Can I plug my 8 or 16 ohm Marshall as an extension cabinet into my Fender Twin Reverb? (Don B.
Most Fender Twin Reverb amps, including the Blackface reissue, operate only on a 4 ohm load and have no means of selecting any other impedance. Exceptions to this are the last original silverface issues that are rated at 135 watts, and later channel-switching models. Operating both together brings the speaker load to 2.7 ohms which is not a problem at all for the Twin Reverb to handle. If, however, you use only the 8 ohm Marshall cab and unplug the Fender speakers, then the amp could be at risk if you play at loud volume. Whenever you mismatch a tube amp with a much higher load (speaker) impedance, a higher signal voltage is produced across the primary of the output transformer. One loud popping note on the high E string and you could arc-over the output tube sockets, fry the tubes, or zap the output transformer. This is why you cannot run a tube amp without a speaker connected to it.
