Curious_George

Google search or search here on the forum for an A or AA schematic. Then compare to the ALK schematic and make the necessary changes. The A or AA uses less parts, so a conversion should be easy. The change from ALK to A or AA will make the most sonic difference. The difference between cap types will be less audible. Choose a reputable brand cap and make the conversion. To start, I would recommend Dayton Audio poly caps or a name brand of polyester caps. Don’t get crazy with boutique parts to start. Just use “good” parts.

As an anecdote, I have 4 USA NOS 211 tubes. These are supposed to be the holy grail of big transmitting tubes. They were supposedly new when I bought them a long time ago for a great price. I compared them to Chinese 211 tubes for many hours and I cannot hear hardly any difference between the two. In fact, the Chinese tubes seem to be more reliable and consistent (measurement wise). I know it is unbelievable, but it is true in my case. Just so you know, Chinese tubes are my least favorite except for 211 and 845's. They seem to have those designs down fairly well.

The ALK universal will change the way your LaScala's sound. Imagine a "bell curve" from your statistics class (stock LaScala) compared to a flat line (ALK crossover mod). This is just a visual, but the sound is different between the 2 crossovers. The A and AA crossover will let more of the midrange (high & low crossover points) bleed into the music spectrum. The A, AA and ALK are all 18dB on the tweeter, but slightly different the way they are derived. We all hear differently (physical & psychological factors) and this is the major reason someone may prefer one crossover to another. It should not be too hard to convert your ALK's to an A or AA. Do it and see how it sounds. The Zener diodes don't do anything unless you are driving the speakers hard. They are invisible at mid to lower volumes.

Tube technology was perfected long ago in the US. It is possible to have a tube made today to be better and more reliable than one made in 1940. The most important part of a tube like a 300B is the filament. It is possible to at least replicate the original, but I would like to imagine technology has brought some refinement to a directly heated filament. Even if the new tube is a perfect replication, who could want more, if the originals are so well regarded? The price is the only factor.

I think the only other place where you can make more money for items you don't need (as in the audio industry) is the pharmaceutical industry! Going off topic for a moment, one of my favorite wives' tales is letting a battery sit on a concrete floor... this will drain all the energy out of the battery, so you put it on a 2x4 or other piece of wood. I can't believe how many people fall for that one.

When I first got my LaScala's with AA's, I transitioned from 1979 Heresy's. The Heresy's sounded great, but I always loved the way the LaScala's looked and sounded (from what I could remember listening to them years ago in my youth). The drivers all looked to be originals and in good shape. Close serial numbers on the driver pairs. The crossovers had the caps changed and were mis-matched with different brands / types. One crossover had a "brown drop" (an orange drop look alike that was brown) and the other had a cheap yellow Mylar cap. I changed the caps to all one brand and type for consistency. My first listening impressions were underwhelming... My main source is a CD player. As much as I am an analog guy, I hate pops and clicks from vinyl. Very forward midrange, rolled of high frequencies and low bass output. These were in the corners of a small living area, out from the wall about 1 to 2 feet. The Heresy's actually had better bass, but not by much. I switched the midrange from tap 4 to tap 3 (making the cap change) and that helped a bit, but still underwhelmed. Apparently that is the way they were designed and people either fall in love with them or modify them. I fell in love with them and modified them, and love them even more now. Nothing like a full horn speaker system. They are an acquired taste though, not for everyone.

I bought most of my tubes 25 years ago when prices were still reasonable for most tubes, except specialty ones like RCA red base, 300B, 2A3, etc. USA NOS 300B, 211, 845 and specialty preamp tubes (6SN7, 6SL7, etc. are crazy. The 2A3 seems to have plateaued. I prefer USA NOS to anything else. When I lived in Orlando, I would go to the Hamfest and spend all day meandering through all the tubes. Lots of good stuff. There are tons of USA NOS tubes out there for cheap and if you are creative like Maynard, you can use them with great sonic results.

