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Old 13th April 2012, 09:11 PM   #1
jpk9876 is offline jpk9876  United States
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Default Tetra Sans PS

Hi,

I preparing to build a Tetra Sans PS and have a couple of questions for those that have built it or are familiar with it.

I'm planning on using 6dj8s and/or 6922s. The manual talked about a 6922 1st, 12AT7 second tube being a v good combination.

What tube combinations are you using and how are they working out for you?

Assuming I stay in the DJ8 family, what's a good B+ voltage to use?

I'm wondering if it's worth adding a soft start to the filament regulator? Being a phono, pre B+ could be manually switched? I like NOS tubes and at least feel better pampering them.

I basically just need a 2nd phono stage for a 2nd table, I'm wondering if I should just go ahead and build a full preamp?

All comments / suggestions are appreciated,

Thanks,

Joe
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Old 26th April 2012, 01:04 AM   #2
cjkpkg is offline cjkpkg  United States
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I first set it up with 12ax7 12ax7 and the gain was WAY too much.

Running 6dj8 12ax7 now and the gain is better. I bet would be even better with some nice 6cg7s.

B+ is right at 250V - my psu is the PS1. VERY quiet.

The only thing I have left to sort out are the RIAA and coupling caps. I went the cheap route (orange drops) and it sounds pretty good but I think with some better RIAA caps and some nice coupling caps it would sound dynamite.

Got a couple other projects so I will not go out and spend a hundred bucks on caps right now but my advice would be not to skimp here.
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Old 26th April 2012, 03:55 AM   #3
alexg is offline alexg  Philippines
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I have tried:

1. 12ax7 - 12ax7, too much gain
2. 12ax7 -5751, sounds good.
3. 5751 - 12at7, sounds better.
4. 5751 - 6sl7, sound good.
5. 12at7 - 12at7, sounds better.
5. still to come: 6sl7 - 6sl7 (am waiting for tubes).

The best sounding that I have tried is 5751 - 12at7 and 12at7 - 12at7.

Am using Denon DL103R into a cinemag step up, Lenco L75.
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Old 26th April 2012, 07:29 AM   #4
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Lots of questions.

I like and use the original Aikido RIAA preamplifier. I like the Aikido cathode follower output; it has the guts to drive the next stage including a volume control.

Lots of talk about too much gain.
Too much gain depends on the line stage if there is one. If the next stage is a line with 20db of gain yes there is too much gain to be burned off in a volume control. I use an Aikido RIAA preamplifier with the typical 40 db of gain plus the insertion loss of the passive filter network. To push a power amplifier to full output no additional gain is needed. After the Aikido RIAA preamplifier I use a 70 db stepped (2 db per step) 100K attenuator, John also sells this kit. Next in line is the Aikido Cathode Follower board with 6BQ7ís. This ACF buffer will drive anything and everything with authority, none of that weak passive preamp sound. With this setup there is still 18 to 20 db of headroom in the stepped attenuator.

B+ voltage?
Remember that the 6DJ8 has a listed maximum plate voltage of 135. Try what you like. Also remember that in the Tetra there will be full B+ voltage at the plate until the heater is hot.

Soft Start?
I use GE Sensing inrush limiters on the primary side of both the heater transformer and the B+ transformer. For small signal stages like this RIAA preamplifier I like a separate heater transformer to keep the SS switching induced high current spikes out of the B+ voltage.

DT
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Old 29th April 2012, 10:21 PM   #5
jpk9876 is offline jpk9876  United States
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Thanks for the comments / suggestions.
Auto delaying the B+ seems challenging, as time delay relays seem rather expensive? Iím also thinking of adding the Akido line stage for a complete preamp?
I forgot about the inrush current limiters, I may use those this time.
I did buy all the parts from John, which should be a very good starting point! Also, I have the PS-1 for it. C16 seems rather large in the 3 terminal adj. to ground, 1kuf, does this ramp up the voltage? Or does it do something else?

If I do the Akido line stage, Iím thinking about using 6CG7 as I have a modest stash of them along with 6DJ8 / 6922. First stage of the Tetra Iím looking at 6922 and it does sound like I may be better using a 12AX7/12AT7 in the second phono stage for improved sonics? Iíll have to see what I have in the 12xxx series?
Wouldnít the volume control be between the Phono out and line in? Would there still be too much gain? Should I start with 2 6922ís in the Tetra?
Thanks,
JP
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Old 14th June 2012, 09:55 AM   #6
rajucc is offline rajucc  India
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I am a newbie .This is my first tube based DIY project, I am attempting to build a Tetra Sans PS Preamp. But confused with some parts value. My tube config are first stage is 6922 and senond stage is 12AT7.Please suggest correct value of following parts. R12, R11, R18, R14, R16, C17, C18, D1, D2.
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Old 14th June 2012, 05:37 PM   #7
cjkpkg is offline cjkpkg  United States
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Quote:
Originally Posted by rajucc View Post
I am a newbie .This is my first tube based DIY project, I am attempting to build a Tetra Sans PS Preamp. But confused with some parts value. My tube config are first stage is 6922 and senond stage is 12AT7.Please suggest correct value of following parts. R12, R11, R18, R14, R16, C17, C18, D1, D2.
Sketch out what each resistor is and for which tube and we can help more...JB's manuals can be inconsistent with the resistor and cap positions.

I ended up putting in some nice new issue EH 6cg7's in mine and went to Solen coupling caps and output caps and it sounds much better than with the WIMA's.

The orange drops are still doing RIAA duty. With a few more hours on it and I might be tempted to use Auricaps for the RIAA network or something along those lines.

Also, I am using the positive feedback scheme so no cathode capacitors are used. I like the sound and it also reduces gain a little.
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Old 14th June 2012, 05:42 PM   #8
rajucc is offline rajucc  India
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Value of C17,C18,D1,D2 not found in JB manual. R11 is the second stage grid resistor I think it is 1M but typical part value suggested by JB is 47k very confusing.

Last edited by rajucc; 14th June 2012 at 05:48 PM.
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Old 14th June 2012, 05:49 PM   #9
rajucc is offline rajucc  India
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Please suggest proper power transformer for Tetra Sans PS.
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Old 14th June 2012, 05:55 PM   #10
cjkpkg is offline cjkpkg  United States
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If you can sketch out the tube schematic and label the positions you are not sure about and take a pic of the board that would help us.

I am not at home so I can not reference my board at the moment.

For example...this JPG is from the tetra all in one manual that you can download...the values will be labeled differently than the Sans PS...
Attached Images
File Type: jpg tetra.JPG (92.5 KB, 234 views)
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