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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 14 Jun 2015, 09:16 
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Location: US Pacific Northwest
So I've had this amp plugged into my system on and off for the last couple of weeks and I am absolutely blown away by the quality of the sound coming from this little unit. I don't know what it is but these little triodes are just the best sounding tubes I have ever heard. :sing:
Attachment:
6CY7 Amp Left Profile.jpg
This is quickly becoming my favorite amp. I currently have a set of NOS Sylvania tubes in it, but I have also used a set of old GE tubes which sound just as good.

This is really a pretty inexpensive build. I highly recommend that anyone looking for a little iPod or computer amplifier give this one a try. You will NOT be disappointed!


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 25 Jul 2015, 23:04 
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So I'm still really impressed by the sound of this little amp. It just seems right. Even better than the excellent 6EM7 Vertical amp on the projects page. So I took it upon myself to do a little more analysis. I decided to apply "Espley's Method for Four Harmonics" to the calculated load lines to see if I could determine anything. This is a simple mathematical method for analyzing load line designs for the first four harmonics proposed by D.C. Espley in 1934.

So here are the results for the 6EM7 Vertical Amp and for this 6CY7 amp:

6EM7 2nd harmonic: 9.4% (-10.3dB)
6EM7 3rd harmonic: 1.7% (-17.8dB)
6EM7 4th harmonic: 0.2% (-26.8dB)

6CY7 2nd harmonic: 4.7% (-13.3dB)
6CY7 3rd harmonic: 0.6% (-22.0dB)
6CY7 4th harmonic: 0.9% (-20.3dB)

These are full output numbers; overall distortion is roughly proportional to output level.

So this is a very interesting result. This amp, the 6CY7, not only has lower 3rd harmonic distortion (relatively speaking), but it has slightly higher 4th harmonic levels giving it an even fuller sound. Of course, this is just a mathematical analysis; the only analysis that really counts is your ears. However, this little amp seems to excel in both realms. This is just one more piece of useful information in comparing the two designs.

Comments?

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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 07 Oct 2015, 18:35 
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A funny thing just happened.

I just completed a 2000mi move to a new city. This amp (along with all my other worldly possessions) was packed up (very well wrapped, padded, and boxed), loaded on a moving truck and shipped to my new home. So I set it up in my new office and turned it on. With nothing playing I could clearly hear a distinct hum.

Upon further investigation, I discovered that the hum is NOT coming from the speakers. The amp is still, electrically, dead quiet. In fact, it sounds wonderful. Except for a hum coming from the chassis itself. The problem is that I cannot find the source of the hum. I simply can't localize it. It just seems to be coming from "somewhere" in the chassis.

So here is my question: Where do I look next? I thought I might be able to isolate it to the power transformer or the main filter choke, but no such luck. I'd like to hear some ideas.

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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 07 Oct 2015, 22:14 
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Location: Vancouver Canada
Have you tried putting the handle end of a screwdriver to your ear and connect the drive end at different points on the chassis, trans, choke, etc? If it's a physical vib, it will defiantly be loudest at the point of origin. Errr works for engines why not tubes.


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 09 Oct 2015, 09:57 
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http://www.ebay.com.au/itm/Sprague-STET ... 27f0f4e0ae

101 uses.


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 20 Oct 2015, 15:47 
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I just realized I messed up the harmonic numbers above. Should be like this...

So here are the results for the 6EM7 Vertical Amp and for this 6CY7 amp:

6EM7 2nd harmonic: 9.4% (-20.5dBv) (-27.4dBv @ 1W)
6EM7 3rd harmonic: 1.7% (-35.4dBv) (-42.2dBv @ 1W)
6EM7 4th harmonic: 0.2% (-54.0dBv) (-60.8dBv @ 1W)

6CY7 2nd harmonic: 4.7% (-26.6dBv) (-28.8dBv @ 1W)
6CY7 3rd harmonic: 0.6% (-44.4dBv) (-46.7dBv @ 1W)
6CY7 4th harmonic: 0.9% (-40.9dBv) (-43.2dBv @ 1W)

This makes the differences more clear by referencing all the harmonic levels to 1W (and also correcting my original mathematics mistake). Now my statement from the previous post is more clear "This amp, the 6CY7, not only has lower 3rd harmonic distortion (relatively speaking), but it has slightly higher 4th harmonic levels giving it an even fuller sound."

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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 28 Oct 2015, 06:22 
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Joined: 26 Sep 2015, 13:59
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This amp looks absolutely brilliant and simple enough for a first power amp build for me. My problem is the power output. I currently have a valve power amp from Audio Innovations which puts out 25 wpc and a solid state Quad 405 putting out 100 wpc! What on earth can I drive with 1.3wpc? Or am I missing something? I'd have thought I would need a minimum of about 10 wpc to be of any real use?

BTW. I am not a lover of heavy rock or loud pop music. I listen mostly to classical music at farly low levels.


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 28 Oct 2015, 11:50 
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Location: Chilliwack, BC
RevM wrote:
What on earth can I drive with 1.3wpc?


1.3 tube watts are different than SS watts.

Here's a writeup a customer did on one of my 1W amps:
http://www.glowinthedarkaudio.com/se12by7a.html

They punch well above their weight!

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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 28 Oct 2015, 14:07 
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Location: Vänersborg, Sweden
OBJECTION! One tube watt is one watt, not more nor less, and ONE transistor watt is also one watt not more, not less.
However the way the tube is clipping the signal at "full speed" and how a transistor is doing it gives a feeling that at maximum power, the tube amp is still giving a reasonable decent signal, where as the transistor amp distorts too much.

What to do with 1,3W?? My small Sonido exponential horns needs less than that to fill my living room with ample of music. A careful choice of speakers and/or speaker topology will solve any low powered problems. I am finishing a project with a pair of 1626 (Darlings) and the 3/4W will be fine.

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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 28 Oct 2015, 16:01 
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RevM wrote:
What on earth can I drive with 1.3wpc? Or am I missing something? I'd have thought I would need a minimum of about 10 wpc to be of any real use?
I'm not quite sure how to say this, but you are yet another victim of the "More Power" Audio Cult. :eek:

This particular group first showed up in the late 1960s and early 1970s. During this period, and with the rise of the solid state amps and their very low damping factors, speaker design took a major turn for the worst. Efficiency tanked and speaker cones became bulky and sloppy. Energy robbing three way, and even some 4 way, crossover networks became the norm. It has even been argued that the rise of Disco music, with it's thumping bass lines, was a outgrowth of the solid state amps and big sloppy speakers. Low damping factors were great for bass but because the speakers were so inefficient, the amps soon grew in power. And the marketing departments kicked into high gear. The amps went to bigger and bigger power stages, and soon the power output of your amp became a measure of manliness. Ten watts per channel meant "little", 50 watts per channel, meant "big", and 100w per channel meant "hung like a bull"! And the major retailers sold big, powerful, gaudy, crappy sounding amps by the millions.

Now, 40 years later, we have learned better, but the cult is still out there and active. The fact of the matter is that most audio amps spend there entire existences putting out less than one watt per channel. And it really is the quality of this first watt that matters most of all. For a much more detailed explanation of why this is so, read this blog entry here (http://www.cascadetubes.com/2014/04/14/how-amp-technology-affects-volume-and-power/) and see if it answers your question.

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