BC-348 Receiver

Discussion in 'Technical' started by W5HRO, May 21, 2016.

  1. W5HRO

    W5HRO Administrator

    Oh, did you find one of those 24V TO-3 7824's?

    You know, I played around on the simulator and the below works fine. You can just put the other 40uF cap across the one 200V zener instead and make sure at least 10mA to 15mA is flowing through the zener under full load. I could modify mine and it wouldn't need any more caps except for maybe an extra one or two small .1uF disc caps.

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  2. W6MQI

    W6MQI Member

    Yep that's what I have.

    Well that's weird can't seem to view your schematic it won't open I'm able view other thumb nails, but not this one. How come you didn't go with 28v instead of 24? Ease of building? I haven't been able to find a 28v linear reg. is one even made sure seems like there should be one available.
     
  3. W5HRO

    W5HRO Administrator

    Because it should be 24V. The 28V was with the APU connected right before takeoff right when it was disconnected. Then it would slowly go down and settle at 24V when airborne after takeoff.
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  4. W6MQI

    W6MQI Member

    Found two of the .5uf oil filled caps 38-1, 39-1 dead short to ground sorta surprised to see this might just replace them all with new. I always thought those types of caps were bulletproof.
     
  5. W5HRO

    W5HRO Administrator

    Mine probably has the same issues. I never really ran it for very long. I just built-up the supply and got the receiver to power-up and tune in a few stations for only one night, then I put it back over on the table and have not done anything with it sense.

    Oh, if you think about it, the BC-224 was for a 12V battery system in the bombers. The 14V was with the APU at full charge. So, the BC-348 was for a 24V battery system. Two 12V batteries, make sense? They doubled the 12V.
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  6. W6MQI

    W6MQI Member

    I just fired things up using a 24v bench supply, and your B+ supply. With 120v line voltage I had to increase the 500 ohm to 3k to 230vdc under load the current draw was around 42ma. There's no audio output so I'll need to find out why, also did a temporary fix on the shorted oil cap so I could fire things up for a test. I have found so many wiring errors that there's noway this thing could have ever ran.
     
  7. W5HRO

    W5HRO Administrator

    Those original AC supplies with the 500-ohm resistor also had a 5Y3 which dropped 60V. Mine and yours have SS diodes so it should be +58.6V higher. It's why I went to the 550V transformer, but you are right, the 500-ohm resistor may not be large enough. It was just a starting point.

    If you were to try that NPN transistor regulator, the TBD resistor down to the base and zener would be somewhere just under 10K.
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  8. W6MQI

    W6MQI Member

    Oh yea forgot about the rectifier voltage drop.

    Miss spoke the 7824 voltage reg. is a T-103 package and so far I have smoked one unit already along with the diode. The BC-348 is drawing around 830ma with dial lights on, and around 600 or so with them off. 800ma doesn't seem excessive and the 7824 is rated to 1.5a so not quite sure why there going up in smoke with a heat sink attached.
     
  9. W5HRO

    W5HRO Administrator

    Post a picture of the regulator to show the label and markings. Where did you get them? If it’s a low-grade Chinese counterfeit that might by why. If so the durability will only be around 25% of the real ones that were made here in the U.S.

    Plus the T0-3 will handle the heat better compared to the other packages.
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  10. W6MQI

    W6MQI Member

  11. W5HRO

    W5HRO Administrator

    The TO-220 will never handle what the TO-3 will.
     
  12. W6MQI

    W6MQI Member

    I'll have to order the T0-3 from Newark like to think there not Chicom copies.
     
  13. W6MQI

    W6MQI Member

    Well I got it working listening to 10 Mhz WWV right now the audio is not real loud and it needs an alignment bad. Band switch is dirty as hell, but everything seems to working just not real well.
     
  14. W6MQI

    W6MQI Member

    Don't do this at home kids here's my mad scientist setup for testing. The B+ power supply is from a URM25D signal generator with input line voltage being bucked to lower the output voltage to around 235vdc. Filament voltage is coming from the bench supply the rest is clip lead spaghetti one false move and it curtains for either me or the radio:biggrin:

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  15. W5HRO

    W5HRO Administrator

    You need one of those Hammond audio output transformers with the 8-ohms output.
     
  16. W6MQI

    W6MQI Member

    Its on order Hammond part #146S along with a T-03 24v reg.
    I might look for a LS-3 speaker if one comes around cheap enough. Today I removed the antenna, rf, detector, and oscillator unit to clean the band switch, also replaced a few more caps inside the units. On initial power up I noticed the oscillator was sorta erratic so I put some Deoxit on the wipers of the tuning cap I guess this a common problem when the receivers sit around for a long time.
     
  17. W5HRO

    W5HRO Administrator

    Any metal-on-metal contact situation is going to have a problem due to dissimilar metal corrosion if it hasn't moved in decades.

    P.S. I got hit by that weird bug that has be going around that takes you out for 2 to 3 days. I'll be going back to work tomorrow. Needless to say, I went bye bye for two days. The XYL and daughter had it early last week and I thought it missed me, but I started feeling it early Sunday afternoon. It’s some kind of weird cold bug that feels like a bad allergy reaction to something in your sinuses.
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  18. W6MQI

    W6MQI Member

    Sorry to hear that I can't remember the last time I was sick bet its been more then 10 years since I had anything (knock on wood). Kids will be bring home all sorts of bugs looks like you have some young ones there at the house who knows? Seemed like my daughter had a new bug every week when she was real young now that she's in high school its tapered off for now thank you. She's very athletic and really watches what she eats better then me most of the time I can't break the Taco Bell habit my only fast food addiction.