captainbeefheart

Looks like you have found the issue, the 6SN7 tubes certainly appear to be the problem. If you would like some extra 6SN7 tubes to roll in the amp I have TONS of them and can match up a couple pairs. They are mostly GE and Raytheon black plates. I have some of the Sylvania Chrome domes and I don't see why they are so popular, they tested the worst in regard to distortion measurements. The Raytheon black plates tested the lowest distortion out of all the 6SN7 tubes I have tested. I will have to look to see if I have any TungSol to test for comparisons purposes.

Give yourself a pat on the back! Maybe the initial reading of .4 ohms was correct and through moving the board around to inspect fixed whatever was causing a short. After that you have been getting normal resistance readings and they play fine now confirming the short is gone, hopefully for good. Everyone likes a happy ending

Matched pair of early ribbed Telefunken 12AX7/ECC83 Gains- 53/53 53/52 where a 'perfect' 12AX7 in circuit gain calculates and simulates out as 53. Also tested on Hickok 539 for gas and leaks and gm. Asking $100 shipped

All test NOS on calibrated Hickok 539 and TV7 testers Asking $110 shipped for all 3

I thought he already said the amplifier can play past '80' with the R26F speakers with no issues.

What do you have for resistance measured directly at the woofer bypassing the crossover network? Are the woofers stock? I am trying to figure out a way for you to test everything with limited test equipment. It would be nice if you could do a frequency vs impedance sweep of the speakers. You can download some free software like Arta and a signal generator app for your phone and do a sweep.

Bingo! They knew exactly what they were doing. They made sure it can provide a transient peak power for short periods which is fine they just should have rated the amplifier like this; "15 watts 20-20kHz with no more than 1% THD, Provides up to 70 watts peak power for dynamic music transients" Power sells, it's just a fact. They certainly knew that if they rated the amplifier as a 75 watt amplifier they can increase sales substantially.

Dear Bob Carver, We know the amplifier sounds good, 2 watt amplifiers also sound good but that was never any part of the criticism towards the Crimson 275. What the concern is that you and everyone else that has responded that is monetarily invested with the sales in this amplifier is dodging any sort of explanation to why the amplifier does not meet advertised specifications. That's great you made a nice sounding amplifier, but why not be transparent and provide the actual real world performance instead of a very bloated version of them? Your specifications, along with the retail price are pretty clear, 20-20kHz 75 watts no more than 1% THD. Power is not actually any measure of quality, as mentioned a 2 watt amplifier can have amazing sound quality and fantastic measurements. Power is merely relative to what the consumer requires for his/her listening pleasure. So I ask, why inflate the power specification? Surely you have been in the business long enough to know how amplifier power is interpreted by how you presented it. How it is currently stated your amplifier should produce 75 watts into 8 ohms between frequencies 20Hz and 20kHz with less than 1% THD. Pretty clear if you ask me, and everyone that purchased it from you seemed to be under that impression as well. It is of no issue that your amplifier produces rated distortion and bandwidth at only 17 watts, power is not a means of measuring an amplifiers sound quality it's a relative quantity to who purchases it for their specific power needs. So again we are back to the sound quality of your amps are not under criticism, the false advertisement is. I think I can sum up your response to this issue with much fewer words. It goes something like this; My amp performs as designed (but not how it is presented in the sales literature specifications). We screwed up with the safety aspect so we will fix it for free. Also since we lied about the specs we will give you full refund. See that is much easier for people to understand without all the excuses and deflection. We know the amp sounds good, I am very happy to see you will resolve the safety issue at no cost to the customer or if they are unhappy with finding out the specifications are inaccurate and the amplifier cannot make the customers power requirements you will give a full refund. Cut through the public relations BS and be honest, glad you are making it right with people who purchased this amplifier. -anon

Looks like there may be some small strands stuck on things, maybe there is one making an intermittent short. Also make sure when putting the board back on there are none of the bare wires touching anything.

