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Post subject: Blues Jr. connecting to Ext. Cab
Posted: Sat Jan 30, 2010 8:31 am
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The manual with the Blues Jr. says it should have an 8 ohm speaker impedance, yet I've read that one popular mod to the Jr. is to add an additional jack to allow using an extension cab simultaneously with the combo's internal speaker. Did this mod include something else to allow the use of two 8 ohm speakers in parallel (4 ohm impedance)?

Could one use a splitter (parallel) in the existing speaker jack to allow the use of both the internal spkr with an external 1X12 8 ohm speaker without doing any harm to the amplifier?

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Posted: Sun Jan 31, 2010 8:32 am
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No comments/feedback????? Let me rephrase the question.....
For those people who have made "heads" of their BJ or added additional speakers, anyone using a 4 ohm total impedance? (with no other related modifications)

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Posted: Sun Jan 31, 2010 8:57 am
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According to a lot of amp "experts" it is safe to do so. But, others say that you shouldn't do it. I've used a splitter to run an 8 ohm ext. cab with my Blues Junior, and had no problem. My personal belief is that it's okay once in a while, but I wouldn't do it on a regular basis.

If I needed to use an ext. cab ALL OR MOST of the time, I'd either:

1. Have the amp modded with an ext. speaker jack and replace the transformer with one that has a 4 ohm tap. This will cost money and void the warranty!

2. Use the amp as a head into an 8 ohm cab (1-12, 2-12, etc.).


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Posted: Sun Jan 31, 2010 11:55 am
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From my personal experience and talking with people that I know it is not a good thing to run an 8ohm amp with speakers that are wired for 4ohms or 16ohms.
My Blues Jr is now a 2x12 combo amp and I am using 2 16ohm speakers wired in parallel to give me 8ohms.

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Posted: Sun Jan 31, 2010 1:13 pm
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Here's what you need.
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Posted: Sun Jan 31, 2010 4:45 pm
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Thanks to all for the input. Looks like the safest thing to do is what was suggested by 63supro. For $80, I'll have to think about how bad I want to really do this since I have other tube amps that are set up for ext. cabs as manufactured.

I'm sure you all understand what happens when tinkeritis sets it! Why do we do this????

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Posted: Sun Jan 31, 2010 9:42 pm
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CAFeathers wrote:
My Blues Jr is now a 2x12 combo amp and I am using 2 16ohm speakers wired in parallel to give me 8ohms.


A suggestion that I didn't make (which would be the safest) would be to replace the amp's stock speaker with a 16 ohm speaker, and use another 16 ohm ext. cab with a splitter to make an 8 ohm load. This is perfect if you'll ALWAYS use the amp plus the cab, but you'll no longer be able to use the amp by itself. This will defeat the whole purpose of the Blues Junior being a nice little "grab-n-go" amp, so that's why I didn't suggest this idea.


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Posted: Mon Feb 01, 2010 5:00 pm
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I got the idea to check Billm's website to see if there is any light to be shed on this topic. Since he does a lot of modifications to the Blues jr. and sells kits for do-it-yourself mods, I thought him most likely well qualified on the subject.

I found that the auxilliary speaker jack kit includes no other parts nor mention of the necessity to do anything other than attach the second jack in parallel (plus drill a mounting hole). It states that the aux. jack is intended to connect an 8 ohm cab. http://billmaudio.com/wp/?page_id=65

I would conclude from this that a total impedance of 4 ohms is OK for a Blues jr. (As is the case for many other Fender tube amp combos with aux. jacks from the factory).

Thought I'd post this 'conclusion/idea' for any who are interested.

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