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Post subject: Blues Jr with ext cab
Posted: Wed Mar 04, 2015 10:37 am
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I want to use my Blues Jr 111 with a Hotrod deluxe extension cab but want the speaker in the BJr to work with it. Does anyone have a recommendation as to what is a goo splitter to do this with?


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Post subject: Re: Blues Jr with ext cab
Posted: Wed Mar 04, 2015 10:59 am
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A standard Y cable will hook up in parallel. This would be hard on the power tubes because of the impedance mismatch. It's not designed to run down to 4 ohms.
But if you got a 1/4 shorting jack, you can wire it into the positive speaker wire.
Connect the wire from the amp to the tip of the jack and the wire to the speaker to the ground and switch of the jack. This will ensure proper phase for the two speakers.

When nothing is plugged into this jack, the shorting switch in the jack will connect and run the internal speaker.
When you plug in the exrension cab, it will hook up the two speakers in series. This will run the amp at 16 ohms. Not ideal, but safe.
Do not mount the extra jack to the chassis of the amp or it will have too many grounds and short the speaker wires. Mount it on an angle bracket and screw it to the side of the wooden cabinet.
Have fun


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Post subject: Re: Blues Jr with ext cab
Posted: Wed Mar 04, 2015 12:07 pm
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Thanks for your reply. The Blues Jr has no issue operation with a 4ohm load.


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Post subject: Re: Blues Jr with ext cab
Posted: Wed Mar 04, 2015 9:23 pm
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TimsAudio wrote:
A standard Y cable will hook up in parallel. This would be hard on the power tubes because of the impedance mismatch...


Not hard on the tubes at all. With a lower impedance, the tubes will not develop as much power. Within reason (ie, within a 2 to 1 ratio), an impedance mismatch is no problem for a tube amp. This myth of the impedance mismatch is a hard one to kill. :wink:

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Post subject: Re: Blues Jr with ext cab
Posted: Thu Mar 05, 2015 6:55 am
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For maximum power and tone in many cases, it's best to match the impedance.
Tim, I use a Weber Z-Matcher to match my old Champ to whatever load I want. Big fun. If I don't, the transformers seem to run a bit hotter. That's what made me look at the Z-Matcher to begin with.
https://taweber.powweb.com/store/zmatch.htm

I know some player who run a deliberate impedance mismatch because they like to way it sounds. I never really cared for the sound myself. YMMV

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Post subject: Re: Blues Jr with ext cab
Posted: Thu Mar 05, 2015 7:47 am
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63supro wrote:
For maximum power and tone in many cases, it's best to match the impedance.
Tim, I use a Weber Z-Matcher to match my old Champ to whatever load I want. Big fun. If I don't, the transformers seem to run a bit hotter. That's what made me look at the Z-Matcher to begin with.
https://taweber.powweb.com/store/zmatch.htm

I know some player who run a deliberate impedance mismatch because they like to way it sounds. I never really cared for the sound myself. YMMV

I think that is the route Im going Bob. I know there wont be an issue running it at 4 ohms but Ill be able to use the Z matcher for other things as well.


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Post subject: Re: Blues Jr with ext cab
Posted: Fri Mar 06, 2015 7:37 am
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tbazzone wrote:
63supro wrote:
For maximum power and tone in many cases, it's best to match the impedance.
Tim, I use a Weber Z-Matcher to match my old Champ to whatever load I want. Big fun. If I don't, the transformers seem to run a bit hotter. That's what made me look at the Z-Matcher to begin with.
https://taweber.powweb.com/store/zmatch.htm

I know some player who run a deliberate impedance mismatch because they like to way it sounds. I never really cared for the sound myself. YMMV

I think that is the route Im going Bob. I know there wont be an issue running it at 4 ohms but Ill be able to use the Z matcher for other things as well.

Yes, I also highly recommend the Weber Z-matcher. I can't notice any tone degradation and it gives me peace of mind regarding mismatches. You will like the new sound of the BJr. with an extension cab....at least I did.

