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Old 27th July 2010, 12:23 PM   #41
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Here's the one I'm using:
Click the image to open in full size.
A lot of people here helped me with the circuit design.
I think removing the .047uF cap is the only change I've made.

Glenn
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Old 28th July 2010, 05:02 AM   #42
alexg is offline alexg  Philippines
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Quote:
Originally Posted by porkchop61 View Post
Here's the one I'm using:
Click the image to open in full size.
A lot of people here helped me with the circuit design.
I think removing the .047uF cap is the only change I've made.

Glenn
Hi Glenn,

I am planning on building this preamp, what is the diode for on the connected to the grid of the second triode?

How many ma across per tube (two triodes)?

Thanks.
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Old 28th July 2010, 12:39 PM   #43
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Hi Alex-
Read post #28 by Sy:
12AY7/6SN7 preamp PSU check

Current draw is the 5.6mA on the schematic (per tube).
The thread I posted above has all the questions I asked about the power supply for this preamp. It's been a while since I built this, so I don't remember what I wound-up with for total current draw from the PS.

Good luck
Glenn
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Old 28th July 2010, 01:14 PM   #44
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I found the PS schematic.
Note that the rest of the schematic is not current, so use the schematic in the previous post!!

Click the image to open in full size.
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Old 11th August 2010, 01:10 PM   #45
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You know, I should mention that this is not really a preamp. I think it has unity gain. The reason I use this is to give my CD's that tube sound.
I just thought I should clarify this.
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Old 11th August 2010, 01:58 PM   #46
Brit01 is offline Brit01  United Kingdom
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Quote:
You know, I should mention that this is not really a preamp. I think it has unity gain.
Trying to figure out why it is a unity gain config.

Common cathode followed by CF no?

Won't there be an amplification of ~20?

Please correct me if I'm wrong or not understanding something here.

If this provides no gain then maybe a better option to a CF between my cdp and ss power amp for that tube warmth.
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Old 11th August 2010, 08:27 PM   #47
piero7 is offline piero7  Italy
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Quote:
Originally Posted by vince76 View Post
hi guys,
I want to try this preamp (6sn7 version).
Can anyone suggest a schem for the PSU section?
I would go with a SS rectifier

V.
Use the Salas high voltage shunt regulator

Click the image to open in full size.

Simplistic Mosfet HV Shunt Regs post #1150
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Old 11th August 2010, 08:36 PM   #48
SY is offline SY  United States
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Quote:
Originally Posted by Brit01 View Post
Trying to figure out why it is a unity gain config.

Common cathode followed by CF no?

Won't there be an amplification of ~20?
Yes, it is. And no, more like about 10.

A well-designed cathode follower will NOT add warmth; it won't add anything. A poorly designed one could possibly give you excess 2nd harmonic distortion which you might perceive as warmth.
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Old 12th August 2010, 01:08 AM   #49
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Originally Posted by alexg View Post
I am planning on building this preamp, what is the diode for on the connected to the grid of the second triode?
It's a polarity protect diode that keeps the control grid from going positive during power up. It shouldn't really be necessary since 6SN7GTBs were designed for operation in Class *2, and the control grids were hardened and equipped with radiator "wings".

You could also avoid the diode by separating heater from DC power. Power up the heaters before turning on the HV DC, and positive grid voltage won't be a problem.

Otherwise, the diode adds a non-linear, voltage variable capacitance to Cgk. Not having nasty, non-linear, voltage variable capacitances is one of the advantages that hollow state has over solid state.
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