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Old 15th October 2010, 10:02 PM   #1
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Default How will this affect my amp?

I'm in the planning and parts ordering stage of my first amp, it's based on a GEC 912 amplifier. Here are the schematics:
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The transformer that I have is rated at 375 volts, but according to the duncan power supply designer software, after the the rectifier it will only supply 289 volts. The schematic shows the high voltage line at 350 volts. How would the reduced voltage affect the amplifier, and is there something I can do to compensate for it?
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Old 15th October 2010, 10:39 PM   #2
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Which rectifier will u use, and how many ma gives the transformer? It's too big voltage drop!
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Old 15th October 2010, 10:49 PM   #3
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Originally Posted by radiostar View Post
Which rectifier will u use, and how many ma gives the transformer? It's too big voltage drop!
The transformer is rated at 110mA and I'm using a 5Y3GT rectifier
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Old 15th October 2010, 11:00 PM   #4
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Hi mossmamc,

This valve line-up is the same as Gingertubes' Baby Huey and requires about 200ma for a stereo amp.
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Old 15th October 2010, 11:01 PM   #5
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The valve rectifier will have a significant voltage drop, and C11 (the reservoir cap) is quite small at 8uF so there will be a big ripple voltage at this point, which will depress the average value. Better to design a modern power supply which will supply the amp's needs. We have access to bigger capacitors than they had in the 1950s.
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Old 15th October 2010, 11:05 PM   #6
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Originally Posted by Soonerorlater View Post
Hi mossmamc,

This valve line-up is the same as Gingertubes' Baby Huey and requires about 200ma for a stereo amp.
I'm only building a mono amp.
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Old 15th October 2010, 11:09 PM   #7
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Originally Posted by DF96 View Post
The valve rectifier will have a significant voltage drop, and C11 (the reservoir cap) is quite small at 8uF so there will be a big ripple voltage at this point, which will depress the average value. Better to design a modern power supply which will supply the amp's needs. We have access to bigger capacitors than they had in the 1950s.
What do you mean by this? I've never designed a power supply before, so I could use some direction.
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Old 15th October 2010, 11:54 PM   #8
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Quote:
Originally Posted by mossmamc View Post
I'm only building a mono amp.
Ah, looks like you're building a guitar amp. It would help to point that out, most people assume hifi unless otherwise told.

A 5Y3 and small caps are probably what you want; they'll get you a vintage sound with plenty of sag.

First thing: did you model the whole PS in PSUDII? You should be modeling the transformer, 5Y3, 8 uF, choke, 16 uF, rough 100 mA load, 10K, 8 uF, rough 5 mA load. Then check voltages and ripples at the current taps to see what those look like.
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Old 16th October 2010, 12:05 AM   #9
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I always found this site to be helpful


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Old 16th October 2010, 12:37 AM   #10
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Quote:
Originally Posted by leadbelly View Post
Ah, looks like you're building a guitar amp. It would help to point that out, most people assume hifi unless otherwise told.

A 5Y3 and small caps are probably what you want; they'll get you a vintage sound with plenty of sag.

First thing: did you model the whole PS in PSUDII? You should be modeling the transformer, 5Y3, 8 uF, choke, 16 uF, rough 100 mA load, 10K, 8 uF, rough 5 mA load. Then check voltages and ripples at the current taps to see what those look like.
No, the intended use is as a hifi amp, but I only want to build a monoblock amp and then build a second one later.
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