23 Apr
2005
23 Apr
'05
3:17 p.m.
I've just remembered that Magic Eye valves/tubes have (I think)
an amplifying triode in the same envelope as the indicator. And I
They do (and sometimes 2 triodes, for the dual-sensitivity indicators
like the EM34).
think they're internally linked together. Does
anyone have any
data on these gadgets that would show this sort of information?
Sure. The data I have on them shows the triode anode is directly
connected to the control electrode of the indicator section. That's then
brought out to a pin.
Conventioanlly, the target is connected to HT+, the triode anode/control
electrode to HT+ via a resistor [1], the cathode goes to ground, and the
signal you want to display (often the AGC line in an AM set) goes to the
triode grid.
[1] This resistor is notorious for going open-circuit. Something to check
if the magic eye seems dead.
-tony