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6sn7 alternative
6sn7 alternative
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Old 8th August 2009, 04:06 AM   #11
gary h is offline gary h  United States
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Default whoops

here's the schematic
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Old 8th August 2009, 04:30 AM   #12
kmtang is offline kmtang  Canada
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Default 7N7

6SN7 in Loctal base. It sounds really nice.

I use the 7N7's in all my amps and the 6SN7's are in boxes.

Get the 7N7's while they last.


Johnny
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Old 9th August 2009, 09:28 PM   #13
kevinkr is offline kevinkr  United States
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6sn7 alternative
Quote:
Originally posted by gary h
Kevin,

I think you and Wavebourn are right, I misunderstand how the anodes work in this circuit. I've attached a schematic of my Aikido PS which includes the heater bias. The audio circuit is JBs Aikido using 4 6sn7s in series. How would you lower the bias closer to the cathode voltage?

thanks

gary
Hi Gary,
Actually I was advocating for a higher, not lower voltage, so go from 70V to 100V, noting that the filament insulation is claimed to be not good for much more than this. (As an aside I do use 6SN7GTA or GTB in SRPP to drive 300B with 400V on the upper anode and I float the filaments for this tube at roughly 100-110V and have not had any failures in 10yrs due to doing this. ) I would change the 300K resistor to 220K in the filament supply bias circuit and see what happens.

I would recommend reducing the 330V to 300V as well on the theory that this will reduce the voltage on the upper cathode by 15V or so and might also help by reducing voltage stress between the filament and cathode in the upper triode of the pair.

One other question would be whether or not the board has grid stopper resistors present.

You don't leave it on continuously like some audiophiles I know, leading both to wasted power and shortened tube life. (?)
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Old 10th August 2009, 03:58 PM   #14
gary h is offline gary h  United States
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thanks Kevin,

I appreciate the help

gary
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Old 10th August 2009, 10:16 PM   #15
MARIANELA is offline MARIANELA  Argentina
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6CG7 IS IDENTICAL
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Old 10th August 2009, 11:19 PM   #16
DrewP is offline DrewP
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For what it's worth, just the same as not all 6SN7's are created equal, not all 6CG7's are the same.

We did some tube rolling a few years back on an MC phono stage with a range of 6CG7's and there was a pretty wide spread of difference in the way they sounded.
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Old 11th August 2009, 02:53 AM   #17
Geek is offline Geek
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Quote:
Originally posted by DrewP
We did some tube rolling a few years back on an MC phono stage with a range of 6CG7's and there was a pretty wide spread of difference in the way they sounded.
Same variation in 6SN7... I used to deal heavily with them a few years back.


Cheers!
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Old 11th August 2009, 10:21 AM   #18
Gordy is offline Gordy  United Kingdom
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Quote:
Originally posted by MARIANELA
6CG7 IS IDENTICAL
Quote:
Originally posted by DrewP
For what it's worth, just the same as not all 6SN7's are created equal, not all 6CG7's are the same.
We did some tube rolling a few years back on an MC phono stage with a range of 6CG7's and there was a pretty wide spread of difference in the way they sounded.
Quote:
Originally posted by Geek

Same variation in 6SN7... I used to deal heavily with them a few years back.
Cheers!
There is only one electrical specification for 6SN7, 6CG7, etc.. All 6SN7s are the same, all 6CG7s are the same, and 6SN7 and 6CG7 are functionally equivalent. The difference that you hear is based upon different MANUFACTURING TOLERANCES. Those that are manufactured exactly to the datasheet specification will perform differently to those manufactured at + 20 % tolerance.
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Old 11th August 2009, 07:31 PM   #19
sepolansky is offline sepolansky  United States
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Gary H,

If you are using a Broskie PCB laid out for octals and don't wish to go 9-pin, then the 6SN7 variants are probably the best sounding you'll find. However, many of the highly sought after and good sounding tubes either start out or with use do go microphonic. I have a pair of Sylvania VT-231s that do just that.

I use them in a line stage application (7mA, 150V per plate) and they sound just fine.

The thing that has worked for me are the Herbie's Damping Instruments. You might try them. See what you think. Cheaper than new tubes.

It can also help to mount the PCB onto a piece of acrylic, Delrin or maple (other woods may also work well). Use nylon standoffs, or hang the PCB from springs connected to standoffs using those little eyelets one uses to solder a conductor to a stud.

Good luck,

Stuart
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Old 11th August 2009, 07:50 PM   #20
Brit01 is offline Brit01  United Kingdom
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That's really cool Stuart.

I see you use red led bias there. How do you find that?

Are you using this for the input and output tubes so you have 1.7V on both?

I'm just beginning to implement this in my designs.
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