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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Now lets try Willie's 26 pre...... posted by vinnie2 on August 2, 2015 at 17:46:30:
Well wouldn't you know one of the biggest problems was I was using a VERY microphonic 26. Just my luck to pull what is probably the worst 26 out of my stash. I discovered this by accident by just saying let's try a different tube for yucks. Low and behold I got music out the other end. So then I put the old tube back in and it played for just a minute. As soon as I touched the chassis of my test mule to adjust the volume it went beserk. Just the slightest little vibration would set it off. Must go into oscilation or something like that. Very unpleasant.
Anyway..... it is playing now with the new tube and very nicely at that.
I have also been trying out some of the suggestions deafbykhorns and others posted. I reduced the cathode cap to 47uf instead of 470 (didn't have 68uf), reduced the voltage to the plate to 150. I tried a 2uf cap and a 1uf cap in place of the 220nf one, but they did not sound as good, so the 220nf stays for now.
Everything else is the same as the schem, except that I decided to try a hum pot and see how that would work since I am using ac on the filament. I paralleled the resistors and the cap shown in the schematic and tied them to the center wiper of a 20 ohm pot and took the other end to ground. The hum is just barely audible abot 5' from the speaker now.
I am very impressed with this circuit to say the least. It has a very smooth, clean sound and seems to mate well with my 91A diy clone. I do believe I may have to build one of these as it really meets my philosophy of having the minimum number of parts between the music and the speakers. To my eaers it sounds better than my current 76 preamp with way less parts. Going to have to pull out some charts for the 26 and see where I might do a little tweaking.
As it stands right now I have 4.5 mA going through the cathode resistors.
Any suggestions anyone might have for fine tuning would be welcome.
Thanks to everyone for all the help with these two (27 & 26 ) preamp circuits, I appreciate it.
Edits: 08/03/15 08/03/15 08/03/15 08/03/15 08/03/15
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Follow Ups
- update..... - vinnie2 11:30:09 08/03/15 (16)
- RE: your speakers may be bass shy - deafbykhorns 17:35:46 08/03/15 (15)
- RE: your speakers may be bass shy - vinnie2 18:00:23 08/03/15 (14)
- RE: your speakers may be bass shy - Tre' 18:16:32 08/03/15 (13)
- RE: your speakers may be bass shy - vinnie2 04:45:06 08/04/15 (12)
- RE: your speakers may be bass shy - Tre' 07:43:36 08/04/15 (5)
- RE: your speakers may be bass shy - vinnie2 07:54:12 08/04/15 (4)
- RE: your speakers may be bass shy - Tre' 08:40:48 08/04/15 (3)
- RE: your speakers may be bass shy - vinnie2 14:59:20 08/04/15 (1)
- RE: your speakers may be bass shy - Tre' 15:18:39 08/04/15 (0)
- RE: your speakers may be bass shy - vinnie2 09:17:44 08/04/15 (0)
- RE: your speakers may be bass shy - deafbykhorns 06:40:09 08/04/15 (5)
- RE: your speakers may be bass shy - vinnie2 07:48:29 08/04/15 (4)
- RE: your speakers may be bass shy - deafbykhorns 10:21:07 08/04/15 (3)
- RE: your speakers may be bass shy - vinnie2 14:49:35 08/04/15 (2)
- RE: your speakers may be bass shy - deafbykhorns 06:57:02 08/05/15 (1)
- RE: your speakers may be bass shy - vinnie2 08:34:03 08/05/15 (0)
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