Curious_George

This is just a little venting, so it probably won't be popular, but oh well... Why do people feel the need to mention they work for a non-profit? Why can't they just say I work at "xxx" and leave it at that? Does anybody need to know or care the status of the company unless it is pertinent to the actual conversation? Most times (99.9%), no, it is not pertinent. And when people say (even reading it) they work for a non-profit, you almost feel dirty if you don't work for a non-profit too because you are engaged with a company that makes profit and distributes that profit. Now I realize what a non-profit is: "a legal entity organized and operated for a collective, public or social benefit, in contrast with an entity that operates as a business aiming to generate a profit for its owners". I proudly own my own (small) business and I am in business to make money. In turn, I provide employees with a paycheck and provide services to customers. I also invest money into the company and after it's all said and done, I leave what is needed to run the company for the next year and take all the profits for myself. Capatilism at its finest. I don't see why people have a problem with it.

No. Not all chip amps are Class D. Chip amps can be analog too, such as the National LM4780. All Catholics are Christian, but not all Christians are Catholic...

No worries Henry. We’re good.

I agree and the problem is sometimes you have to “look behind the curtain” and in some cases you may not like what you find. A lot of manufacturers are reputable, however, there are quite a few companies that have a great looking product and the guts are cloned junk circuits or just terrible overall. Then you have a great circuit and great amp and the looks are mediocre and then everything in between. The consumer really has some homework to do, but audio seems to be much worse in this area than other categories.

Yes, but you’ve taken my quote out of context. I was specifically talking about output transformers. For example, a $3000 pair of silver MQ transformers are not going to sound magnitudes better than something that cost $400. A good circuit design will yield better results. For someone just starting out, that “best iron” would be a waste of money.

If Bob can do it, obviously someone else can too. It’s not mapping the human genome.

Price (money) does not equate to the best. The boutique transformers are always much more just because they don’t have the sales volume. That doesn’t make them better. Take Hammond transformers for example, if you listen to the “experts” Hammond is pure junk. My first tube amp I built 23 years ago used 1627’s and the amp sounds wonderful. Especially if you use an 8 Ohm speaker on the 4 Ohm tap for a 5k load. However, a lot of people will spend money on “the best” to make themselves feel good.

Are you looking to use the existing K77 mount or are you going to mount them on top or in separate "top hats"? If you are not going to use the original tweeter location, the JBL ST-200 is the closest thing to a K77 from a sonic (and harmonic signature) standpoint, but handles a lot more power. The ST-200 has a phenolic diaphram like the K77.

It says "Tube Rules" (not Tubes Rule), which is different...

Yep. When I build an amp without feedback I swap input & output tubes (after a good break in) until I get the best distortion and match output levels to within 0.5dB. Then those tubes are mated for life.

Unfortunately, I have never had the pleasure to (physically) work with mentors in the tube audio field. I guess in a manner of speaking, reading countless hours of forums (with a grain of salt), books, periodicals and RDH4 (from front to back), I had mentors from afar. I am self-taught, which makes you even more focused sometimes when designing circuitry and amps.

I have not measured new (or even old) WE 300B’s. If someone was to lend me a set, I’d be glad to. For SE 2A3 and 300B amps, I prefer 5~6k OPT’s… for as you say “musicality” not maximum output power.

300B @ 1% THD+N This measurement was made of 2 different sets of 300B's with about 200 hours on each set. A newer set of 300B's (with only about 75 hours on them) had much higher distorion and lower power output based on 4 Watts as a refererence.

I can capture the FFT like the other images I post. You can see the harmonic signature very easily. Any tube preamp is going to have predominant 2nd harmonic distortion unless it has feedback.

70’s classic rock ROCKS!

I can do an FFT on the 12V6 preamp.

It is a stand alone unit - Audio Precision System One (circa 1995). It is obsolete by today’s audio standard in self-contained systems such as this. However, for DIY audio it is awesome. The newer systems are unbelievable but very expensive. At my previous job, I used one in the lab for 20 years. In 2003, I didn’t want to cause a conflict of interest at work, so I bought one for my home workshop. PC based stuff is out there now, so that is what people usually gravitate toward.

I’ll have to go back and see where 1% is power wise. Unless you drive the 300B into Class A2, you are not going to get 8 Watts @ 1%. And this would be biasing the 300B in an unconventional manner closer to 0V. This is just a guess messing around with SE Tubecad.

For SE amps, I aim for less than 0.5% THD @ 1Watt, 1kHz. It’s easy to do but you have to carefully choose the primary transformer impedance, driver & output tube load lines to compliment each other. Distortion isn’t the only parameter that matters, but it helps to keep it low to begin. If you have enough gain, of course you can add some feedback to improve damping and reduce distortion a bit.

Unity gain distortion Full gain distortion

Here is a tube preamp design that uses an output tube at line level signals. The concept is to utilze the linear plate curves of a triode strapped pentode. The 12V6 is the same as a 6V6, but with a 12.6V filament and a bit cheaper to purchase. The 12V6 triode plate curve is extremely linear and makes a great preamp. One caveat though is the 12V6 can be a little microphonic, but that issue is easily handled with a silicone damper ring or a rubber grommet isolating the tube socket from the chassis. The design to use an output tube as a preamp is not new, and many types of output tubes can be used. The 12V6 is nice because without feedback, the gain is just right to take line level signals and give them just enough boost to drive modern sources with. I have included a cathode follower in this design, which means the output impedance is very low and the preamp can now drive just about any type of source/cable combination. Due to the low gain of the 12V6 in triode mode, noise is naturally low as well. Parts count is fairly low, so the price to build is not too bad. If you can find a metal enclosure around that could substitute as a chassis, the cost can be even less. The design is very forgiving, but a few areas need to be implemented properly such as grounding. Again, I am throwing this out as a DIY build. I'll try and come up with a BOM (Bill of Materials) soon to help locate parts, if needed. Some of the parts, I have and will let them go cheap because I have an abundance of them such as the LM317K regulators, mounting socket for regulator, and 8200uF/35V capacitor. An LM317 TO-220 package can be used of course, but I find it hard to mess with those small leads some times. The LM317K is a TO-3 metal case package and it is easy to work with and just. Anything TO-3 from Mouser or any parts house is sky high nowadays. I also have a lot of the resistors / caps you'll need too in small quantity. My 12V6 preamp is not anything to look at, but it sounds great. It is a test bed, so it won't get any prettier. Unity gain frequency response Full gain frequency response

I did like the original "motor run" caps in my Heresy Type E networks, but the ESR was getting up there and that is when I made the Universal clones. I may have to try some of the Russian PIO caps for the mid & tweeter circuits.

Sounds like Mark read "Atlas Shrugged" and took it to heart... would not surprise me given the turn the world has taken the last few years. I've have somewhat taken the path. If you have not read the book, it should be on your list. I read it when I was 20.

Do you think ESR will be high in these old(er) surplus caps or an issue being used decades later for audio purposes?

Can you rephrase your question? What is your intent?