...and now, the "PentaDriver" 12 volt Pentode Overdrive using Submini 5672 tubes

[frequencycentral]

I'm pretty sure that a CV4092 (only 20ma current draw!) or VX9184 are equivalents - you should check the datasheets beforehand though. An Ebay seller I looked at was offering them both as equivalents to the 5672.

[frequencycentral]

A Note About The Heater Voltage and the LM317

It would appear that not all LM317's are equal.

Forumite Jered PM'ed me:

The minimum resistor I could use to get 1.254 volts to the heater was 237 ohms. If I use 100 ohm resistor I get .965 volts.

I did some checking on the LM317 datasheet - and Jered is right, the datasheet quotes 240 ohms.

BUT....................

I'm using an LM317T - which only requires a 100 ohm to achieve 1.25 volts.

SO......................

What I would suggest is this:

Build the voltage regulator first - test the output voltage before applying it to the tube heaters. If its not 1.25 volts (or thereabouts) tweak the resistor value until it is. The resistor could even be replaced with a 1K trimpot I guess.



I wasn't aware of this variance with different versions of the LM317.......Heyho - you learn something new every day !!

[frequencycentral]

Circuit board populated. Enclosure drilled. Graphic printed.

It's on the way!

[danielzink]

A Note About The Heater Voltage and the LM317

It would appear that not all LM317's are equal.

Forumite Jered PM'ed me:

The minimum resistor I could use to get 1.254 volts to the heater was 237 ohms. If I use 100 ohm resistor I get .965 volts.

I did some checking on the LM317 datasheet - and Jered is right, the datasheet quotes 240 ohms.

BUT....................

I'm using an LM317T - which only requires a 100 ohm to achieve 1.25 volts.

SO......................

What I would suggest is this:

Build the voltage regulator first - test the output voltage before applying it to the tube heaters. If its not 1.25 volts (or thereabouts) tweak the resistor value until it is. The resistor could even be replaced with a 1K trimpot I guess.



I wasn't aware of this variance with different versions of the LM317.......Heyho - you learn something new every day !!

I've got an LM7812 that I'm going to use to drop an 18v laptop computer supply down to 12v (for my PepperShredder) - the main difference between the LM7812 and LM317 is that the 317 is "adjustable" correct ?

Thanks, Dan

[frequencycentral]

I've got an LM7812 that I'm going to use to drop an 18v laptop computer supply down to 12v (for my PepperShredder) - the main difference between the LM7812 and LM317 is that the 317 is "adjustable" correct ?

Thanks, Dan

Hi Dan, yup that's correct. Have a look at the Subcaster schematic in the Valvecaster thread for how to set it up for a variable voltage: http://www.diystompboxes.com/smfforum/index.php?topic=63479.0

The LM317 data sheet is worth reading.

Handy to have one on your breadboard too, for dialing in different voltages.

[danielzink]

I've got an LM7812 that I'm going to use to drop an 18v laptop computer supply down to 12v (for my PepperShredder) - the main difference between the LM7812 and LM317 is that the 317 is "adjustable" correct ?

Thanks, Dan

Hi Dan, yup that's correct. Have a look at the Subcaster schematic in the Valvecaster thread for how to set it up for a variable voltage: http://www.diystompboxes.com/smfforum/index.php?topic=63479.0

The LM317 data sheet is worth reading.

Handy to have one on your breadboard too, for dialing in different voltages.

I guess my question is more along the lines of - do I have to use the 317 or will my 7812 suufice ?


Thanks, Dan

[Renegadrian]

You mean for the Pepper?? It works at 12v, so yes the 7812 works good.

[danielzink]

You mean for the Pepper?? It works at 12v, so yes the 7812 works good.

Thank you sir.

Dan

[Isaiah]

Ah, this looks cool!
Good timing as well, I'm in the planning/experimentation phase of building an 18V pentode pre-amp for my bass.

[frequencycentral]

Ah, this looks cool!
Good timing as well, I'm in the planning/experimentation phase of building an 18V pentode pre-amp for my bass.

Hey Isaiah, I'm in Coventry myself!

[Steben]

Hey Rick,
do I read this correct on the package: march '38? 

[frequencycentral]

Hey Rick,
do I read this correct on the package: march '38? 

No - they are from February and March 1958 - 'Valvo' - made in Hamburg.

[frequencycentral]

I'm in the final stages of building this circuit into a pedal and I would like some advice from you guys.