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Post subject: Re: Blues Jr with ext cab
Posted: Fri Mar 06, 2015 2:58 pm
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shimmilou wrote:
TimsAudio wrote:
A standard Y cable will hook up in parallel. This would be hard on the power tubes because of the impedance mismatch...


Not hard on the tubes at all. With a lower impedance, the tubes will not develop as much power. Within reason (ie, within a 2 to 1 ratio), an impedance mismatch is no problem for a tube amp. This myth of the impedance mismatch is a hard one to kill. :wink:


It might be a myth to you, but IMO the power and tone loss isn't worth it. Running efficiently is important. I do agree, it's not going to hurt the tubes, or the transformers as long as everything's in good shape. I remember pulling a pair of power tubes was a big thing when I had my Twin Reverb. I thought it sounded like arse and didn't really lower the volume enough to matter. Just because something works, doesn't mean it sounds as good as it should.

Tim, the Z-Matcher doesn't affect the tone one bit. It's pretty cool to plug an olf Fender Champ into a Marshall 4x12 cab :lol:

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Post subject: Re: Blues Jr with ext cab
Posted: Fri Mar 06, 2015 3:33 pm
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A slight impedance mismatch (2 to 1) being hard on the tubes or the OT is a myth period, opinions really have no place as far as the electronics are concerned. :wink:

I agree, it's all about the sound, and I suggested that sometimes a mismatch will sound better, for me and others sometimes it does, but if not, use what sounds best. 8)

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Post subject: Re: Blues Jr with ext cab
Posted: Fri Mar 06, 2015 9:37 pm
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A creative guitar artist can take poetic license to mismatch impedance any time he/she wants. Both on the input and on the output. If that's the sound he's looking for, it doesn't matter if it's a mismatch, You won't get into too much trouble if its under say, 25 watts...
Alas, I am just a technician without ears. So I stick to the design.
You can set the alignment of your car to "toe out" and it will be very interesting to drive. But an alignment technician wouldn't consider doing it. And I don't intentionally mismatch impedances.
So when asked for a "good" splitter setup, maintaining impedance is a basic part of the design. This series method is tolerant of any impedance or shorted speaker.

I love the sound of the OLD Champs. coupled to a 4X10 ..... I can hear it now. Sweet.
You can expect a Class A Champ to run a warm OT. Since the tube runs at half power DC, it works harder than a push-pull OT.
On the scope, changing the impedance of the speaker or a power tube with different gain changes the DC balance from 1/2 B+ to a higher or lower voltage. This imbalance means early clipping on one end of the wave. Early Tweed Champs were designed to be very unbalanced. The positive wave is pure, but the negative half clips early for a nice touch sensitive distortion capability. The new ones i've seen are mostly balanced.
So a Class A amp can have a tunable breakup by changing load and bias point.
So your impedance matcher could couple the load better without affecting the DC balance of that Classic old Champ.


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Post subject: Re: Blues Jr with ext cab
Posted: Mon Mar 09, 2015 6:22 am
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A slight 2 to 1 mismatch is okay, but go further and see what happens. Just read any amp owner's manual. A slight impedance mismatch could affect the tone sometimes for the better, but in my experience, not usually, depending on the ohms whether the speaker are wired in series or parallel. Loads are specified for a reason. Let your conscience be your guide. :wink:

Here's something from an interview with Mike Soldano. This guy designs not only his own line of amps, but Jet City Amps too. I think he might know a little more than many of us here.

https://bareknucklepickups.co.uk/forum/ ... ic=12607.0
"Well, Dave, I don't know who you've been listening to or what you've been reading, because they're just plain wrong. Here's how it works: If the load is lower than what the amp is set for, like using a 4 ohm cabinet with the amp set at 16 ohms, the power tubes will be worked harder and will run hotter. This, of course, will shorten the life of the power tubes. However, if the load is higher than the amp's setting, like using a 16 ohm cabinet with the amp set at 4 ohms, the voltages in the output transformer will be higher than normal. These excessively higher voltages increase the risk of arcing, which can destroy the output transformer and/or tube sockets. That's why running an amp with no load at all invariably ends up blowing the output transformer. I'd say tubes are easier to replace, wouldn't you?"