Very true Maynard. There are a lot of tubes that can be strapped for triode operation and be used for a good SET amp. I missed the whole tube craze and only started building tube stuff in the mid to late 90's. After reading about DHT's, I just had to try one out to see what all the hype was about, so I built a pair of mono 2A3's. I have to admit, their performance astounded me, especially with the right speakers. Since prices have gone up considerably, I don't think I will be buying more DHT's anytime soon. I'll just strap my 1625's and use them as triodes.

I've never heard them either, but I have heard NOS 2A3's vs newer recent production 2A3's and to my ears, there is a "dimes worth of difference" as the late Bob Crites would say. There is so much hyperbole in audio, it is truly unbelievable. I have a pretty good ear, but a lot of the things people say they can hear, I'm suspicious of. I have a friend who has "one of those ears" and we constantly banter back and forth between what we can hear and usually in the end, he relents and says he can't hear much difference between A & B, but initially he could hear a "world of difference".

They say a picture is worth a thousand words... perhaps now we can "see" what the desired effect is. Below is a generic image I found on the Internet. (oh no, not the Internet. I saw it there so it must be true...)

If you have ever read about a 300B or 300B amp design, you've read that the 300B is "so hard to drive" compared to a 2A3. As PWK would say... Bullshit! Parameters 300B 2A3 Filament Voltage 5V 2.5V Filament Current 1.2A 2.5A Plate Voltage 400 250 Electrode Capacitance Grid to Plate (Cgp) pF 15 16.5 Grid to Cathode (Cgk/Cgf) pF 8.5 7.5 Plate to Cathode (Cpk/Cpf) pF 4.1 5.5 Total Cin (pF) 82 93.3 Mu 3.9 4.2 Plate Resistance 750-800 800 Above are the specs for the 300 B & 2A3. They are very similar. So similar that the driver circuit for a 2A3 could easily be used for a 300B and the driver would not know the difference. I don't see anything special about the 300B parameters that would make it hard to drive. Now a 211 or 845, those I would agree need a good driver circuit. It's all above in black & white. I guess people read it or hear it and they think it is true. Unfortunately, there is so much of that non-sense in the audio world. If you Google search 300B schematic, almost every circuit that comes back is a 3 stage design. Most 2A3 circuits are 2 stage, with some exceptions that are 3 stage. If you are going to drive your 300B or 2A3 amp directly from a source (something I never do), then you may need the extra gain of the 3rd stage depending on your speakers. When I design amps, I always try and have the amp input driven to 1 to 2VRMS for maximum output. Not that there is an amp input voltage standard, but most amps have an input sensitivity in this range for full power output unless there are specialized amps for particular purposes. In my experience the 300B and 2A3 are somewhat forgiving of input tube used and sound good with even a basic input tube circuit such as a 6SL7. In addition, the minimum transformer impedance I would use for either tube is 5k. Anything more than 6 or 7k requires more drive from the input tube. Even though the recommended transformer impedance for the 2A3 is 2.5k, that is for maximum power output. You can still get max output using 5k, you just have to drive it a bit harder.

I have noticed that earth ground and signal ground are connected at one point in the above schematic... An alternate grounding scheme may eliminate or prevent hum in the amp depending on interconnected equipment. See below; This circuit will break the possible current paths between earth ground and signal ground. The cap and resistor values are not critical, but should remain within a range of values. I use a 4.7nF X cap because I happen to have a huge stash of them (they were free). Alternate value X caps can be used up to 0.1uF with good results too. The resistor can range from 75 ohm to 150 ohm and still perform its function. I use this circuit in all my amp builds (SS & tube) and have yet to have a hum problem regardless of what equipment is connected.

It will be interesting to see how many they sell at that price. I’m sure they are priced according to what the market will bear.

The woofer has a lot of mid-bass and lower mid-range energy. This is the energy I speak of to be damped by the insulation.

The standing waves I am referring to are more mid-bass & mid-range frequencies. I can't speak to a conversation taken out of context, but from experience, a lot of different insulating materials will work for the above application. Are they all equal? No, but they seem to work in varying degrees. I don't think anyone here was looking for the "perfect" material to accomplish the given task.

