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    DC heated driver stage for ST70 type amp.

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    sailor

    Posts : 269
    Join date : 2011-04-04

    DC heated driver stage for ST70 type amp.

    Post by sailor on Fri Apr 13, 2012 1:08 pm

    Dear bottle heads please forgive me!
    If a diode style rectifier is used for the 5AR4 then it would free up the 5 volt 4 amp 5AR4 heater. If this was run to a voltage doubler circuit you would have 10 volts at 2 amps. Then run to a voltage regulator to lower the voltage to 6 volts. Then use this regulated 6 volt DC to run the driver board heaters. If 10 volts is too high you can add a resistor and another capacitor before the regulator. Maximum required parts I would think would be 4-1N4007 diodes, 4 electrolytic caps. 1 resistor, 1 regulator with heat sink and a small board to mount everything. This would free up an extra .6 to 1 amp of 6volt heater to heat up KT88 or KT 120 that would normally push the limit of the older amps. The transformer should run a little cooler and I would think lower noise in the driver stage a little.
    But of course you commit the sin of replacing the 5AR4 with diodes. That would surely send a good bottle head to purgatory for a long while. What do you think?

    sailor

    Posts : 269
    Join date : 2011-04-04

    Re: DC heated driver stage for ST70 type amp.

    Post by sailor on Tue Apr 17, 2012 9:37 pm

    Actually I caught a couple of errors. First the 5 volt transformer taps would need to be run to 2 rectifier diodes to turn it into positive DC. Then 2 caps arranged to double the voltage to 10 volts. [Google voltage doubler] Then a resistor to lower the voltage to around 7 volts and then another cap. Next is the 6 volt regulator on a heat sink. Then to the driver board.

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