6418 Sub Mini Tube OD

[tranceracer]

There was some interest in this little overdrive pedal so I finally did a little sound demo/video.





The tone is very dry no amp or cabinet sims.  Guitar straight into the mixing board into the recording PC.  All tone settings are flat.

http://s215.photobucket.com/albums/cc70/tr-stompboxes/axe-boxes/?action=view&current=6418TubePreDemo.flv

These tube are very microphonic and ring if they are tapped or chassis is jarred.  It has a nice kind of starved tube sound.

[Renegadrian]

Aron, I believe you should change the name of the forum - another couple of tube related topics-schems and it should be called DIYTUBESTOMPBOXES.COM!  <---Sorry for being green and stupid...

[chi_boy]

I know you're kidding about the name change, but a sub forum might not be a bad idea. I want to try my hand at some of this mini tube stuff, but it is a little hard to keep up. A sub forum could really help organize and grow the efforts.

[Renegadrian]

Why not, it's not a bad idea!

[punkin]

I 've got to say +1 to that. different strokes for different folks and I for one eat this stuff up.

[Ripthorn]

That is a nice sounding box.  I agree that a sub forum would be nice, because tubes are what I am mostly into right now.

[frequencycentral]

Nice video, great chops too! Would love to see a schematic out of interest.

As for a sub-forum, I'm not so sure. I think it would take tube projects out of the public domain that is the main forum and into a less visited backwater. People would only come across the tube projects if they were specifically looking for them. So I'd vote against.

[aron]

The idea of a sub-forum is not a bad idea, except that for our purposes, building a tube pedal uses a lot of the same ideas as say a FET based pedal, except if you use high voltage. I've been trying to keep the forum from being too fragmented. Maybe a keyword TUBE in the subject title might be good enough at first. I will revisit this idea later if things take a different turn.

Thanks!

Aron

[snap]

poll:
http://www.diystompboxes.com/smfforum/index.php?topic=27501.0

[petemoore]

  Is this what you're looking for ?
  http://www.diystompboxes.com/smfforum/index.php?board=27.0
 

[tranceracer]

Nice video, great chops too! Would love to see a schematic out of interest.

Thanks!  I'll post the schemos soon.

It sounds MUCH better thru a reverb and a cab sim.  Maybe I'll make another demo of that.

As far as sub-forum... I like it the way it is one big happy family because I'm lazy and prefer to look in one area for my daily read.  I also think that there's not much difference in the design and building of tube stompbox effects and JFETs. 

But hey, that's just MHO, I'm cool w/ whatever the majority of the forum want's to do.   

[tranceracer]

finally found the link to the site that I built this from.  (lost link due to browser crash)

The power supply section on this schematic is interesting too.  It basicly brings the voltage down to 5V then a resistor to feed the heaters w/ 1.5V.  Very low power consumption and could probably run this thing off a battery for days.  But since the chassis was so tight on space I didn't put a battery in it.  It also has a low battery indicator!  This ckt cheats a little because there's a little booster BSN254A MOSFET to boost the signal.  I wanted to modify it to bypass the MOSFET and make it a pure tube but it sounds pretty good with it in I may just leave it how it is.  (if it ain't broke philosophy in play here!) 

Anyway enough of my babbling here's the link:
http://secure.oatleyelectronics.com/files/K270notes.pdf

More babble...
There's also another cool single tube preamp higher voltage feeding the tube 30V rather than 9V and has a lot more head room and very clean.  This one is also very microphonic.  Once I get it boxed up I'll post some clips.  So far it sounds really nice with accoustic guitar and rounds out the top end of the electric quite nicely w/ out distortion.  Almost like a mild compressor with very very mild overdrive.

Frequency Central, I think you'll be interested in this one because has a nice power supply section that feeds 30V to the tube.  Very quiet w/ 9V battery and w/ regulated PS.
http://secure.oatleyelectronics.com/files/K261notes.pdf

Maybe a keyword TUBE in the subject title might be good enough at first.
Aron

Most of the valvesters here already do this and I agree, "Tube" in the Subject, that's a great suggestion.

[Threefish]

Hi Tranceracer,

I know this is quite an old thread, but how is your OD different from the schematic of the K270 kit? I like the look of this kit. I can only see a volume pot on the schem and your box has two knobs - have you a second pot at the output for master volume? Is it a 1M pot to replace the 1M resistor at the output, or another value pot (and have you kept the 1M). Any other changes you made?

Thanks,

Reid.

[chris2002rocklin]

Is the schematic and or sound samples published anywhere?


I bought one of these and I am starting to build it today; http://www.oatleyelectronics.com/files/K270notes.pdf

I can let folks know how it sounds when I get it running.

[Threefish]

Ha! Mine arrived yesterday  Good luck with your build.
I might get to put it together sometime in the next week. I'll post my results anyway.

Have you listened to the sound sample at the link in the first post?
I'm guessing that all Tranceracer did differently from the schem that comes with the kit was put a 100k pot at the output, so that's what I'll start with.

[ozbird]

I bought one of these and I am starting to build it today; http://www.oatleyelectronics.com/files/K270notes.pdf

I can let folks know how it sounds when I get it running.

Bumping an old thread...

How did you get on with the K270 preamp?  I bought one recently, plus a couple of extra 6418 tubes.

I measured them using the tube matching circuit in the K301 RIAA preamp notes.  I didn't have an 820 ohm resistor,
so tried a 1k resistor first, then two 390/470 ohm resistors in series which gave me close to 1.2V for the filament.
Anyway, I found that two tubes gave a low current reading (23 and 33uA), and two a high reading (80 and 95uA.)

Any ideas on which tubes would be best to use?  I was going to keep two as spares, but I'd prefer to pick two for
the K270, and use the other two for something else instead.

Cheers!

[iccaros]

Hmm, so the test circuit is using 9v and the datasheet shows running 22.5 volts to get 240 uamps off the plate and 60 uamps off the grid.  but inferring from the 15v test in the datasheet your 80 and 95 are closer to to what the tubes should put out. So off hand, I would think that in terms of are the tubes good, the 23 and 33 are reading low and may be going bad.

but for your preamp purposes of the test, you want the closest two lower readings are 10uamps different while the higher are 15, which at first glance is your lower readings.  But I do not like the low readings compared to the datasheet.
I do not think in this design it make any real dirrence, and I would use the higher draw as they look "healthier",  plus the designer makes a point in stating for "Tube Purest" Which is kind of a slam to the HIFI community.
 



NOTE before I would call the two low emission tubes bad.. I would build the same circuit but use 15v, and use as close to 1.3K resistor for the heaters. you should read close to 100uamps +/- 10 - 20%, There are better designs to test this, but for a quick check, it would be my first attempt.

[ozbird]

Thanks, iccaros; I'll use the high current ones in the preamp, and keep the low current ones for experimentation.

[stomp_calderon]

Hi,

I also have some low emission tubes, what is a better circuit to test these things?

thanks