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28th October 2009, 09:04 PM
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#1 |
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Tubie Noobie
diyAudio Member
Join Date: Apr 2003
Location: Southern Tier NY
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Joined the 12b4 line stage club. And worth it!
Been a few years since I built anything, but worth the wait. Read just about every post on the 12b4 and all of its variation. I came up with the following:
660Vct with CLCLC filter and 0D3 regulator tubes. B+ = 300V running 25mA through a 6k plate resistor. Using tube rectification 5U4GB. The 12b4 have the lm317 plus 440uF bypass caps. ( highly bypassed electrolytics ). The heaters are set up at 6.3V DC. The heaters are biased to 20V from B+. The 12b4 drives a DIY Aleph 5 and takes the place of my BOSOZ. Too new to give detialed comment, but so far OUTSTANDING. My son made the comment that he could here the musicians make mistakes and move around. I do have a little edgy hum that varies proportional to volume, until it is at full volume. At full volume the preamp goes dead quite with respect to hum. It plays fine. Havn't found my probes for the oscilliscope to troubleshoot yet so if you have an idea please let me know. Attached are the photos.
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Living Life Doing the Waltz in 4/4 meter. |
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28th October 2009, 09:13 PM
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#3 |
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diyAudio Member
Join Date: Mar 2007
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Very cool woodworking! Tightly twisting the wires to the power switch might help with the hum (or maybe even shielding them altogether).
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28th October 2009, 10:54 PM
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#4 |
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Tubie Noobie
diyAudio Member
Join Date: Apr 2003
Location: Southern Tier NY
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Thanks for the feedback. put twisted wire in for the switch, unfortunatley made another change of bypassing heater voltage divider with capacitor at the same time.
Preamp is DEAD quite. Now if I could get my P2P skills to match woodworking.
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Living Life Doing the Waltz in 4/4 meter. |
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28th October 2009, 11:36 PM
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#5 |
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diyAudio Member
Join Date: Jul 2003
Location: Ann Arbor, MI
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hey-Hey!!!,
Nice job on the build. Is the large knob the volume( with the dark dot on it? ). Wish you were my neighbor...  cheers, Douglas
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the Tnuctipun will return |
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28th October 2009, 11:46 PM
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#6 |
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Tubie Noobie
diyAudio Member
Join Date: Apr 2003
Location: Southern Tier NY
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Yes that is the volume. The small one next to it is the input selector. It is a small inlay of bubinga from a piece I had laying around. The wood is cherry and hard maple which I had laying around from building the interior of the house.
Wish I had a neighbor that enjoys this stuff. Living in the Southern Tier of NY, it is hard to find anybody.
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