Hot Rod Deluxe Extension Cab

[Marshallplayer]

I’m thinking of hooking an extension cab to my hot rod (I have an extra random cabinet). It seems that adding a speaker should keep the ohms at 8 ohm each... Even though normally 2 speaker should be 16ohm each?

Also, when you plug the extension cab into the extra speaker input on the hot rod, the extra input has MUCH less voltage than the regular input. So are you hearing the extension cab at half the volume (and distorted from tube gain)?

 

[pdf64]

The speaker jacks are wired in parallel. Note that if plugging a speaker into the ext speaker jack whilst the main speaker jack is unused, the latter’s shorting contact will hamstring the output. And plugging into the ext speaker jack will actuate the load impedance switch.
https://el34world.com/charts/Schematics/files/Fender/Fender_hotrod_deville.pdf

 

[xtian]

To repeat what Pete said: Use an 8-ohm extension cab, and leave the internal speaker plugged into it's proper output jack. The HRD switches to its 4-ohm OT tap when both jack are used.

 

[Marshallplayer]

I see. You guys know your stuff. So it’s only less voltage in the second jack because I am not supposed to be plugged into it alone.

Do I need the actual “extension cab” or could I use my own? Just a speaker in a cab

 

[xtian]

You experienced it as "less voltage" when nothing was plugged into the internal speaker jack--that causes the OT secondary to be shorted to ground. It's surprising that you could hear any signal at all!

Yes, you can use any external speaker cab with an impedance of 8 ohms.

 

[pdf64]

So it’s only less voltage in the second jack because I am not supposed to be plugged into it alone

Correct
Any suitable 'speaker in a cab' can be fed from the ext speaker jack; or equally, from the main speaker jack.

You experienced it as "less voltage" when nothing was plugged into the internal speaker jack--that causes the OT secondary to be shorted to ground. It's surprising that you could hear any signal at all!

I remember an old interview with EVH, in which he recounted that he got a quiet overdriven tone when practicing as a kid at his parents house by doing just this, ie plugging a speaker into the ext speaker jack of a Fender BF amp (Bandmaster I think).