[ARC5] Receiver Voltages.

[Brian]

Hello Ian,

The supply to the Collins 51J family of receiver oscillators is not plate regulation; it is whole circuit supply regulation. Have a close look at the circuit; sure the circuit is fed by a 150 V regulated supply, but then there is an RC filter and then plate load resistors to each 6BA6.  Definitely NOT plate regulation. Care to have another throw of the die?

A VR tube works in cycles: as the Voltage applied reaches striking Voltage, the glow starts; but this causes a heavy current to flow and drops the Voltage across the tube below ignition and the low impedance becomes high impedance again ... and the cycle repeats. This is truly a noise generator, not a power supply noise attenuator.

Have you heard of tail trimming? Try it some time. Anyone reading this stream knows we are discussing Command receiver HT Voltages – we really don’t need reminding – and not trimming tails takes up a lot of bandwidth.

73 de Brian, VK2GCE. 

On Saturday, May 02, 2015 3:40 AM, Ian asserted:

<snip>
VR tubes can be seen in use as plate regulators in the Collins 51J
(look at the supply to the PTO) and in numerous other tube
receivers, once LO stability became an issue.

A resistor + VR tube would offer power supply rejection owing to
the low dynamic resistance of the VR tube. The small-signal
equivalent circuit of this is a potentiometer with the upper arm
being the resistor, and the lower arm being the VR tube.

73, ian K3IMW