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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 31 Oct 2015, 17:15 
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Joined: 30 Oct 2015, 07:44
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Hello all,

I'm collecting parts for the 4S Universal Tube Preamplifier and noticed that byt the schematics no ratings or requirements are shown for the two rectifiers. Anyone who has made this have any recommendations?


Thank you!


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PostPosted: 31 Oct 2015, 17:38 
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If using the one with solid state rectification, use UF4007 diodes. Otherwise use the 6CA4.

Hey Gio; Can we move this to the project thread. We already have two 4S Universal threads. We really don't need a third. :)

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PostPosted: 31 Oct 2015, 23:39 
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Suncalc wrote:
Can we move this to the project thread.

merged

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PostPosted: 01 Nov 2015, 09:26 
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Suncalc wrote:

Hey Gio; Can we move this to the project thread. We already have two 4S Universal threads. We really don't need a third. :)


Oh, I thought THIS is the main project thread. Maybe that is why there were no new posts here for several weeks until now.


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PostPosted: 01 Nov 2015, 13:22 
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Since this project was posted, several people have suggested that I post a version of this preamp for other tubes. There have been a lot of suggested tubes and, for various reasons, I had put this off for a long time. However, Chris65 gave me the suggestion recently that I post a version for the 6v equivalent dual triode tubes. These are the 6AU7, 6GU7, 6CG7, & 6AX7. The thing is, all these tubes will work in this preamp with the same circuit values. There is only one hitch; the heaters are 6.3v, can be up to 600mA, and don't use pin 9 in the 6.3v configuration. Here are the various basing diagrams.
Attachment:
basing diagram 2.jpg
So with a little rewiring of the tube socket, these tubes can be accommodated in this design with no other changes. Pursuant to the 600mA heater requirement, of course.

Here are the performance numbers for these tubes:
Attachment:
Variant Performance.png

Finally after looking at this, I thought that since the components are all the same, a simple DPDT switch could be added that would allow the preamp to be used with both sets of tubes. All that needs to be done is to switch pin 9 out and switch pin 5 from one side of the heater supply to the other in the 6**7 version. So here is what that switch wiring would look like.
Attachment:
Heater Switch s.jpg
When the switch is in the left hand position, the heater is wired for the 12A*7 family of tubes (i.e. pin 9 to one side of the heater and pins 4&5 to the other), and when the switch is in the right hand position, the heater is wired for the 6**7 series of tubes (i.e. pin 9 open and the heater applied to pins 4 and 5). Simple.

Now a single preamp can be used with the following tubes: 12AU7, 12AV7, 12AY7, 12AT7, 12AZ7, 12AX7, & 12BH7 in heater switch position 1 and 6GU7, 6AU7, 6CG7, 6FQ7 (electrically equivalent to the 6CG7), & 6AX7 in heater switch position 2. That's a total of 12 tubes in the same preamp without any circuit changes.

How's that for "Universal"? :beerchug: Well, what do people think?


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PostPosted: 01 Nov 2015, 19:06 
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The 12V versions work for me because often I use a 24V AC 1A wall wary. Then I uses two small bridge recs. One for HT after a step down tranni backwards and the other to a 12V regulator. DC on the filaments is unessecary but it allows me to control the voltage to the filaments. But there are 100 ways to skin a cat.

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PostPosted: 09 Nov 2015, 04:20 
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My project is nearly done. The power transformer coming from Edcore appears to be on delay, all else is complete. My IEC connector has a built in fuse holder and after reviewing this thread it seems I can't locate the recommended fuse size. Any recommendations?

Thank you,
Steph


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PostPosted: 09 Nov 2015, 08:40 
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I should have mentioned, I'm building this with the 6CA4 rectifier.

Thank you,


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PostPosted: 09 Nov 2015, 11:53 
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Steph wrote:
My IEC connector has a built in fuse holder and after reviewing this thread it seems I can't locate the recommended fuse size. Any recommendations?
By "size" I assume you mean "value". Fuse values should be based on the transformer used. If you are using the Edcor XPWR136 (my favorite for small tube pre-amps), then this is a 42.6VA unit. So figure the draw on the primary (42.6/120)=0.36 then add some margin for core losses and overall efficiency; 0.36x1.2=0.43 (20% margin). So go with a 1/2A slo-blow fuse. You could go with a 1A If you wanted lots of margin.

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PostPosted: 09 Nov 2015, 17:27 
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Sorry, I should have been more clear. I thank you for the info. The transformer I have on order is the XPR177.


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