How about an old RF trick Build a grounded grid output stage using the output winding of the 45 amp as a cathode drive winding for the KT88s. If the 45 amp output transformer is taped for 8 and 16 ohms you can treat the 8 ohm tap as the common, connect the 16 ohm and common taps to the cathodes of your KT88s and adjust the bias by using a resistor to ground from the center tap bypassed with a good cap. Remember that now you will have the cathode current of the KT88s on the output winding of the 45 amp transformer. That should be OK but make sure that the transformer doesn't heat up by passing this DC current. Now you can just ground the grids through some grid stopping resistors, about 1k to 10k should be OK.
Grounded grid amps have low input impedance and very good noise performance. This might work well for your application.
Grounded grid amps have low input impedance and very good noise performance. This might work well for your application.
HDTVman said:
Actually the 4 ohm tap is the electrical center in a 0,4, 8, 16 ohm secondary. The turns ratio is the square root of the transformation ratio therefore.. (Effectively the 4 ohm tap is at 50%, the 8 ohm tap is at 70.7%, and 16 ohm tap is at 100%.)
Output voltages from a 45 based SE amplifier are going to be insufficient to drive the KT88 to reasonable output levels. (More than 60Vrms grid to grid is required.)
HDTVman said:
The gain driving the cathodes is only 1+mu (triode connected) so this is still not going to be nearly enough, it's actually a very clever idea particularly if a custom opt was going to be used in the driving amplifier or in the actual power booster...
As described depending on the pp output transformer winding ratio you would not even achieve unity voltage gain with the implication that there would be no power gain either obviously.
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