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tube fanatic

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About tube fanatic

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    tube amp designer

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    extracting the best possible sound from single ended tube amps using modestly priced designs and tubes.
  • My System
    Now specializing in extreme near-field desk top systems using flea power SEPs and SETs. This mode of listening must be experienced as it can be totally enveloping.

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  1. Found this in a Radio Maintenance magazine from 1951. Maynard
  2. The easiest solution is to order some JJ 12dw7s from Tube Depot for $12.95 each. Maynard
  3. There are 2 ways to reduce distortion in SEP amps. One is to use it at a fraction of its maximum output power, and the other is to use nfb. I prefer the latter (as voltage fb) as it reduces the typically high output impedance as well as increasing the bandwidth. If applied within reason, it does not ruin the resultant sound in my experience. In fact, it can provide a very triode like experience in some systems. Maynard
  4. Class AB refers to a specific set of operating conditions which are usually somewhere between class A and class B. So unless the amp has provision to change that, it is running in AB at idle through its maximum power output. It combines the advantages of both classes while minimizing their respective disadvantages. Maynard
  5. Here is the perspective of an EE from the Steve Hoffman forum. I agree with him. I believe that using multiple caps in parallel, regardless of type or price, craps up the sound. My ENT doc friend showed me some frequency response plots of typical males in their mid to late 70s which have convinced me that some of what we believe we hear is wishful thinking. Also, the nonlinearity of the human auditory system is so great, and so varied from one person to the next, that universal recommendations about audio components are worthless. Maynard John DysonForum Resident Location: Fishers, Indiana If I was making the decision for myself, I wouldn't change the cap unless I had a concrete reason to do so. Some people like to change things -- and that is fine also, perhaps part of the enjoyment. Put my EE hat on (I am an EE RF/Audio/Systems, SW Operating Systems/DSP -- and generally pretty good at all of them ), so here is a quick (back of scrap pad of paper) analysis of the situation: Lets see -- cathode resistor/capacitor (I dont know the tube, so I'll guess a gm of about 2mmhos or 2mS.) That would imply an effective resistance of about 500ohms at the cathode (without bypass.) With an electrolytic with perhaps 0.1ohms of ESR, lets guess at 10% of that is nonlinearity. That would mean a delta of 0.01ohms with a 500ohm impedance at the node... The additional amount of distortion caused by the electrolytic changing by the 0.01ohms would be less (much less than) 0.002% additional distortion, and I am guessing VERY, VERY HIGH. In reality, the amount of distortion caused by the nonlinearity of the resistance would be pretty small. Now, we have an issue about the nonlinearity of the capacitance of the capacitor, and the best success there is to make sure that the capacitance has a reactance that is very small (relative to the lowest audio frequency) in relation to 500ohms. Also, unless the tube/valve is in a negative feedback circuit, the changing gm will totally swamp the nonlinearity of the capacitor (either the resistive or the capacitive reactance nonlinearity.) If I was making a design decision, I would simply try to choose a reasonably high quality capacitor with fairly low ESR -- the rest will take care of itself. The difference in distortion of a reasonably good electrolytic vs a perfect capacitor will be vanishingly small, and probably not even measurable. Of all of the things that might need to be improved (other than as a failed/degraded parts replacement) I don't think that changing the capacitor would be all that helpful. Audio source material and transducers (speakers, headphones, microphones, etc) are much more important. John Dyson, Apr 25, 2018
  6. Here’s what Rozenblit had to say about OTL output capacitors on the Transcendent forum: Maynard Bruce Rozenblit03/29/04 There seems to be a lot of confusion about what an OTL is on other message boards. OTL stands for output transformerless. The idea is to eliminate the output transformer from the signal path. That's what I do. It is a very difficult task because of the impedance mismatch between tubes and speakers. There also seems to be a great deal of resistance to the use of an output capacitor. Many people for some unexplained reason, have gotten the idea that an output capacitor will greatly injure the signal. That is baloney. A transformer is about 1000 times more injurious to a signal than a capacitor. Most tube amps have output transformers but that is OK. Most speakers have internal coupling capacitors but that is OK. When an amp has an output capacitor, its the end of the world. I don't get it. Many people have spent a couple of hundred dollars to replace the stock caps in the SE OTL with black gates and all have reported back that there was no improvement. All have wasted their time and money. There is a big difference between conceptual idealistic notions and what works in the physical world. I concern my designs with what works in the physical world. The T16 is direct coupled and the SE OTL sounds even better but it has an output capacitor. Its the results that matter, not the concept. QUOTE
  7. There’s no question in my mind that the OPT is the weakest link in a conventional tube amp design. Anyone who is willing to deal with a larger number of tubes should certainly consider OTL. If I weren’t so cheap, and did not spend my time with similarly minded audio folks, I would do a few OTL designs myself. Maynard
  8. Richard, I am not the least surprised that you enjoyed an OTL amp as many audiophiles consider them the best. Having a capacitor in the circuit does not in any way degrade the sound. Remember, interconnect cables are capacitors as are the tubes themselves! I am sure that Ralph Karsten and Bruce Rozenblit, both of whom sell some excellent OTL designs, would have a great deal to say about this. All amps are flawed in some respect, and OTL designs are certainly no more flawed than any other. Maynard
  9. His description of his early days in audio are a riot. I totally agree with his conclusions about mono listening. I went back to full time mono, with a single speaker in the corner, some time ago and will never go back to stereo. Even my collection of poorly mastered stereo cds sound terrific when listened to in mono. http://www.drowninginbrown.com/dib_sp.htm Maynard
  10. Actually, I think Mike Stehr’s builds are nicer than mine! Maynard
  11. Jeffrey, once again you are on the soapbox claiming that any amp designed by anyone other than yourself, with your power supply, is no good. You claim to be able to hear a 0.5dB difference. I don’t believe you! You need to accept the fact that there are thousands of amp designs out there that are truly outstanding. As to some of your comments about tubes, I just don’t have the time to show that much of what you say is incorrect. My advice to any tube newbies who are following this discussion is to do a lot of research, seek many opinions, and make your own decisions. Also, run from anyone who claims that a particular tube will sound the same regardless of the circuit in which it is used. Maynard
  12. A triode strapped 6Y6 for $4 will get you 2A3 performance without all the fuss and bother....... Maynard
  13. I have always thought that PWK favored Brook push pull triode amps but could be mistaken. Maynard
  14. This was done in 1956. The results were not stated in the article. I’m surprised that such powerful amps were used considering that PWK had once stated that far less power would be needed to fill a huge concert hall. Maynard
  15. Thanks for posting the link Carl. One of the OPTs looks like it was replaced, and the other presumed original looks a little questionable from the picture. For what he is asking, I would pass. Maynard
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