You can do it with signal generator and scope but it's a little more time consuming.

I downloaded the service manual and it states FTC Both channels driven same time into 8 ohms minimum 100 watts @ .08% THD 20-20kHz Surround sound mode 170 watts into 6 ohms @ .9% THD 1kHz IEC 160 watts x7 into 6 ohm load @ 1% THD 1kHz Effective maximum power 175 watts x7 into 6 ohms @ 10% THD 1kHz

The insulation on the bare magnet wire is very thin and can get scratched off possibly touching something else causing a short.

Or moving the crossovers around has temporarily fixed the issue and you are now reading both correct resistances. I still recommend with the better probes to connect the meter and do the wiggle test, you won't damage anything. Does your meter auto-range or do you have to manually choose your ranges? Have you looked at the wiring on the drivers themselves?

I kinda get a kick out of the subjective gear reviewers, they just haven't learned that price has nothing to do with performance. They are always going on and on about how much this costs and that costs and being confused when something less expensive bests something more expensive. They make the wrong conclusions about price to performance and haven't figured out yet that the audiophile business is one of marketing hype and BS most of the time with huge marked up price tags just to fill the need for people with deep pockets to get something 'poors' cannot afford. I love music and I love electronics but the business aspect of the industry has always been bad and has continued to get worse. Same with record companies taking advantage of musicians and making it into the mess we see today. Making money from untalented one hit wonders, chew them up and spit them out and on to the next 'big thing'. There is hardly anything good about modern pop music, sorry to say.

It would have to pass CE safety standards to be sold in Europe, which is why it isn't sold there because it is unsafe.

.4 ohms, yup that is definitely the problem right there. Not gonna lie whoever worked on these did an absolutely horrendous job, just awful. You aren't looking for bad solder joints or connections, .4 ohms means there is a short so you want to look for two things touching that shouldn't be. I would start around C3 as that just looks like a short waiting to happen. Leave your meter connected while wiggling each components and their leads and watch the meter to go back to normal resistance. That will at least pin point where the issue is.

Yup exactly. If the rails is say 35v and its rated to deliver current into a specific load, if you change the impedance setting lower it will not allow the outputs to swing up to their rail potential, it will limit them to where the maximum output current is. My example above for 160 watts into 6 ohms is 31v, this is about 5 amps of current and most likely the most the output is allowed to deliver into any load. So for a 4 ohm load if say lowered by the setting it will limit the output voltage to 20v instead of the 31v it's capable of in order to keep the current at 5 amps. Now 5 amps at 20v is 100 watts, you have now reduced your output power by 60 watts. They won't increase current through the output devices because it increases the temperature over rated amount. Note: They don't change the rail voltage, instead they usually use a limiter/compressor circuit to reduce output signal to keep output current within rating. The amp in question doesn't do this, it is just rated for a 4 ohm load at 160 watts. I have not looked at the schematic but it most likely will have a thermistor on the heatsink and if too much current passes through the output devices for too long increasing the temperature it will open the relays at the output and go into protection mode. It also may have direct current sensing from the output which will open the relay also if it exceeds a specific current amount.

If you have a multimeter you can put it in continuity mode or lowest scale of resistance and connect the test leads to the input jacks of the speaker. Then wiggle things around and see if it changes to a short circuit or very low resistance. You can also gently move the drivers in and out while doing the same test to see if it's shorting out in the voice coil area during excursions. Put your thumb on the face of the cone and a couple fingers through the basket to the back side of the cone, once you have the cone gently 'pinched' between thumb and fingers gently move it in and out, the voice coil should move freely through the magnet.

