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Post subject: Help! Blues Deville 2x12 speaker wiring
Posted: Wed Feb 15, 2012 3:27 am
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To start I would like to say I feel dumb asking this but I combed the web and did not really find anything exactly like this scenario so I'm just going to ask. I just purchased this beautiful 95 blues deville from usedguitarcenter.com and was shipped with the tubes wrapped up etc.. and I found this stray white and black clip that undoubtedly attaches to both speakers. The problem I am having is that the previous owner looks to have instead attached the second speaker to the external jack to kind of have a two 1x12 cabinet type thing going on. I've never heard of anyone doing this to a combo amp, am I correct to assume this is essentially the same thing as just clipping both speakers together and just using the main jack (4 ohms in Parallel)? Secondly, why would one do this? Third, would it be a bad idea to connect the black and white wire to both speakers as well as leave the second speaker connected to the external jack (Isn't that series for total 16ohms?) like in picture 4? My last question is, when connecting that white and black wire from one speaker to the other; is there a right and wrong way to do it or does it not even matter as long as one goes to the other? Any input would be greatly appreciated, thanks!

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Post subject: Re: Help! Blues Deville 2x12 speaker wiring
Posted: Wed Feb 15, 2012 9:49 am
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Hi DKH,

Nice amp, congrats!

Hooked up the way it came to you (not standard), the speakers are still parallel giving 4 ohms, but they are connected to the 2 ohm tap on the output transformer because the ext jack is a switching jack to switch taps on the output transformer. Not really wrong using 4 ohms speakers on 2 ohm tap, but the amp won't develop full power. The sound might be more to some peoples liking with the slight impedance mismatch of using 4 ohms speaker on 2 ohm transformer tap. Wiring the speakers the way that you received the amp is not the same as the factory wiring, the impedance is mismatched the way you received it and is matched the way the factory wired it.

The stock connection, remove the extra speaker plug from the speaker and jack, then connect your "extra" wires that you found to both speakers. The white wire connects the positive of both speakers together (+ sign next to speaker tab), and the black wire connects the negative of both speakers together (- sign next to speaker tab). The main speaker cable connects to one speaker as it is now. And, no, don't leave the ext speaker jack connected when both speakers are connected together with the white and black wire.

The stock factory wiring puts both of the amp's 8 ohm speakers in parallel for 4 ohms, and connects them both to the 4 ohm tap on the output transformer using only the main speaker jack. Plugging in an external speaker of 4 ohms into the ext jack, and using both of the internal 4 ohm speakers on the main speaker jack (two 8s in parallel) at the same time will give a total of 2 ohms and the amp is switched to the 2 ohm transformer tap using the ext jack.

Edit:
Looks like you have some other mods to the amp also. The two things that are just to the left of the speaker jacks, with the red wires coming from them, are not stock on the amp. If you can show a picture of the inside of the chassis where those two things are and where the red wires connect to the amp, we might be able to figure out what they are. One thing looks like a push button. :?:

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Post subject: Re: Help! Blues Deville 2x12 speaker wiring
Posted: Wed Feb 15, 2012 11:04 am
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Thank you very much, I definitely feel more educated on the layout of these speakers. For that red button thing it almost looks like a self bias system along with a pot underneath it. The red wire from the pot leads to the first 6L6 tube and the second red wire from the red button leads to the spot of the "R87" spot of the PCB board.

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Post subject: Re: Help! Blues Deville 2x12 speaker wiring
Posted: Wed Feb 15, 2012 1:25 pm
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Thanks for the pics!

That's what it looks like, the red jack being a test point. I can see the resistor added to the output tube for the test point voltage. Typically a 1 ohm is used between the Cathode of both tubes and ground for bias test point. Reading the mV across a 1 ohm resistor can be read as mA and is the Cathode current for both tubes (I can't see if it is wired for both tubes, but it typically is). The original BDvl and BDlx didn't have a bias adjust and R87 set the C- voltage for the bias, so it looks like someone added an adjustment pot in place of R87, and added a test point. Cool. :)

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