[AMPS] AL1500

[measures]

>
>Hi ,
>I have a problem with an AL1500 which came on suddenly.
>    The grid current indicated is now showing about three times what it used
>to.
>The meter even indicates 10ma on cw standby ie no drive. My O/P SWR is OK
>and also the I/P amp SWR is OK so the fault would appear to be in the
>metering circuit. The amp is giving the same O/P for I/P as it has always
>given, just the indicated grid current is higher and there does not appear
>to be any faulty components in the metering circuit at first sight. Any body
>had the same fault?

I would check the valve for gold sputtering, Clive.  To do this you need 
a high-pot. tester.  The grid is common.  The anode is hot.  Apply pos. 
8kV.  If the leakage is above 10mA you may have a problem.  Apply neg. 
8kV.  If the leakage decreases substantially, you probably have gold 
sputtering.  Keep the tube upright and tap the top firmly in the vertical 
plane with a plastic hammar.  If the leakage decreases, you have loose 
gold.  

cheers.  

-  Rich..., 805.386.3734, www.vcnet.com/measures.  


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