BC-224 Receiver

Discussion in 'Technical' started by W5HRO, May 3, 2017.

  1. Dnminbax

    Dnminbax Member

    ok
    Rebuilt the power source using a Hammond 270 DX (550VCT) and the 500 ohm resistor in place of the choke. Seems to be much better.
    B+ is 253v B- is -19v and the voltage at the tubes is now 236v. I assume that this is with in an acceptable range.
    I thot I would start checking/fine tuning the alignments now that the voltages are where the need to be. After that, probably should go thru and start checking components but I'm thinking that if it ain't broke, don't fix it. Yall's insight on that would be greatly appreciated.

    Thank you again for sharing your knowledge and being very good teachers.
     
  2. W5HRO

    W5HRO Administrator

    The HV on the one I built came out to around +230V on the tubes too. Without the 500-ohm resistor it was around +250V. Are you also using the 125V input taps on the Hammond Transformer?

    I'm guessing a 1K resistor max would be about the right value and would keep it just above +200V. Just consider how hot the 500-ohm resistor gets and go higher-wattage if necessary if you switch to a 1K instead.
     
  3. Dnminbax

    Dnminbax Member

    Yes, I used the 125v taps. I bought a 100w 500 ohm resistor but I'll probably go on and see if I can find a 1K resistor.
    Thank you again
     
  4. W5HRO

    W5HRO Administrator

    Once you have the final resistor installed and the voltages are done moving then you should try to do a slight alignment and then see what you have. Sounds like yours was updated and used by someone in recent years or last decade. It might have components that need to be replaced, but for now if it powers up and you have full volume coming out of the speaker and on all of the bands then I would just tweak and use it for awhile.
    .
     
  5. Dnminbax

    Dnminbax Member

    That sounds like good advice. I know one of the .5 mf oil filled caps had a pinhole and a minute amount of oil would bubble out when the receiver was running and warmed up. I touched the end with a soldering iron and sealed it but I am not sure how much may have oozed out over the years. I found some 400v replacements but I do not want to mess with it unless it matters. The audio is strong through an LS-671 but it has a lot of hiss/static, it sounds really "tinny". My model only has a post at 5 on the audio output, I assume 4000 ohm.

    bc-224b cap pin hole.jpg
     
  6. W6MQI

    W6MQI Member

    I had two of those .5uf caps that were bad in my BC-348 they showed no signs of leakage at all, but when tested with a ohm meter they were a direct short to ground. So if you see excessive current draw when powering up I would look at these caps first would be a good starting point anyway.
     
  7. Dnminbax

    Dnminbax Member

    You were right.
    Installed the 1K 100w resistor, I am now at 226v at B+, -18v at B- and 226v at the tubes. I figure that's pretty close for now. Piddled slightly with the IF alignment just for giggles. The adjustments were negligible. The RF alignment is pretty darn close. I rec'd the oil fill caps but I figure I otta run it for awhile and check all the components first before changing out the old one that leaked. Regardless, its running like a champ and I'm no longer worried about it running too hot.
    I'm gonna listen for awhile (picking up Radio Espana broadcast from Madrid loud and clear right now) and I'll holler back once I complete the checks. Thanks for all the help from you and W6MQI. I would still be stumbling around without ya'll.
    Don
     
  8. W5HRO

    W5HRO Administrator

    Glad it worked, and yeah, that HV level is good enough.
    .