Blackface Bassman Ext. Speaker Jack Question

[dumb donnie]

Is the Ext. Speaker jack on the back of a Bassman wired in parallel? I have two 8 ohm cabs that each only have one input jack and I want to run both of them (for 4 ohms). So can I just plug one into the main speaker out and then the other into the Ext. Speaker jack and get 4 ohms?

[Blue Strat]

Yes, yes and yes:)

[dumb donnie]

Thanks a lot. I was just worried because I have heard people say "if you are only going to use one cab, make sure that you plug it into the main out and not the ext. speaker jack". They were actually talking about a Traynor YBA-1, but why aren't both speakers jacks usable for a single cab?

[Blue Strat]

In some amps, there's a shorting switch (for safety) on the main speaker jack in case you don't have a load plugged in. This also disables the ext speaker jack.

[Blue Strat]

Usually the 'main out' speaker jack is a shorting type, and the 'ext jack' is a non-shorting type. Meaning... that if you unplug the 'main out' speaker jack, you are shorting the secondary side of the output transformer to the chassis. This is done to prevent inadvertent no-load condition, where the secondary side of the output transformer would see an open circuit (infinite resistance, or whatever the resistance of air is). 0 ohms is better than infinity ohms. The ext spkr jack shares a common (chassis) connection with the main out jack, and the hot side is connected in parallel with the main out jack. If you disconnect the main out, you are shorting both the hot side of the main out and the ext out to chassis, so even if you plug in spkrs to the ext jack, the hot side is still shorted to chassis. hope this makes sense, I'm writin' in a hurry today.


It's like "Deja Vu all over again", except longer:)

[dumb donnie]

Thanks!