Peavey Delta Blues 115 question

thumbpicker

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I think I finally came across an amp that will suit my purpose. My X700 sounds great through it. It has a Blue Marvel speaker 16 ohms. I have a JBL D 130 15 " that I was thinking of trying. Only problem is that the JBL 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.
 

capnjuan

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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
 

thumbpicker

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Thanks a lot capnjuan. The only specs. I can find is 30 watts into 16 or 8 ohms. It is a 2 channel pre amp. There is a jack for an external speaker cabinet and a footswitch jack. The external jack says minimum total impedance is 16 ohms. Somebody told me you can disconnect the speaker and tape the ends, then put in the other speaker and plug it in the extension speaker jack. Don't know if that is right. Guess you can tell I'm not too savy in electronics. I have a multimeter that I can't figure out how to use.
 

capnjuan

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thumbpicker said:
The external jack says minimum total impedance is 16 ohms.
Okay; then it's in parallel and the mfr is telling you that with the factory 16 ohm speaker connected, you can't connect an external speaker with less than 16 ohms impedance; not less than net 8 ohm load on the output transformer.
thumbpicker said:
Somebody told me you can disconnect the speaker and tape the ends, then put in the other speaker and plug it in the extension speaker jack. Don't know if that is right.
That will work.
thumbpicker said:
I have a multimeter that I can't figure out how to use.
... Hmm ... I just gave up driving around lost for an hour before asking directions last year .... For these purposes, set your meter to measure resistance and put one probe on one speaker contact, the other probe on the other, you should get anywhere from 10 - 15 ohms across the Blue Marvelette's ... sorry ... I meant Marvel's voice coil ... dang age showing again. :wink: Good luck! CJ
 
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