[ARC5] ARC-5 VFO question

[Neil Barnett]

In the ARC-5 transmitter, why is the return side
of the 1626 heater connected to the (cathode) tap
on the oscillator tank coil?

Is it because:

a. The 1626 was not the original choice for VFO
    tube (a directly-heated tube being the prior
    choice) and when it was later decided to use
    the 1626, a decision was made to simply
    connect the cathode to the filament pin?
    If this is the case, was this done so that a
    substitute (directly-heated) tube would be a
    plug-in replacement if the 1626 proved to be a
    bad choice?

b. Heater current (noise) was deliberately
    introduced into the VFO tank circuit in order
    to ensure reliable start-up of the oscillator
    each time its turned on by the relay?

c. Some other reason related to wear and tear of
    the heater caused by DC operation of the
    heater?

This q. has puzzled me for 35 years, and I never
have seen a satisfactory answer.

73 de Neil, ZL1ANM
Auckland, New Zealand.

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