Bill Fitzmaurice

Don't do anything until you get the cab and at the very least post the pictures. The Delta 12LFA is a subwoofer driver, best for electric bass when mated to midrange drivers. The BN12-300 is unsuitable for electric bass, at only 2.5mm the xmax is far too short. As for OEM versus Eminence branded, when Eminence creates a new driver they test a number of variations. The ones that test the best are the ones that end up being sold under the Eminence brand name. I've seem some OEM Eminence that were pretty good, but I've seen some that were pretty bad. That includes one relatively well known manufacturer's version of the Delta Lite II 2512. 🙄

Post a picture of a driver. Also post the exact dimensions of the cab. The only way to know what will work well in any cab is via loudspeaker modeling software, which allows for reverse engineering.

A harsh tweeter is an indication of high THD, which can be sourced by the amp and/or the tweeter. When it's the tweeter the usual reason is a poor crossover, which allows far too much low frequency content to reach it. The only thing most manufacturers go cheaper with than the tweeter is the crossover.

That's one of the most basic calculations. Where the barrier is at least one wavelength high sound is reflected back. Where it's less than one wavelength high sound goes over it. One wavelength at 100Hz is about 3.5 meters, so reducing transmission above 100Hz isn't difficult. One wavelength at 50Hz is about 7 meters, so reducing bass is impractical.

Start here: https://blog.soton.ac.uk/soundwaves/ We have difficulty understanding sound because of our assumption that sound waves behave in the same fashion as light waves. They don't. Not only do speakers as sound sources not behave like lamps behave as light sources, they behave differently at every frequency. That means the first step in knowing how speakers work is to learn how sound waves work. That would be easy if anything about sound waves was intuitive, but almost nothing is. Much of what intuition tells us is incorrect.

It could be done, but not by auditioning cabs. If you have the full specs on cabs it is possible to predict how they'll work together. The problem there is that full specs, including FRD, Z and phase response charts, aren't available for any cabs.

I understand the science, and that's why my advice is never mix cabs. Doing so is just like what Mama Gump said about a life and a box of chocolates: "You never know what you're going to get".

Yes, if that's what the amp and cab are configured to use. It would be in your manual.

Even perfectly shielded single coils will buzz, while reduction of buzz when touching the strings or bridge is normal. Blame it on whoever invented the magnetic pickup, making it high impedance to avoid the need for an additional gain stage in the amp.

You probably wouldn't be able to tell them apart. Back in the day we all found it odd that you couldn't hear any major difference between a Bandmaster, Bassman, Twin Reverb or Dual Showman when played through the same speakers. That was long before we knew about decibels and logarithmic hearing response.

It's not complicated, if you know how to use speaker modeling software, like WinISD, the process takes less than ten minutes, if you have the specs. IMO every speaker should make them available. Every driver manufacturer does, but that opinion isn't shared by the cab manufacturers. 🙄

It would be a simple matter to calculate the OBC 112 frequency response, sensitivity and maximum output using the driver Thiele/Small specs, but since there's no way of knowing what they are you're back to comparing it to other cabs the old fashioned way, trying them side by side.

The amp rating is moot, the transformer only powers the pre-amp tubes. I agree that the only reason it would blow is if there's something downstream is drawing a lot more current than it should be.

Based on the size I agree. You may find numbers on it if you pull it.

No. First off the position of the volume control doesn't indicate the power output. Depending on the level of the input signal halfway on the volume control could be full power, could be 1/10 power, could be clipping. Then there's the matter of the impedance load, which isn't constant. A nominal 4 ohm load will have an actual impedance anywhere between 3 and 30 ohms, depending on frequency. Power varies with impedance, so with 20 volts output the power can range between 13 watts at 30 ohms to 133 watts at 3 ohms with the same volume control setting depending on the note being played. Lastly, perceived sound levels are logarithmic with respect to power, not linear. To sound twice as loud doesn't take twice the power, it takes ten times the power. As for measuring power output, to do so requires simultaneous measuring of voltage and current, which requires two separate meters and a method to extrapolate the result, which will still vary with frequency. Engineers don't even try. We measure voltage, which is constant into any impedance load. We know the voltage output that an amp can cleanly deliver, and the voltage limit that a speaker can cleanly handle.

It works for their material. He's no slouch. I saw a video of him playing 'Roundabout' with 'Yes'. Not everyone can play like Chris did. Geddy nailed it, including the tone.

The first thing you need to do is to get schematic. That in hand it should be easy to determine what's required for a transformer. Without it you're up a certain creek sans paddles.

I assume you say that because at its limits the amp is clipping. That can cause a problem for tweeters, because clipping creates abnormal high frequency content that can over-power a tweeter. But it has no effect on woofers.

The 2225 was more of a PA woofer, with weak highs. The king of bass drivers back in the day was the Altec 418. Even today it would be competitive.

I liked my '65 Bassman amp well enough, but the speaker was gosh awful. I'll forever be thankful to Leo Fender for that, as it's what prompted me to study loudspeaker design, which eventually became my profession. 😉 If I was going to do a total rebuild of a Bassman I'd ditch the Fender tone stack, which was fine for guitar but not for bass, in favor of the Ampeg B-15 design.

I can't tell if those are threads or just ribs but either way it appears that the horn is stripped to the point that it won't hold. I'd use epoxy to secure it. There should never be a need to separate them, as a replacement driver and horn would come as a unit. Do not use superglue, it can destroy some plastics.

Get a book on how to repair valve amps. You may even find it free as a download with a search. They're very easy to work on, and the older the model the easier they are.

They do have a shortcoming, he has to add more coins between songs.

Tweeters don't hiss, amps do. That said, the response of the BGH25-8 rolls off above 8kHz, where there's no useful electric bass content, but plenty of hiss.