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Is there any way of figuring out if an amp with an ext. speaker jack is wired in series or parallel?
I have an Allen Old Flame with 2 x 10 Scumbacks in it. The speakers are both 16 ohm wired in parallel for an 8 ohm load. The amp has an ext. jack and a 4 or 8 ohm switch on the back. I'd like to try adding a 1 x 12 8 ohm cab and figured it would be fine if I just turned the ohm switch to 4 ohms. Anyway of checking this out before I blow something up?
 

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davetcan said:
Is there any way of figuring out if an amp with an ext. speaker jack is wired in series or parallel?
I have an Allen Old Flame with 2 x 10 Scumbacks in it. The speakers are both 16 ohm wired in parallel for an 8 ohm load. The amp has an ext. jack and a 4 or 8 ohm switch on the back. I'd like to try adding a 1 x 12 8 ohm cab and figured it would be fine if I just turned the ohm switch to 4 ohms. Anyway of checking this out before I blow something up?
That would be my guess. Similar to my Hot Cat.
 

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Try this...

davetcan said:
Is there any way of figuring out if an amp with an ext. speaker jack is wired in series or parallel?
I have an Allen Old Flame with 2 x 10 Scumbacks in it. The speakers are both 16 ohm wired in parallel for an 8 ohm load. The amp has an ext. jack and a 4 or 8 ohm switch on the back. I'd like to try adding a 1 x 12 8 ohm cab and figured it would be fine if I just turned the ohm switch to 4 ohms. Anyway of checking this out before I blow something up?
Hi Dave!

Here's an easy way to figure it out! If the amp has the external jack wired in parallel with the main speaker jack then you can plug in just one speaker to either jack and things work just fine.

If the external jack puts the extra speaker in series then it will have to be wired to short with nothing plugged in. The regular speaker jack will have its return path to ground through the extension jack. Plugging in an extra speaker will open the jack's shorting switch contacts and place the two speakers in series. Like most old Fenders and such, this means that if you plug just one speaker into only the extension jack you don't get any power through it, 'cuz there's nothing plugged into the main speaker jack.

Quick and easy!

Wild Bill
 

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Discussion Starter #4
Wild Bill said:
Hi Dave!

Here's an easy way to figure it out! If the amp has the external jack wired in parallel with the main speaker jack then you can plug in just one speaker to either jack and things work just fine.

If the external jack puts the extra speaker in series then it will have to be wired to short with nothing plugged in. The regular speaker jack will have its return path to ground through the extension jack. Plugging in an extra speaker will open the jack's shorting switch contacts and place the two speakers in series. Like most old Fenders and such, this means that if you plug just one speaker into only the extension jack you don't get any power through it, 'cuz there's nothing plugged into the main speaker jack.

Quick and easy!

Wild Bill
Damn, that's slick. I figured you'd know :food-smiley-004:

Thanks Bill, you too Jeff.

btw Bill the Traynor/Busen has become my go to amp. I'm getting some hum from the reverb when turned up past 2, any thoughts? It increases as the reverb increases.
 

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Well...

davetcan said:
Damn, that's slick. I figured you'd know :food-smiley-004:

Thanks Bill, you too Jeff.

btw Bill the Traynor/Busen has become my go to amp. I'm getting some hum from the reverb when turned up past 2, any thoughts? It increases as the reverb increases.
Dave, that type of reverb was pioneered by Fender. That circuit ALWAYS has a bit of hum that gets worse as you crank the reverb control!

Sometimes its worse with some amps than others and you can move a ground wire or two and get a bit of reduction in the hum level. I've never known any amp using this reverb circuit to be completely hum-free. It's just a design thing. Leo probably figured it was too expensive to go to a more elaborate circuit.

The reverb in the Marshall Pete is so strong that hopefully it will always swamp out the hum. Unless you've been getting a little "Dick Dale" nostalgic and have been cranking it to 10? :)

I could spend some time on it for you if it's really aggravating Dave but honestly, I don't expect much success. Crank the knob on an old Super Reverb and you'll hear what I mean.
 

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Discussion Starter #6
No problem. Not bugging me at all, I just noticed it today for some reason. You're right about the reverb strength though, anything over 3 is definitely getting into Dale/Ventures/Shadows territory :D
 
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