That's a good sign the caps are measuring correct values. They should be checked for ESR at frequencies of interest, 500Hz and up for 13uF and 4.5kHz and up for the 2uF. My La Scala's from 1982 have the original oil filled capacitors in them and last I tested them they were within acceptable parameters so I left them in there as the speakers confirm they sound great. If you can keep it original, I.e. you like the sound of them then I recommend leaving them stock for a while and listen to them. When I end up having to replace the capacitors I plan to use Paper capacitors, either paper and foil or metallized paper both oil impregnated. They will retain the Klipsch sound and I actually prefer them as I feel they are a tad smoother overall.

I cannot find a frequency vs impedance plot for the R26F. Looking at R28F it drops to about 3.8 ohms at ~150Hz Forte II looks about the same, just below 4 ohms at same frequency. This kinda leads me to think there is something wrong with your Forte II speakers. Either something is shorting during higher excursions, have a look at the woofer wiring and tinsel wire for frays that may cause a short. Make sure crossovers are okay as well.

Audio related gear is no different than any other appliance you have in your home. I should reword my statement into "the majority of electrical appliances and products you own will have a UL certifications or a CE certification. It's just good business practice. Again by law this isn't necessary in the USA but it is necessary that you still meet the safety standards, if you don't someone can get hurt and if they decide to bring you to court of an unsafe device you will most likely lose. It wouldn't be very difficult to prove the Crimson 275 doesn't follow basic safety standards because it's enclosure isn't grounded to earth safety ground.

It proves sound quality doesn't necessarily equate to vanishingly low distortion and DC to daylight bandwidth. It also proves many people do not require the power they think they do. I don't think the actual sound is in question ever, it's more of a problem of price to quality ratio, lack of safety standards, and the grossly bloated specifications which they darn well know will greatly improve sales figures. The issue with ASR rating system is they are basing it off signal to noise AND DISTORTION, so they are putting too much weight into distortion figures than I think is appropriate for sound quality. So as long as someone understands the data they can just dismiss the SINAD rating and read the remaining review.

Don't you think I know the difference between CE and UL? In Europe they need to get the CE certification for sales. My point is that don't you think if a device exceeds the CE standard for being safe that it is a safe product? So although a product is sold in the USA doesn't have a UL certification they can easily prove in court that their device meets some sort of safety standard and most likely will also meet the local USA standard. More products are going to have the CE standard because it is the law for European sales. Building codes have nothing to do with any appliance you purchase. The reasons you see the UL on appliances is because they are much more widely sold and so the company is covering itself legally getting a certification helping against liability. Everyone has a microwave, washing machine, Television sets etc..., not everyone is going to have a Conrad Johnson amplifier, the sales pale in comparison compared to appliances. The smaller amplifier company makes the decision to not get certified which is fine knowing they will probably never be sued especially if their gear is safe which most is. I have no idea what the issue is here. Do you feel the Crimson 275 meets safety standards?

In this case we are discussing a design defect as it isn't designed to current safety standards UL 60065, there are other specific standards like CE about consumer safety with electronics. I am not trying to argue either and maybe I wasn't clear enough at first but I am in no way saying anyone has to get any sort of third party certificate but many do. The marking doesn't have to be directly on the gear, it can be on the owners manual, box it came in, or in any literature about it. I can clearly see the 'CE' on the McIntosh 275 which means it meets that European product safety standard. Europe is stricter in that they by law require the certification which is why McIntosh probably put it on there. In the USA it isn't a law to have it certified but it's smart to to avoid liability. If you don't want to get it certified that's ok but it should still meet current safety standards or else you are asking for trouble.

Going by the SINAD rating most tube amplifiers will not rate high. If someone sells one with low enough distortion to signal ratio it will rate highly. The thing is most of us that listen and design tube amplifiers (some solid state also like Nelson Pass) knows that THD isn't the end all in good sounding amplifiers, well to a degree. So most will have higher distortion vs your average solid state. The thing with transistors is their output characteristics aren't very linear but also they have very high hfe or current gain. So it's extremely easy to get extremely high open loop gain which allows for more feedback, add in the fact they do not have an output transformer which makes adding high amounts of feedback even easier so naturally they will test lower for distortion.