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Old 22nd July 2005, 01:08 PM   #1
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Default Your favourite filament supply for DHT's?

I have a Ba tube for a customer that is still getting far too much noise in via the filaments. Right now I have a LM317 as voltage reg followed by a current reg LM317...but there is still a huge amount of noise coming in through there. Diodes are Schottkey's.

Common mode filter after the regs the solution? With some 2200uF caps after the common mode filter?..

I know I'll get them silent...but was curious about how you guys solved it.
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Old 22nd July 2005, 01:35 PM   #2
bigbulb is offline bigbulb  Canada
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Hi,

May I know what tube you are using? If 2A3 even AC filaments should be no problem.
My 2A3 running AC filaments and noise level across 8 ohm load is 2.8mV RMS, should be good enough.

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BigBulb
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Old 22nd July 2005, 01:36 PM   #3
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Hi Bigbulb,

Ba tube in preamplifier type setup.

Regards,
Bas
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Old 22nd July 2005, 02:05 PM   #4
kmtang is offline kmtang  Canada
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Hi Bas,

How is the schematic looks like for the preamp and PS?

Johnny
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Old 22nd July 2005, 02:10 PM   #5
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Hi Johnny,

Here's the schematic of the psu
http://www.triodedick.com/cleo_5/cleo_voeding_gif.GIF
Click the image to open in full size.

And here for the preamp...
http://www.triodedick.com/cleo_5/cle...terker_gif.GIF

Regards,
Bas
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Old 23rd July 2005, 12:14 AM   #6
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Assuming that you have a perfect HV supply (with very few mV ripple)

I`ll try a switching power supply desing for computer.
You can found 5V@1.5A and 12V@2A for less that $5...

I use it myself and feed a RC circuit to provide the exact voltage on my hum free #26 preamplifier.
And for the C, I use only a small 150Uf elna cerafine...

Of cource, common mode choke on the main to isolate the SPSU is a must because they might produce noise in your HV supply and get the sound worse... (I use an isolation transformer + some 0.1Uf)

give-it a try.



Regards
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Old 23rd July 2005, 12:25 AM   #7
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Quote:
You can found 5V@1.5A and 12V@2A for less that $5...
Thanks for the tip..but aren't these units huge? And only part of a complete computer psu?

Regards,
Bas
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Old 23rd July 2005, 12:28 AM   #8
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By the way...how can I get detailed photo's from your yahoo photo's? I know in the uk version you can click on a button to download the original high quality version..I am interested in your 10 amp.
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Old 23rd July 2005, 01:25 AM   #9
agent.5 is offline agent.5  United States
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Maybe you can tried ultrasonic heating. The transformer costs $15 on Ebay. Here are some threads:

http://db.audioasylum.com/cgi/search...&forum=tubediy
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Old 23rd July 2005, 03:46 AM   #10
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Right now I have a LM317 as voltage reg followed by a current reg LM317...but there is still a huge amount of noise coming in through there. Diodes are Schottkey's.

You don't have a filament hum problem, you have an instability in your regulators. These IC voltage regulators have internal frequency compensation, however, it only works if you connect 22uF (tantalum) -- 100uF (aluminum) across the outputs. The 100nF capacitors the schematic shows are too small. One or both are oscillating and feeding that signal into the tube via the cathode.
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