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Old 23rd August 2012, 06:35 AM   #1
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Default Help with this schematic? B+? B++?

Hey, i'm pretty new to building amps and other DIY electronics. I feel silly bringing this question to a forum with seasoned enthusiasts, but i did a fair amount of searching online but didn't find anything that was sufficient to help me.
this is the schematic i am dealing with:
http://i263.photobucket.com/albums/i...uitarAmp-1.gif

i don't understand what B+ and B++ are.
i found a site that explains B+
The Power Supply

but it doesn't make sense to me with the transformer shown in the schematic. and it doesn't state what the "++" one would be.

once again, sorry to clutter up the board with "noob" stuff, but could someone shed some light on this for me?

thanks for any help.
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Old 23rd August 2012, 06:41 AM   #2
Mooly is offline Mooly  United Kingdom
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They are different voltage rails. Look at the PSU section. B+ is after the rectifier. This is the main HT supply and can supply most current. B++ is fed from this via a resistor and another smoothing cap. It's a cleaner supply but able to supply less current.

B+ and B++ goes to the appropriate parts of the main circuit. Using the B++ rail which is "cleaner" to supply the first (low current) stages will result in less hum and noise.
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Old 23rd August 2012, 07:24 AM   #3
Enzo is offline Enzo  United States
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IT just indicates different B+ voltage points. ON some other schematic they could have called it B+a and B+b, or B+1 and B+2. SOme other schematic could have not even used the term B+ at all. They might label those points simply X and Y, and maybe Z if there was a third position. This circuit is fairly simple, on a more complex amp they might have five or six different B+ voltages, and each would get some sort of unique identifier label. So the next one might have been B+++. Don't read anything into the sysmbol itself, it doesn;t imply more positiveness or something, they could have used any symbol they wanted to.
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Old 23rd August 2012, 06:16 PM   #4
DF96 is offline DF96  England
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Isn't B++ a supply rail which goes 1V higher every time you switch on?
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Old 23rd August 2012, 06:47 PM   #5
wayne is offline wayne  United States
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B++ is just a filtered lower screen supply voltage for the 50C5 pentode.
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Old 23rd August 2012, 06:47 PM   #6
Sherman is offline Sherman  United States
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Quote:
Originally Posted by DF96 View Post
Isn't B++ a supply rail which goes 1V higher every time you switch on?


I like that, incrementing B+!!!
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Old 23rd August 2012, 07:05 PM   #7
DF96 is offline DF96  England
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Sorry, I used to be a C programmer many years ago.
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Old 23rd August 2012, 09:58 PM   #8
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Actually, you're right, and the term should be saved for a higher voltage, typically stacked on top of B+.

Thanks,
Chris
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Old 24th August 2012, 04:58 AM   #9
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thanks for the info.
is the resistor and smoothing cap that you spoke of between the B+ and B++ the one shown in the power supply (3.3k resistor and the polarized 220/160v capacitor)
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Old 24th August 2012, 06:16 AM   #10
Mooly is offline Mooly  United Kingdom
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The 3K3 in combination with the 47uf form a simple filter. Any noise on the main HT line (on the 220uf) is attenuated by these two components and appears less on the 47uf. The 3K3 value limits the current that can drawn however. You could add yet another R and C to the right of these and make a still cleaner rail and so on.
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