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  1. " It would be easy enough to add some voltage fb at the output tube to deal with that issue." 100% agree Maynard I would add strapping the output pentode as triode to control the output impedance. Dan
  2. I suspect the output transformer is more probably the cause instead of the tube itself. Not enough primary inductance will cut into the bass.
  3. There is a Part 2 ! http://www.x3mhc.no/dokumenter/SE-v-PP-Part2.pdf Quite interesting stuff about low listening level PP with respect to hysteresis curve induced distortion. Anyone with high efficiency speakers will fall in this category most of the time. The first watt matters most, and this is where Push-Pull design relatively lacks the more.
  4. I'm operating my 807 at 75% of maximum plate dissipation and already have 7000 hours on them. The amps are turned ON when i get-up and turned OFF when i go to bed. They are driven from TV, radio, bluetooth all day long. They are still at about 80% of new spec after two years of this regime Dan
  5. Jeffrey, I kind of agree with you on the negative feedback. The better the open loop, the less correction required. So, the solution regarding the high output impedance effect Vs Speaker load is to have a flat impedance curve speaker. Problem solved without feedback :-) dan
  6. A single ended pentode final stage without feedback is going to get you a high output impedance. This is of no concern if your speaker impedance curve is flat, which is not the case for older Klipsch speakers. Since you are interested in the first watt, operation in pseudo-triode mode will result in a much lower output impedance, as I now use in my amp. This is just my humble opinion, to each his way in this fun hobby. Dan
  7. Jeffrey, Thanks for sharing your built here. I also designed and built my own amplifiers. i choose to use 2 parallel 807 that I first operated as single ended pentode, and later converted to pseudo-triode mode. What I like is your decision to operate your KT88 at 62% of max plate dissipation. I choose 75% in my case, and i am close to 7000 Hours on my Russian 807, and still going strong. Using 100% of max plate dissipation, to extract the last watt, is heavily paid in short tube life. What is your computed output impedance? dan
  8. But Mark, you are right in the sense that in the absence of the swamping resistor, the amp will effectively see an easier load (40 ohms in many of the old klipsch xovers). it ensue that in the presence of the said resistor, the amp will work harder compared to when there is no resistor. And as you are pointing, some energy will be absorbed by the swamping resistor. The thing is that the swamping resistor (Which we should name an impedance matching resistor) is there to accommodate higher output impedance amplifiers who will have their amplitude perturbed by a high midrange impedance. Simple ohms law in fact that can easily be demonstrated. Dan
  9. Marvel is right, the swamping resistor is only there to make the midrange an 8 Ohms speaker, as the tweeter and the woofer already are. Dont worry, if your amp is able to generate 3 watts at 200 Hertz into 8 Ohms, it will also do it in the midrange with the same 8 Ohms without sweating. Regards, Dan
  10. Deang, ever heard about a Zobel?? Hint...it is used to nullify the VC inductance when required. If I remember, ALK used one of them in his Forte crossover , and other design. On the other hand, in another one, he states that he utilizes this inductance as part of his filter. It's there and cannot be ignored. https://www.trueaudio.com/st_zobel.htm
  11. John, thanks for the factual post. My goal is to understand. Basically you state that in order to get rid of the big 2000 Hz bump, the crossover must be lower in order to get enough attenuation at 2000. You propose around 500 Hz, which make sense. But in this case, the crossover will be stated to be @500Hz. Speaker's acoustic output is proportional to electrical signal that drives it. So when I measure voltage at the electrical crossover, that must be reflected in the acoustical response. The fact is that I measure a lower electrical crossover with the 2.5mH on my crossover. It is quite an easy measurement to do using an AC voltmeter and tone generator. So do you propose that electrical and acoustic crossover frequency are not the same?
  12. Wrong crossover. You can run any amp on a constant impedance one :-)
  13. Mark, I consider the ALK crossover in high regard. Mine is inspired by his work. But as you noted, I slightly modified, simulated, constructed and measured the result. My hearing is not so good, so i will trust a good design methodology and measurement over my hears anyday :-) I cannot stress enough that you need a constant impedance network with Single Ended Triode (SET) amplifiers or even more so with pentode (without feedback). The key is the damping factor, or say another way the amplifier output impedance. The worst offenders are the original Klipsch networks. The midrange is boosted by several DB without controlled impedance, but is flat with a constant impedance network. been there, done that! Dan
  14. Thanks Mike, i don't remember exactly which one is which, but as you noted it shows the phase shift. i strongly encourage you to try and confirm the measurement. You don't really need a scope, just an AC voltmeter. Use "onlinetonegenerator dot com" to drive your amp. I'm jealous of your K-horns , but in my case haven't corners to put them in. Dan
  15. the other using 2.5mH crossing @300Hz:
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