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Vertical 6EM7 Portable Amp
http://www.diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5134
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Author:  mwhouston [ 03 Mar 2019, 06:18 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Draw your PS. Give us a schematic.

Author:  john55 [ 03 Mar 2019, 06:37 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

I thought I'd go one step further as I'm not quite so scared of the oscilloscope now.
The distorted 50Hz signal that I posted earlier, was measured across the speaker terminals. (5).
I hooked a signal generator and decided to follow the signal through from the input.
On test points 1, 2 and 3 a perfect sine wave. Signal distorted on test point 4.
Could the 6EM7 be too close to the mains transformer?

Author:  john55 [ 03 Mar 2019, 06:40 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

mwhouston wrote:
Draw your PS. Give us a schematic.


This is the PS. It's Matts' original design, just adapted for one channel.

Author:  mwhouston [ 03 Mar 2019, 06:50 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

It could be but I’ve infrequently seen it a problem.

Author:  mike567 [ 03 Mar 2019, 07:20 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Add center tap to filament winding?

Author:  john55 [ 03 Mar 2019, 11:07 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

mike567 wrote:
Add center tap to filament winding?


Oh, well spotted. No center tap on my transformers. Just soldered in two sets of 100 ohm resistors and both amps are hum free. Thanks a million.

Author:  john55 [ 04 Mar 2019, 03:02 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Really enjoyed building these mono blocks. A bit tight to work on when wiring, but I was able to build a couple of sub assemblies first and then drop them in, which made it a lot easier.
In the end I decided to use one half of a 12AU7 for the buffer and one half of a Psvane 12AT7-T-MII to get back the 20Db loss from the tone stack. The reason for this is, I just love the sound of that particular valve. I think the extra cost is worth it.
I don't think I'll ever build another 6EM7 amp without the tone stack, it's a worthwhile, versatile addition to what is already a beautiful sounding amp.
Thanks for all your time and effort Matt, and thanks for the help of others on this forum. I can never seem to quite get there on my own. Always need a little help.

Author:  ILoveHiFi [ 04 Mar 2019, 03:42 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

My dad owns a pair of psvane 12AT7-T-MII and I own a pair of shuguang 12ax7-t.
Both sounds on quite a smilar level but the psvane is more hard sounding but at the same time more clean.
IMO if its more hard and theres less tube colour mayaswell listen to transitors so I like shuguang 12ax7-t more.

mwhouston also owns a psvane tube so I wanted to bring this up.

Shuguang treasure series has been advertised before as best tube from China, the first treasure series came out in 2012 and the fancy shuguang tubes is a new thing.

Author:  john55 [ 04 Mar 2019, 03:48 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

ILoveHiFi wrote:
My dad owns a pair of psvane 12AT7-T-MII and I own a pair of shuguang 12ax7-t.
Both sounds on quite a smilar level but the psvane is more hard sounding but at the same time more clean.
IMO if its more hard and theres less tube colour mayaswell listen to transitors so I like shuguang 12ax7-t more.
mwhouston also owns a psvane tube so I wanted to bring this up.


I've not tried any Shuguang valves. Would like to hear other opinions, especially mwhoustons'

Author:  ILoveHiFi [ 04 Mar 2019, 03:51 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Unless its Shuguang treasure seires (fancy series) otherwise the standard ones and very poor sounding. Mayaswell buy some NOS tubes like 6n4 cause those are really great value for the sound you get.

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