Barford Radio Social - Sunday 4th July 2021

Barford Socal 2021 1 
  • Where: Barford Village Green, NR9 4AB, 9 miles south west of Norwich off B1108
  • When: Sunday 4th July - open 0900-1400 (please do not arrive before 0900)
  • All outside event - please bring your own deckchair and refreshments etc
  • Private sales only - sell from own car boot or 1 table - no commercial traders please
  • Not a radio rally - no refreshments, catering or inside activities - inside toilets are available
  • Bring your own Sunshade or Gazebo if you would like to - there is plenty of space!
  • Entry FREE for all - Sponsored by Norfolk Amateur Radio Club. No need to book - just turn up
  • Voluntary donations with all proceeds to E A C H and Barford Village hall Emergency roof repair fund

Please spread the word to other local amateurs, friends and clubs as everyone is welcome, but be
sure to say that this is not the usual full radio rally event and is all outdoors. The event will only take
place if it is well within government advice at the time and will be cancelled if it becomes the
responsible thing to do - watch our website. Contact David G7URP This email address is being protected from spambots. You need JavaScript enabled to view it.

construction-competition

  • Tony G0MQG Tips 1

    Repairs to a BNOS power supply

    A club member brought a power supply for repair with no output. (a Bnos) a search on the internet provided a schematic for a smaller version which uses the same control circuitry.

    A check with a multimeter showed that there was a short circuit across the output and the schematic showed that it uses “crowbar” over voltage protection so I removed the crowbar Thyristor, the short circuit disappeared and the output voltage reappeared though slightly high at over 15 volts but was adjustable.

    Clearly the control i.c. was ok as was the output transistors so I obtained and fitted a replacement driver transistor (a TIP121 darlington) this got the output correct and adjustable to 13.8 volts leaving just the crowbar circuit to sort out.

    Question:- how to test the crowbar circuit without placing a short across the output.

    Answer :- put something in series with the thyristor anode to limit the current, I used a small 12 volt bulb so that I had a visual indication of the thyristor firing.

    I replaced the thyristor with a BT152 but although the short circuit had disappeared the thyristor wouldn’t fire even with the output voltage set at maximum (about 16.5 volts).

    The crowbar circuit is controlled by an MC3423 crowbar driver IC. which I replaced and now the thyristor fired fine at 16.1 volts which seemed to fit nicely with the component values fitted by the manufacturer.

    Now just need to load test it, I use high power rheostats for this and found that all was ok (output voltage 13.7 volts at 18 amps load).

    So I refitted the cover and passed it back to the owner

    Tony g0mqg

  • What have you made…..?

    We always have a construction display and contest at the AGM each year but normaly have very few entries and some people told me there was too little notice so.....

    If you have made or intend to make anything from a kit or your own design which is radio or electronics related (inc aerials) please remember to bring it to the AGM on the first Wednesday of April. Yes its a long time away but I am giving good notice and you know how time flies!

    David G7URP