In addition to all the above suggestion, a roll of R-13 will also work, it is cheap and can be found easily. An egg crate mattress pad from Joann's or similar will work well too. In this particular case, the insulation is strictly to absorb standing waves, not to add volume to the enclosure. Will an enclosure with and without insulation measure different for tuning frequency? Yes, slightly, but the change is miniscule if the insulation is installed with the premise of only reducing standing waves.

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For simplicity, yes, you can go by uF/voltage. Cap types have different characteristics (electrolytic vs film, etc.), but you've got to learn and get started somewhere, so use what you can and keep tweaking it until you are satisfied and have learned more.

The spec sheet says for "full power handling", 1200Hz, 12dB/octave is recommended, so basically, you could cross this driver over just about anywhere you needed to match the mid-range driver. There is a lot of versatility with this driver. The D260my-B comes with a 2/3 bolt to 1" adapter. It is also a ring radiator, which some people may not be a fan of, but I think it sounds outstanding. I have not heard the B&C DE120, but the 260My-B is the most natural compression driver "tweeter" I have heard. It sounds like a nice dome tweeter, but compression based. Your horn selection will also affect the sound, but the APT200 has a good reputation for tweeter applications. Price does not usually sway me, but I believe the old saying "you get what you pay for", however, there are exceptions and you can find less expensive alternatives in most cases. Plus, half the fun is seeing what is out there and trying it, especially when it comes to audio. I also recently bought some Selenium ST200 tweeters and for $19.99 they are unbelievable. Almost (i am guessing because I've never heard them) like a T-350, but better. The ST200 has the same tonal character as the K77, because it is phenolic too, but more power and wider frequency response so you can cross it over lower (if needed). It blows away the K77 for power handling, if you need that too. No shaping per say on the 260My-B, just connected to the same tap as the K77 on the crossover (universal Heritage type that you can find here on the forum).

I recently bought a pair of these compression drivers and have been experimenting with them on an Eminence APT200 horn. I moved recently and don't have all my equipment set-up, but just from listening they seem to be a good candidate for Klipsch Heritage speakers. I have them sitting on top of my LaScala's with the K77 disconnected. They look to have inherited some JBL technology in the phase plug area. Has anybody else heard or played around with these? PRV-Audio-D260My-B-Datasheet.pdf

Here is a cleaned up schematic with the correct values for LaScala's with Type AA or Heresy's with Type E crossover. After listening for sometime, I discovered a low mid-range bloom in the LaScala's and added the 80uF cap across the woofer making the woofer section 12dB/octave. I can't find the REW graph I generated when I added the 80uF cap, but it definitely took care of the anomaly. Edit: I should remind members looking at this thread that my LaScala's are ported, so you may or may not need the 80uF cap. Experiment and decide. You can attenuate the midrange and tweeter to your liking.

I've driven my LaScala's with various solid state amps and tube amps (PP & SE) and the LaScala's always sound great. Does the amp make the LaScala's sound different? Yes. I guess it depends on the mood you are in and if you want to listen critically or just have background music. I have a Music Angel XD850 Mklll that has been redesigned (by me) and it has turned out to be one of my favorite amps - 6.5 watts/ch. It drives the LaScala's with ease and sounds great. No problem at all driving the speakers. However, I must emphasize that I am not using the original AA crossover, but a variation of ALK's universal heritage crossover. This will help keep the impedance constant and easier for the SE amp to drive. I did not do a comparison with my modified crossover and the OE AA crossover so I do not have any comparison for that, but the new crossover does make an audible difference with tube or SS amps.

Broadcast FM is far from dead, much less AM. As Fast996 pointed out, new music is a driver for their audience, but it depends on the format of the station. Of course advertisement is what makes this possible for the listener. When HD Radio was first introduced, HD maintained that is was about pushing more content, but in reality, and later admitted by HD, it was always about more channels for advertisers. Am is popular with the older segment for talk radio and sports.