[R-390] 3tf4 mod

[Steve Hobensack]

Here is neat little mod that will let you use either a 3tf7 or a 3tf4 and is 
reversible. Above the IF deck mount a 25 ohm 5 watt resistor using a 
terminal strip. Wire the resistor to pins 2&3 on the ballast tube socket 
below deck. Short/solder together pins 7&8 on the ballast tube socket. 
Carefully cut off pin 9 of a 3tf4 ballast tube. Being careless here might 
crack the glass. Install the 3tf4 with the cut-off pin directly over the 
keyway (one space removed from normal seating). The 3tf4 will now engage the 
new resistor in the circuit. If you happen upon a 3tf7, simply install it 
normally. Remember to always plug the 3tf4 in the odd way, otherwise you 
will burn it out.

a few weeks ago I saw a posting where a diode could be used in series with 
the 3tf4. Anyone tried it?

Steve......KJ8L

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