Date: Tue, 14 Dec 1999 22:06:07


I enjoyed the articles on the GE Phasitron tube. I have scanned them and will read them in detail a little later. It is (was) a fascinating device; a bit cantankerous and downright difficult to maintain in practice. It was quite temperature sensitive in my memory, but produced very good results when properly adjusted.   The RCA exciter to which you referred was called the "Iron Fireman". I'm not sure where the term originated. It was a direct FM device which began life at about fourteen mc if my memory is correct. The modulator was phase locked to a low frequency crystal operating at about 100 kc via a chain of regenerative dividers. Thus the reason for the one inch scope in the middle of the chassis. The division ratio was inadequate for the phase detector type used in the AFC circuit. It would unlock at a little more than 75 kc deviation at 50 cycles and Katy bar the door if it got hit with a high level bass drum!  I've seen the butterfly capacitor in the motor driven AFC circuit spin a few revolutions before the AFC circuit locked up and regained control of the monster. It was capable of sweeping the beast at least a megacycle or two in each direction. This often produced interesting artifacts from the associated RF PA, particularly the ten kilowatt version!   The serasoid modulator was developed in the mid to late 1950's. Gates built at least three models, one with octal tubes in the mid 50's and two versions using the miniature tubes. These were the M-5535 and M-6095 versions which differed on in the number of modulator stages. The 5534 has a single modulator stage and the 6095 had a pair in cascade to make the low end work. I don't know anything about the earlier model. The crystal and the modulator operated in the 100  kc region.   I hope all is well with you. Have a Merry Christmas.


Jack Sellmeyer

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