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5e3 to bare bones PRRI conversion?

Discussion in 'Amp Tech Center' started by regispenguin, Aug 19, 2020.

  1. printer2

    printer2 Poster Extraordinaire

    May 24, 2010
    So given the bias board Rob has up top the only thing to cover is the power supply. The 5E3 runs at a lower voltage, a lower drop tube or a couple of SS diodes will bring the voltage up as well as liberating some VA's from the power transformer that can be used for the actual amp rather than the tube rectifier's heater. A 1K dropping resistor between the plate and screen supplies like the PR. Then there is the two 18k 1W resistors and the 22 uF caps for the preamp. I can see the added filtering will reduce the hum and reduce any sag effecting the preamp. I would stick to the single stage filtering in the 5E3 with the 22 uF and just change the resistor value to get in the 200-240V range. The resistor value will depend on what the power transformer gives you for the 6V6 plate voltage. I would start with 36k 2W and put a resistor in parallel with it to drop the resistance to suit to taste.

    One thing that I found interesting, the gain dropped with the 3.3M divider is sort of in the range of the split plate reduction of the 6G3 Deluxe. So if a person was inclined they could go that way reducing the signal level. Or if you really want a gainy amp leave it out. But then layout may cause some oscillations, not like this was designed for higher gain. And I think that is it. If anyone can look over my instructions and find an error or a better way of routing, placement, that would be great. Sometimes you don't see the forest for the trees.
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