[ARC5] Receiver Voltages.

[don davis]

Brian:

Following based on circuit design experience for Space tube / lamp  applications over 40 years.  Yes, they still are using them in some limited applications.  VR tubes may, indeed, cycle briefly during start-up while circuit C is charging, but once charged should never cycle as you state.  In a properly designed circuit there is enough head-room to ensure that once struck the tube will remain in conduction.  This is the reason why VR circuits are such power hogs during normal operation.  As an example (using a 0A2 from the RCA HB-3 data sheets) normal output is 73 v with 15 mA through the tube.  The tube requires 105 v to start, yielding 108 v assuming 130 v input, Iout = 5 mA, 2850 Ohms dropping R, 14.6 kOhm load.  For reliable operation the Vin would have to increase or dropping R would decrease.

Yes, VR tube circuits provide power supply noise rejection.  By "noise" I mean 60-400 Hz plus some reasonable range of audio (similar to MIL-SPEC-461 CE-01/-02 limits).  In the instant example the dynamic resistance of the tube is about 120 Ohms.  When considered in the circuit the rejection from Vin to Vout is ~25X.  Any simulations I've made in the past have assumed an ideal voltage source in series with a resistor representing the dynamic impedance of the tube.  My understanding of the RF / uwave noise is due to individual atoms turning on / off or changing orbit to other excited states.  But my notion of this is hazy, having last studied gases in the '60s...  These effects can be reduced by bypassing, but one has to be careful since a parallel C across the VR tube will make a relaxation oscillator at some conditions.   Note that Zener diodes have the same noise issues and are used for RF noise sources, like the tubes were / are.

BTW:  The firing voltage is dramatically influenced by light / photon sources.  I troubleshot a subcontractor's neon calibration cell circuit for the xxxx Space Sensor system for xxxx where we had the wrong bulbs installed.  Correct ones were doped with (some isotope of...) Kr to provide Alpha stimulation.  With the wrong bulbs we had intermittent firings.

73 de don ad6pb

-----Original Message-----
From: ARC5 [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Brian
Sent: Friday, May 01, 2015 7:17 PM
To: Ian Wilson; Mike Feher
Cc: ARC-5 Maillist; AKLDGUY .
Subject: Re: [ARC5] Receiver Voltages.


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.