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I have a Monoprice Stage Right 15 Watt tube amp which has an internal 8 ohm speaker. I have built an external cabinet, and installed a 8ohm speaker, which I had from an older amp.

How about if I wire the two speakers in series by using a new speaker jack, wired off of the installed speaker mounted on the amp case? I then would run a speaker rated cable, from the internal "bypass" jack I will install, to the external speaker cab jack with the reversed polarity. (I hope that is the correct term.

Am I correct that this will be seen as 16 ohms by the amp? These amps have a panel on the back saying rated at 8-16 ohm near the external speaker factory installed jack. That jack, disconnects the internal speaker, and allows only the external to be used, which seems like a wasted idea, if you ask me.

I have worked as an electricians' helper for a couple of years, so I have some knowledge of how electricity works.

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Two 8 Ohm speakers. In parallel they represent 4 Ohms. In series they represent 16 Ohms. Your amp. is designed to drive 8-16 Ohms, so the answer impedance-wise is obvious.

If you're hoping it will be twice as loud, though... you'll be disappointed. It will be richer in tone, with twice the air volume being moved (roughly), and if the two speakers, and/or their cabs are different, there will of course be a difference in tone between them. And, you could point them in different ddirections for more sound spread.

Bottom line, best, in the long term, not to present a smaller load than the amp. is designed for, so parallel isn't the way to go. You could, though, consider extra speakers and go series/parallel, (or use different impedance speakers), to give the original 8 Ohms.

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  • Thanks, Tim! I wasn't seeking "louder," just the tonal richness, and harmonics that may result. The main amp speaker is a Celestion 70/80, 30 watt, and the external is a Flextone, 70 watt, taken from a Line6 Spyder 212. I had wired a stereo junction box to it and pushed two 4-10 speaker columns for live stage concerts, and that booger was LOUD when cranked, but sweet and rich when mellowed out. It did not have a bypass switch, and when the columns were not plugged up, the main speakers worked without problems. So that made me ask about you saying neither speaker will work. Thanks again, Bill
    – Bill Welch
    Apr 3, 2022 at 15:48
  • @BillWelch 'twasn't I, 'twas another T....
    – Tim
    Apr 3, 2022 at 16:50
  • From the standpoint of preventing damage, a transformer-coupled tube (valve) amp will be a lot better off when presented with too low of a speaker impedance (even a short) than it would with too high of an impedance or an open circuit. (For a transistor amplifier, it's the opposite). The details are probably a bit off topic on this stack.
    – Theodore
    Apr 4, 2022 at 19:59
  • Thank you, Theodore. I don't feel any subject is off-topic when it involves sharing of knowledge about any manner relating to the subject. This one brings further knowledge about amps and speakers, so it is on topic enough for me. I have played Transistor amps for years, but this is the first tube amp, and the first mods of that type. I finished the cabinet, and the speaker I loaded in it, a Line6 Tube Tone, is perfect . Similar to the 70/80's tonality in the Monoprice, but the LINE6 seems to be slightly "louder." Is that possibly due to 70 vs 30 watt speaker rating, do you think? Later.
    – Bill Welch
    Apr 6, 2022 at 16:37
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Yes, two 8 ohm speakers wired in series will present to the amplifier as a 16 ohm speaker.

Not sure where you're coming from with 'reverse polarity'? If the two speakers are out of phase with each other (to use the common, though inaccurate term for reverse polarity) you're in danger of ending up with LESS sound output.

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