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HG Branded Transistors

Discussion in 'Amplifiers' started by Ranch55, May 18, 2019.

  1. Shockwave

    Shockwave Sr. Member

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    BINGO! I don't know why people are so slow to embrace 50 volt parts for higher power applications in the vehicle. They simply don't understand how easy it could be to get 50 volts, regulated from any old alternator that was capable of powering a similar sized 2879 amplifier. You don't really needs batteries either.

    Take an old school Lecce Naville for example. They all have 3 phases of about 15 volts AC coming out prior to rectification. You could easily get in front of those rectifiers and isolate all 3 phases of the windings on the stator. Once they are isolated, they can be individually rectified and filtered with electrolytics. They can now be wired in series with the first one referenced to ground and used to drive the sensing line to the regulator. The alternator should be wired and keyed like it was feeding an AC box.



    In other words the field should be deenergized BEFORE the amplifier is unkeyed in order to prevent a voltage spike when the load is removed. That would be very critical with these transistors and the first thing I would do is build a sequential keyer that kept the TX on for a split second after the mic was released and the field switched off.

    The field can be turned on at the same time the amp is keyed but residual magnetism in the rotor is usually not enough to quickly get the voltage up where it needs to be when starting under load. The trick to that is to simply "pulse" an external voltage into the field, through a resistor and diode, from the stock battery. Even better is using a cap that was just charged in receive through your control relay. The resistor should supply just enough current to get the voltage to start. Any more and it will cause a voltage spike when it's current exceeds that of the regulator.

    For the price of a zener diode and a few paralleled SCR's, I would add a "Crowbar Circuit" across the output of the 3 series wired electrolytic banks and AFTER an appropriate fuse just to make sure a spike never gets to the expensive transistors. You can't take this for granted like you might with a less fragile tube. This should not be used on SSB without batteries because the load fluctuates too much to maintain proper voltage regulation. AM works well with just electrolytics and a reasonable carrier to PEP ratio. Without batteries or an unusually large bank of caps, you will need to maintain RPM's just like an AC box.

    Everything mentioned above has already been done way back in the 1980's. The only difference is the voltage is a little higher than what I used back then. This is why phase isolation is required with separate rectification and filtering before the voltage can be wired in series and set at 48 volts. Reference only the first cap in the string to ground and use its output as the regulator sense line. If the regulator is not adjustable or does not have enough range, just start stacking some 10 amp barrel diodes in series with the sense line until you get to 48 volts.
     
    #16 Shockwave, Jun 11, 2019
    Last edited: Jun 11, 2019

  2. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    I would almost use an inverter to get 120vac and then go from there.
     
    Tallman likes this.
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    It is less efficient to go that route. You would also need a GOOD pure sine wave inverter as most transformers do not like modified sine wave and cannot tolerate the old square wave inverters.
     
  4. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    The voltage of the stator determines the voltage of the field winding. Like for a 12v output the stator would need to be 6v. So you if we put 25v on the stator we would get 50v on the field? Seems too easy.
     
  5. Shockwave

    Shockwave Sr. Member

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    The amount of voltage placed across the field or rotor determines the output voltage of the stator. It was very common to just increase the field voltage to get about 21 volts to charge a 6 and 12 volt battery in series. That is about the maximum you could push a good 12 volt alternator because both windings are under considerable stain with this much voltage across them. The field doesn't have enough resistance to stay cool and the stator doesn't have enough inductance to keep looking like an open under no load.

    The most efficient way to get to 50 volts is to trade the extra current the alternator could produce at 13.8 volts for more voltage and less current. The simplest way to do that is to rewire the stator in a series configuration after rectification and filtering so that it does not provide 3 times the current, but 3 times the voltage. Then you only need to boost the regulator output by a tiny percentage to get to 48 volts.

    Interestingly enough, car manufacturers are pushing to change the electrical systems over to a 50 volt standard in order to keep up with the high power demands new electronics and accessories are drawing. By then there will probably be enough other sensitive equipment in the car to prevent any high power RF operation.
     
  6. nomadradio

    nomadradio Analog Retentive

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    The three stator windings in a typical automotive alternator feed into three pairs of rectifiers. This puts the three stator windings effectively in parallel.

    The field voltage to the rotor is what the regulator will control to hold the DC output voltage steady. It can be controlled for an output higher than the typical 14 Volts.

    Seems to me that if the three windings get separated you can feed each one into a full-wave bridge rectifier with its own filter cap. Stacking the three of those in series should get you pretty close to 50 Volts if you goose the rotor current. Not so different from the external 16-Volt regulators used in the bad old days to crank 'competition' amplifiers to a higher output than stock.

    And no, I haven't tried this.

    73
     
  7. rabbiporkchop

    rabbiporkchop Sr. Member

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    Shadetree Mechanic likes this.
  8. Shockwave

    Shockwave Sr. Member

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    If the inverter and power supply are a more attractive option to you, it's worth noting that very good results are possible when using the least expensive equipment. Feel free to use cheap square wave inverters just as long as you also use cheap 50 volt switching power supplies without line transformers. Switch mode power supplies rectify and filter the AC input as the first step and these parts easily handle a square wave input without hum or added ripple. This is not the case when using a class A, linear regulated power supply.
     
    Shadetree Mechanic likes this.

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