Cabinets for Fender Bassman 135

[Muck Luto]

No need for a shorting plug with the Bassman 50 (or any other Bassman but the 135).

The output jacks of the Bassman 50 are simply two identical jacks, wired in parallel to the single transformer winding.
The speaker cab(s) can be connected to either jack, as long as the total load is not less than 4 ohms.
A shorting plug in either jack would short the output to ground and silence the amp.

The switching arrangement of the output jacks of the Bassman 135 (using a center-tapped 4/8 ohm transformer winding) is unique.

The shorting plug in the normal output jack is only needed because hooking a single 8 ohm cab to the EXT speaker jack is a "hack" or "kludge".
The amp designers never intended the amp to be used that way.
Otherwise, they would have fitted the main speaker jack with a beefy, high-current switching contact!

Ok, thanks again.

By now i only have a 4 ohms cab connected to the SPKR output.

Correct me if I'm wrong (or if this has already been discussed many times...) but for the 50/70/100W version, the connection options are as follows:
- a 4-ohm speaker connected to the SPKR output (and nothing on the EXT output)
- two 8-ohm speakers connected to the SPKR and EXT outputs
- two 8-ohm speakers connected in series (one after the other) to the SPKR output (and nothing on the EXT output)

 

[Wasnex]

- two 8-ohm speakers connected in series (one after the other) to the SPKR output (and nothing on the EXT output)

This part is not correct. Two 8 ohm cabs in series is 16 ohms.

If you mean daisy chain two cabs off the SPKR out, usually the jacks on each cab form a parallel connection. So two 8 ohm cabs should provide a 4 ohm load.

 

[Muck Luto]

This part is not correct. Two 8 ohm cabs in series is 16 ohms.

If you mean daisy chain two cabs off the SPKR out, usually the jacks on each cab form a parallel connection. So two 8 ohm cabs should provide a 4 ohm load.

I knew it was incorrect while writing it ...
Of course, I meant in parallel for a total of 4 ohms.

If I understand correctly, you definitely shouldn't connect two 4-ohm speakers to these amps ? Unlike the 135W version, they aren't designed for that, and you run the risk of seriously damaging them. Is that right ?

 

[Wasnex]

If I understand correctly, you definitely shouldn't connect two 4-ohm speakers to these amps ? Unlike the 135W version, they aren't designed for that, and you run the risk of seriously damaging them. Is that right ?

I think it's best to show the amp the expected load. However, it's generally assumed that Fender amps of the era could safely tolerate a 2:1 or 1:2 impedance mismatch.

AFAIK Fender amps of the era were generally sold with a single cab that showed the amp the expected load.

As you see above, the speaker has two 8 ohms drivers, so the amp sees the expected load with a single cab.

A matching extension cab could also be used. If both cabs were used, the amp would see an impedance mismatch. This is harder on the amp and tubes, and reduces how much power the amp can make; so not really worth it IMHO.

Keep in mind the amp is ~60 years old and the output transformer may have been degraded over the years.

 

[bknop]

I am curious what characteristics the OP had in mind as most desirable for a cab. With only 135 watts, there are lots of cab options. For example, I built a 6cuft acoustic suspension cab to use with a 200 watt tube amp using an Eminence 1540sf. It's a totally different sound having all that low end. The efficiency was lower at 94db, but the -3db point was around 30hz. Here are the ts specs for the woofer. Found the info on fleabay. My biggest mistake with the cab was not including a 6-8" midrange and crossing over the woofer around 400 hz or so.
If I were gigging in a loud band I would find the most efficient speakers I could find and installing them in as large of cabs as possible without exceeding the cone's excursion capabilities (xmax) for the power output of the amp being used. If higher power amps are a possibility, the cab volume would need to be reduced accordingly.
Others on the forum would be way more qualified than me on recommending any of the commercially made cabs. There may be some large vintage cabs that could be a good match too.

 

[bknop]

Edit for clarity in my last post, I plugged in the ts specs into winisd alpha I found, response differs. The online specs differed some from the ones I measured 20 years ago, the f3 is 40hz, f10 is 27hz. Still decent, it's possible there is variation in the drivers over the years or my measured specs were off.

