# Would it be possible to........(Vintage Fender bassman mod question)



## Chitmo (Sep 2, 2013)

I have been considering getting a 65 bassman head. However I don't really have the space to have extra cabinets around, nor do I want to buy another attenuator. Would it be possible to install an impedance selector switch so that the amp could be used at 4, 8 or 16 ohms like modern amps? If so what would something like that cost?


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## greco (Jul 15, 2007)

Wouldn't you have to swap out the output transformer in the Bassman to one that is tapped for 4, 8 and 16 ohms? You could then install an impedance selector switch.

However, maybe there are other ways to accomplish this. 

Cheers

Dave


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## Lincoln (Jun 2, 2008)

Correct Dave, I'm pretty sure you'd have to replace the output transformer with one that has 4, 8, & 16 ohm outputs.


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## davetcan (Feb 27, 2006)

Unless you have a 2 ohm cab I wouldn't worry about it. I've done this before with no issues but I've heard it argued both ways. Perhaps some of the more knowledgeable amp folks can chime in. An 8 ohm cab would be OK in my book but I wouldn't use a 16 ohm cab.

http://forums.fender.com/viewtopic.php?t=37890


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## Chitmo (Sep 2, 2013)

davetcan said:


> Unless you have a 2 ohm cab I wouldn't worry about it. I've done this before with no issues but I've heard it argued both ways. Perhaps some of the more knowledgeable amp folks can chime in. An 8 ohm cab would be OK in my book but I wouldn't use a 16 ohm cab.
> 
> http://forums.fender.com/viewtopic.php?t=37890


My main issue is that my attenuator is only good for 8 or 16 ohms, which covers just about everything I need except vintage fenders. I have gone through quite a few attenuators and the rock crusher is the one that covers my needs. My cab on the 8ther hand will soon be modded to do 4 or 16 ohms at 100 watts or 8 ohms at 50 watts, so I am covered there.


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## knight_yyz (Mar 14, 2015)

you could also look into the pentode triode switch to reduce the wattage of the amp. Then ditch the attenuator


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## numb41 (Jul 13, 2009)

Chitmo said:


> My main issue is that my attenuator is only good for 8 or 16 ohms, which covers just about everything I need except vintage fenders. I have gone through quite a few attenuators and the rock crusher is the one that covers my needs. My cab on the 8ther hand will soon be modded to do 4 or 16 ohms at 100 watts or 8 ohms at 50 watts, so I am covered there.



Get (well) over $200 in mods done to an old amp for a new transformer with ohm options, or get a different Attenuator with a 2 ohm out. I know what choice I would make. Try the Weber Mass 100. I have one. Great attenuator


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## dcole (Oct 8, 2008)

Here are your choices with the Bassman with an 8 ohm cab and an 8 ohm attenuator on hand:

1. Get new power transformer and switch for 4, 8 & 16 ohm taps - $300 done by a tech or more
2. Gain mad skills and rip original transformer apart, tapping into the correct spots for 8 & 16 ohm taps - mad skills are free but take time to develop
3. Plug cabinet into one speaker jack and attenuator into other speaker jack - free and this should give the amp the ~4 ohms it is looking for
4. Plug in the cabinet and play - free and one less thing to plug in that will turn ~half the power output into heat only

I would suggest trying #3 & #4 as they are the cheapest and lest destructive to the amp in question.


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## sammyr (May 7, 2013)

As far as I know there is no reasonable way to do this without replacing the output transformer. One thing to look at would be an impedance matching box like Weber's Z Matcher http://www.tedweber.com/z-matcher-100. This will be cheaper than a new output transformer and require no surgery on your bassman.

*edit* woops resurrected a dead thread. I hope OP figured it out.


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