I'm using a 100K pot for the volume control at the moment. With the gain full up, the output of the circuit is MASSIVE.

I tried a 10K* volume pot, and with the gain at minimum (clean sound) and the volume at maximum there is unity between the bypassed and effected signals.

I still have to add a Valvecaster-like tone control, which will cut the volume a bit - but not that much.

What I'm thinking is this:

Do I keep the 100K volume control, so with the gain at minimum the pedal can be used as a clean boost (versatile) ?

or

Do I attenuate the overall output volume a little by using a 47K* or 22K*, which would make tweaking more meaningful with higher gain settings (but losing the clean boost ability) ?

At the moment, when using higher gain settings, the volume control has to be pretty low down (using the 100K pot) so it's quite sensitive. Lowering the pot value would make it less sensitive but also less versatile.

I'm erring towards just leaving as is (100K) - what do you guys think?


* Actually I'm just bridging lugs 1 and 3 of the 100K pot with a resistor of that value to make a 10K, 47K or 22K pot or whatever.

[Jimmy-H]

Hi Rick,

Maybe it's an option, to make a signal divider before the volume pot.
And make this switchable.
Low gain -----> OFF
High gain -----> ON
Just experiment with the values of the two resistors for the divider.

[frequencycentral]

Ok thanks Jimmy. I've reconsidered the matter and decided to use a 22K volume pot instead of the 100K.

Here's why:

The versatility of having the choice between clean boost or heavy overdrive would be nice, but I'll be using the pedal mostly for overdrive, not clean boost. So, if I were to use a 100K pot I would have it turned right down most of the time. As a friend (also a member here - thanks AletheianAlex) on the AX84 forum said: "So let's say 100k output pot set at 25% output... thta makes 75k series resistance... and I just measured a cheap guitar cable that was sitting on the ground and measured 800pF, and we'll say 150pF for the grid... that means that your treble response will be down -3dB around 2.2kHz (not counting the grid stopper)."

The only other change I'm gonna make is to add a small resistor between the gain pot and ground, so it can't be turned fully down - just mostly down. There is a point just before the end of the travel where it cuts off, I'll measure it and add a resistor of that value.

[Isaiah]

Hey Rick!
Good to know there are other Coventrians into DIY audio electronics.

I have a few questions -
Is the cap on the input just due to personal preference, or do you find the bass frequencies actually need limiting to some extent?

Have you tried wiring the second Pentode as a Triode? I believe you could install a switch to flick between.
Add a 1K resistor onto pin 2 and connect it to the same junction of the R/C network like your schematic for Pentode mode, or
connect the the 1K resistor to pin 1 for Triode mode.
I might have that completely wrong though, so take it with a large pinch of salt.
I'd try it myself, but my Pentodes haven't arrived yet.
I'm pretty new to tubes.

As far as post-clipping filtering goes, do you find there are as many harsh frequencies needing to be removed as in, say, a similar JFET circuit?

Do you have any soundclips please?

Cheers!

[frequencycentral]

Hi Isaiah,

First thing I would say it that I have more enthusiasm than EE knowledge or maths. I grab what information I can and experiment on my breadboard until I get good results. I post schematics in the hope that greater minds that mine will suggest improvements. So, feel free to tweak away, please post any good results you find. I'll be finishing my PentaDriver pedal build tonight, and will live with it for a few weeks before I consider any changes - it's one thing using it at home with my VJ clone, quite another using it through my rehearsal/gig rig.

The input cap worked well in my Valvecaster, so I used it here too.

A triode/pentode switch is a good idea - I'll try it on the breadboard. As I already have a Valvecaster and a Pepper Shredder I have triode overdrive/distortion well covered, so I was more thinking about doing the pentode thing here.

I've never built a JFET circuit, so I can't comment - but I'm not finding any harshness with this design.

I'll get round to posting some soundclips here once I've finished my build - hopefully tonight!

[Solidhex]

Yo

  I would love to hear an audio sample! I have some mini tubes I've been meaning to stick in a pedal...

--Brad

[frequencycentral]

Yo

  I would love to hear an audio sample! I have some mini tubes I've been meaning to stick in a pedal...

--Brad

Just finished the build, worked first time, no debugging needed.....................cool!

Perfect build - the best I've done - really pleased - I only designed it this time last week! I've so proud!

I have to eat and sleep now, so soundclips and photos tomorrow....

[mth5044]

Man I dont think I can wait until tomorrow. I think I'll skip all my classes hitting the refresh button every few minutes.