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#26 pre amp
#26 pre amp
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Old 14th March 2011, 03:29 PM   #901
bequerel is offline bequerel  Norway
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Vinysavor
Off topic...
I see your location is Lindau. If this is Lindau at the shores of Bodensee in the south of Germany, I go there every summer! Nice place!
I have of course also "burnt" some money in Spielbank Lindau and Konstanz (casinos).
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Old 14th March 2011, 05:33 PM   #902
Vinylsavor is offline Vinylsavor  Germany
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Hi!

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Vinysavor
Off topic...
I see your location is Lindau. If this is Lindau at the shores of Bodensee in the south of Germany, I go there every summer! Nice place!
Yes I live in Lindau / Bodensee. You can see the lake in the background of some of the photos on my blog. Next time you are here, drop me a mail and we can meet up!

Thomas
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Old 15th March 2011, 11:11 AM   #903
bequerel is offline bequerel  Norway
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Cool
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Old 19th March 2011, 03:26 PM   #904
andyjevans is offline andyjevans  United Kingdom
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Who's using plate chokes in their 26 preamps? I've been playing about with four 156C Hammond chokes - 150H at 8mA - using them in series as pairs. I put them bottom-to-bottom and wired them out of phase since I read that somewhere. Resistance in series is 7K.

Sound is damn good! Quite surprising. I'm using Teflon FT-3 output caps and filament bias with 10 ohm resistors. 140v on the plate, 10v on cathode. Rod Coleman filament supply - his original one which was posted early on in these pages. This is a really cheap and effective way to build a 26 preamp, except that in my case I'm using choke input supply to Rod's boards with a 280mH choke, 2.7A, and 20,000uf caps.

Now I know that this works I can look at some more exotic plate chokes!! I was thinking output transformer, but Thomas is always telling me to have more inductance and it really does sound very clean.

Andy
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Old 19th March 2011, 07:18 PM   #905
Bas Horneman is offline Bas Horneman  Netherlands
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Quote:
Now I know that this works I can look at some more exotic plate chokes!! I was thinking output transformer, but Thomas is always telling me to have more inductance and it really does sound very clean.
I know you have another thread on this. But just go for the Lundahl. Their 1667 is excellent and available of the shelf. You can always try a parafeed transformer. And then you get to keep the plate choke. Just another avenue to consider.
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Old 21st March 2011, 06:36 PM   #906
andyjevans is offline andyjevans  United Kingdom
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Here's a picture of my 26 preamp. Power supply on left - AZ1 mesh, choke input, motor run caps. Middle is filament supply with two large 280mH chokes for choke input. Preamp on right is tiny! Rod Coleman boards, filament bias with a 10 ohm resistor. Sounds very nice. The preamp bit is ultra cheap - just four Hammond 156C plate chokes, wired in series in pairs with FT-3 cap outputs. Chap on the plate is Disraeli.

andy
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Old 21st March 2011, 07:17 PM   #907
costis_n is offline costis_n  Greece
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Originally Posted by andyjevans View Post
Here's a picture of my 26 preamp. Power supply on left - AZ1 mesh, choke input, motor run caps. Middle is filament supply with two large 280mH chokes for choke input. Preamp on right is tiny! Rod Coleman boards, filament bias with a 10 ohm resistor. Sounds very nice. The preamp bit is ultra cheap - just four Hammond 156C plate chokes, wired in series in pairs with FT-3 cap outputs. Chap on the plate is Disraeli.

andy
Very nice. What does the 10 ohm resistor do?
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Old 21st March 2011, 09:07 PM   #908
andyjevans is offline andyjevans  United Kingdom
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With filament bias the filament supply is connected between one side of the filament and ground. The other side of the filament has the 10 ohm resistor going to ground. So the filament supply goes through both the tube and the cathode resistor. This can sound really excellent, but only on condition that the filament supply is really pure and clean, since the signal goes through it. Compromise the filament supply and the sound can get sharp or gritty - some people have tried and rejected this, but I suspect they really needed a no-compromise filament supply. You can see the size of the filament chokes I use!!

Andy
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Old 22nd March 2011, 11:27 AM   #909
merlin el mago is offline merlin el mago
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Quote:
Originally Posted by andyjevans View Post
Here's a picture of my 26 preamp. Power supply on left - AZ1 mesh, choke input, motor run caps. Middle is filament supply with two large 280mH chokes for choke input. Preamp on right is tiny! Rod Coleman boards, filament bias with a 10 ohm resistor. Sounds very nice. The preamp bit is ultra cheap - just four Hammond 156C plate chokes, wired in series in pairs with FT-3 cap outputs. Chap on the plate is Disraeli.

andy
Thanks to share, could you post the schematic used?

Felipe
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Old 22nd March 2011, 11:28 AM   #910
Bas Horneman is offline Bas Horneman  Netherlands
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And do you have a bigger picture? The current one is hardly larger than the thumbnail.
And perhaps a picture of the guts?
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