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Vertical 6EM7 Portable Amp
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5134
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Author:  john55 [ 08 Nov 2016, 01:43 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Hi Gio,
I used Fostex FF165WK 6.5" Full Range drivers and 2.5" diameter x 5.75" long ports. I'm looking to build some back loaded horns to see if i can do away with the subwoofer. I would like to try a pair of Fostex FE168E Sigma 8 ohms but because of costs will probably go for a pair of Fostex FE166En 8 ohms instead. Your Tang back loaded horns look nice. Do they sound as good as they look?

Author:  Gio [ 12 Nov 2016, 20:57 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

The TB kits is very nice. Decent in-room response given the small size. I have FE206E (8") in a BLH. While I have not measured it, I would say it rolls off quite steeply 50-60 Hz. Bass is generally tough with the small Xmax Fostex drivers without a larger elaborate enclosure. Enjoy your builds. I really love the cowhide finish!

Author:  mwhouston [ 12 Nov 2016, 21:33 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

I think you find all high efficient speakers have poor bass response. My 15" Beymas have a -3db point of 40hz. Low enough for me and for classical music. I used an online simulator which indicated a 50hz -3db. Fortunately room re-enforcement pushes that point lower. Also I have a node boost at 80hz too.

Personally I liked the original three box set as above. Looks so retro - love it. Mind you these days I'm Mr Class D!

Author:  jwhitmor [ 12 Nov 2016, 23:13 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

I have a question about the power triode (output) section of the 6EM7 tube used in this amplifier. Looks like the plate voltage is over 200 volts. I am a noob, and I think it is 225 volts from the 260 volt supply, but correct me if I am wrong. From the 6EM7 data-sheet it looks like the maximum plate voltage for the power triode section is 150 volts. The amplifier obviously works very well, so I must be missing something. I am building one for my daughter, and would like to make sure I understand how it operates.
Where have I gone astray? :?:
Thank you,
J.W.

Author:  thehoj [ 14 Nov 2016, 10:38 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

mwhouston wrote:
I think you find all high efficient speakers have poor bass response. My 15" Beymas have a -3db point of 40hz. Low enough for me and for classical music. I used an online simulator which indicated a 50hz -3db. Fortunately room re-enforcement pushes that point lower. Also I have a node boost at 80hz too.

Personally I liked the original three box set as above. Looks so retro - love it. Mind you these days I'm Mr Class D!


I've got a pair of Klipsch Forte's, which are pretty sensitive (98dB @ 1w/1m) and they have a -3db LF point of 32Hz. Pretty great speakers in my opinion.

Author:  mwhouston [ 14 Nov 2016, 15:50 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Stiff surrounds, as with the Beymas, are great for natural, highly articulated, non-bloated bass but have a naturally higher free air resonance. My old 12" poly-cones had a a free air resonance of 25hz and have no problems delivering 31hz in a 60ltr sealed box. But the Beyams produce a bass which sounds so much more like part of the music rather than some sort of added bass as I feel some systems sound.

Author:  Suncalc [ 14 Nov 2016, 16:06 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

jwhitmor wrote:
From the 6EM7 data-sheet it looks like the maximum plate voltage for the power triode section is 150 volts.
I think you are looking at the average characteristics section of the data sheet. The maximum plate voltage is 330v for both sections. See below from the Tung-Sol 1962 data sheet.
Attachment:
Screen Shot 2016-11-14 at 3.03.37 PM.png

Author:  Suncalc [ 01 Jan 2017, 16:42 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

I've been doing some investigations of low frequency transformer performance and had the opportunity to gather some more data on this amp. For anyone interested, here it is.

First the raw gain data. This data as taken at nominal output power of 1W into an 8Ω resistive load.
Attachment:
Gain Data.png
And here are the plots.
Attachment:
Gain Plots.png
And for anyone thinking about playing with feedback (I don't recommend it, but YMMV) here is the phase plot across frequency.
Attachment:
Phase Plot.png
I wouldn't trust the phase numbers below about 30Hz. There is enough distortion in the waveform that the numbers may be off by a fair amount.

And if anyone is interested, I did measure the distortion at 1kHz for two different drive conditions. One is at 1W output (0dBW) and the other one is 20dB down from this at 10mW output (-20dBW). This first is representative of a serious listening volume, the second a more casual (or "the baby's asleep") listening level.
Attachment:
Distortion_at_1kHz.png

This should help people get a feel for how the amp performs before they build it. Personally, I really like the sound from this design. Definitely SET on a budget.

Author:  RossD [ 01 Jan 2017, 17:02 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

What does the phase shift mean for the listener?

Author:  Suncalc [ 01 Jan 2017, 18:14 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

RossD wrote:
What does the phase shift mean for the listener?
For the listener, absolutely nothing.

However, if you are designing a feedback loop, it is important to preserve phase margin across the operational bandwidth to prevent oscillation. This generally means putting some frequency shaping in the feedback loop if the forward path has too much phase shift within it's passband.That's why I prefaced the phase plot with the statement...
Suncalc wrote:
And for anyone thinking about playing with feedback...
If you're not attempting to play with feedback, you can ignore the phase data.

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