[MRCA] The Navy MAK so far

[Ray Fantini]

The MAK project has been going well. At first I intended to use a Narco 12 volt power supply - Modulator that provides the 190 VDC for the receiver without issue and also provide 350 VDC with modulation for the plate of the PA but have had issues getting the modulation to be linear over the tuning and loading ranges with the radio. With the output tuning and loading being between five to ten watts depended on loading.
I decided to abended the idea of an external modulator and use the original modulator in the radio itself. It uses a Heising Modulator that loads the PA plate to modulate the radio. With the internal modulator the radio produces clean modulation regardless of tune or load settings and way outperforms the external unit but it now has presented a couple new problems.
First with external modulation I can remove the two modulator tubes and reduce overall current drain by more than four amps, from eight amps in transmit standby to four using the external modulator. The external modulator is solid state so no filament loads. But I think I can live with the higher current drains. The MAK has a switch that disables the PA and Modulator filaments in standby that drops overall current drain down to just a little over two amps in receive, so think I can work around the higher DC current requirements. But the second problem is that when using the internal modulator a Negative DC Bias is required, just around -12 to -15 Volts. Originally HV was provided by a dynamotor with the negative side isolated from ground to provide the bias voltage but the Narco won't let me do that without some redesign. Using a external power supply to provide the bias now. Also I found that with 250 volts for the PA and modulators the output is too light to properly work the antenna current meter so a little bit more B+ can help. The set originally had 500 VDC on the PA/Modulator plates.
What I think I need now is something like an old 2 Way vacuum tube radio power supply like what would be with the GE Master or RCA Super carphone. Or one of the power supplies that went with the old Heathkit radios for portable operation like the HP-11 or 13 Anything that can give me 190 to 250 VDC in receive and 350 to 500 VDC along with 10 to 20 volts of Bias in transmit. Remember that it has to work from twelve volts because this radio is for field operation only.
If anyone has anything please let me know, now starting to regret all the old 2 Way stuff that I junked years ago.

Ray F/KA3EKH

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