6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum
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Man.... now you guys are making me wonder if I should just change out the EF86 preamp I have in my 18W for a 6U8. Bought a couple to put in another amp which I can't find the time to build, so they're just sitting there. Same valve socket, change the pentode/triode switch (which I never use) out for an interstage volume, and I'd be good to go. Gone off the EF86 stage quite a bit lately anyway. Mmmm.....
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Now here's an interesting idea ... having a triode in front of the 6SJ7 with a TMB between the two ... (Not Absolutely Minimum , but I guess we're not bothered with that any more )
Referring to the words of our Fearless Leader ZP ... " You can also place the triode and a TMB tone stack in front of the pentode, since the triode has a very low anode impedance suitable for directly driving low-impedance tone stacks.This also helps overdrive the pentode more, so you can enjoy more of those nice rich chimey harmonics. "
Very interesting , and a bit more gain to play with !!!!!!!
DP, anxious to see the pic...
Referring to the words of our Fearless Leader ZP ... " You can also place the triode and a TMB tone stack in front of the pentode, since the triode has a very low anode impedance suitable for directly driving low-impedance tone stacks.This also helps overdrive the pentode more, so you can enjoy more of those nice rich chimey harmonics. "
Very interesting , and a bit more gain to play with !!!!!!!
DP, anxious to see the pic...
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Ok, I finished the amp tonight. At first it was extremely clean and chimey at all volumes and the gain had no effect. I rechecked the wiring and found it was incorrect. I fixed that and it was louder with a little breakup with the gain. I had a 330uF voltage divider after the first 6c4 so I removed that and gave it a 2k cathode resistor. This thing rocks now. It is very chimey with the 5654 but lacks some of the 18 watt punch with the 6c4 PI. I'd like to find a hi MU 7 pin to put in there. the tone has a little bit of a muffled sound like the mids are a little low. I'll continue to tweak. All in all I'd call this a success. Definitely a different amp from the 18 pentode.
Here are some crappy iphone pics of the finished product.
http://s924.photobucket.com/albums/ad89 ... 20pentode/
Here are some crappy iphone pics of the finished product.
http://s924.photobucket.com/albums/ad89 ... 20pentode/
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Here you go bud, I'm pretty sure this is the as built.
http://i924.photobucket.com/albums/ad89 ... e/7pin.png
http://i924.photobucket.com/albums/ad89 ... e/7pin.png
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It's a very interesting design. Very original
I would like to hear it after you get it tweaked. The 18watt guru's might want you to move it to Watkins or something though. I have two Hammond ao29's i was planning to get to soon that have a couple of these 6c4's in them. That's why your design piqued my curiosity. good job though.
I would like to hear it after you get it tweaked. The 18watt guru's might want you to move it to Watkins or something though. I have two Hammond ao29's i was planning to get to soon that have a couple of these 6c4's in them. That's why your design piqued my curiosity. good job though.
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