thumbpicker said:
... a Blue Marvel speaker 16 ohms. I have a JBL D 130 15 " that ... is 8 ohms. Could it be switched. The speaker is wired direct into the amp but has an extension speaker jack in the back. Any thoughts on this.
Hi thumbpicker and congratulations on your new amp. If the Blue Marvel is original, the answer is yes; you can substitute the 8 ohm speaker for the 16 ohm speaker without risk to either the speaker or the amp. The rule of thumb(picker :wink: ) is 'half or double'. Assuming the 16 ohm speaker is original and if the amp doesn't have an impedance matching switch to switch output transformer taps, your amp's output transformer is rated at 16 ohms.
If you put an 8 ohm load on the output transformer you are substituting 'half' of the original load. If you wanted to, you could load the OT with 32 ohms 'double'; two 16 ohm speakers in series and not damage anything. I don't know if you have the mfr literature or whether the extension speaker jack is a 'shorting' type; that is, if something plugged in, no sound from the internal speaker. Finally, I don't know whether the external jack is wired in parallel or series-parallel with the internal speaker.
These might seem like picky little points but if you change to an 8 ohm internal speaker, jack in another 8 ohm speaker, and the external jack is in parallel with the internal speaker, you will only have 4 ohms load on the assumed-to-be 16 ohm output transformer falling below the safety margins of the 'half or double' rule. Chances are the adverlit would be specific on these points. Good luck! CJ