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Old 9th July 2014, 10:35 PM   #151
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Lightbulb "Hybrid madness" continues ;)

OK, here is what I came up with so far (next hybrid) - created the new thread - see it HERE. Ideas are welcome. We have to prototype this one - it's going to be a lot of fun - "tubish" sound with low distortion
By the way, we can easily control distortion there - no problem to increase it, just add up to your taste

Output buffer is designed by Damir - I just utilize it here as one of the best ones for the purpose.

Cheers,
Valery
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File Type: jpg @LinearGain-Hybrid-01-NoGNFB-00-sch.jpg (218.8 KB, 207 views)
File Type: jpg @LinearGain-Hybrid-01-NoGNFB-50W-20k.JPG (379.9 KB, 192 views)
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Old 10th July 2014, 09:55 PM   #152
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Quote:
Originally Posted by vzaichenko View Post
Hi Terry,

Wrote you the answer and then lost it completely somehow
Ok, here is take two

The output of the front end gives 4.5 - 4.7 mA when idle, no adjustment needed normally. If it will still be required - R17 (schematic from post #35) allows adjusting it (lower R - higher output current).

Regarding the DC offset - it is set automatically, assuming the triodes are matched enough within the tube. I have simply selected the tubes with very close parameters for the triodes. In the worst case, it is possible to put a 50 ohm pot between R5 and R8 - see attached picture - it allows adjusting the offset in the range +/- 2V - and then simply measure it and exchange it with 2 normal resistors. Sorry I did not reserve some space for it - just really hoped it would not be required (and in my case it's not).

Cheers,
Valery
Hi Valery,

I have another question if you don't mind. Please keep in mind, I am not questioning your design, I'm trying to learn. You list C16,C17 as 160V. Looks like they only see one rail and go to ground. Why 160V?

Thanks, Terry
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Old 11th July 2014, 01:54 AM   #153
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Terry, you're right - they only see the rails, so they can be 100V-rated or even 80V-rated easily (though I like to have some safety margin). Sometimes, whem I work on PCB (and re-draw schematic for PCB design purposes), I copy-paste some elements from my previous designs, when I know the physical size is right, even if they are slightly over-rated. This is where 160V came from.

Cheers,
Valery
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Old 11th July 2014, 04:32 AM   #154
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Hi Valery,

Which files did you use to have your boards made? I sent the ASCII file and the silkscreen is pretty badly offset. It works but it makes it a little more difficult to locate the parts. I am attaching a pic of the boards.
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Old 11th July 2014, 05:12 AM   #155
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Quote:
Originally Posted by still4given View Post
Hi Valery,

Which files did you use to have your boards made? I sent the ASCII file and the silkscreen is pretty badly offset. It works but it makes it a little more difficult to locate the parts. I am attaching a pic of the boards.
Hi Terry,

I used exactly the P-CAD ASCII file, attached to post #35.
From what I see on your photo, there is some mismatch in silk-screen font (the one pcb manufacturer used for printing the silk-screen) - on your PCB characters are somewhat bigger than expected.

See my PCB attached.

By the way, it is possible to download a free P-CAD viewer HERE - it shows PCB layout from P-CAD ASCII format.

Cheers,
Valery
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Old 11th July 2014, 05:44 AM   #156
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Attached is the picture the board house sent me. I am trying to get to the bottom of it.
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Old 11th July 2014, 10:13 AM   #157
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Quote:
Originally Posted by still4given View Post
Attached is the picture the board house sent me. I am trying to get to the bottom of it.
Yes, looks a little bit strange - characters are larger than the ones on my PCB and some of them are slightly moved to the left...
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Old 11th July 2014, 01:00 PM   #158
Bigun is offline Bigun  Canada
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I have known of an issue just like this and in my case it is not produced at the board house. The issue is in a mismatch between what you see on the screen in Eagle edit mode and the creation of the Gerber files (the master images used to manufacture the boards). You should create the Gerber files yourself, then view them carefully with a suitable viewer before you submit them to the board house. The Gerber files will be faithfully reproduced. If you leave the board house to create your Gerber files you can get all sorts of issues. The default in Eagle is to use variable width fonts and these often don't convert well when making Gerbers - at least that is what I have found. So I used fixed width (they are a bit boring!) fonts and then I check the Gerbers - in many cases I still have to adjust the position of text as there is sometimes an offset between what you see in Eagle edit and what shows up on the Gerbers. Check and double check your Gerber files and you'll be fine.
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Old 11th July 2014, 01:10 PM   #159
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what font did you use for silkscreen ?
looks like boardhouse did font substitution, maybe ?
or just font size difference ?
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Old 11th July 2014, 01:20 PM   #160
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When I first sent the files in to get a quote, I sent both Gerbers and ASCII files for the Low TIM and Valery's Class A. When they sent the quote back they did it based on the ASCII files so when I got ready to order the boards, that is what I sent. I was able to look at the gerbers and they looked right but I couldn't look at the ASCII files. This board house has always sent nice boards before. Now, using the viewer that Valery linked, the screenprint looks fine so I wonder why the board house screen shot looks like what they made.
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