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Old 27th April 2011, 01:21 AM   #1
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Default 6sl7 6sl7 dynaco driver board

Tried making a driver board for my dynaco stereo 70 and well it doesn't have much power.
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Old 27th April 2011, 01:35 AM   #2
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Looks like you forgot something.

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Old 27th April 2011, 01:40 AM   #3
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Ok? What?
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Old 27th April 2011, 01:55 AM   #4
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WAG is your driver stage doesn't have enough swing for the finals. Also, what's the scoop on the screen taps connected to the feedback loop? Hard to see the schem. (voltages etc.)

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Old 27th April 2011, 02:07 AM   #5
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A DC voltage map would help.
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Old 27th April 2011, 02:46 AM   #6
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Quote:
Originally Posted by vinylkid58 View Post
Also, what's the scoop on the screen taps connected to the feedback loop?
This was something Dynaco did to compensate for the imbalance in the primary of the output transformer.
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Old 27th April 2011, 03:46 AM   #7
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Ok, thanks.

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Old 27th April 2011, 11:21 AM   #8
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voltage map

input tube 6SL7

pin 1) 0

pin 2) 142vdc

pin 3) 1.262

pin 4) 0

pin 5) 142

pin 6) 1.244

pin 7 h

pin 8 h

6SN7

pin 1) 141vdc

pin 2) 194

pin 3) 141

pin 4) 141

pin 5) 194

pin 6) 141

pin 7) h

pin 8) h

power supply voltage feeding the 100k plate resistor (6sl7) is 277vdc

voltage feeding the 22K plate resistor on the 6sn7 is 331vdc
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Old 27th April 2011, 01:00 PM   #9
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You've only got 50V or so across the 6SN7. Not good. Get the B+ higher.

Morgan Jones reported that when he separated the supplies for the input voltage amp and split load inverter, he had some instability, so watch out for that. I might consider upping the B+, using it in common for the two stages, and increasing the 6SL7 plate resistor.

As you have it drawn, the feedback is quite low- this may or may not be what you want, but you should be aware of that.
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Old 27th April 2011, 03:00 PM   #10
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Just finish making some changes

Changed the input tubes 6SL7's plate resistors from 100K to 200K

Upped the power supply voltages from 331vdc to 387 and 277 to 342

Voltage map

6SL7

Pin 1) 0

pin 2) 115

pin 3) 1.24

pin 4) 0

pin 5) 117

pin 6) 1.23

pin7&8 heater

6SN7 voltages

pin 1) 115

pin 2) 267

pin 3) 120

pin 4) 117

pin 5) 265

pin 6) 122

pin 7&8 heater

Sounds a lot better now. Do I need more plate voltage on the 6SN7's?

Do you have suggestions for feedback?

This is my second try and designing a driver circuit.


Picture of my 6SL7/6SN7 driver board.

Picture of my 6SL7/6SL7 driver board.

The 6sl7/6sl7 has a 6sl7 input with a 6sl7 long tail. While it sounded very good I will make a change to the plate resistors on the input tube and see how it sounds.
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File Type: jpg 6sl7 6sl7 002.jpg (842.6 KB, 195 views)
File Type: jpg 6sl7 6sn7.jpg (814.1 KB, 160 views)

Last edited by Original Burnedfingers; 27th April 2011 at 03:08 PM.
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