Ext. Cab Impedance Setting

Boondocks

Dear friends,

I have read lots of post about impedance variations on our favourite amps. So, I wonder:

As you can see on my pic (from the back of my RP65) the sign says "wired in parallell". Now, I have a newly built cab of 2 Celestion Vintage 30's (16 Ohm) and the impedance will therefor be 8 Ohm when wired and ready to go.
Should I follow the sign and "switch to 4 Ohm when ext cab is connected"?

What say you?

//Peter

Full Name
Lars Verholt
Music Man Equipment
HD-130 head, 210X cab, 210RH cab, RD-50 110 combo, Sixty-Five 112 combo, RP65-112

Member for

10 years 9 months

lmv Tue, 01/22/2019 - 15:06

Your existing internal 12" speaker is 8 ohm, your cabinet is 8 ohm. When combined this makes a 4 ohm load for the amp, so you set the switch to 4 ohm (as suggested by the instructions).

Sincerely
Lars Verholt

Full Name
Peter Sunesson
Music Man Equipment
Music Man 112RP Sixty-Five
Other equipment:
Marshall Bluesbreaker, Fender Deluxe Custom, Gibson 335, Gibson 330, Gibson SG ’61 Original RI,
Chandler Austin Special 1990

Member for

6 years 10 months

Boondocks Wed, 01/23/2019 - 02:16

Thank you, Lars. Reason for my questioning is that I have heard that even though the instructions say "wired in parallel" some has been wired i series. Is there an easy way to check...?

//Peter

Full Name
Lars Verholt
Music Man Equipment
HD-130 head, 210X cab, 210RH cab, RD-50 110 combo, Sixty-Five 112 combo, RP65-112

Member for

10 years 9 months

lmv Wed, 01/23/2019 - 05:38

Hi Peter,

the series connection is only applicable for 2-channel amps, the single channel amps all had parallel speaker outputs.

Cheers,
Lars Verholt

Full Name
Peter Sunesson
Music Man Equipment
Music Man 112RP Sixty-Five
Other equipment:
Marshall Bluesbreaker, Fender Deluxe Custom, Gibson 335, Gibson 330, Gibson SG ’61 Original RI,
Chandler Austin Special 1990

Member for

6 years 10 months

Boondocks Wed, 01/23/2019 - 09:25

Thank you Lars. This community is really helpful...

//Peter