MechEngVic

You might have a failed crossover component or the voicecoil of a driver going bad. If you can take the speakers apart, you can switch drivers between the two speakers. If the problem moves with the drivers (woofers, tweeters, etc), then your problem is with them. If the problem stays with the speaker cabinet, then it is most likely a crossover. What kind of speakers and amp do you have?

If the input signal isn't mismatched for the amp and the speakers aren't distorting, an amp should run indefinitely without going into overload protection. I'm guessing he's over-driving the speakers.

If you're getting a good deal on the III's, you can buy them, listen to them, sell them later for not much loss, and upgrade to the IV's. If you're looking to buy a permanent set of speakers, the IV's will be the last set of speakers you will ever need.

Would love to see some close-ups of your components!

Can you tell us which tester you bought?

This is fantastic info, I'll go over it with a fine tooth comb asap.

The response Carlosrs got for the Forte was similar to the one Klipsch published in their spec pdf.

Nevermind I just saw where you told us. I was right though. The Forte has its midrange "hump" at 1000hz which is a little early for Heritage and some other Klipsch, but the RF's midrange hump is right where is should be, @ about 2300-2500hz. The RF's are nice and flat but look at that low frequency response! That's subwoofer territory! That 500hz hump of the RF is interesting, it accents that frequency, whereas the Forte dips there, no doubt due to the handoff between woofer and midrange. I bet the RF's 500hz hump adds a nice lower midrange fullness. The dip between 1-2k is where the RF's woofers are handing off to the tweeter, and it does it very well, subdued at 1200hz where things can get "honky". The high frequency crossover is seamless in the Forte, and a couple db's higher than the RF no doubt due to the 3-way tweeter support absent in a 2-way. All very minor differences, room acoustics could make these graphs look much different, (The Forte graph looks similar to the graph Klipsch put out, so you're pretty close though), and these graphs tell us very little of the speakers sound signature, but the RF is a big surprise to me.

I'm gonna guess the blue line is the Forte. Green is RF-83

Wow! Those Forte's look tiny compared to the RF-83's. I didn't realize they were such an imposing speaker. Which is which in your graph?

Dood! That's a great space for Cornwalls! And with that brick wall between you and your neighbors you could experience some pretty decent Dee-Bee's without pissing them off. It's not just about volume, a bigger speaker can deliver a much bigger soundstage, more 3-dimensionality. Especially if you're buying new, make your speakers the best part of your system. Cornwall IV's will be the last speakers you will ever need.

I bet all those nice Italian drivers were the first to run out.

Alex Kitic, Thank you for taking the time to comment. I'd like to respond to the various items you mention. First, I bought this amp new in 1993. It has been the source of sonic joy for many years, and it has also given me its share of challenges. When I first bought it, it started blowing tubes after a few hundred hours of use, taking the bias resistors with it. So for several years I lived with this amp blowing tubes and resistors. Eventually it blew other resistors on the board and I pulled it from service. Just over a year ago I rebuilt it, replacing it with all new resistors and capacitors. 400v coupling capacitors. After about 100 hours of running I started getting loud popping and arcing, red-plating and blown resistors. This is when I began my first foray of serious research into this amp. There is next to no info out there because so few of them were sold. But I can tell you one thing without the shadow of a doubt: This amp absolutely needs 600v coupling caps. The original caps were Sprague 400v, and although tough, even they only lasted a few hundred hours. This is the number 1 design error of this amp. I replaced the new but failing 400v caps with 600v caps and in several hundred hours I am no longer blowing tubes and bias resistors, except for the trouble with V5, which I don't see as the same problem. I will be replacing the coupling caps with lower value caps (still 600v), for the reasons you mention and to further reduce leakage. What you're saying here is where most of the good advice I've received has been leading me. Your explanation is very good and I'm gonna give your idea of c19 a serious look. In fact I am gonna go over the bias circuit very carefully, including careful measurement of bias voltages. Agreed. I had the original tube sockets in when the first V5 event took place (always checked for connections and corrosion when installing a new tube). I replaced all six tube sockets after the first event and keep checking tightness of connections. It has happened to V5 two times since replacing sockets with 2 different brands of new prod tubes. I had spare matched tubes but am down to the last one so I'd like to get this figured out before I put the last one in. As this had been happening, I have been moving tubes around and checking connections at all positions so I really think it's in the circuit somewhere. Again, thank you for the advice. I am including a PDF of the whole schematic and would appreciate you commenting on anything else you see. ST-70wScreenResistors.pdf

