2. amps-preamps
  3. 140029-80294

Does anyone care to ask an amplifier designer a technical question? My door is open.

I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.

I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer.
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Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.

I like to tell true stories of my experience with others in this industry.

I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.

On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.

I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.

Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.


128x128ramtubes
prof
3,474 posts
 
@ramtubes

First, the concept of your building the type of switch box I mentioned is very intriguing.  I'm not sure the idea still fits well with my system, which has become more complex (I'm introducing subwoofers, crossover etc).But I will certainly cogitate on the idea.

Also, love your idea for building switch boxes to text cables etc!  If the timing were right financially for me, I'd likely take you up on that (just out of my own interest.  I'm far from sold on the worth of high end cables, but I do have access to a bunch and it would be fun to test under more ergonomic circumstances, fast switching, etc).
fleschler
2,021 posts
 
I’ve tried a dozen 6SN7s for my amps’ cathode followers. What a huge range of sound characteristics.

The worst (thinnest,brightest) were Russian 80s or 90s ones under the Sovtek label, which looked identical to the Counterpoint branded ones and an English branded one. NOS GEs were generally noisy/distorted sounding.

The best were Raytheons for my amps, with the older VT-231 my favorite for its huge dynamics and warmth. Raytheons from the GT era can be more neutral sounding and harmonically thinner than the VT-231.

Sylvania’s Chrome dome had too tipped up sound for my amps but very clean and dynamic too.

RCAs, for decades of production, were warm sounding but less dynamic. My amp manufacturer uses 60's RCAs to great effect in the same amps but with very different speakers.

Ken-Rad was similar to VT-231s.

Any of the NOS tubes are superior to the 80s/90s Russian made tubes. I haven’t tried the latest tubes. In my application, the tubes can last possibly 10,000 hours (I know it’s lasted 5,000 hours already).

Maybe microphonics are not an issue with cathode followers.

I just don’t understand VAC using only 6SN7s in all their current amplifiers if they are worse than 6SL7s.

ramtubes's avatar
ramtubes OP
460 posts
 
Here is the best data I found for the 6H30. The curves look right and the table of parameters done at different plate voltages and currents are very interesting. The first 3 columns are his set up values and the rest are the results. 

 http://www.triodeel.com/6h30.html

Is this like a 6FQ7?  Granted the pin out is the same.

After I get a few responses I will give mine. I want the questioners to do a little thinking on this one. Kinda like Homework.


tomic601's avatar
tomic601
12,956 posts
 
thanks for awesome thread Roger

i got to page 27 of the Williams book and he says “ but as you learned in your AC theory course... “

so....now what book do I need ? Dont answer, I will figure it out...
Tektronix scope is on order...@$&*(#### this is fun.

ramtubes's avatar
ramtubes OP
460 posts
 





@fleschler

Maybe microphonics are not an issue with cathode followers.

I just don’t understand VAC using only 6SN7s in all their current amplifiers if they are worse than 6SL7s.


VAC is likely using them because thats what the current customer base has been told its the tube to have.

Cathode followers have a gain of 1. 6SN7s have a gain of 20 when used for line gain. The Microphonic sensitivity is thus 20 times less in the follower.

SNs and SLs are not interchangeable, nor meant to be. They are two different animals. SNs run at almost 10 times the current and most circuits would not bias up properly.

Do you know if your circuit is a cathode biased or a constant current biased follower? Makes a big difference when you swap tubes. big big big

2 seconds and a schematic will answer that question.

I thank you for this question because, with additional information and some simple schematic understanding, we might come with an alternative answer to what is going on. We really dont know why these differences between tubes exist. Or if these same things would be heard in another preamp that had the other kind of circuit. In other words, is the difference really in the tube alone or more likely how the tube performs in your circuit.


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