linear Low voltage tube project(pedal)

[iccaros]

hmm , May need... Gasp.... an opamp, Don't throw rocks.. to give a better input impedance.  Or someone way smarter than me.. But I have faith they are on this board.

[ThunderShowers]

Yeah, fiddling with volume knobs on the guitar, even a LITTLE, kills the Linear Booster...

[iccaros]

Yeah, fiddling with volume knobs on the guitar, even a LITTLE, kills the Linear Booster...

I don't have that issue with the les paul..

I turned up and down volume on the guitar in the video..


What are your voltage readings?

[iccaros]

ok so far the 6112 is a no go for this.. I can not get anything out of them.. I may have bad tubes.. but I will readjust tomorrow. 

[ThunderShowers]

pin 1 5.35
.9
0
0
9.45
9.45
5.34
5.17


I think the 1M r is too small of a input resistor for this circuit, because with it off, it gets worse.

[frequencycentral]

I never found 6112 to work well at low voltage.

[iccaros]

pin 1 5.35
.9
0
0
9.45
9.45
5.34
5.17


I think the 1M r is too small of a input resistor for this circuit, because with it off, it gets worse.

Ok I noticed.. I have a 1K from the input to pin 2.. Updated schematic..

Also Pin 5 should be ground (or pin 4)
and pin 8 should not be that high.. It is a cathode ...

Edit, I have been testing 6112, so I have to reconnect the power to the other..

[iccaros]

I never found 6112 to work well at low voltage.

I believe you.. Its specification is so close to a 12ax7 I just want it to work.. well really a 5751, but that also worked..

In this case the Grid seams to leak less giving me almost no negative voltage on with the pull up, unlike with the 12ax7 I get .6

I will have to build one of your 6112 designs to test the tube..

[ThunderShowers]

pin 1 5.35
.9
0
0
9.45
9.45
5.34
5.17


I think the 1M r is too small of a input resistor for this circuit, because with it off, it gets worse.

Ok I noticed.. I have a 1K from the input to pin 2.. Updated schematic..

Also Pin 5 should be ground (or pin 4)
and pin 8 should not be that high.. It is a cathode ...

Edit, I have been testing 6112, so I have to reconnect the power to the other..

Pine 4 is ground, pin five is 9v in.

Pin 8 is connected to ground (And output, as per your Schem.)

I'll look over this again sometime tomorrow.

[iccaros]

I got
5.37
(bad) something not right
0
12
0
12
5.39
5.29

so 8 is cool with voltage..

I hate bread board.. one time everything is good.. 10 min later things are off.  I would bet if you are using bread board, then your are getting capacitance that is causing issues.

I will have to leave this for tomorrow also..  Thanks for the help

[iccaros]

I never found 6112 to work well at low voltage.

I believe you.. Its specification is so close to a 12ax7 I just want it to work.. well really a 5751, but that also worked..

In this case the Grid seams to leak less giving me almost no negative voltage on with the pull up, unlike with the 12ax7 I get .6

I will have to build one of your 6112 designs to test the tube..

Ok for those following @ home,  I calculate the 6112 would need a ~1.3 meg pull up resistor to get -.2 volts on the gird. The 6112 has only .9ua of leak current compared to 9 ua for a 12ax7.  so 12.2 / .9*10^-6 = 1,355,556oms

[iccaros]

6111 no go.. I get signal but no boost..

So this is only good for 12XX7 series.

[amptramp]

It would be interesting to figure out the input impedance of this amplifier.  By pulling the grid positive, you have reduced the input impedance of the tube substantially as its grid is now conducting current.  It may be necessary when using 12 volts on the plate to get any conduction - otherwise, the contact potential from electrons hitting the grid would bias it negative and cut off the current.

[iccaros]

It could go the other way, we could bias it off the cathode, But would that change a lot, this is just like the valvecaster, low input impedance

[iccaros]

I have a butt ton.. of 2n222A... If I put one of those infront of this would that fix some of the impedance issues?

[iccaros]

It would be interesting to figure out the input impedance of this amplifier.  By pulling the grid positive, you have reduced the input impedance of the tube substantially as its grid is now conducting current.  It may be necessary when using 12 volts on the plate to get any conduction - otherwise, the contact potential from electrons hitting the grid would bias it negative and cut off the current.

according to the link I provided at says its 11K

[iccaros]

Ok ..
so I got submini tubes to work

Had to kill the pull up part, put a 150ohm resistor on the cathode pin (4) to give me -.4 on the grid
then instead of a 1m from pin 2 (grid) to ground, used a 120 ohm.. Still got a good clean linear boost,

Used the 5840 design Rick had..

A nice overdrive.. But I got the same with the valvecaster. So I am not sure the point.  I am going to try the 12ax7 to the 5840 and see what that does..

I can not get any audio from the 6112 @ all (any suggestions Rick on a way I can test these?) . I may have some bad tubes... Which would suck ... I expect to get something

Switching a 12u7 and 12AU7 farts out.. So that will take some adjustment..

Right now this sounds good to me with the 12AX7 and the 6AU6.. If I could find a modern replacement for the 6AU6 then this would be good to go.. I did pick up 3 for $5 off ebay..

[iccaros]

I am thinking of doing a cathode follower for both stages.. This should give me better input impedance... ?? opinions?

[iccaros]

Mini Version.. I hope I did not make any mistakes.. I think this sounds as good as my valvecaster @ 30 volts.. but more smooth.. The valvecaster seamed to be too harsh all the way up, to farty..

SkyHunter Mini...  where the name comes from.... ->

Now all Airborne units use this phrase..

Sound clips coming tomorrow.


thanks to Frequency Central For allowing me to build on his work..
Also to the reading from the valve wizard and Merlin Blencowe

[ThunderShowers]

Interesting thing to report: Mesa tubes seem to be less then liking this design; One tube outright refused to work, returned that one, the second one works, is clean - But barely adds anything.

So far, I'm getting good results out of long-mid plate tubes only (Ruby's work nicely.)