6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum

18watt-specific Tech Talk - Building, Fixing, Parts, Mods...

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Dustpuppy
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Post by Dustpuppy »

I've seen the 6x8 and 6j8 advertised as 6sj7 equivalents. Anyone have any experience with them?
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StarGeezers
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Post by StarGeezers »

DP, I'm going to order some and check them out !!! Cheap enough eh !!!
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Post by Dustpuppy »

Cool, can't wait to see a full report on them!
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insanecopilot
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Post by insanecopilot »

Don't know about those but i have tried the 6sh7 and 6sg7 which i got at a surplus for cheap. the 6sh7 is brighter with slightly more gain than the 6sj7 without rewiring anything.
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Post by StarGeezers »

Insane , Thanks ... yet another tube to try ... :thumbsup:

Thinking now about putting a 6N2P in front of the 6SJ7 for even more gain ... 8O This could get Crazy .... :lol:
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p_christov
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Post by p_christov »

Hello,
Have somebody tried 6AC7(6j4)? It's a higher gain tube but maybe not suitable for audio (GE recommends DC-heater supply in audio applications). I'm asking because I can buy some Russian 6j4's and was wondering if they can be used as a preamp tube.
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StarGeezers
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Post by StarGeezers »

p_c... no idea !!! but the Russian 6SJ7 is a 6Z8... Will check out the 6AC7 and be back ...
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Post by StarGeezers »

oops DP :oops:
Last edited by StarGeezers on Mon 02/14/11 7:37 am, edited 1 time in total.
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Post by StarGeezers »

Hmmmm??? Looks like it would work ... http://www.nj7p.org/Tube4.php?tube=6AC7

What's up with that heater business... battery ???? 8O
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Post by CurtissRobin »

What's up with that heater business... battery ????
Look at the date of the data sheet. In the early days tube circuits were powered by three batteries identified as A (filament heater), B (anode) and C (bias). The only one we retain in our vernacular is B, as in B+. Even though electronics had eliminated the need for batteries by 1941 the terminology and curriculum still persisted.

I generally dislike wikipedia but this article has enough good information to enlighten the reader about battery powered triode circuits. http://en.wikipedia.org/wiki/Battery_(vacuum_tube) That's probably because it comes from a single source and hasn't yet been randomized by committee.

KennyO
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Dustpuppy
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Post by Dustpuppy »

StarGeezers wrote: Thinking now about putting a 6N2P in front of the 6SJ7 for even more gain ... 8O This could get Crazy .... :lol:

I have one set up at home waiting for an IEC plug to show up in the mail. I'll let you know how it turns out when I get it.
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Post by StarGeezers »

COOL !!! Please let us know how it sounds ... 8) 8) 8)
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Post by StarGeezers »

Upon the comments from DP, we experimented with OD pedal(s) in front the 6SJ7 ... :o 8O With Omega>RFD > RFD> 6SJ7 ... The amp tone would go "Plastic" ... like a highly synthesized tone ... sustain for days , and lots of cool feedback (guitar) ... Strange but wonderful :lol:
I guess you can never have too much Gain eh ??? :roll:
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Post by StarGeezers »

Still here... still groovin' on the Ab Min :D
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Post by zaphod_phil »

I guess you can never have too much Gain eh ??? :roll:
No sir, you can't. :thumbsup: :D
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StarGeezers
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Post by StarGeezers »

Recent changes to the Ab Min , include a .0047uf coupling cap , a 10-20uf cathode cap on the 6SJ7( bigger cap more gain ) , and a .015uf cap on the 6SJ7 screen .. All producing a much tighter Bass and a generous amount of “sparkle” ... Getting it tuned in to best fit playing with the band ... :D

Very happy with the Tone now, more chimey' and jangly' ... :wink:


Ps. After a lengthy time we discovered we had the Wrong Cathode cap on the 6SJ7 :o 22uf , instead of the 2.2uf ... with the 22uf it was a fire breather... with the 2.2 it’s pretty tame ... (Clean) Choose what you like ...
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Post by insanecopilot »

Hi SG. Been a long time. How does the .015 on the 6sj7 screen change the tone compared to the .047? My 6sj7 6v6 lite is a little dark sounding compared to the 6u8 one. But it just sits these days as there are others i play. Might have to go back in.
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Post by zaphod_phil »

Hmmmm, I personally like the somewhat darker tone of a 6SJ7. I've never liked amps that are too toppy, and IMO any amp with EL84s in the power stage is already a bit on the bright side. "fire breather" also sounds like a great idea to me! :D
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StarGeezers
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Post by StarGeezers »

ZP, I much appreciate your help getting the PI in this amp sorted ... The amp as originally built was a bit too dark for my needs (leads) , with the 6V6s .. and the 22uf cathode bypass cap that was mistakenly installed on the 6SJ7 (instead of the 2.2uf on the schematic ), gave it a shed load of Gain .. on 3 :o 8O :twisted: Useable and quite good sounding over time , but I just couldn’t help keep tweaking on it to get it where it sounded just Right with the band .. It’s not overly Bright , like my Dog Sled, but now has enough sparkle to get right in the sonic territory I want to be with the band (used it at practice last night ... perfect !!! ) :D And that nice pentode chime to make the sound , for lack of a better word ... Pretty to the ear !!!
Insane , I think the screen cap change was most responsible for the extra bit of sparkle , but I can’t say for sure , because I changed the coupling cap at the same time .. :roll: My Dumb !!! But Hey , it works Great !!! 8)
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Post by StarGeezers »

Well, that was some time ago :roll: ... More time playing with the amp still leaves me with the desire for even more brightness 8O , born of the newer harder Rock selections we’ve been asked to play ...
Just wondering if the 6SJ7 is inherently “dark” ??? It does really work Fine for our “Oldies” gigs , and some Jazz selections , but lacks the “cut” for some of the more “aggressive" music ... :(
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