Originally Posted by
Simon Barden
Note that it was rated at 350 ohms RMS. That 700W is 'program', so the original speakers are likely to be rated at around 80W RMS each (maybe 75W with an allowance for the HF speaker). 'Program' (or 'music') power is a rating deigned to give a maximum suitable amp output value to match with the cab. RMS is obviously based on a continuous, fixed amplitude, sine wave, and as bass (and guitar) signals aren't continuous or fixed amplitude, but dynamic and with gaps between, then you can get away with using a bigger amplifier, normally rated at up to twice the speaker RMS value, as the overall power level handles by the speakers will be roughly the same when used with an instrument like a guitar or bass (less so with synths that can give constant amplitude outputs). The wattage rating of a speaker is a measure of how much maximum average energy the voice coils can handle (normally tested for 1 hour these days) before they run into thermal problems and voice coil insulation starts melting.
The 2:1 power amp:speaker rating really works best for solid state power amps, where the rating (normally measured at around 5% THD) is very close to the maximum power the amp will output, even with serious amounts of distortion. With a valve amp, where the rating is still made at a clean level, there is still often a lot of extra power available once the power amp is overdriven, maybe an extra 80% or more, so you are best limiting a valve amp to the speaker RMS rating. So anything above 200W RMS should be fine.
If you can compare the internal dimensions and port size with Marcel's cab and they are the same or very close, then those Legends sound like they would be a good choice as we know they work in Marcel's cab.