[Amps] Another use for Neon Lamps

Will Matney craxd1 at verizon.net
Tue Jan 3 02:45:10 EST 2006


Bill,

We used to use a NE-2 as a tuning indicator. On a KW (about 1800 watts PEP) we took two 10 pF ceramic disc caps and seriesed them (5 pF), then hooked one end to the Load C, and the other to a leg of the neon bulb. The other end of the neon bulb was left unconnected. As the power raised the bulb grew brighter, and brighter yet on modulation. On smaller amps, we used a 10 pf to Load C (300-500 watts). I wouldn't recommend using this though over a good wattmeter to tune by. The same method can be used to sniff parasitics like Rich mentioned by using one leg of the bulb on the probe tip and the other unconnected. If there's any RF when the amp is idle, it will show it quickly. You can mount the bulb on the end of a wood dowell rod, or piece of plastic rod to make the probe up. Just be safe around that plate voltage.

We used another neon buld to show when line voltage was appled by using a NE-2 with a 100K resistor in series with one leg of the bulb for 115 Vac, and the other leg to the neutral wire. For 230 Vac, use X2 the resistance. They make some pre-made neon lamps with a 100K resistor already installed.

Best,

Will


*********** REPLY SEPARATOR  ***********

On 1/2/06 at 9:07 PM Bill Turner wrote:

>ORIGINAL MESSAGE:
>
>At 08:37 PM 1/2/2006, kenw2dtc wrote:
>>My elmer told me that if you put DC source in series with the neon bulb
>and
>>a resistor and set the voltage just below the ignition voltage of the
>neon,
>>it became a more sensitive indicator of RF.  The old guys used "B"
>>batteries.  Today one could charge up a decent quality cap and get the
>same
>>result.
>>
>>73,
>>Ken W2DTC
>
>
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>That's a good idea, but remember that when a neon "fires", its 
>internal resistance drops. Most likely it would continue to glow even 
>after the RF is removed. One way around this is to put a capacitor 
>across the neon and a moderately large value resistor in series to 
>the DC source. When the neon fires it will discharge the capacitor 
>and the large value resistor will take some time to recharge the cap. 
>With the right selection of values, you will have a neon that is 
>quite sensitive and actually blinks in the presence of RF.
>
>Another thing to try - haven't done it myself - is to raise the 
>voltage enough to fire the neon continuously, but use a large series 
>resistor so it is very dim (no capacitor). Putting it in an RF field 
>would make it glow brighter. Should be very sensitive.
>
>Fun, huh? :-)
>
>73, Bill W6WRT
>
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