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

[kleuck]

Minimalistic first stage that should work

[klingo]

Hi,
i once put a switch to A/B the 820R PI biasing resistor with a red LED...and it sounded good may be more voxish with the LED. finally the resistor stay in.

[kleuck]

Hi,
i once put a switch to A/B the 820R PI biasing resistor with a red LED...and it sounded good may be more voxish with the LED.

Because with less than 3mA idle current, the Led still exhibits an internal resistance, therefore creates a local NFB.
And the bias point (anode) was a little high.

[StarGeezers]

Andre , Thanks !!! I went back over the L2B schematic and sorta' understand what's going on now...
Sorry,l I lied !!! (unintentionally ,of course) I do have a Tweed tone control ,wired on the pots , not shown on the schematic... My Bad..
Kleuck, Thanks for the drawing!!!That IS nice and simple!!!
Klingo, find when I put something on a switch ,it usually requires a decision, a choice of what we like best ... I'm starting to really like Bigbecks idea of using this stuff on jumper wires for testing... solder in what works/sounds best...

[kyoungsteadt]

Geezer,

IMO you just need one input jack with the 12AX7 set up as a parallel gain stage. Wire the rest up like the schemo and let there be ROCK!

[zaphod_phil]

i once put a switch to A/B the 820R PI biasing resistor with a red LED...and it sounded good may be more voxish with the LED. finally the resistor stay in.

Since resistive biasing works well in this kind of preamp stage, I honestly don't see a reason for using LED biasing. Now, if it was a bass amp, it could make a lot of sense.

[klingo]

IMO you just need one input jack with the 12AX7 set up as a parallel gain stage. Wire the rest up like the schemo and let there be ROCK!

Yes, the classic parallel input gain stage rocks with EL84....and the pentode input stage not a bad idea with lesser amplification factor tubes like 6V6.

[kleuck]

Since resistive biasing works well in this kind of preamp stage, I honestly don't see a reason for using LED biasing. Now, if it was a bass amp, it could make a lot of sense.

Perhaps to get rid of one cap and one resistor ?
To experiment a little rather than clone always the same schematic ?
I don't understand why it should be best with a Bass amp ?
Because of the lower gain ?

[StarGeezers]

It would be simple to just stick one in there and see how it sounds..the benefit of P2P building...with all the experimenting going on around here,somebody's just gotta' try it...schmaybe' a Bass player???
The Pentode preamp does really sound nice with the JJ 6V6s

I currently have a 5751 in the PI...I LIKE it!!!

[kyoungsteadt]

what do you like about the 5751 in the PI?

[zaphod_phil]

Perhaps to get rid of one cap and one resistor ? To experiment a little rather than clone always the same schematic ? I don't understand why it should be best with a Bass amp ? Because of the lower gain ?

The LED bias will give an excellent low frequency response, plus the reduced gain, along with the NFB are also likely to be beneficial. In a Marshall 18W type guitar amp, we are trying to squeeze all the gain we can from just a few stages, so LED biasing is less likely to be helpful. It's still fun to experiment with these things of course.

[StarGeezers]

Enough of this cutting the gain business... We keep playing ours and are still EXTREMELY HAPPY!!! We only have been able to detect one problem ....It's too Free Ken LOUD!!!! Great in our largish' club gig, but for small clubs,"bedroom"practice or rehearsal in my studio...forget it, by the time we get it into the dirt (on 4) all the other equiptment is blown over, band deaf... It just seems so much Louder than many amps we've had at twice the power+...I LOVE it!!!
Getting used to the Insane gain now . Hey ZP, Gain is Good !!!
Controlling same with the guitar V pot as KY suggested...FUN!!!

[kyoungsteadt]

Geezer,

The amp you are talking about is a low gain amp . Plenty of gain for your uses though.

[cGil]

Hey Stargeezer, try this switch

http://www.18watt.com/modules.php?name= ... 58&start=0

In half power power mode, it sounds the same, it just tames the output a little bit, and probably just enough for those gigs where a full power 18watt is too much. In 1/4 power mode, it may as well be a Junior as the power tube distortion thickens up like an SE amp, and it's about as loud. Maybe a tiny bit louder. Anyway, it's well worth the effort and the price of a switch.

Gil...

[klingo]

+1 on the 1/4 switch

Pros:
-cheap
-easy
-no bad sound out of it
-mismatched tube is less an issue

Cons:
-you loose a hint of grind ( it may be my ears less overdrived)
-only ~6db power reduction, you will hear it but the rest of the band won't

If you have enough room in your chassis try it.

[StarGeezers]

KY, if this is a low gain amp , I'd be really scared to see a high gain one ... Really scared...
CGil , Thanks !!! The benefit of having so many amps now,Thanks to you guys, is that we can make them "gig-specific"...For the smaller gigs and rehersal , we can use the P2P VJr or the O1s...(not so crazy LOUD), for the bigger gigs we'll just use this one ..
That switch idea is pretty Cool though!!!
Klingo , got Plenty of room ...may have to give it a go...

[zaphod_phil]

+1 on the 1/4 switch.....
-you loose a hint of grind ( it may be my ears less overdrived)

Personally, I would recommend using a VVR, so you can reduce the volume to almost any level you want, and without losing any grind....

[klingo]

-no bad sound out of it

-you loose a hint of grind

so sorry Phil, i really apologise for this antagonism

don't touch to the grind

just kidding or trying to in a foreign language

[zaphod_phil]

don't touch the grind

The grind is sacred!

What would the word "grind" mean to a French speaker, I wonder.... Would "growl" be better to use...?

[GUITARmole]

So is the 1/4 power switch worth it then or does it screw up the tone too much?

Also, does the 1/2 power option provide enough of a volume cut to make it worth adding it to a simple build??