[R-390] Parts Request

[2002tii]

Barry wrote:

> >Does the EA53 and/or 2-01C have a
> >similar voltage drop so it won't be an issue?  For larger voltages
> >it wouldn't matter, but on the
> >low ranges, it might be an issue.

I replied:

>I don't have curves for the EA53 and 2-01C handy, but
>indirectly-heated small-signal diodes operated at very low current
>generally start to conduct when the plate is slightly negative WRT
>the cathode.

A kind list member did have data handy for the EA53, and it appears 
that it draws 1 uA when the plate is 0.5 V negative (yes, it draws 
positive current even though the anode teminal is still negative -- 
thank the Edison effect due to the space charge, which causes "space 
current," and, to a lesser degree, the contact potential due to the 
dissimilar materials used in the cathode structure).  When the plate 
voltage is 0 V, an EA53 is drawing 10 uA; at +0.7 V, about 100 uA; 
and at 1 mA it is up to +4 V and rising fast (not surprising, given 
the 0.5 pF plate-cathode capacitance -- it takes a tiny cathode to 
get the capacitance that low, which is also why the useful life of 
these tubes is fairly short).  Rated cathode current is 300 uA (peak 
5 mA for no more than about 5 mS at a time).  Extrapolating from the 
characteristic curve, the current is probably about 100 nA for an 
anode voltage of -1 V, and 10 nA for an anode voltage of -1.5 V.

Best regards,

Don