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  1. duke37

    The Ultimate Tube RIAA-Amplifier?

    I have looked up the output resistance of the EL84, it is 40k. The optimum load impedance is 5.2k.
  2. duke37

    The Ultimate Tube RIAA-Amplifier?

    I have watched Wallander but not learned much Swedish! I looked up Child-Langmuirs in the english version of Wikipedia. There was an interesting paragraph. Quote On the other hand, space charge was useful in some tube applications because it generates a negative EMF within the tube's...
  3. duke37

    MOSFET switching problems

    As I understand it, the two primary coils are linked by a mutual inductance. Thus when the drain voltage of one fet rises on turn-off, the drain voltage of the other fet will go down to zero or below. There is a diode in the fet to return this current to the supply. Low voltage invertors have...
  4. duke37

    MOSFET switching problems

    What is the purpose of the output chokes L7 to L10? If each bridge fed a capacitor, then transient voltages would be reduced.
  5. duke37

    The Ultimate Tube RIAA-Amplifier?

    Roger Here are some more pages. When you have fully understand these, you can explain them to me! I was just wondering way back whether a simulation model was available for a valve operating in this bias condition. Load resistance To get maximum power out, you need a load resistance...
  6. duke37

    BT150 Thyristor equivalent(BT151) has just exploded !!!

    I made abig boob when I suggested limiting current with a car headlight bulb. I thought you were running at 12V To check the motor, put a filament bulb (mains) in series to limit the current. To check the thyristor, use a light bulb as a load. It looks as if you have a dead motor. What...
  7. duke37

    A few questions about transistor

    The collector voltage should be at least 0.5V above the emitter, not equal to it. Neglecting base current, the emitter current equals the collector current so, with 4.8V across the collector resistor those voltages will be obtained when R3 is four times R4.
  8. duke37

    The Ultimate Tube RIAA-Amplifier?

    Here are a couple of pages out of 'Electronics' by A.T.Starr 1954. I assume that this circuit is used to give minimum noise.
  9. duke37

    BT150 Thyristor equivalent(BT151) has just exploded !!!

    To protect the thysistor, put a car headlight bulb in series to limit the current. I have never heard of a collector in this application, I assumed commutator was intended.
  10. duke37

    BT150 Thyristor equivalent(BT151) has just exploded !!!

    Disconnect the motor. Measure the resistance from one brush to the other. Turn the motor slowly and see if the resistance changes. Look for signs of burning on the commutator. Check the brushes for wear. If a winding has failed, there will be a burnt section on the commutator. The...
  11. duke37

    The Ultimate Tube RIAA-Amplifier?

    But this is used in self bias mode. The hot cathode emits electrons at a low energy and with a very high grid resistive load will generate a low bias voltage. With a high anode voltage, the electrons will go to the anode and the grid voltage will be reduced. If the resistance is dropped to...
  12. duke37

    Help with replacing component on circuit board

    Excellent, glad to know that you have been succesful. I have a Sony audio system here which had an argument with a thunderstorm and the amplifiers have blown apart. Will have to get a round tuit !
  13. duke37

    The Ultimate Tube RIAA-Amplifier?

    The ECC83 valve is equivalent to 12AX7 tube and also B139. To be the ultimate, I would take the transformer off the chassis or at least use a conducting belt around it. If 1N4007s are permitted, then why not use a full diode bridge, getting rid of the 6X4. Some hum could be eliminated by...
  14. duke37

    The Ultimate Tube RIAA-Amplifier?

    The input power is AC and goes to the heaters, it is centre tapped with a potentiometer to reduce hum. The ECC83 is self biassed with 10M grid resistances and low anode voltage. You would need to do a simulation to obtain an indication of its properties. But where do you get the models for...
  15. duke37

    Battery Charging

    You should charge a lead acid battery to a defined voltage, 13.8 to 14.4V, say 14.0V. A 7812 will not be able to output 12V from a 12V supply.
  16. duke37

    How to re-wire an old AC drill to a new switch

    I do not think that solid state relays would be suitable in case there is a glitch enabling forward and reverse at the same time. You can use a two pole change over mechanical relay to eliminate this possibility. I would not know how to control speed from a micro.
  17. duke37

    How to re-wire an old AC drill to a new switch

    I am out of my depth here also ! It looks as if you will need to keep the drill case to hold the motor bearings. If so, can the change direction switch be used in the drill? If you wish to use an external direction switch, then an intermediate (crossover) switch as used for a third switch...
  18. duke37

    How to re-wire an old AC drill to a new switch

    Do not assume anything. Trace out the original circuit and post it here. Use the terms 'brush' and 'field' rather than 'motor'. There will be some interference suppression capacitors somewhere. You should not use two relays giving opposite output, that is a recipe for disaster. You can...
  19. duke37

    Egg Incubator Turner Motor Circuit :::: Need Help PLEASE

    The circuit diagram is in Steve's zen.co.uk reference. You could build it as shown on matrix (Vero) board using a similar layout. Edit You have not said the current consumption of the motor. I would replace the transistor and relay with a mosfet. unless you need more than 5A.
  20. duke37

    Equivalent parts - need of help

    It depends on where you are. In the UK, both are available on e-bay. The OA47 could perhaps be replaced by a Schottky diode. 3.3V seems to be more common than 3.0V. Is your circuit fussy?
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