[Hallicrafters] SX-42 meter - use a ZENER or DIODES

[Rich Oliver]

There are lower voltage Zener diodes available in the 1N52XX series:

1N5221   2.4 Volts
1N5222   2.5 V
1N5223   2.7 V
1N5224   2.8 V
1N5225   3.0 V
1N5226   3.3 V

Zeners have the advantage of a sharper "knee" than forward biased 
rectifiers.

73, Rich

Rodney Bunt wrote:

>Use a zener diode across the meter movement. Check out the maximum voltage across the meter when
>full scale, add a bit and put a Zener across the meter terminals. any excess voltage/current will
>go through the zener, should the zened be destroyed, it will go short circuit ( and protect the
>meter anyway) then you can blow your fuse at leisure.....
>
>If the voltage is not greater than the smallest zener diode ( I think it is 3.3 volts not shure on
>this) use ordinary 1 Amp diodes in a string, each will develop .7 volts across them, so three will
>be 2.1 volts etc. same deal with this configuration, when the voltage is too high the diodes will
>conduct ( protect the meter) and then your fuse can blow...
>
>Rodney
>VK2KTZ
>  
>