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5F1 ext. speaker cab jack?

Tubes 'n Wood

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Nov 9, 2013
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368
Just posting a question to the collective knowledge here. Can an ext. cab jack be added to a Tweed Champ? I'd like to be able to use the internal 8" speaker and a 10" ext cab at same time. My immediate questions would be: 1) can it be done? 2) would the amp be able to handle it? 3) can it be wired like the 5E3 ext cab jack? 4) what of the ohms ratings on the internal speaker and the ext cab?

Just kind of thinking out loud? Any thoughts on the subject would be appreciated.
 

PaulD

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Jun 25, 2007
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An original 5F1 (and many of the clones) will have an output transformer that is designed for a 4 ohm load, some of the clones may have a transformer designed for an 8 ohm load, it depends what amp you have. In either case if you connect an extension speaker in parallel to the existing speaker you will reduce the impedance, 2 x 4 ohm speakers in parallel will result in a 2 ohm load so you would be running with an impedance mismatch.

Generally speaking with a valve amplifier if you are going to run a mismatch it is better to go lower than higher so connecting an additional speaker in parallel is probably not going to cause any problems. It is however less than optimal and by lowering the load you will be reducing the output power, this will probably be offset by the effect of having an extra speaker so there will likely be little change in the overall volume, there may also be some effect on the tone, typically an amp will sound thinner into a lower load than it was intended for. In the long term running into a lower load will put more stress onto the output valve and may reduce it's lifespan (running into a higher load puts more stress onto the output transformer which is less desirable). If you were intending to run it with the extension cab all the time the best option would be to replace the internal speaker with one of double the existing impedance and use an extension speaker of the same value (2 x 8 ohm speakers for a 4 ohm load or 2 x 16 ohm speakers for an 8 ohm load).
 

sonar

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Jan 10, 2003
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It can be done with most clones. Garden variety Champ power transformers (Heyboer, Classictone, etc) can be wired for 8 ohms. Obviously you should switch out the speaker to 8ohm. Then you can wire an external speaker jack like a typical Fender. Theoretically you'll burn through the power tube sooner, but the difference on a 5 watt amp like a 5F1 is negligible.
 

Tubes 'n Wood

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Nov 9, 2013
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I've thought about this a lot, and want to add an ext speaker jack... but not sure how? There is a bunch of different wiring examples for ext jacks on different tweeds. Would I be able to copy the wiring from my 5E3 ext speaker jack?
 

PaulD

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Jun 25, 2007
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Not quite sure what you mean by there being a bunch of different wiring examples, any Fender tweed amp that has an extension jack will have it wired in parallel to the main speaker (the only other way it could theoretically be wired is in series with some sort of switching jack arrangement and Fender never did this). As previously stated if your output transformer only has a single output tap then however you wire it you will be running into the wrong impedance which is never ideal or advisable. The extension jack on a 5E3 is simply wired in parallel with the internal speaker and plugging in an 8 ohm extension speaker means the amp is running into 4 ohms instead of the 8 ohms that it was designed for, you can get away with it but it is not ideal and will put extra strain on the output valves.

If your amp is a clone as opposed to an original or re-issue Fender Tweed it may have multiple output taps on the transformer and there may well be a way of adding an extension speaker in a way that is optimal. However without knowing what taps are available on your output transformer and what impedance speakers you have it is impossible to say.
 

Tubes 'n Wood

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Nov 9, 2013
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PaulD, tyvm for reply. I guess what I mean by different wiring examples is that on the Mojotone tweed diagrams for the 5E3 Deluxe, the 5E5APro Amp, and the 5F8A Twin HP (for example) the ext speaker jack looks to me as a different wiring configuration?

I was thinking if I leave the 5F1 kit as is with the 4 ohm speaker, I could use it that way as a practice amp and just plug into the main jack. But if I add the ext speaker jack and then run a cable from each jack to a separate 8 ohm, 1x10" cab, the output transformer would still only be seeing 4 ohms? Am I thinking this correctly?

So then could I just mirror the ext speaker jack wiring like my 5E3?

Thank you for reply again.
 

PaulD

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Jun 25, 2007
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All of those amps have the jack sockets wired in parallel, possibly the fact that two of them have negative feedback loops connected to the outputs is making them look different on the schematics but they are still wired in parallel.

What you suggest is fine and as you say using the 2 x 8 ohm cabs will result in a 4 0hm load, just wire the extra jack in parallel (tip to tip and sleeve to sleeve). You could also just use a 2 into 1 jack adapter if you wanted to avoid adding another socket.
 

Tubes 'n Wood

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Nov 9, 2013
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PaulD, thank you very much for the info and clarification! Is the a certain 2 to 1 adapter better than others?
 

Tubes 'n Wood

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Nov 9, 2013
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PaulD, All I'm finding are ones used for headphones? Is there specialized ones to handle using them the way you are talking?
 

Tubes 'n Wood

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Nov 9, 2013
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PaulD, Thank you again, I just wasn't sure with the ability of any of the adapters since they would be used after the power amp. Hope all is well with you and yours.
 

PaulD

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Jun 25, 2007
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You're welcome. All good here thanks, albeit that everything is locked down. Pubs, restaurants, non-essential shops all closed and can only go out for essential supplies etc. Hope things improve soon!
 

Tubes 'n Wood

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Same here, highly recommended self quarantine unless getting food or medical help. But I work a hospital in a critical access area, so... no quarantine for me!?
 
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