[ARC5] Receiver Voltages.

[Brian]

Hello Dennis,

Very interesting.

I was aware that VR tubes are used for screen regulation, but I can’t recall an instance of plate regulation; please remind me.
I wasn’t aware that VR tubes provide power supply noise rejection – what is the mechanism?
Noise travels by radiation and conduction. Putting a capacitor across a VR tube may attenuate some conducted noise but not radiated. In some of the better-designed applications, you will find that the VR tube is shielded to attenuate radiated noise.
I think your suggestion of putting a neon tube under the chassis of a Command Rx ignores radiated noise, unless you plan to shield it.
The resistor divider chain in the Command series of Rxs has 0.22 uF capacitors at its top and at the screen-feed tap. I think you will find that the 3 dB point for this LPF is around 100 Hz per section, which is a long way below the commutator noise frequency of the genemotor.

73 de Brian, VK2GCE.

On Friday, May 01, 2015 2:02 PM, you said:

Brian,


Not wishing to argue, but gas filled breakdown tubes of all types generate some white noise, not just neon.  Yet VR tubes are commonly used for screen or plate regulation.  What little noise exists can be bypassed by a cap.  At least the breakdown tube has some power supply noise rejection; a resistor divider has none.  As for light, it's a pretty small effect and how much light gets into the underside of an ARC-5 type receiver anyway.   

I think Dave came up with the best reason for using R's.  You can run the set more easily at low voltages if the screen is allowed to track down with a sick B+ line.

Dennis AE6C