omikin Posted March 10, 2016 Share Posted March 10, 2016 I have a question about my 70's Fender Bassman. It has two speaker outputs and underneath them it says "TOTAL LOAD 4 OHMS". Does this mean each output is 8 Ohms? I have been using a 4 Ohm cab through a single output for years with no issues. Would it be better to use an 8 Ohm cab? I am genuinely confused... Quote Link to comment Share on other sites More sharing options...
GazWills Posted March 10, 2016 Share Posted March 10, 2016 (edited) I think it means you can use a single 4 ohm cab, or two 8 ohm cabs. I have the same amp, I use a 4 ohm cab (over 10 years now), no problems The output from the amp is 4 ohms, either 4 ohms through one output or 8 from each if you are using 2 cabs... Edited March 10, 2016 by GazWills Quote Link to comment Share on other sites More sharing options...
omikin Posted March 10, 2016 Author Share Posted March 10, 2016 I think that's what I always thought. Does that mean if I were to use an 8ohm cab on its own I would be getting less out of the amp? Quote Link to comment Share on other sites More sharing options...
Truckstop Posted March 10, 2016 Share Posted March 10, 2016 That's right, approximately half to two thirds of the available power but it depends from amp to amp. Just make sure you don't use two 4ohm cabs! Quote Link to comment Share on other sites More sharing options...
omikin Posted March 10, 2016 Author Share Posted March 10, 2016 I doubt there's any chance of that! When you say less power does that equate to less volume? I'm guessing it's not quite as simple as that... Quote Link to comment Share on other sites More sharing options...
Dan Dare Posted March 10, 2016 Share Posted March 10, 2016 The outputs are paralleled. As others say, just make sure you don't connect two 4 ohm cabs. I had the Bassman 135. Nice beast. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted March 10, 2016 Share Posted March 10, 2016 [quote]Does this mean each output is 8 Ohms?. [/quote]It means the transformer tap is rated for 4 ohm operation. Since it's a valve amp you may use a 4 ohm OR LOWER load. For that matter you may use an 8 ohm load, the Fender output transformer and power valve circuitry is very robust. I wouldn't use higher than an 8 ohm load though, while 2 ohms is perfectly OK. Back in the day when we didn't know better we ran Fenders day in,day out with 1 ohm loads with no ill effect. As for the previous replies, they would be accurate if the Bassman was a SS amp, but it isn't. Quote Link to comment Share on other sites More sharing options...
3below Posted March 10, 2016 Share Posted March 10, 2016 [quote name='Bill Fitzmaurice' timestamp='1457637496' post='3000540'] .....As for the previous replies, they would be accurate if the Bassman was a SS amp, but it isn't. [/quote] Age and experience both of which I place myself in. Sense and sanity are another set of issues Quote Link to comment Share on other sites More sharing options...
The fasting showman Posted March 10, 2016 Share Posted March 10, 2016 (edited) I've owned a few Bassman 135s and a 100 and I seem to remember from the circuit diagram that the '70s Fenders break from the convention of parallel outputs (tweeds etc) and are wired in series but with a switching jack on one of the outputs that switches the output transformer to an 8 ohm tap. That then enabled you to use two of the stock cabs (4 ohm pyramid 4x12s) with one head presenting an 8 ohm load overall. If you are going to use a single 4 ohm cab then you use the regular speaker output, hence why it says 4 ohm min over each output but states 4 ohm minimum overall. Having said that, back when I was a kid in the '80s I used an 8 ohm cab on the regular (not ext) output with no issues. It may be better in this instance though to use the ext jack with an 8 ohm cab if using a single 8 ohm cab as (I think! Please check the diagram) that the switching jack is on the ext output and would switch in the 8 ohm tap. Hope this helps, there will be better informed people doubtless but I'd check the circuit diagram. Don't want the output tranny getting fried because of my rambling! To add if you are using a 4 ohm cab on the regular (not ext speaker out) then all is fine. Martin Edited March 10, 2016 by The fasting showman Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted March 10, 2016 Share Posted March 10, 2016 (edited) [quote name='The fasting showman' timestamp='1457648371' post='3000715'] I've owned a few Bassman 135s and a 100 and I seem to remember from the circuit diagram that the '70s Fenders break from the convention of parallel outputs (tweeds etc) and are wired in series but with a switching jack on one of the outputs [/quote]The 135 may be different, but the standard Fender arrangement used a switched main speaker jack which shorted to ground when there was no plug inserted. This prevented damage that would occur if the amp was used with no load. It also caused consternation if you plugged into the extension jack and not the main jack, as the amp wouldn't work. We didn't know at the time why they did that, but you didn't have to make that mistake very many times before you learned not to do it. Edited March 10, 2016 by Bill Fitzmaurice Quote Link to comment Share on other sites More sharing options...
omikin Posted March 10, 2016 Author Share Posted March 10, 2016 Every time I've plugged the cab in I've thought "these inputs are the same - it doesn't matter which one I put the lead into" but each time I've plugged it into the normal socket, not the extension... Quote Link to comment Share on other sites More sharing options...
bumnote Posted March 10, 2016 Share Posted March 10, 2016 The 135 may be different, but the standard Fender arrangement used a switched main speaker jack which shorted to ground when there was no plug inserted. This prevented damage that would occur if the amp was used with no load. It also caused consternation if you plugged into the extension jack and not the main jack, as the amp wouldn't work. We didn't know at the time why they did that, but you didn't have to make that mistake very many times before you learned not to do it. [b]Edited by Bill Fitzmaurice, Today, 10:53 PM.[/b] Same arrangement on the current Bassman 100T Quote Link to comment Share on other sites More sharing options...
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