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Old 22nd May 2014, 7:41 am   #3
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
Default Re: Varible Speed Tape Drive System

That is the screen grid supply resistor, with no marked value. The maximum screen current for an EF80 is 2.8 mA; maximum screen grid dissipation is 0.9 W. You could work it out but I'd just start by sticking in 100K, measuring the current and tweaking the value as appropriate. Though it'll probably oscillate anyway, whatever value you use, just because it's an EF80.

I take it the idea is for this oscillator, via a fairly hefty amplifier, to power the capstan motor and thus provide controllable tape speed?
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