Late 1930s(?) Homebrew Rack Transmitter



This transmitter is owned by W0HIO and is yet to be restored. It looks like it came right out of Frank C. Jones' Radio Handbook. It is a 100W, AM/CW transmitter, and for the most part, looks to be of late 1930s origin. It is about 6 feet high. Referring to the pictures of the back of the transmitter below, the transmitter consists of the following sub-units: starting at the bottom is the HV power supply for the final and the PS for the exciter stage. A marking on the HV terminal indicates 1000 VDC was available for the final. The modulator deck is the next unit up. The final was modulated by a pair of 807s. Above the modulator is a bias supply and some antenna relay switching circuits. Immediately above the bias supply is the exciter and final, which reside on the same chassis. The exciter is crystal-controlled, with a switch brought out to the front to select the crystal. The exciter looks like it had a tube for the main oscillator, and a tube for the doubler. These were not present. The driver to the final consists of an 807. Through a process of elimination and by the details of the final circuit, it was concluded that the final tube was an 35T. Immediately above the final/exciter unit is an ARC-5 transmitter and a power supply for it. The ARC-5 was not connected in any way to the lower decks, and seems rather out of place. Obviously, this portion is post-WW2. The ARC-5 was link coupled to an antenna tuner which is at the very top of the transmitter.

W0HIO plans to get the transmitter running on 40 meter AM.




The modulator deck


The High voltage Power Supply (left) and the odd ARC-5/power supply ( right )



The final amplifier. The tank coil is a unit designed for 10M The 807 driver can be seen on it side pointing towards the front of the transmitter. The 35T would have gone to the right of the neutralizing capacitor.


Underneath the final amplifier.


Underneath the exciter portion.



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