Bill Fitzmaurice

24 minutes ago, warwickhunt said:

 

Yes I believe the transformer is purely for the preamp / valves.

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

7 hours ago, Harlequin74 said:

 if i run my Orange Terror 500 at half volume , is it operating at 250 watts? ( running thru 2x obc112 400w cabs)

 

 

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. 

On 03/11/2022 at 15:00, Chienmortbb said:

The sound of Geddy Lee's bass, he might as well be using washing machines.

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.

1 hour ago, bassbloke said:

A 250W amp pushed to its limits will do more damage to the speakers in a 400w cab than a 500w amp.

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.

4 hours ago, Chrisan2 said:

 i smelt a electrical burning smell for a couple of seconds before it stoped , sent it to the fender repair agent. He said there was a blown power tube , and a blown fuse. Maybe there was more to it than that, and i just didn't get all the details .

A blown tube can take out other components and cause a blown fuse. If you were to just remove a tube it wouldn't stop the amp from working, although if one does that because they notice a tube is ready to go they should remove two, from opposite ends of the amp, to maintain balance.

It should have. There are two banks of three tubes, those three tubes being parallel wired. The amp should still work even with only two tubes, on from each bank, in place. Four tube models, like the Twin and Showman, had two banks of two tubes. With one or two tubes removed the difference in how they sounded was imperceptible.

2 hours ago, Owen said:

My hearing is too compromised to get excited about loud any more. But deep is The Bomb. I had an ACME 12" which was appreciably bigger than the "standard" 12" cabs. It went beatifully deep.

The reason I said deep and loud is that one can make a small cab that goes deep without boom. But doing so one sacrifices sensitivity, so while it's an option for home hi-fi and auto sound it's not for electric bass. The sensitivity issue can be offset by having a lot of power, and a driver that has both the electrical and mechanical ability to use it, but that sacrifices midrange response.

2 hours ago, GlamBass74 said:

 I'd expect an enclosure of this size to be quite boomy if driven hard, but it isn't. 

Boom isn't caused by cabs that are big, it's caused by cabs that are too small for the drivers within. One common shortcoming of commercial cabs is that they are too small, a marketplace concession to the desire of players to have a smaller rig to haul. But just as our instrument necks are long and our strings are fat our cabs need to be large if one wants to go deep and loud without boom.

It's logical to assume that the air volume of the room is the main factor, especially as decibels measure the intensity of an acoustic pressure wave. But cabin gain is something else entirely. This will help: 

4 hours ago, uhuglue said:

Hi Folks. I am looking for an amp to pair with my Orange Cab but am unsure whether to go for a 200w (4 ohm) or 500w (4 ohm).

Anywhere between one half and twice the speaker rating is appropriate for the amp size. One half is usually enough to drive the speaker to its full mechanically limited output. More power gives more amp headroom, while too much power will cause distortion that will encourage a sensible person to turn it down. The mechanical limit of your Eminence Kappa 15 loaded Orange in the critical 50-80Hz range is 100 watts, so even a 200w amp has sufficient headroom.

13 hours ago, Dan Dare said:

Low frequency reproduction is, of course, "possible even in small volume" - my headphones tell me that. However, the tiny drivers in my cans only need to energise the minute amount of air between them and my eardrums.

What you've hit upon here is Pressure Vessel Gain, more commonly referred to in audio as Cabin Gain. It has to do not with the volume of air but the dimensions of the room. There is a sensitivity gain at a rate of up to 12dB per octave as frequency goes down below where the longest room dimension is one-half wavelength. In a living room that's 5 meters long cabin gain starts around 34Hz. In a car that's 2 meters long it starts at 85Hz. Cabin gain is what allows the silly high bass levels achieved in auto dB competitions. A club is too large to have any cabin gain, but in an ear canal it covers almost the entire audio range.

With isobarik the result of using two drivers is halved Vas, the volume of air having the same acoustic compliance as the driver suspension. This allows halving the internal volume of the cabinet, not counting the space taken up by the second driver and the air space between the two drivers, without any loss of low frequency response. As always there is a trade off. In this case since the cone area and excursion radiating to the outside air is that of only one driver the maximum output is the same as with one driver in the net doubled cab volume. One could stuff the chamber of an isobarik, with the same result as with a standard alignment, lowered Q.

Isobarik was a reasonable alternative to huge enclosures fifty years ago, when driver Vas was generally much larger than today. For instance, the fifteen inch Altec 421 8LF Vas was  600 liters. The modern equivalent Eminence 3015LF Vas is 159 liters.

15 minutes ago, itu said:

Adding volume by filling the cabinet with denser material, or making it "look" bigger to the element have not been as succesful as using bigger cubic volume.

That's because stuffing doesn't make the cab look bigger. It lowers the cab Q, which can tame a midbass hump. Making the box larger does that, but making the box larger also lowers the speaker cutoff frequency, stuffing does not. Some 25 years ago a well respected audio expert measured some data and made the conclusion that stuffing made a box act as if it was larger. His conclusion was erroneous, because he didn't measure enough data to reveal what actually occurred. He published his conclusion, and based on his reputation alone much of the professional audio engineering community accepted it at face value without testing to make sure it was true. In both audio and nuclear arms treaties you can trust but you also must verify. 😉

19 minutes ago, Dan Dare said:

 That's an iron rule, I'm afraid.

Hoffman's Iron Law, to be precise. It's not all that far off from what itu said. On the subject of small drivers they give better midrange dispersion, and can be used in multiples for adequate volume, if they're arranged vertically. When they're not, which is usually the case, you lose their advantage in the midrange dispersion and introduce comb filtering in the highs.

For guitar, sure. For bass, probably not. Bass speakers require much larger enclosures than guitar to go low. About the smallest you can go with a twelve for good low end is 60 liters. Their 12B is in the vicinity of 20 liters.

7 hours ago, gjones said:

I am playing at a venue, which has a terrible boomy stage, next month.

Weirdly, the boom could only be heard onstage. But was so bad it was drowning the guitar out.

That's room modes too, although in the opposite of the usual fashion. The more common result is cancellation of low frequencies on and near the stage when reflections off nearby walls and ceiling meet the original wave front 180 degrees out of phase. When you move away from the stage into the room the relative boundary positions shift, the cancellations cease and the lows return. This phenomenon is what gave rise to the myth of wave propagation, the notion that a wave won't be heard until one is far enough away for the wave to develop. Believers of this myth have no explanation as to how headphones work. 🙄

Whether the bass is too much on stage and not enough out front or the other way around the best solution is to adjust the bass amp for the stage tone and volume and the PA for out front. The problem lies when you don't have PA. I don't know about the UK but in the States it's always been the band's responsibility to provide the PA in most venues. We used to say that we played the gig for free, what we were paid for was providing the sound system.

40 minutes ago, Jaybeevee said:

just talk bass and other forums. Just punters putting in their two penneth

We've got a saying in the States about sphincters and opinions, I've got to assume you have a similar one on your side of the pond. That's especially true of Talk Bass. I had to leave there ten years ago lest I lose what was left of my sanity completely. 😳