AC0FP Ham Member QRZ Page

    0.22 uF ceramic caps are not frequency stable, partially hot! Don't even think about there cold (-30) performance! That is unless your talking about monolithic ceramic cap with a X7R rating.
     
  9. VK2TIL

    VK2TIL Ham Member QRZ Page

    Wr5rw

    Pot values are generally non-critical (half or twice the specified value will work in most cases) but you can "change" a pot's value by paralleling an appropriate resistor.

    This changes the "law" of the pot but it often doesn't matter.

    It tends to make a linear pot more like a log pot and a log pot more "loggy". :)

    I saw an on-line calculator for this a long time ago but I can't find it now.

    Edit; here's a calculator (note the position of the fixed resistor in this one);

    http://www.mindspring.com/~clist/PotGraph.html
     
    Last edited: Aug 24, 2008
  10. AE1PT

    AE1PT Ham Member QRZ Page

    Mouser Electronics has them. They have all sorts of sizes of enclosures--these sorts of things have not become hard to find or obsolete--just consolidated in the hands of a few specialty suppliers!
     
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