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

StarGeezers · Post by **StarGeezers** » Tue 10/28/08 7:27 am

National Red Special (i just love those Red tubes), Telefunken 12AX7 (old), and two JJ 6V6s... extremely short P2P wiring (see pics),minimum wires, sozos (they probably haven't "formed" yet, it can only get better), 125E wired 8K.....Sounds better LIVE ,where it counts,than any other amp I've Ever owned...VERY HAPPY!!!!!!!!!!!

it does look sorta' ..."plain"

ZP, built it exactly as the revised Mini schematic..except for Big's V divider, which I plan to try out...for gigging I can only turn it up to 3 out of 11, any more than that and I'd be doing heavy metal...never turn it up more than half way...too scary after that...

bigbeck · Post by **bigbeck** » Tue 10/28/08 4:22 pm

StarGeezers wrote:
ZP, built it exactly as the revised Mini schematic..except for Big's V divider, which I plan to try out...for gigging I can only turn it up to 3 out of 11, any more than that and I'd be doing heavy metal...never turn it up more than half way...too scary after that...

Have you tried the 330K or 220K gridleaks on the power tubes? The 220K voltage divider will take a little hair off the beast too

It will also make it a little less bright .

StarGeezers · Post by **StarGeezers** » Tue 10/28/08 5:00 pm

Big, the tone is so Good now, I'm somewhat afraid to mess with it...Through an open back speaker , it's bright and clear(not to be confused with clean), through my closed back 4/12 cab, it has a somewhat darker sound,and a little boominess on the extreme bass tones(it's the cab,all the amps do this on this particular cab), but really full Gutsy' tones ... changing this might affect this particular balance, allthough I could un do it if it sounded like

kyoungsteadt · Post by **kyoungsteadt** » Tue 10/28/08 5:22 pm

Geezer,

How about a final schemo as a recap? If it sounds really good now don't mess with it. Good job!

StarGeezers · Post by **StarGeezers** » Wed 10/29/08 7:43 am

KY, as far as I can tell..this is it...Oops !! File size has been reached

..It's the last posted schematic...
I just saw where sewatt just went down...again...lots of action over there...

kyoungsteadt · Post by **kyoungsteadt** » Wed 10/29/08 1:42 pm

The last schemo has BB's voltage divider in it.

StarGeezers · Post by **StarGeezers** » Wed 10/29/08 2:17 pm

Just an indication of Big's VD

Optional... not on mine ...yet

bigbeck · Post by **bigbeck** » Wed 10/29/08 7:24 pm

StarGeezers wrote:Just an indication of Big's VD

And you promised not to tell!

kyoungsteadt · Post by **kyoungsteadt** » Wed 10/29/08 9:34 pm

Geezer,

Sounds good without the voltage divider?

StarGeezers · Post by **StarGeezers** » Thu 10/30/08 7:15 am

Big ...Oops!!!

VD=voltage divider...

KY, better than anything I've EVER had.....Totally Free Ken HAPPY!!!!!!

May have to build another as a backup... exactly the same as this one... just can't think of doing without that TONE ....Spoiled!!!

StarGeezers · Post by **StarGeezers** » Thu 10/30/08 3:20 pm

OK, here's the amp as it exists right now....

kyoungsteadt · Post by **kyoungsteadt** » Fri 10/31/08 6:22 pm

Geezer,

Build a Lite IIb next. You'll love it.

kleuck · Post by **kleuck** » Fri 10/31/08 7:04 pm

With a pentode, you can't manage to have the minimum parts count.
I would go for a classical first stage, with a LEd cathodyne polarisation.

StarGeezers · Post by **StarGeezers** » Sat 11/01/08 8:48 am

Kleuck, "would you believe"..almost minimum... LEDs

Hmmmm???? how does it sound???
KY, what benefit of building the L2B??? This one sounds Super, and with no BS..Easy to make (even for me) and if I could figure out a smallish PI board , it would be even easier..

You guys got me "spoiled' with all those "simple" amps ... Tone

kleuck · Post by **kleuck** » Sat 11/01/08 4:51 pm

Kleuck, "would you believe"..almost minimum... LEDs icon_eek.gif Hmmmm???? how does it sound???

