Output transformer matching question.

[Tapsnap]

Hi everyone,
I’ve been putting together a small single ended practice amp. The schematic asks for a 4000 ohm primary and 8 ohm output transformer. I happen to have an output transformer that has either 5000ohm or 8000ohm primary and 4ohm and 8 ohm secondary. My question is, if I wire it with the 8000ohm and 8 ohm connections, would a 16 ohm speaker be appropriate?. I understand that an output of 8ohms requires an 8 ohm speaker but if I double the impedance in the primary it would double the impedance in the secondary which should be 16, ohms. Is this correct?

[sluckey]

You need to halve the primary to make your schematic happy. So you need to halve the speaker impedance. IOW, put a 4Ω speaker on the 8Ω tap.

[pdf64]

Alternatively, a 5k loadline will be as near as makes no difference to a 4k loadline.

[Tapsnap]

OK thanks, I think I’m just going to wire it using the 5000ohm taps and buy an 8 ohm speaker.

[PRR]

If you needed MAXIMUM power, today you'd surely go push-pull.

If this is a home hobby amp you probably DON'T want Maximum power. An impedance "mismatch" is entirely acceptable, even better. I would not fret a 16 speaker on a "8" OT, that's close.

The tube does not care much (aside from power). Try to get within 2:1 between OT and speaker, so the OT is not left under-loaded and spiking.