Blackface Fender Bassman: ext speaker ohms?

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rjd2
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Blackface Fender Bassman: ext speaker ohms?

Post by rjd2 » Wed Nov 30, 2011 10:08 am

hi all, ive got a blackface bassman that i love. would be super bummed if i had to replace output tranny. here's my question: ive been running it on a 4 ohm 10" speaker. i just got an 8ohm 8" speaker. i'd like to try running the ext speaker output to the 8" 8ohm speaker; my understanding is that this would be a total load of around 3 ohms. i know a 4ohm load is suggested. does this sound potentially harmful? do i need to dig up a 16ohm 8" speaker? thanks for the help, rj

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Post by kslight » Wed Nov 30, 2011 5:52 pm

In my experience Bassmen are rather forgiving as far as speaker loads go, I'd give it a whirl and if the output starts getting screwy you know its time to turn it off.

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Post by 0xeneye » Wed Nov 30, 2011 11:57 pm

Please don't do what kslight suggests - it's a nice amp, and you want to keep that transformer happy : if it wants 4 ohms, give it 4 ohms : your 1 4ohm speaker you have, or two 8s in parallel. Mismatched speakers (4 and 8)would divide the load unevenly, and just be plain wrong.
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Post by Jim Williams » Thu Dec 01, 2011 10:34 am

If it sounds right to you, abuse it.

If the transformer burns, just buy a replacement for fifty bucks.

I used to use a Bassman to intentionally burn up speakers. We would set up open frame 5" car stereo jobs and fry them with feedback until the voicecoils melted and burned up. Sounded great, put on a good light show too. Lighting the cones on fire also made cool sounds.

The amp was fine.
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Post by tdbajus » Thu Dec 01, 2011 12:54 pm

Also, since the extra speaker jack just combines the second speaker with the first in parallel, you'd actually be closer to 4Ω using a 4Ω+8Ω than a 4Ω+4Ω.

Most people agree that running a vintage Fender at half the posted impedance is fine. Ever hear of someone blowing up their bassman by running it with the two bassman 4Ω cabs that they sold with it?

Me either.

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Post by Mudcloth » Thu Dec 01, 2011 3:36 pm

Tweed Deluxes had under-built output trannies. Blackface Deluxes had under-built output trannies in that they don't hold up well to running the external speaker jack.
60's Bassman heads have the most over-built trannies of any Fender amp, in my opinion. I have never, ever seen one with a blown power or output tranny. Granted, I've only been repairing amps for 5 years, but I've seen a bunch and the older guys never ran into those problems with Bassmans. It's kind of what they're known for.

I got my 68 Bassman on craigslist for $200 because it "didn't work". It had a 20 amp fuse in it. It had a shorted power tube that in turn fried the 100 ohm pilot light resistors to blackened cremation. PT was fine.

I routinely run mine into my 8 ohm Vintage 30. Love it.
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Post by kslight » Thu Dec 01, 2011 5:45 pm

0xeneye wrote:Please don't do what kslight suggests - it's a nice amp, and you want to keep that transformer happy : if it wants 4 ohms, give it 4 ohms : your 1 4ohm speaker you have, or two 8s in parallel. Mismatched speakers (4 and 8)would divide the load unevenly, and just be plain wrong.
You probably shouldn't listen to me...I definitely don't know what I'm talking about, between the 3 various eras of Bassmen I own that have regularly mismatched speakers attached without problems...

I don't think the OP asked whether it would be "correct"...he asked if the amp would be fine... The answer is "yes."

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Post by rjd2 » Fri Dec 02, 2011 5:33 am

Mudcloth wrote:Tweed Deluxes had under-built output trannies. Blackface Deluxes had under-built output trannies in that they don't hold up well to running the external speaker jack.
60's Bassman heads have the most over-built trannies of any Fender amp, in my opinion. I have never, ever seen one with a blown power or output tranny. Granted, I've only been repairing amps for 5 years, but I've seen a bunch and the older guys never ran into those problems with Bassmans. It's kind of what they're known for.

I got my 68 Bassman on craigslist for $200 because it "didn't work". It had a 20 amp fuse in it. It had a shorted power tube that in turn fried the 100 ohm pilot light resistors to blackened cremation. PT was fine.

I routinely run mine into my 8 ohm Vintage 30. Love it.

thanks to all who responded. mudcloth, as you repair amps, i especially appreciate your feedback. as much as i REALLY dont want to damage this amp cause i use it all the time, it sounds like its safe for the amp to do 4ohms+8ohms. thanks guys!

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