A very general description from my experience: Paper In Oil: Very warm, good detail. Possibly the best sounding. (Russian PIO's good value good sound, Mundorf & Jupiter considered the best) Film and Foil: Best bang for the buck. Also warm, maybe a bit brighter than PIO. These measure very well, some of the lowest ESR ratings. Can almost match detail quality of PIO's. (Solen SA, SB, SE, SM, SN, SY Series, and Mundorf ZN represent great sound and great value. I've never really heard a bad sounding F&F) Metalized Film: Cheapest to buy but may be only minimal improvement over cheap polys or electrolytics: If you get good ones sound improvements can be described as SMOOTH. (Mundorf good but expensive, Clarity Cap sound great and better value)

Ok, I guess I had is right originally. I've been going back and forth between two threads and three members and I'm getting all mixed up. There was the KLF-30 thread with Alexander and jjptkd and an a55, and this one with dtr20, and I'm not even sure who I was answering about which experiment! You know, you were there. I owned a pair of chorus II's from 1992 to 2005 before I sold them due to moving into a smaller place. I experimented with them extensively, including mounting the mids and tweets on a stand and using a pair of 10" sub woofers for the bass! I re-did the crossovers externally in a wooden box with a Lexan top and I by-wired them. I also coated the midhorn with a thick layer of spray on rubber, and replaced the connector tabs on the woofers with gold plated 5 way binding posts. Nothing I did ever made them sound any better because they already sounded amazing. I learned a lot, but I never even once felt the need to change the drivers.

By endorse, do you mean that he no longer considers its use in new or updated designs?

Sorry, wrong driver. I was trying to comment on the subject of this thread, in which the OP swapped the chorus II driver with an a55g. The Chorus II mid driver is actually a k-61-k. The focus of my comments was supposed to be on the merits of doing these experiments as opposed the merits of specific drivers, but I did a bad job of it.

I'm pretty sure the a55g, properly implemented, will out-play the k52. But can any of us implement the a55g into an existing design which used the k52, better than Klipsch has done with the k52? Maybe. Can we do it by playing swaptronics? Doubtful. But here's the thing: This is where it starts. At some point even PWK had to get all the mistakes out of the way. At some point our learning will involve making changes for the worse. In my 35 years of building speakers I've made more mistakes than successes, but I've learned a lot and have enjoyed my life more because of it. One thing I know, I'd love to be allowed into the rooms where Roy keeps all his projects, failures, and works in progress.

Agreed. If we just throw money at a speaker expecting a better product we will probably be disappointed. If it is done thoughtfully with proper adjustments to impedance and frequency response, and most importantly, with the express purpose of keeping the spirit of the design, we can exceed the limitations placed on the speaker maker by their budget.

I think the one thing that we can all agree on is how we're all salivating at the thought of buying some of those Forte III horn lenses... and how mad we are at dtr20 for not buying several pairs and selling us some.😉

Yeah, but for ones of us who have heard the amazing potential of the KLF line, we can be happy that we get basically heritage quality sound at a fraction of the price. I got KLF-10's in perfect condition, late construction so no unglued panels, for 400 bucks. I thought they were gonna be a transition speaker, but the cabinets are so big and solid and the woofers so powerful that an upgrade of the crossovers and horn drivers, and a super tweeter on top, have given me a real deep musical satisfaction.

Well believe it or not, but I've learned most of this stuff from scouring the various audio forums, especially this one. You learn a lot of theory in school but nothing beats practical application!

Please note in the thread where we talk about using 600v coupling caps instead of the 400v written in the schematic. If you keep blowing tubes your coupling caps may need upgrading to 600v.

http://dynacotubeaudio.forumotion.com/t4323-same-tube-keeps-going-bad

Like dirtmudd mentioned, the bias is balanced by adjusting a trim pot so that two led's are of equal brightness, one set of 2 led's per channel. It's pretty reliable. I haven't measured with a meter recently but I did when I first rebuilt the amp and all voltages were good.