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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 30 Mar 2018, 22:58 
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Ok Mark. I've been doing some reading and some back of the envelope calculations. I now believe that the prohibitions about which I was reading in the data sheets apply primarily to oscillators and RF conditions. Examination of the transconductance curves leads me to believe that this tube can be used in a CCTA configuration, with fixed bias, without thermal runaway problems.

So the circuit will look something like this.
Attachment:
6J6 Preamp Fixed-Bias Schematic.jpg
Note that these component values are only preliminary at this time. I will need a few days to prototype and test to make sure it works ok. I also have a way to generate the bias voltages without the addition of much circuitry to a normal power supply.

I'll let you know when I have some test data to confirm my calculations.


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PostPosted: 30 Mar 2018, 23:50 
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Now we're cooking. Thanks.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 18 Apr 2018, 17:36 
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Grega wrote:
i did this over lunch too ;

Image

matt - better?
mark, sorry, what better to do over lunch (than eat) :D


Thanks a lot for that board layout. I understood a lot about the wiring

I am fully new to tubes and want to start with them.
As far as I understand 1 tube 12A*7 deals with both channels for stereo.
As I use balanced source and power amp, does 2 4S preamp do the job by using one per channel ?


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PostPosted: 18 Apr 2018, 22:21 
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I love my component to component wiring (better than point to point) but this board would make it so easy. Oh the dilemma.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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PostPosted: 18 Apr 2018, 22:26 
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Suncalc, any advances on the 6J6 preamp with fixed bias. I sold the PP headphone amp with the OPTs but fortunately it came with 5 X 6J6s and I managed to keep one.

I also received four ceramic B7 sockets. I'm hot to trot!

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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PostPosted: 19 Apr 2018, 04:20 
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Tostaki wrote:
Grega wrote:
i did this over lunch too ;

Image

matt - better?
mark, sorry, what better to do over lunch (than eat) :D


Thanks a lot for that board layout. I understood a lot about the wiring

I am fully new to tubes and want to start with them.
As far as I understand 1 tube 12A*7 deals with both channels for stereo.
As I use balanced source and power amp, does 2 4S preamp do the job by using one per channel ?


I had a first level of answer from Matt @ http://www.cascadetubes.com/the-univers ... ment-23130
Thanks to him. I understand I am not able to make a proper balanced preamp using such a design.

His suggestion is using a 6J6 tube as mixer at the input, using the 12A*7 tube as preamp followed by a Concertina phase splitter. As said at the link above, this is not anymore a 4S preamp.

As all cards are redistributed, I am open to any suggestion considering my newbie level with tubes


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PostPosted: 03 May 2018, 13:23 
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Joined: 31 Jan 2015, 17:59
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Hi, I built 6CG7 preamp.
6CG7 valve
B+ 285 volts
Rp 20K ohm
Rk 150 ohm
Rg 100 ohm
Output capacitor 2uF 400 volts
POT 20K input
What do you think?


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PostPosted: 29 Jun 2018, 09:30 
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Joined: 13 Jan 2018, 21:33
Posts: 80
Location: australia
tombethe wrote:
This is the latest and final version.
I have replaced some caps to allow different sizes and some tracks were changed a little.
Attachment:
Comp layout potless.gbr.png

The files will come soon.

Hi, i see several years have passed,but was this pcb ever made commercially available and is it still?

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PostPosted: 01 Aug 2018, 07:56 
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I'm about to build the MKII version of this tube preamp. This is where a suggestion was made early in the thread to make Rp 28K and Rk 800ohms. Matt believed it would produce very low distortion.

I built it as "The Black" and can remember thinking it sounded really excellent. It use a 12AU7 which is a tube I have come to respect in the 12A?7 series. And later using 12AT7s in my power amp driver stage with a 4SU schematic.

A preamp I built for a guy using the two stage cathode follower never really work for him producing a lot of hum in his system. Didn't do it mine but there seemed to be issue between his system and the preamp. So I have the preamp back.

I want to change the active section in the preamp "Lagoon" to a single stage tube pre and thought the MKII the way to go. What this post is about is the output caps.

I have some 0.68uf yellow high voltage caps which have a "MP" marking. Wiki-ing the marking claims the caps are Metalized Paper and oil. I'm cool with this and think the caps should be of quality and are close enough to the suggested 0.47uf cap to be a contender.

Can anyone else shed some light on these yellow MP caps. Good or bad sonically?

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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PostPosted: 04 Aug 2018, 22:32 
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The preamp - Lagoon- had a lot of noise issues. After stuffing around for two days I moved the earth from the pot to the RCAs to have most of the noise vanish. BUT before then I had built a 4S MKII. Most the preamp was built so it was just a case of making the preamp brd. Due to lack of room under the brd. I used a strip of veraboard or strip board. Wired the socket to the strips and mounted parts on top. It worked and worked very well. even looks sexy. A technique I may use in the future.

The caps are MP - metalised paper with oil I believe. Sounds OK.
Attachment:
P8053700 (800x600).jpg


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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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