#1
hi there im new to this forum !!!! can anyone advice me on this topic. i have a sound city 20c valve combo. with a speaker ext output on the back when i plug in my extension cab the main speaker cuts off is this normal? the speaker impedance is 16ohms the same as main speaker. also i was thinking about wiring the two speakers in parallel would this harm the amp ! any advice would be greatly appreciated.
#2
Well I can not say for your amp, but many amps will mute the internal speaker.

does the amp have an ohms selector on it? if not look for the manual online or maybe someone here more familiar with your amp can help.
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#3
if it does mute the internal speaker it'd make sense that the extension jack would want to be the same impedance as the internal speaker.
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#4
To run both you'd have to mod the amp, specifically the ext speaker jack.
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#5
Quote by mrmuller
i have a sound city 20c valve combo. with a speaker ext output on the back when i plug in my extension cab the main speaker cuts off is this normal?


i can't find a manual of the amplifier, but i have seen pictures and this amp seems to just have a single speaker output and no impedance selection.

in modern amps this would imply that an external speaker would bypass the native speaker and the extension cabinet should be the same impedance as the native speaker.

Quote by mrmuller
the speaker impedance is 16ohms the same as main speaker.


that is what you'd want.

Quote by mrmuller
also i was thinking about wiring the two speakers in parallel would this harm the amp ! any advice would be greatly appreciated.


if you hooked the cabinets in parallel and used two 16 ohm cabinets then the amp would only 'see' 8 ohm at the speaker output. i wouldn't exactly call the good, most like less optimal.

not matching impedance to the output of a tube amp places stress on other components of the amp. most guitar amps are over-engineered to protect the amp from some mismatch, but the tone of the amp generally suffers and the amp is not working at it's optimal efficiency.

i'd say a small mis-match wouldn't harm the amp, but it has the potential to. it is up you to decide whether you want to take the risk. (i do, but i don't advise others to do so).
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