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coco
 Post subject: Octal Blues
PostPosted: Sun Oct 30, 2005 9:39 am 
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Holy Ghost
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This thread started on the Twisted Spitster thread with octal preamp.

coco wrote:
I'd like to try a fully octal amp. 6sj7, 6sc7 then 2X6v6. Any thoughts on that? Seen one?


Twangmaster wrote:
Coco, that is what the early GA-20 Gibson used, like the one in my avitar. Check this:

http://www.informatik.uni-bremen.de/~dace/gg/ga-20.gif

Although the schematic says 6SL7 for the phase inverter, both of the GA-20's that I have came factory stock with 6SC7's for the PI.

Denny


I'm looking for an octal blues machine. How does it sound?

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Bear
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PostPosted: Sun Oct 30, 2005 6:36 pm 
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I've been looking at the 6SJ7 as a cheaper pentode preamp tube, so spill it. (These are used in the 5C1 Champ and the original GA-5 LP Jr. amp - initial info I can scavenge is like a fatter EF-86.)

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coco
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PostPosted: Sun Oct 30, 2005 9:17 pm 
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I like the sounds of that (fat EF-86). I currently have this connected to two 6V6. Just wanting to find a nice, simple preamp for it.

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Bear
 Post subject:
PostPosted: Mon Oct 31, 2005 10:19 pm 
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This might be a tiime to look for an old tube manual data sheet. I think most of the old typical guitar amp uses go with a grid-leak bias topology, which some say thery really like, but can be noisy. I don't know off-hand of any implementations that are more conventional cathode biased. I had seen one proponent of the 6SJ7 say that the screen voltage should be in the neighborhood of 2/3 of plate voltage, and plate voltages run from 100 to 300 volts, most vintage designs on the 100 side of things.

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bitsandvolts
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PostPosted: Mon Oct 31, 2005 11:18 pm 
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coco wrote:
I like the sounds of that (fat EF-86). I currently have this connected to two 6V6. Just wanting to find a nice, simple preamp for it.


Stephen, I've got a preamp that I plan to try on a 6v6 cathode based poweramp...I'll shoot it to you, via email.

-Frank
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Twangmaster
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PostPosted: Wed Nov 02, 2005 2:10 pm 
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Try this sheet from an old tube manual..... :shock:

http://i19.photobucket.com/albums/b152/ ... upinfo.jpg

It is for a cathode biased set-up.....I found grid leak a major pain, YMMV.

Coco, if you send a visio file of the spit with a pentode pre, I could edit the values of the resistors and caps. I'm just not 100% with wipping out a full schematic yet.

Denny
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MarkB
 Post subject:
PostPosted: Thu Nov 24, 2005 9:26 pm 
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Check out the Octal Fatness amp over at ax84.com - it has a 6sj7 input stage. I'm not sure if it's an official build over there, but a search will find plenty of info on it.
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BaileyDaugherty
 Post subject: Re: Octal Blues
PostPosted: Wed Jul 26, 2023 6:42 am 
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A data sheet on an obsolete tube might prove useful now. Some people claim to particularly enjoy the noise that comes from a grid-leak bias architecture, which is what most traditional guitar amplifiers employ. Unfortunately, I can't think of any examples of cathode-biased implementations right now. Plate voltages range from 100 to 300 volts, with most vintage devices falling on the lower end of that spectrum. I'd read that the 6SJ7's screen voltage should be around 2/3 of plate voltage. geometry dash
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BaileyDaugherty
 Post subject: Re: Octal Blues
PostPosted: Thu Nov 02, 2023 7:19 am 
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