Just as good as with a resistor/capacitor bias, BUT, you need to provide a minimum idle current for the led to really behave as a 0 ohms (say a few ohms) component, my own tests seems to show a 5mA current as a good starting point..And you need to find a suitable bias point on a 1,6 volts line minimum (red led).
The bias point of the regular first stage of a 18 watts, and actually the 12AX7 are not really well suited for that, a 12AT7 or 12AY7 would be easier to use.
But the 12AY7 will provide less gain, and the 12AT7 according to ZP and others a somewhat "arsh" sound.
I think it would be a great idea to test with a 12AT7, as most of the time, when tested, these tubes are biased with the same idle current as are the 12AX7, though they are built to work with a lot more.
I'm not sure the harshness would still be an issue with a 2,5 mA or 5 mA idle current per triode.

I tested this trick with Fets, and my amp will use 6N3P.

Kleuck, "would you believe".

Looks like a joke, but i don't understand

StarGeezers · Post by **StarGeezers** » Sat 11/01/08 6:34 pm

Kleuck, you guys ever hear of Maxwell Smart ??? The American TV equivalent of Inspector Clouseau..sorta' (but there is no real comparison to Clouseau, of course)
That LED device is way over my head

, but I'll try to understand it better with more reading...like my jokes

kleuck · Post by **kleuck** » Sat 11/01/08 7:05 pm

Héhé !
I didn't know Maxwell Smart, but with the great Inspector Clouseau i understand more.
The led trick is very simple : the cathode resistor purpose is to generate a positive voltage between its terminals, wich is for the tube equivalent to the negative grid bias voltage (positive between cathode and ground, but negative between the grid -wich is grounded via the grid resistor- and the cathode)
With a Led, you can get the same (led direct voltage drop), minus a capacitor wich is useless as a conducting led is equivalent to a short-circuit regarding both DC and AC.
Useful in Hi-Fi (where gurus usually find that there is no good enough capacitor on earth

), when you want a great bass response without using a BIG capacitor (especially if your cathode resistor would be of low value), when you want a minimalistic design...the reason why i begun to try this trick.

If you want to see the work in progress : http://www.flickr.com/photos/kleuck/2992985145/sizes/l/ (B+ ~275 volts)

Great ideas here : http://www.diyparadise.com/simpleel84.html
A way to simply get rid of the Pi !!! Won't have the gain or sound like a 18 watts though.

kyoungsteadt · Post by **kyoungsteadt** » Sat 11/01/08 8:01 pm

Geezer,

I think you need to stick with the normal 18 watt PI. It has a lot to do with the sound of the amp in a positive way.

A Lite IIb is a little more work but not much and I think you would like the tone. Lots of people love these amps.

StarGeezers · Post by **StarGeezers** » Sun 11/02/08 7:08 am

KY, studied it thoroughly (the M.Huss drawing) L2B...not really too different than what I have now ...couple different values in the PI, and that dual input 12AX thingie' going on..What does that sound like ??? Just more/less gain eh??? Where do you get those input jacks ...?? or am I just reading it wrong..?

Don't care for those recto tubes, although some love em'...just another tube to feed ...hahahahaha

andrekp · Post by **andrekp** » Sun 11/02/08 10:56 am

Lite IIb sounds great 'Geezer. You might consider that it also adds a minimalist tone control to the package.

The input thing is so that one input just uses one side of the 12AX7 for low gain, the other input uses BOTH sides of the 12AX7 (but in parallel, not cascaded), for a little more gain. And if you plug into both at the same time, each input will use one side of the 12AX7. Gives you some options.

Plus, with your be-anything chassis, you could set it up for a third option of cascading the two sides of the pre-amp as well.

You can get the input jacks (Cliff jacks) from Hoffman, Mouser, wherever. If you REALLY want to be frugal (which I know you like) you could salvage those jacks off the old VJ boards. The have tabs, rather than solder lugs, but I suspect you could make that work for you.

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