Spark Gap: Unusual 9V Hybrid Valve Overdrive

[benl560]

let there be light!!!  i have power now.
let there be sound!!!  nope.

hay, im just happy for power at this point.  sitll could you check these numbers over for me?
here are the voltages on tl072.
1    7.83
2    7.83
3    7.83
4    0
5    7.82
6    7.84
7    7.84
8    7.81
9    7.84
10  7.84
11  8.30
12  7.83
13  7.83
14  7.78

thanks

[misterg]

let there be light!!!  i have power now.
let there be sound!!!  nope.

hay, im just happy for power at this point.  sitll could you check these numbers over for me?
here are the voltages on tl072.
1    7.83
2    7.83
3    7.83
4    0
5    7.82
6    7.84
7    7.84
8    7.81
9    7.84
10  7.84
11  8.30
12  7.83
13  7.83
14  7.78

thanks

Nope. Something very wrong. Where is the -ve lead of your volt meter? Pin 4 should be ~9V (8.xx would be OK), Pin 11 should be 0V - these are the supply to the TL074. Either you've installed the chip backwards, your meter is backwards, or your power supply is  (It should be centre -ve for this circuit.)

The large areas of copper on the PCB should be 0V.

Pics??

Andy

[benl560]

you've installed the chip backwards

yep. i must have been drunk when i assembled this one
i installed the f...ng socket backwards!!! so....i installed the chip backwards. glad that i usually order 2 of things like that.  feeling like a moron, but i really appreciate the help in making me realize these little blunders!
one question though...
what effect do the caps C4 and C6 have on the circuit?
i have tons of volume. as in unity volume is about a quarter of a turn, and C4 is the only sub i made.
although it does overdrive the crap out of my amp...
anyway, thanks

Through Google Shopping search, I found the 6AL5 available from Triode Electronics, as well as a bunch of eBay listings. Where did you get yours?

thats where i got mine. it was something like 16 bones shipped for 2 tubes and sockets. if you get the pc mount sockets(maybe the others too), you will have to CAREFULLY drill the center out and CAREFULLY glue/epoxy the two piecs together to get the cool led thing. also you may have to dremel the pins or make large holes.

[misterg]

i must have been drunk when i assembled this one

Glad you sorted it 

what effect do the caps C4 and C6 have on the circuit?
i have tons of volume. as in unity volume is about a quarter of a turn, and C4 is the only sub i made.
although it does overdrive the crap out of my amp...

C4 & C6 (& other components) mainly determine the frequency reponse of each clipping section, rather than overall gain (what did you sub C4 with?) . There is plenty of gain available - unity gain on mine is about 2:00 with a log pot in the P3 position - that could well correspond to 10:00 or 11:00 if you have a lin pot for P3. If your gain seems hgher than this, check the connections to the valves, as they're supposed to limit the gain by clipping.

Andy

[majornoob]

Could someone post easy to find equivalent transistors? I found relatively good ones for the two bc's but I'm stumped as to the bd 437.
Thanks

[PRR]

The BC327 and BC337 may be any PNP NPN pair, such as 2N3906 2N3904.

The BD437 may be "any NPN" except it MUST be physically large.

The BD437 is TO-126, the plastic body is 0.3" by 0.4". That's just about big enough, but Merlin added a bolt to spread the heat. DigiKey has thousands of BD437 under a buck each.

An alternate which may be at Radio Shed is PN3055 (plastic 2N3055). This is in the larger TO-220 package, does not need any heatsink in this use, but you may have to squeeze the outer legs to fit the holes.

[merlinb]

I'm stumped as to the bd 437.

The BD433 and BD435 are the same as the 437( except for voltage ratings, but they're way beyond pedal requirements), so you can also look up those numbers.

In my first prototype I actually used a BC337! It worked, but it got pretty hot, so I swapped it for a larger package transistor just for peace of mind. As PRR said, any NPN in a big package should work.

[merlinb]

Here's a very dirty sound clip. LP into a home made 18watt and 4x8 cab, SM58 into sound card. Practice volume. No processing.

First is the bypassed sound, then with gain pots at about 3/10. Then with both gains close to max.
Then I switch two of them in series at max gain (but unity volume), just for fun!

www.freewebs.com/valvewizard2/SparlGapMixdown.mp3

(If it tries to redirect you back to this page, just cut and paste the URL into the browser instead)

[joelap]

Amazingly cool pedal and refreshingly original idea.  LOVE the blue LED backlit tubes!  So cool.  If only I can get around to putting my bench together at my new place so I have a space to build things these days...

Joe

[Joecool85]

Here's a very dirty sound clip. LP into a home made 18watt and 4x8 cab, SM58 into sound card. Practice volume. No processing.

First is the bypassed sound, then with gain pots at about 3/10. Then with both gains close to max.
Then I switch two of them in series at max gain (but unity volume), just for fun!

www.freewebs.com/valvewizard2/SparlGapMixdown.mp3

(If it tries to redirect you back to this page, just cut and paste the URL into the browser instead)

You should have finished the intro to "Sweet Child O' Mine" !

[benl560]

what did you sub C4 with?

100pf.

i used log pots throughout. unity gain on mine is about 9 oclock. i guess the tolerance difference could account for some of this... either way it sounds good.
i guess it dosnt really matter to me too much because i can always turn it up 

[danielzink]

My Spark Gap - an homage to the designer.....

I did modify the layout a bit - I used off board pots so I elminated the dummy pad for the pots.

Definitely have a bit of hum...using a Voodoo power supply - so it should be clean power...not sure where to start tracking it down at. Please take a look and be kind..

Thanks !

Dan

[Ben N]

Hmmm... I seem to recall having seen a mess of submini diodes out there for cheap. Some of them might go nicely with this project.

[amptramp]

If you are getting hum, are you running DC on the heaters?  The 6AL5 takes 6.3 volts at 0.3 amps and you appear (from the view of the printed circuit board) to be running them in series.  This is a bigger load than most pedals require, so make sure the filtering is good.  If you are running AC on the heaters, lift the connections off the board.

[merlinb]

My Spark Gap - an homage to the designer.....

Definitely have a bit of hum...using a Voodoo power supply - so it should be clean power...not sure where to start tracking it down at. Please take a look and be kind..

That looks smegging amazing!

The Voodoo supply appears to be rated for 250mA max, and this pedal needs 250 to 260mA, so your PSU may be struggling.  Suggest trying a 300 - 500mA power supply.

[CynicalMan]

Just posting here to confirm that 6BJ7 tubes work as clipping diodes. I used a 16 ohm 10W resistor in series with the heater for 3.7V at the heater, and I got clipping at 0.6-0.8V. Since they are triple diodes, you could use two of them here and have assymetrical clipping, or you could double up the diodes in the second stage like the Crank.

[Steben]

This needs to be tested in a clippeer to ground !!! 

Would make a true OCD - killer.....

[juansolo]

Wizard's Sleeve

Continuing the wizard theme





Untidy insides galore... I seem to be going through a scruffy phase in that respect.

[sgmezei]

Man that thing looks Great. That picture is really creepy to me hahaha. I wanna hear it!!

Scott

[merlinb]

Wizard's Sleeve
Continuing the wizard theme

Amazing! I'm even reading Unseen Academicals at the moment! Is that just printed onto transparency and then lacquered on?