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Mark51

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  • Gender
    Male
  • Location
    Florida
  • Interests
    HIFI, guitar, banjo, ham radio, photography.
  • My System
    Forte 1, DIY tube and solid state amps.

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  1. I'm about to upgrade the output transformers on a couple of single ended amps I have built. One is a 6V6 and the other is an el84 both triode strapped. Both are using budget Edcor transformers with an 8 ohm secondary only. The input terminals on the Forte's say 4 ohm but the original Klipsch spec sheet says the nominal impedance is 8 ohms. Some guy on another forum says that's because many solid state amps only had an 8 ohm tap. Before I buy a pair of more expensive output transformers I'd like to know I've selected the best sounding secondary impedance. Does anyone have any experience with the Forte 1 in this regard? Perhaps the only way to know is to purchase transformers with multiple output impedances but the only ones I know of I could possibly afford are the higher end Hammond transformers and I'm hoping not to spend that much money being an old retired guy. I must say the Forte's sound good on the current 8 ohm tap even with the cheapo output transformers.
  2. Do you own both all tube and all transistor amps and switch back and forth? And why?
  3. Turns out some of the problems I was having with the sound of this amp through my Forte 1 speakers was not caused by the tubes, the biasing of the tubes or anything else like that, but the very crappy Chinese coupling capacitors. I was in a local surplus electronics store yesterday and they had some Nichicon plastic film capacitors. (see attached). So I got them just to see if it made any difference and it completely changed the sound of this amp. Now I'm seeing why tubes are so good on Klipsch Heritage designs. Getting in a new Edcor output transformer next week so I will see if there is any further improvement. I'm seeing the problem with these cheap Chinese tube amps. You might have a solid design but the quality of the parts may be terrible. Coupling Caps.pdf
  4. What I'm going to do is just short out one of those two, 1K resistors - the one connected directly to the cathode. That leaves a 1K biasing resistor and the NFB connected to the cathode directly. I'll see how it sounds and that should get some more current flowing.
  5. I lowered the value of one of them, the biasing resistor, to 500 ohms and I believe it gave the amp a more pleasing tone. That moved the tube into a more linear mode according to the graph. Perhaps the 1K resistor that connects to ground forms a voltage divider with the NFB resistor, setting the NFB level and operates independently of the 1k bias resistor it is in series with. Sound plausible?
  6. Voltage drop is 3 volts total across both resistors. 1.5 plus 1.5. Measured resistance is 2k. I have attached some voltage readings. Voltages.pdf
  7. More questions about this amp, which sounds really good. I have a bunch of those 5654 tubes and some EL84's so would like to make another se amp using them. However, looking at this one, the resistance values around the 5654 seem awfully high. Looks like a total of 2K for the cathode resistors when typically it seems around 470 ohms is normal. Measured voltage at the cathode is 3 volts, which I suppose is about right. But why so much resistance? The supply voltage to the plates of the 5654's is 225 volts with 20 volts dropped by the 82K plate resistor. Using ohms law that means the plate current is less than 1ma. This makes no sense to me.
  8. Henry I was told the grid stopper should be between the grid leak resistor and the grid, not where it is on the schematic. Well since they can be removed I suppose it doesn't matter a lot. The data chart for the 5Z4 tube calls for a 4 mfd cap.
  9. Guys henry4841 was right. It wasn't the output transformers. It was some errors in the parts and circuit board which I purchased from Ali Express. I know what your saying now - Well no wonder knucklehead look where it came from! Well I wanted to try a tube amp after many years of transistors and this looked like an easy way of doing it. I really don't enjoy building as much as I did but I like the $ I save and the end result. I recently build a First Watt F5 which is a terrific transistor amp and that's got me back into building again. Look at the attached schematic. Some guys on DIY Audio Forum helped me. The grid stopper resistor in the first stage is in the wrong place and the 33mf cap following the 5Z4 tube is the wrong value. It should be 4 mfd for that tube. Once I corrected those errors and did some tube rolling the amp sounded totally different and I am impressed, after never hearing a tube amp into my Forte's. An error that I probably made was buying the wrong output transformers. I bought Edcor CXSE5-5K - 5W, 5K Ohms single ended tube output, which appears to be for guitar amps, when I should have purchased a XSE10-5K - 10W, 5K Ohms single ended tube output, which is more of a hifi amp transformer and has a UL tap. I actually have them on order now. But I must say the ones in there now don't sound too bad. Not even sure I will hear a difference. I also plan to add a switch so I can go from UL to triode mode. I've also attached a photo of the finished product so far. Looking forward to more of your comments. A6409066-B36B-41F9-8633-27BFBD3B4D4B_1_201_a.heic
  10. I just assembled a SE 6V6 tube amp with Edcor output transformers with an 8 ohm output. I chose 8 ohms because that's what the specified impedance was in the early literature for the Forte 1. But now I see that it says 4 ohms on the back of the speaker at the terminals. I never noticed that before. And the Forte's are kinda bright and bass shy on the 8 ohm tap. Edcor only lets you choose one output impedance which kinda stinks. Do I have any solution other than to order new transformers?
  11. I just got a Pass ACA amp on eBay. It was already assembled - not a Chinese copy but the DIY store version. Sounds good with my Fortes. I'm curious if anyone has listened to both and ACA and a First Watt. How would you compare? I realize the price difference is thousands of dollars and I would expect the First Watt to sound better, but how much? Thousands of dollars better?
  12. https://spacecoast.craigslist.org/ele/d/rockledge-klipsch-kg4-speakers-and-kv1/6935449495.html
  13. https://www.stereophile.com/content/klipsch-forte-iii-loudspeaker
  14. I really only need to protect them for the move itself but have no objection to something more permanent.
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