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Hi there. Pretty simple speaker question which is fitting for a first post I suppose.
I'm just wondering:
My early 70s Fender Twin says 4 ohm total load on the back.
I have two 16 ohm speakers, and am wondering if I can install them safely. I was told that if it is wired in parallel this should be fine.
Any help is appreciated.
Also, does anyone have a diagram of parallel wiring?
 

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Hi there. Pretty simple speaker question which is fitting for a first post I suppose.
I'm just wondering:
My early 70s Fender Twin says 4 ohm total load on the back.
I have two 16 ohm speakers, and am wondering if I can install them safely. I was told that if it is wired in parallel this should be fine.
Any help is appreciated.
Also, does anyone have a diagram of parallel wiring?

It is my understanding that 2 X 16 ohms wired in parallel will result in 8 ohms total impedance. How "safe" this is seems to be a matter of opinion. The mismatch (8 ohms instead of 4 ohms) can possibly be somewhat harder on your tubes and possibly on your transformer. I'm not sure how significant it will be with this particular amp.

You could wire 2 X 8 ohms in parallel for 4 ohms total.

Please wait until others to give their comments before you
decide on anything and/or install the speakers.

What (brand of) speakers are you putting in?

Good luck.


Dave
 

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:smile:
Hi there. Pretty simple speaker question which is fitting for a first post I suppose.
I'm just wondering:
My early 70s Fender Twin says 4 ohm total load on the back.
I have two 16 ohm speakers, and am wondering if I can install them safely. I was told that if it is wired in parallel this should be fine.
Any help is appreciated.
Also, does anyone have a diagram of parallel wiring?
Although it's not generally recommended to do this, the Twin can handle the mismatch easily...you will lose a little wattage due to the higher impedance but it won't be drastic....interesting thing you can do with the speakers being 8 ohms is pull two of the output tubes. This will put the amp back in balance and you'll get a little more overdrive at the top end as it will be a 50 watt amp instead of a 100... * remember, if you do this, pull either the ouside two or the inside two power tubes...never both on the left or right:smile:
 

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:smile:

Although it's not generally recommended to do this, the Twin can handle the mismatch easily...you will lose a little wattage due to the higher impedance but it won't be drastic....interesting thing you can do with the speakers being 8 ohms is pull two of the output tubes. This will put the amp back in balance and you'll get a little more overdrive at the top end as it will be a 50 watt amp instead of a 100... * remember, if you do this, pull either the ouside two or the inside two power tubes...never both on the left or right:smile:
+1! I shudda thought of that!

My brain worked fine until the kids came...

:food-smiley-004:
 

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With the Twin being approx. 100WRMS at 4 ohms it would have only about 50WRMS at 8 ohms. Most amps will take the higher load without issue, but won't tolerate a lower load.
 

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With the Twin being approx. 100WRMS at 4 ohms it would have only about 50WRMS at 8 ohms. Most amps will take the higher load without issue, but won't tolerate a lower load.
Er...not really!

If you have all 4 tubes installed and you go to an 8 ohm load the power may drop only a few watts. Output transformers convert impedances by a fixed ratio. If the 4 ohm design load meant about 3300 ohms on the plate/tube primary (typical for a quad of 6L6's) then running an 8 ohm load means the plates will see 6600 ohms total. This would mean double the proper load for such a quad.

Tubes deliver power over a broad curve for a given plate load. It's not at all like working out Ohm's Law with resistors. If you look up the data sheets on 6L6's you'll see curves of typical operating conditions. Power, distortion, plate and screen currents are all plotted in curves and the drop in power of a speaker load mismatch changing the primary load might only drop a few watts and not half like you stated.

Best power and distortion rarely work out to the same points on the curves so the designers go for a compromise. I just looked up the curves and it seems you'd actually get 3 or 4 EXTRA watts with such a mismatch. Typical distortion goes from less than 2% to over 10%!

http://www.pmillett.com/tubedata/HB-3/Receiving_Tubes_Part_2/6L6-GC.PDF

There's the link for the specific curve page for load impedance vs. power or distortion.

Incidently, you'd have been correct if it was a solid state amp!:smile:

:food-smiley-004:
 
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