Ampeg B25 2x15 Cab Conversion

[Gunsmoke86]

I recently decided to upgrade a vintage Ampeg B25 2x15 cab with 2 brand new Eminence Delta 15a’s. My goal is to make the cab suitable for use with my Heritage SVT. By upgrading the speakers I now have the required impedance of 4 ohms (8 ohm speakers wired in parallel). I’m mostly happy with the sound except for the ports. It sounds like there is way too much air moving through the ports.

It seems like a no-brainer to just increase the size of the ports. However, the science of cabinet construction is not my strong suite. Is it really that simple? Is converting a cab meant for 55 tube watts to a cab that can withstand 300 tube watts a terrible idea? I’m interested in any opinions.

 

[daveman50]

My memory of this cabinet is that it's quite shallow. I doubt it can be converted to this use, but others more knowledgeable can and will chime in. "Upgrading" a cabinet is not as simple as you might think! You can't just drop new drivers into a box and expect it to work. (There are probably hundreds of threads on this subforum on this general point.)

 

[grouse789]

You can't just drop new drivers into a box and expect it to work. (There are probably hundreds of threads on this subforum on this general point.)

That ^^^^^^^^^^^^^^

Find a box that can handle the SVT and install said drivers.

old Ampeg 15e cabs are cheap. 2 of those and you should be good to go. Bot im no scientist on the matter.

 

[grouse789]

Also, the original Altec Lansing 421A cones were rated at 100 watts each. (so 200 watt total?)

 

[daveman50]

Also, the original Altec Lansing 421A cones were rated at 100 watts each. (so 200 watt total?)

Mine were CTS, nowhere near 100 WRMS each. Maybe 100 total. On a good day. I always thought the 215 cabinet was the weak part of that setup but I was young and dumb and didn't think to sell the cabinet and keep the head. So I sold them as a set.

 

[Basslice]

You cannot change drivers and predict what it will sound like. All you can probably predict is that it will sound different. Maybe better, maybe worse. Older cabinet designs may not have closely followed T/S design parameters. But newer drivers are almost definitely different than stock drivers that were used in 1970.

Also, I am pretty sure most SVTs were designed to work best with one or two 8 X 10 cabs, so how it will sound with any 2 x 15 cab is unclear. The B25 and V4B amps were original sold to be paired with 2 x 15. The B25 speaker was a front ported 2 x 15 front mounted. The V4b cab was a 2 x 15 folded horn config.

At this point, mixing and scrambling cabs is fine, but each setup will sound different from the next. If you complicate things further by swapping drivers with different performance characteristics will add more variables. I don't know what you will get. Again, not necessarily bad, but also you cannot predict it will sound better. In the end your ear will tell you. If you wanted to get scientific about it, you would probably need to design a cabinet around your drivers, not the other way around.

 

[coreyfyfe]

I had a B25 cab at one point. Got it with dead speakers, replaced with deltas and used that with my SVT for a while. I don’t recall what prompted the deltas, fliptops recommends the beta 15 as a close replacement for the CTS 15s originally used in these and the B15 cabs. Used it like that until someone was borrowing it and blew the drivers. Replaced them with betas and liked it much more. I eventually sold the cab. The wide/thin design was not well suited to having a big heavy tube amp on top, especially with a caster cart attached to the cab. When I used it with my SVT I usually left the amp on the floor. It lived in my practice space for a while and I gigged with other cabs.

You can try calculating new port size/depth in winISD if you really want to go this route.