 

[Longwheelbass]

Just saw your post on the purchase of the 135 head. Like a couple have already mentioned two 15's or two 2x12's will give you a great setup. I tried for years back in Australia to find two Fender 2x12's but gave up, too hard to find so I built my two 15 cabs with hardware store "marine ply", and for some reason went with open back, no front ports a la a lot of the Fender combos and cabs from the 70's and I've been gigging with them since I built them in 2010. Never had a complaint from a sound engineer either in a studio or a venue.

 

[John D Harris]

Recommendations for best speaker cabs for Bassman 135

A pair of these:

Fender Bassman 115 Neo

 

[John D Harris]

Recommendations for best speaker cabs for Bassman 135

... or a pair of Barefaced Super Compact or one of their Six10 cabinets.

 

[bknop]

. . . . I built my two 15 cabs with hardware store "marine ply", and for some reason went with open back, no front ports a la a lot of the Fender combos and cabs from the 70's and I've been gigging with them since I built them in 2010. Never had a complaint from a sound engineer either in a studio or a venue.

Cool cabs. I bet those cabs work really well for close miking with a full bottom end. It's rare to see open back cabs for bass these days. It can be done. The best woofers for the application have their resonant frequency around 30-45 hz, a qts around 1 or higher and high xmax. For example, the Eminence Alpha 15 which would be good in a 40 watt open back amp, the Multicomp Pro (MCM) 55-2963 sold by Newark Electronics has a higher excursion ability than the Eminence and is good for around 80 watts in an open back cab. A woofer with a low qts like .3 would rolloff bass fast in an open back cab.

 

[Longwheelbass]

Cool cabs. I bet those cabs work really well for close miking with a full bottom end. It's rare to see open back cabs for bass these days. It can be done. The best woofers for the application have their resonant frequency around 30-45 hz, a qts around 1 or higher and high xmax. For example, the Eminence Alpha 15 which would be good in a 40 watt open back amp, the Multicomp Pro (MCM) 55-2963 sold by Newark Electronics has a higher excursion ability than the Eminence and is good for around 80 watts in an open back cab. A woofer with a low qts like .3 would rolloff bass fast in an open back cab.

Wo you really know the maths n physics - impressive! Zero science or maths went into this apart from making sure there was an inch at 12, 3, 6 and 9 o'clock between the cutout and edge on the baffle, so I guess it's an absolute fluke for me ending up with nice sounding cabs. I had used the original 4x12 angled baffle cab with replacement ceramic mag Eminence bass speakers which did upgrade the woolly sound of the OG crappy 4 25 watt jobs, but it still wasn't bitey/beefy enough for me hence the plywood experiment. Being that the Lorantz 15's I bought are designed for bass amps and PA usage and are rated at 500w at 8 ohms I guess it's a minor miracle they sound good in these very agricultural cabinets.

 

[Bill Whitehurst]

If you want to get loud enough to make up for the relatively low power, try a pair of TL 606s.
Sensitivity is your friend for that.

 

[bknop]

Wo you really know the maths n physics - impressive! Zero science or maths went into this apart from making sure there was an inch at 12, 3, 6 and 9 o'clock between the cutout and edge on the baffle, so I guess it's an absolute fluke for me ending up with nice sounding cabs. I had used the original 4x12 angled baffle cab with replacement ceramic mag Eminence bass speakers which did upgrade the woolly sound of the OG crappy 4 25 watt jobs, but it still wasn't bitey/beefy enough for me hence the plywood experiment. Being that the Lorantz 15's I bought are designed for bass amps and PA usage and are rated at 500w at 8 ohms I guess it's a minor miracle they sound good in these very agricultural cabinets.

Sometimes it just works out. I've built some open back cabs the same way with little science involved. I sometimes use science to design and verify stuff I build, but I've built a majority of stuff with my ears and eyes as my only test equipment. That being said, using programs like Room Eq Wizard, Winisd, and Hornresp are great aids in speaker design. I would not take such a casual approach if I were to design stuff to be sold as a product though.