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  1. duke37

    how can i adjust the Av gain of this amplifier from 12 to 10, the AC signal is 10mV, 1kHz,

    I should have said 10k/1k
  2. duke37

    how can i adjust the Av gain of this amplifier from 12 to 10, the AC signal is 10mV, 1kHz,

    I do not think that a precise answer was required but an understanding of what gives the gain. As a rough calculation 10k/830 = 12 For a gain of 10, use 10k/100 We should not do school work without help from the student. An appreciation of the difference between 10MV and 10mV would be welcome.
  3. duke37

    how can i adjust the Av gain of this amplifier from 12 to 10, the AC signal is 10mV, 1kHz,

    Is this a school question? I have given all the information you need. The gain is the ratio of the resistors at present 10k/830. What would you do to get a gain of 10?
  4. duke37

    how can i adjust the Av gain of this amplifier from 12 to 10, the AC signal is 10mV, 1kHz,

    10MV is quite a good voltage. Do not get within 20m of it. If the transistor has reasonable curret gain, then the collector current is similar to the emitter current. The voltages will be proportional to the resistors.
  5. duke37

    Help finding fault with old bass amp that blows fuses

    Use a lamp limiter, this is just a filament bulb (40W?) in series with the mains. This enables a voltage to be applied but the current is limited, saving your fuses. Then measure the voltages in the amp. Since the problem is intermittent and may be voltage dependent, you might have difficulty...
  6. duke37

    HELP please OTL tube headphone amp (again)

    I am worried, I woke in the middle of the night and could not get to sleep again. The filaments seem to be excessively bright which may indicate far too high a voltage on all components. Since it has run in the present condition for a while perhaps another 2 seconds may not do any more harm...
  7. duke37

    HELP please OTL tube headphone amp (again)

    In #13 I gave the pin connections of the 6080 which are the same for the 6SN7. Starting at the reference tag, and working clockwise, the connections are grid anode cathode grid anode cathode heater heater The 6080 is two valves combined, one for each channel. You should measure the cathode...
  8. duke37

    HELP please OTL tube headphone amp (again)

    Take a lead with a crock clip at each end and clip one end to the grid and the other to the chassis.
  9. duke37

    HELP please OTL tube headphone amp (again)

    Remove the 6SN7 and earth the grids of the 6080. Does it still hum?
  10. duke37

    Motor Speed Control

    This is a messy way of doing it and is likely to be unsucessful. An AC motor is designed to run at a certain speed depending on the mains frequency. Throttling the input may involve extra current and poorer cooling. The modern way is to use a three phase motor driven with a variable frequency...
  11. duke37

    What should I get for beginning electronics?

    Building kits will teach you how to solder properly and how to follow instructions to the letter. A good way of learning about circuits is to repair faulty eqipment. Here you will have to understand the circuit and replace the cause of the trouble. Start with low voltage circuits for safety...
  12. duke37

    HELP please OTL tube headphone amp (again)

    The valve base connections in both cases are gak gak hh international octal IO26 and IO145, I do not know why they were given different numbers. Disconnect the HT supplies at the rectifiers. Measure the voltage at p7 to p8 on both valve bases. It should be 6.3V or a bit above. Plug in the...
  13. duke37

    TDA7297 cascade channels?

    I have not played with these. The output of channel1 is on pins 1 and 2, both centred on half PSU voltage. An output signal could be taken from either of these and fed to channel2 through the 2.2μF capacitor. The gain could be too high. Channel1 may need a load resistor p1 to p2 for stability...
  14. duke37

    How did you start to learn programming?

    My experience was similar except that pundhed tape was used. This had the advantage that you did not have a half hour job sorting the cards if you dropped them. The language was ALGOL. We eventually got an Apple11E (48k) and used it to control a large brake dynamometer. BASIC and 6502 assembler...
  15. duke37

    Testing Oddball MOSFETs

    Connect the base (no gate!) to the source, the FET will then be turned off but will show a 0.6V drop in the reverse direction due to the internal diode. A floating base can leave the FET turned on.
  16. duke37

    Voltages - continuation of the discussion

    The point is that the circuit is given with the battery already connected. There are no currents and no charge transfer. Numbers can be derived by building the circuit without the battery and then connecting it but this was not the original problem. I may be pig headed but I think it is time to...
  17. duke37

    Series bulbs with rectified AC

    With half wave rectification, the filaments will run cooler and will have a lower resistance so the light does not go as low as might be expected. Valve radios often use 6.3V heaters and dial bulbs, I replace failed bulbs with 8V bulbs and have not seen another failure but the use is not intensive.
  18. duke37

    Voltages - continuation of the discussion

    I learned the reason for this when I went to school 70 years ago. Just Google 17 camels. There was a sheik with 17 camels and 3 sons. His will said 1/2 the camels should go to the first son, 1/3 the camels should go to the second son and 1/9 to the third son. Much argument ensued until a poor...
  19. duke37

    Series bulbs with rectified AC

    14 months ago, I was volunteered to be the light string repairer. It took ages to find the dead bulbs or poor connections so I thought 'blow this for a lark' and I placed a 1N4007 in the plug to run the bulbs slightly cooler. This Christmas one of the strings gave a short flash and died. The...
  20. duke37

    Voltages - continuation of the discussion

    Taps don;t really block water. They neutralise it by building up a reverse pressure. When I saw a calculation containing 17, it reminded me of the camel problem where the question was altered to give a solution. There is no point in continuing with this. I would like to know what the official...
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