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New Project Coming for Diyers who like Triodes [message #88786]

Fri, 07 September 2018 16:46

gofar99
Messages: 1949
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi Everyone, I'm in the building process for a class A push-pull triode amp using 6AS7s. Target is 10 watts. It might deliver as much as 14-15 though. I'm waiting on transformers right now. I hope to post the info in about 4-6 weeks. I hear from good sources that the 6AS7 is a really nice tube and makes really nice sounding amps. We shall see. This particular amp is actually a hybrid with a digital front end and remote control. It does have the option to operate directly from a line stage though.

For those of you not familiar with the tube it is a dual triode. Low (under 250) voltage, high current (about 125ma each triode) low gain (2 ugh!) and has a dissipation of 13 watts per triode octal tube. Definitely a different thing for me since most of my designs are running about 450VDC.

Good Listening
Bruce

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Re: New Project Coming for Diyers who like Triodes [message #88787 is a reply to message #88786]

Fri, 07 September 2018 17:12

Wayne Parham
Messages: 18789
Registered: January 2001

Illuminati (33rd Degree)

Wow, Bruce, that's exciting news! Can't wait to see your next post about this new design!

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Re: New Project Coming for Diyers who like Triodes [message #88796 is a reply to message #88786]

Sat, 08 September 2018 14:13

johnnycamp5
Messages: 354
Registered: June 2015
Location: NJ

Grand Master

Awesome!

So its SRPP....like your other amplifier designs?

I built your mono blocks "kt88's" and they serve as my everyday amps. I've never had anything better for my taste.

All my other amps sit on standby lol.

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Re: New Project Coming for Diyers who like Triodes [message #88798 is a reply to message #88796]

Sat, 08 September 2018 16:01

gofar99
Messages: 1949
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi, Yes it does use a SRPP driver. I'm glad you like the KT88 amps. The configuration has proved quite well for over 10 years now. They are not the most powerful amps as all class A U/L amps are pretty inefficient, but IMO they sound far better than many others that have different designs and are seeking more power output.

Good Listening
Bruce

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Re: New Project Coming for Diyers who like Triodes [message #88927 is a reply to message #88798]

Tue, 02 October 2018 21:25

gofar99
Messages: 1949
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi, I hope no one was holding their breath on this one...essentially it is a bust. Yes the concept works....no it doesn't do what is needed. The problem is with the 6AS7 itself. A nice push-pull amp can be made. The problem is drive voltage. One running at 250 B+ with about 50ma per triode needs...get this (from Sveltena) 250 volts peak to peak to deliver about 10 watts. Ouch. They make an audio grade version of the tube BTW. The B+ and current is easy, 250 volts of signal drive isn't. The most logical way I can see doing this is with an interstage trannie. A healthy driver something like maybe a 6V6, EL84 etc with a step up ratio of at least 3 to 1. All in all though it defeats the constant current source in the cathodes and SRPP driver stage. Back to a pretty much conventional design. I have not decided if I want to go that way or not just yet.

Good Listening
Bruce

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Re: New Project Coming for Diyers who like Triodes [message #88928 is a reply to message #88927]

Wed, 03 October 2018 09:08

Wayne Parham
Messages: 18789
Registered: January 2001

Illuminati (33rd Degree)

Gotcha, I understand. I remember your first post said 6AS7 gain was 2x.

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Re: New Project Coming for Diyers who like Triodes [message #88934 is a reply to message #88928]

Thu, 04 October 2018 16:21

gofar99
Messages: 1949
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi, I have not given up yet. I just need to rethink the amp.

Good Listening
Bruce

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Re: New Project Coming for Diyers who like Triodes [message #90794 is a reply to message #88934]

Thu, 15 August 2019 22:42

Porter
Messages: 77
Registered: December 2018

Viscount

I know this is an old thread, but did anything ever come of this? Did you figure out an alternative or was the project not workable in the long run?

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Re: New Project Coming for Diyers who like Triodes [message #90795 is a reply to message #90794]

Fri, 16 August 2019 21:24

gofar99
Messages: 1949
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi, Not as old as some. Anyhow it did not perform as well as I would like so it is dead. My various designs using pentodes had better sound and fewer issues. I made four, one SE, one P-P with small triodes and two with 6AS7s. None could match the sound quality of the pentode ones. All needed a lot more gain and drive and put out less sound.

Good Listening
Bruce

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