x4 6L6 OT ok for duet?

[allsavy]

The tiny/crappy OT in my 1484 silvertone (PP 6L6 duet) is pooched. I have on hand an old organ output transformer that had 4 6L6s. there are three output taps: marked 4,8, and 16 ohms. I'm going into a 2- 12 cab (x2- 8 ohm parallel spks.) Seems appropiate to use the 4 ohm tap or does this change because I'm only going to use 2 tubes?
What about the primary impedance being intended for 4 tubes when only two are used... any major concerns there?

[Robert M. Martinelli]

The tiny/crappy OT in my 1484 silvertone (PP 6L6 duet) is pooched. I have on hand an old organ output transformer that had 4 6L6s. there are three output taps: marked 4,8, and 16 ohms. I'm going into a 2- 12 cab (x2- 8 ohm parallel spks.) Seems appropiate to use the 4 ohm tap or does this change because I'm only going to use 2 tubes?
What about the primary impedance being intended for 4 tubes when only two are used... any major concerns there?

Yes, things change, because ( see other threads on this subject ) OTs don't have an inherent impedance of their own, they just reflect whatever impedance they "see" at the primary on the secondary according to their ratio.

The relationship is Ratio = Sqrroot ( Zprim/Zsec ), or if you like it more, (Ratio)^2 = Zprim/Zsec.

2x6L6 in PP have an output impedance which is double than a 4x6L6 PP, so under these conditions your OT's 8 Ohm tap actually matches with a 16 Ohm load.

This said, you should wire the two speakers in series ( 8+8=16 Ohms ), paying attention to the phase ( otherwise you're going to lose the low end ) and connect them to the 8 Ohm tap ( which actually matches perfectly a 16 Ohm load because you're using only two tubes ).

Hope this helps

best regards

Bob