[Amps] sb-220 non uniform grid current ??

[Dan Sawyer]

Thank you,

The exciter is a Heathkit 5400. In the last reading below it is driving 
the amp with about 30 watts. If I increase the input drive power from 
that point the grid current rises very rapidly and the output wattage 
flattens. Due to the cautions about grid current I have stopped there. 
(At that point plate HV has dropped to about 2KV) Is it feasible that if 
the amp were incrementally tuned it would return to a more linear 
relationship??

btw - ZSAC is about 100 ma on the CW/TUNE tap and about 150 on the SSB tap.

Dan

R. Measures wrote:

>**  Thanks.  These grid-I figures seem normal to me.  However, the ZSAC 
>(zero signal anode current) seems a bit low.   With the reduced anode 
>supply V on the CW tap, grid current is higher because the anode is less 
>attractive to electrons - so more of 'em go to the grid.  
>-   To fully drive a pair of 3-500Zs, it takes well over 100w.  
>
>  
>
>>Thanks,
>>
>>The following data was collected from an antenna with an SWR of about 1.5.
>>
>>Plate ma       Grid  ma
>>100                0
>>120                10
>>140                20
>>160                30
>>180                40
>>200                50
>>300               100
>>600               150
>>
>>These were obtained by carefully increasing the drive and incrementally 
>>tuning first load and then tune. These appear to be good results. 
>>Attempts to tune directly have to be approached very slowly and 
>>carefully. Is it possible the high grid current readings are a result of 
>>poor tuning skill on my part??
>>
>>Dan
>>
>>
>>R. Measures wrote:
>>
>>    
>>
>>>With 700 - 800mA key-down on the CW tap, what is the grid-I?  Tnx.  
>>>
>>> 
>>>
>>>      
>>>
>>>>All,
>>>>
>>>>I have an sb-220 with non-uniform grid current. With low to medium drive 
>>>>grid current is linear (or apparently close to it) with plate current 
>>>>(minus about 100 ma base) and output power. However if input drive 
>>>>exceeds the medium level of 25 to 30 watts grid current starts to hockey 
>>>>stick "high". It is not a digital switch; but a very steep response.
>>>>
>>>>The components in the bias and grid meter side of the circuit have been 
>>>>checked in circuit. The grid bias coil has been replaced with an 1/8 
>>>>watt 33 Ohm resister.
>>>>
>>>>Thanks,
>>>>Dan
>>>>
>>>>
>>>>
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>>>>
>>>>   
>>>>
>>>>        
>>>>
>>> 
>>>
>>>      
>>>
>
>  
>