Can I safely add another speaker output to my amp?

[Molly]

Bought a H&K Puretone combo the other week. The spec says:

SPEAKERS: The PURETONE features two speaker outputs for connecting speakers with an overall minimum impedance of 8-ohms. This means that you can connect either an 8-ohm cabinet or two 4-ohm cabs to the PURETONE head. On the combo version, the output is factory-connected to the internal 16-ohm speaker. You'll find the connector for an external cabinet behind the rear panel next to the connector for the internal speaker. Bear in mind that if you want to connect additional speakers, you can only connect a 16-ohm cabinet.
However, if you first disconnect the internal speaker,
you can connect an 8-ohm cab.

I don't really get this. There's no impedance selector and my combo only makes use of the external speaker connector socket. So, how do I add a socket and make use of other combinations of 8 or 16 load? Is it running at 8 all the time?

Thanks.

[tubeswell]

How many secondary taps does the OT have?

[Molly]

Sorry. No idea what that means.

If I understand the handbook statement below then when new the combo's speaker is factory connected though there is an output socket to enable an extension cab. However, when I got it the original factory connection had been removed and the amp now relies on the extension socket. Can't see how or where I'd put it back to stock. Could really do with a look at another one.

From Handbook: "On the combo version, the output is factory-connected to the internal 16-ohm speaker. You'll find the connector for an external cabinet behind the rear panel next to the connector for the internal speaker. Bear in mind that if you want to connect additional speakers, you can only connect a 16-ohm cabinet. However, if you first disconnect the internal speaker,"

[tubeswell]

All output transformers have primary and secondary windings. The primary winding is connected to the plates of the output tubes and to the high tension power supply in the amp. The secondary winding is connected to the speaker(s). Some OTs have several points on the secondary winding at which the winding is tapped, in order to allow different impedances of speaker to be connected (so as to enable the same reflected load for the output tube plates on the primary side). If your OT has several secondary taps, then you will be able to connect differ speaker loads without harming the amp. If not, then you will want to disconnect the internal speaker and run an external speaker with the same impedance.

[Molly]

Ah. Thanks for that. I'll investigate.

Much appreciated.