Bassman 135 Ohm and cabinet questions!

mpaulb1386

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Alright! So this always confuses me and I have been searching the web all day. So I have came across a Fender silver face bassman 135 that someone found in a storage locker. I made an offer on it and they took it! So today I have been searching for a cabinet to go with this.
Ok the amp head has two outputs both rated at 4 ohms. My understanding is that I need to find a cab that is 4ohm or less. This greatly limits my cab selections. Then I came across this

"1) The Bassman 135 is designed for speaker cabs of 4 ohm minimum
impedance, for both the main cab and any extension cab.

2) The Bassman 135 and the similar 135 watt Twin Reverb amps are
unique among Fender amps, in that the jacks for the main and extension
speakers are wired so that when both jacks are in use the cabs are
connected in SERIES rather than parallel, and plugging in an extension
cab also switches the speakers to a different tap on the output
transformer (switched from the 4 ohm "center" tap to the "whole" 8 ohm
secondary winding)."

Can anyone confirm this info? And what exactly does this mean? If I plug a cable into the ext jack it will allow me to safely go with an 8 ohm cab? Well anyway I have been searching everywhere so I thought Id ask the pros.

Thanks in advance!
 

Syrus

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if that is correct, you need to add ONLY a 4 Ohm cab.
As it will be series: R1+R2 must equal 8 Ohm total.
(My advice would be to just mail Fender and see what they say.)

Schematic clearly says 4 OHM MINIMUM and if you follow the wiring, it is indeed series wiring for the external jack. My reasoning would be that they made this choice to that people will not blow speakers or kill the tranny easily, as 135W is a whole lot of power (for 1970's?) and that is probably clean power, when overdriven it becomes even more.

bassman135.gif


If you know you electronics part without the risk of killing yourself, check the chassis for the colours on each jack and the taps on the tranny.

That should be sufficient to tell. Or take some pics?
 

mpaulb1386

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Hey thanks a lot thats really helpful. When the head arrives I will take some pictures. There seems to be a lot of debate about this particular head on many forums.
 

Syrus

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Hey thanks a lot thats really helpful. When the head arrives I will take some pictures. There seems to be a lot of debate about this particular head on many forums.

No prob.

Mind PM'ing me when you get it?

Debate all they want, if it is the 135 and that's the correct schematic then it is a series wiring. Which is one of the safest ways to extend an amp.
 

mpaulb1386

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Yeah sure thing. I am actually rerating (changing jobs) in the US Navy to be a Gas Turbine Electrician. So I am about to take a basic electronics course so this is all eye opening to me.
 

Syrus

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Yeah sure thing. I am actually rerating (changing jobs) in the US Navy to be a Gas Turbine Electrician. So I am about to take a basic electronics course so this is all eye opening to me.

Once you understand the basics, it's all very simple.

The course will help you in your spare time too. Win win.
 

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