[Guest]

This is a question for the super-members(with more experience than me!). I went back to Ron's instructions on neutralizing a neutradyne(511) radio. I have made up adapters for both four-pin (26s) and five-pin (27s).
But wouldn't a 26 or 27 with a blown filament do as well? This is simply academic, as I do just as Ron says to do, with the tube that will be used in the circuit.
I've already done My Freshman AC 31, and it sounds pretty good. But then it should, because it has an electrodynamic speaker. Only neutradyne
I've seen that doesn't have a "cone" speaker.
At any rate, it's EASY to find a 26 with a blown filament. I wouldn't cut a filament pin off even under a death sentence!!

[Ron Ramirez]

It would do...but you will achieve more optimal results by using the tube that will actuallly be used in the circuit for neutralizing that circuit. Using the actual tube to be used in that circuit when neutralizing will neutralize as much of THAT particular tube's interelectrode capacitance as possible (interelectrode capacitance within each of the RF amplifier tubes is the reason these sets need to be neutralized in the first place). True, a bit of stray capacitance is introduced by usning the adapter, but the end result is still better than using a tube with a bad filament or one with a filament pin cut off.

Oh, and those neutralizing instructions may be found here:
http://www.philcoradio.com/tech/neutral.htm