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Post subject: Re: Blues Jr with ext cab
Posted: Mon Mar 09, 2015 9:46 am
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Well, I don't want to argue with a legend, but I will anyway
He's right in that a lower than specified load will run more current through the tubes. This is safely limited by the resistance of the OT windings. Any extra current will shorten the life of tubes. From a technicians point of view, that's a bad thing. For musicians, however, It's the price you pay for tone. I heard Merle Haggard changes his power tubes every show due to raging hot bias.
As for too high an impedance causing excessively high voltages in the OT, DC voltages are highest when no sound is produced, The load has no effect at that point.
When you turn on the standby switch before the power tubes are warmed up, that's when the excessive voltages appear.
The unloaded power supply usually shoots up 50-80 volts above operating conditions until the tubes start conducting. This rarely cause transformers to blow up. Manufacturers take these conditions into account.
I agree that an unloaded OT can cause problems with reactance dumping current back into the windings. This can burn up a transformer. But most manufacturers have a shorting jack on the speaker output to prevent this from occuring.
So why would he say that? I can only guess that he's a technician, like myself, and we like to see things done right. He's also a builder who doesn't want warranty returns for any reason.

I can afford to cut musicians slack on impedance up to a point. If that's their sound, I won't get in their way. I just explain the effects and possible consequences and let it go.


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Post subject: Re: Blues Jr with ext cab
Posted: Mon Mar 09, 2015 9:56 am
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The condition and quality of the output transformer and power tubes will have some bearing on this too. Everything looks great on paper, but actual may conditions vary.

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Post subject: Re: Blues Jr with ext cab
Posted: Mon Mar 09, 2015 4:10 pm
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:lol: How convoluted!

I'll stick by what I've stated numerous times; An impedance mismatch within a 2 to 1 ratio for a tube amp is absolutely and unequivocally, 100% fine. Further, too high an impedance connected to a tube amp can and does cause the OT to arc internally. A shorting output jack on a tube amp will protect the amp from harm if no speaker cable is connected to the amp. If a short circuit (zero ohms) protects the amp from harm, it is obvious that a 1 ohm, 2 ohm, or 4 ohm speaker load will also cause no harm for a 2 ohm, 4 ohm or 8 ohm amp.

With all due respect to Mr Soldono, he neither invented tube amps, nor did he come up with any laws of physics or electricity. He also can not alter the physics of how a tube amp operates, no matter how good his amps are. The fact is, impedance changes with changes in frequency. So at any given point in time, how "matched" is the impedance of amp and speaker during the constant changes in the frequency output of the amp? The amp is rated/tested using a purely resistive load anyway, and not using a speaker. With a speaker connected, the load impedance that the tubes see is constantly changing as the frequency changes. So, it can't possibly be matched at all times. :wink:

Interesting to note that the examples given, 4 ohm speakers with a 16 ohm amp, and 16 ohm speakers with a 4 ohm amp, are both outside the 2 to 1 ratio. :wink:

More people shorten the life of their tubes by not having the bias set properly, than by using a slight impedance mismatch.

"The proof is in the pudding." Not one thread here about an impedance mismatch within a 2 to 1 ratio causing any harm, or even shortening tube life, while myself and many others routinely use our amps with the slight impedance mismatch. That is really all that needs to be said. 8)

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Post subject: Re: Blues Jr with ext cab
Posted: Mon Mar 09, 2015 4:35 pm
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shimmilou wrote:
:lol: How convoluted!

I'll stick by what I've stated numerous times........................................................"The proof is in the pudding." Not one thread here about an impedance mismatch within a 2 to 1 ratio causing any harm, or even shortening tube life, while myself and many others routinely use our amps with the slight impedance mismatch. That is really all that needs to be said. 8)

I will certainly defer to your superior knowledge and expertise vs. mine on this topic....might even go so far as to concede you are 100% correct.

I'm still going to match amp and speaker impedance OR follow the manufacturer's recommendation OR use a Weber Z-matcher. Nothing wrong with that is there?

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