Just Thinking Aloud Here

[Dan C]

So Hypothetically, Say I had a Blues Jr III LTD Tweed (15Watts, 12" Jensen C12N) & wanted to make an extension cab...

What would the specs of it need to be?

- Size (Similar to the Blues Jr?)
- 1x12" Speaker (Same as the amp or different?)
- Ohms Rating?
- Wattage... 15? Same as Blues Jr?
- Power? How would it be Powered?
- How would I connect them?

What do you think?

Sorry for posting this in two sections, didnt know which was best

[Silverface]

Those questions are SO basic I recommend you do not attempt anything until you 1) spend a couple hours searching this forum and Amp Central Station for similar threads (you'll find hundreds - they do NOT have to be specific to your amp), and 2) having some basic knowledge of electronics. There are simple 100-page introductory books anyone who plans wo work on an amp should read if they have no electronics background.

I'd also recommend - even though it has many flaws - Gerald Weber's first book, the "Hip Guide to Vintage Tube Amps" (something like that). It takes basic electronics and applies it to guitar amps.

Part of the reason for needing all this is that there are not single answers to each of your questions. Some are subjective and depend on tech opinions (some applied electronics has flexible application of very specific equations) and others depend entirely on *why* you want to add something and very specifically what sound you are looking for.

Example - small/large and open back/closed back cabinets sound very different. If we don't know what kind of music you play or what the rest of your rig consists of we're throwing darts in the dark, and any answers you get will be either posted as guess work or because a poster is trying to raise his/her post count.

Short version - You need to know what you're doing by educating yourself, and not by asking questions on a forum that have been asked hundreds of times. Then search the forums. THEN ask questions specific to fine-tuning the setup, not simple electronics, woodworking and acoustic design questions.

[DirtyMacSpecial]

Agree with SF, some of these questions are subjective and depend more on what you want and not what "should" go with it, its your tone do what sounds good to you. But the majority of these can be answered by searching the forum or pulling a google search before posting the questions (tends to be quicker that way too)

[misterjohn]

- Size (Similar to the Blues Jr?)
Whatever makes you happy.

- 1x12" Speaker (Same as the amp or different?)
Whatever you want.

- Ohms Rating?
8ohm, will give you a slight missmatch if you use both speakers together, no biggie

- Wattage... 15? Same as Blues Jr?
15 or more

- Power? How would it be Powered?
By the amp

- How would I connect them?
With a speaker cable, that's all you need. Or two.

[jefrs]

The BJ has a single 8ohm load outlet, it only supports an 8ohm load, do not mismatch the load.

To use an ext cab you disconnect the internal speaker (without modifying the amp). The speaker jack socket is hidden up the back. Use a speaker extension lead, never use a guitar stage lead.

The BJ box is too small, get a larger volume ext cab.

The Jensen C12N is a 50 watt speaker. You need speaker(s) rated for more than 15 watts, imo at least 25 watts (overloaded EL84 p-p can deliver >23 watts).

Suggest a 2x12 cab with two 16ohm speakers in parallel = 8ohm, the correct load for BJ