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  1. duke37

    Good rosin flux paste brands?

    I have a small 40 year old tin of Fluxite "The most effective flux known" which is very occasionaly used, mostly for copper pipe joins. The critical thing is to get the parts clean. I recently bought a small jar of LA-CO regular soldering flux paste. This seems to be more effective than...
  2. duke37

    FM fading

    A quarter wave vertical as used on a car should be fed against an 'earth' which is the car roof. For a simple earial, I use a vertical dipole, fed in the centre. This will have a gain not a lot different to your loop. The verticle is made from 300Ω ribbon cable. Take a piece 60 inches long and...
  3. duke37

    Converting US/EU to UK plug

    I have a hot glue gun which appears to be temperature controlled with a thermister. The voltage rating encompasses 120V and 240V. If yours is the same then swapping plugs would be OK,
  4. duke37

    Fast Switching Relay for High frequency Signals

    The obvious way of doing what you want is to switch the amplifier input and dispense with the relay, that should give low attenuation. Rapid switching of input or output will give spurious frequencies. More information of what the signal is to be used for please. Incidentaly, I do not see where...
  5. duke37

    Fast Switching Relay for High frequency Signals

    You have not defined by fast. Many small relays will switch at 50Hz and you may be able to go faster if you overdrive the relay and use appropriate snubbers. If the relay is to be switched often it will soon go out of adjustment or wear out. Consider using solid state such as a fet.
  6. duke37

    LED Help needed

    There is a resource about driving leds, Click on resouces and then select the led section. 5V will drive one led with a series resistance. Many strings can be added in parallel. If the power supply can deliver 1A and each led takes 10mA, then 100 leds can be driven. If you use 20mA, then 50...
  7. duke37

    Ferrite rod antenna explanation

    Transformer. I think it all depends on what is meant by a transformer. The mains power transformers have windings on a common core and a coupling factor between windings near 1. Intermediate transformers (IF) have windings with much lower coupling, perhaps 0.01. A radio transmitter produces a...
  8. duke37

    UM66 is not giving full tone

    I know of no houses, in the UK or elsewhere, which have low voltage supplies. All houses are fitted with ring mains, lighting circuits and 13A 230V sockets.There are loads of plug in small power supplies for lights and electronic apparatus. A central low voltage supply seems like a good idea.
  9. duke37

    UM66 is not giving full tone

    In #6 I suggested that the amplifier is powered continuously (it uses little power) and the BT66 is switched by the push button, Then a smaller capacitor is needed to provide power to the end of the tune. The tone will depend on the output of the BT66 and the speaker used.
  10. duke37

    UM66 is not giving full tone

    Are you being deliberately difficult? Where is the switch connected in the circuit. If it is connected to the primary of the transformer, then a shock is very possible. To add more safety, use a 'wall wart' to supply a low voltage, 12V 1A is probably enough. Connect the amplifier to the power...
  11. duke37

    UM66 is not giving full tone

    That diagram does not tell us where the bell push is connected. Does the switch connect the transformer to the mains, giving the possibility of electric shock should the switch get wet. The transformer should be placed where it is shielded and never gets wet and is energised all the time. The...
  12. duke37

    UM66 is not giving full tone

    I have had another look. The input transformer is shown as a centre tapped resistor. Presumably the push switch is in the mains feed. Q1 is not a transistor but an integrated circuit supplied with 3.3V. To get a output for longer, then the supply must be held on for the required time. This could...
  13. duke37

    UM66 is not giving full tone

    Where does the collector current of Q1 come from?
  14. duke37

    Current flow in or out?

    I have a vague memory that twin conductors on high voltage transmission lines are used to reduce the inductance.
  15. duke37

    Ferrite rod antenna explanation

    You do not quote any formula. If the coupling is tight, then the turns ratio will be Sqrt(400/50) or about 3. The number of turns will be dependent on the core and the power to be transferred.
  16. duke37

    Ferrite rod antenna explanation

    A mains transformer has a primary winding and a secondary winding. The coupling between them is enhanced with a metal core. The coupling approaches 1. The ferrite cored aerial has a three coils each coupled to the others and the coupling will be dependent on the permeability of the ferrite and...
  17. duke37

    Ferrite rod antenna explanation

    L1 is the resonant circuit. The other windings are much lower impedance because of the fewer turns. A regeneration radio has positive feedback which modifies everything. I cannot help with how to determine the correct values.
  18. duke37

    Ferrite rod antenna explanation

    The formula for resonant frequency is F = 1/(2*Pi*Sqrt(L*C)) If you want to pick up a transmitter on 640kHz with a 200pF capacitor, then you can calculate the required inductance by re-arranging the equation. A tuning capacitor will have a ratio of about 10:1 maximum to minimum. Because of the...
  19. duke37

    Need help finding power supply

    What makes you think the transformer is faulty? Do the reservoir capacitors have flat tops? The transformer runs at high frequency so will have few turns. You may be able to rewind.
  20. duke37

    Ferrite rod antenna explanation

    The coils need to have a certain inductance to resonate at the wanted frequency. The number of turns on the ferrite rod controls the inductance and the permeability of the ferrite will ehhance the inductance. So put on a few turns and measure the inductance and increase to give the required...
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