[Amps] sb-220 non uniform grid current ??
r at somis.org
Wed Feb 25 09:28:48 EST 2004
** 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.
>The following data was collected from an antenna with an SWR of about 1.5.
>Plate ma Grid ma
>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??
>R. Measures wrote:
>>With 700 - 800mA key-down on the CW tap, what is the grid-I? Tnx.
>>>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.
>>>Amps mailing list
>>>Amps at contesting.com
More information about the Amps