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-   -   BDT Preamp build (http://www.diyaudio.com/forums/tubes-valves/129940-bdt-preamp-build.html)

jkeny 17th September 2008 11:24 PM

BDT Preamp build
 
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Here are some pics of my convoluted build of this preamp: http://www.4shared.com/dir/9351477/a...DT_Preamp.html

It's my attempt to make this into an integrated amplifier = BDT preamp + Baby Huey amp with the ability to use either separately. I'm building Zeus & SS Tabor amplifiers also & wanted to use the preamp with these - all differentially.

This pic is the final casing for it.

All comments welcome

jkeny 17th September 2008 11:26 PM

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And the innards:
- Brass sleeved trafos are the Dave Slagle OPTs for the BDT (nearly as big as the original Rogers Cadet III OPTs (from which this whole chassis is extracted)
- The black box to the left of the PS trafo is a 12V SMPS for the CCS supply to the BDT tube heaters.
- One 250V voltage Reg (ala John S) is seen on perf board stuck to the inside of the front panel. The other 130V VR is to be mounted yet. Other little perf boards are
- one CCS for both BDT tubes (at the front of the case)
- two CCS boards for the diff input to the Baby Huey

Part of my slowness with this build was trying to fit it all into the Rogers Cadet case - an impossible task which I finally gave up on when the Slagle OPTs arrived (much bigger than I anticipated)

jkeny 17th September 2008 11:32 PM

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Underside of chassis - in a disconnected state. I have lost one tube socket of the four in the Baby Huey section (broke too many pins & had to pull it). Also this section is in flux so ignore the wiring.

The part nearest the viewer is the front of the chassis & I've used two of the 3 tube sockets for the BDT preamp

jkeny 17th September 2008 11:52 PM

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Building CCS & HV voltage regs became so much easier when I got some CCS boards

- pic of CCS

jkeny 17th September 2008 11:53 PM

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sketch of CCS board

jkeny 17th September 2008 11:57 PM

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Modded CCS board into HV Voltage Reg - top

jkeny 17th September 2008 11:59 PM

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Modded CCS board into HV Voltage Reg - back

ErikdeBest 3rd November 2008 02:50 PM

Hi Jkeny

Interesting build, have you made further progress?

Yesterday I was going through the net and stumbled upon the 'improved' version of the BDT by Swenson: the regulated power supplies and the cascodes on top of the 6ER8.

What I would like to ask, do you know if Swenson is using it in his main system again? I ask it because he mentioned in the earlier thread here at diyaudio that he was not using it anymore due to noise/distortion, having replaced with a switched attenuator. But now, an improved version with expensive transformers, etc...apparently it made its way back to his mains system?

Pity I forgot to buy some 6ER8's when I got the dampers from AES.

Erik

jkeny 3rd November 2008 04:31 PM

Hi Erik,
Unfortunately, I'm out of action with a sciatic nerve problem, which I'm finding difficult to get rid of - been with me for 6 weeks now.

I believe he is using it now as his preferred preamp after flip flopping between it and Gary Pimms Solid State Pentode (I'm also building this as a low power amp)

I think a couple of things in the end won the day for the BDT - the trafos, the use of metglas to magnetically shield the tubes & the new operating points that he is using with the Gary Pimm voltage Regs. I believe the tube microphonics also had to be tamed with some isolation/damping.

I am dying to get back to it as I was just about finished the build & he is so positive about its sonics.

The tubes are 6AR8 - about $7 in thetubestore - if you find them cheaper let me know.

ErikdeBest 3rd November 2008 08:22 PM

Hi Jkeny

That doesn't sound good. Have you had some bad luck when lifting something? Take care, and hope you get well fast!

Thanks for the comments on the BDT. It gives me confidence! (although I have to find out what this metglas thing is...)

I found the 6AR8 being sold at 4 dollars the piece at www.vacuumtubes.net , not cheaper, yet.

Take care! Erik


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