Hej!
I do not have the schematic on this amplifier but maybe it uses a similar
circuitry as the SB220? I repaired one years ago that draw a lot of grid
current even without without drive and if I remember right even without
anode supply. What the meter showed was AC rectified by the 3-500Zs grids
and the reason was just a shorted rectifier diode in the supply for the
antenna relay serving also as blocking voltage when the PA was in receive.
Hej daa de Hans SM5KI
----------
>Fr?n: "G0MJW" <mike@g0mjw.freeserve.co.uk>
>Till: "c penna" <clive@gm3poi.prestel.co.uk>, <amps@contesting.com>
>?mne: Re: [AMPS] AL1500
>Datum: fre 5 nov 1999 09.30
>
>
>> 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.
>
>Rich is probably correct about it being a problem in the valve (tube).
>However, do check there is nothing wrong in the metering and PSU circuitry.
>I think a leaky cathode bypass cap might produce a similar effect, but so
>would a damaged grid current meter shunt.
>
>Depending on how the AL1500 does its supply, there may be some false grid
>current indicated, perhaps from an interlock or trip circuit or EHT
>measurement. This might only be a mA or so, but if your grid meter shunt has
>burnt out, it will appear as much more.
>
>
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>
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