Author Topic: ...and now, the "PentaDriver" 12 volt Pentode Overdrive using Submini 5672 tubes  (Read 61591 times)

frequencycentral

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Following on from the "PentaBoost", I cascaded two pentodes using two 5672 submini pentodes to create the "PentaDriver". Warm pentode distortion/overdrive is the result.

I'll be playing about with resistor values over the next few days to see what else it can do!

5672 tubes require a 1.25 volt heater voltage (at only 50ma), I used a LM317 to provide that.



« Last Edit: September 04, 2008, 06:48:11 PM by frequencycentral »
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Franky

Great, 50mA only! How's the headroom under 9V? If that sounds right, that could lead to a pedal easy to put in a pedalboard (not that big, consuming not much, and under a common voltage)
42

frequencycentral

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Great, 50mA only! How's the headroom under 9V? If that sounds right, that could lead to a pedal easy to put in a pedalboard (not that big, consuming not much, and under a common voltage)

I haven't tried it at 9 volts yet - I would guess it will be fine. The two tubes together consume 100ma.

It's getting late here at Castle Analogue, I'm sure the local peasants are trying to sleep - so I have to power down the lab before they show up with pitchforks and flaming torches.

More experiments tomorrow Igor......................
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Franky

Lol, yes master Frankency Centralstein..  Same issue here.. 

(anyway: IT'S ALIIIIVE!!! ;) )
42

Jimmy-H

Hi Rick,

Interesting little circuit!
So you have been busy again.
I was looking on the web, to see if there are other solutions for the heather supply.
And I found this, just a resistor and two diodes:
« Last Edit: September 05, 2008, 04:22:42 AM by Jimmy-H »

frequencycentral

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Hi Rick,

Interesting little circuit!
So you have been busy again.
I was looking on the web, to see if there are other solutions for the heather supply.
And I found this, just a resistor and two diodes:


Yeah the same guy did a 5672 VCF - but it's not pure tube, also having a BC547 and BS107 in the audio path.
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lvs

« Last Edit: September 05, 2008, 06:58:25 AM by lvs »

Jered


     "5672 tubes require a 1.25 volt heater voltage (at only 50ma), I used a LM317 to provide that."

         I don't understand how this could work. Your running 12 volts to your heaters. Your tubes would last about ten seconds. Is there something I'm missing here? As the schem is now I can't see it working.

frequencycentral

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     "5672 tubes require a 1.25 volt heater voltage (at only 50ma), I used a LM317 to provide that."

         I don't understand how this could work. Your running 12 volts to your heaters. Your tubes would last about ten seconds. Is there something I'm missing here? As the schem is now I can't see it working.


.....so I have had it running for hours. The heater is provided with 1.25 volts at pin 3.

Do you think it's my "magic tubes".....................or a gap in your knowledge?
« Last Edit: September 05, 2008, 09:23:26 AM by frequencycentral »
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Jered

  How are you adjusting your voltage?

frequencycentral

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  How are you adjusting your voltage?

The LM317 minimum output voltage is 1.25 volts - by coincidence just what the 5672 heater requires.
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frequencycentral

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I don't understand how this could work. Your running 12 volts to your heaters. Your tubes would last about ten seconds. Is there something I'm missing here? As the schem is now I can't see it working.

The LM317 provides its minimum output voltage of 1.25 volts if you connect pin 1 directly to earth and run a 100R resistor between pins 1 and 2, as shown on my schematic. By coincidence 1.25 volts is just what the 5672 heater requires, so it's just a case of powering the 5672 heater at pin 3 with 1.25 volts.

Take a look at the 5672 VCA schematic which Jimmy H posted in this thread. This schematic takes a different approach, using a 275R resistor and two 4007 (1 amp) diodes to drop the 12 volt supply to something that the heater can cope with, again powering the 5672 heater at pin 3. The VCA schematic (and it's sister 5672 VCF schematic which powers the heater identically) has been built by a number of people successfully, check it out: http://electro-music.com/forum/viewtopic.php?highlight=tube+vcf&t=23067

I don't happen to have any 4007 diodes lying around (only 1N4148 which are not suitable), so I used what I did have - the LM317.

It's a little hard for me to accept on your say-so that this circuit won't work for a number of reasons:

- I did the research.
- I asked questions of knowledgable people on this and other forums.
- I experimented on my breadboard.
- I have the working circuit sitting in front of me, which I tested and tweaked for considerably longer than your estimated 'tube survival time' of 10 seconds. Hours in fact.

I would suggest that you get hold of a 5672 tube and a LM317, build the circuit on your breadboard and post your results.

Jered, you said basically the same thing in the Subcaster thread regarding my idea of running two 6111 submini tube heaters in series from 12 volts: "If you do that they will glow like a lightbulb and die. 5.7 V min-6.9 V max on the heaters." I checked it out, did some reseach asked some questions, got some answers: http://www.diystompboxes.com/smfforum/index.php?topic=69736.msg559547#msg559547 I know from experiment and experience (I have the working pedal to prove it) that this method of powering 6111 heaters works perfectly and is within the quoted tolerance.

The Earth is not flat. Evolution did happen.
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Jered

  Hey, if you say its working, then its working, not here to argue with anybody. Its just, looking at the schem, there is nothing to attenuate the voltage. Its directly connected from the 317 out, to the tube filament. So if your filament is not getting 12 volts, then for some reason, electricity is NOT taking the path of least resistance, in this instance. I'm very intrigued. Can't wait to try this on the breadboard when I get home. Oh and the heater V. min/max for the 6021, 6111, 6112 tubes is 6.2 min to 6.6 max. Anything outside of that and your killing your tube. Its on the datasheet.
  If you need any 1N4001 to 4007 diodes PM me your address and I'll get a bunch in the mail to you. You wouldn't believe how many I have.
  Peace,  Jered

frequencycentral

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  Hey, if you say its working, then its working, not here to argue with anybody. Its just, looking at the schem, there is nothing to attenuate the voltage. Its directly connected from the 317 out, to the tube filament. So if your filament is not getting 12 volts, then for some reason, electricity is NOT taking the path of least resistance, in this instance. I'm very intrigued. Can't wait to try this on the breadboard when I get home. Oh and the heater V. min/max for the 6021, 6111, 6112 tubes is 6.2 min to 6.6 max. Anything outside of that and your killing your tube. Its on the datasheet.
  If you need any 1N4001 to 4007 diodes PM me your address and I'll get a bunch in the mail to you. You wouldn't believe how many I have.
  Peace,  Jered

Hi Jered, no offence meant, and I hope none taken. ;)

The first thing to do is to just try running an LM317 with the adjust tab (pin 1) grounded so that you get the minimum output voltage... which happens to be around 1.25v. You will need to add the 100R resistor across pins 1 and 2, or the LM317 will put out about 7 volts. When you are satisfied you are getting a stable supply around 1.25 volts - apply it to the tube. Maybe add a filtering cap after regulator too - something i should have done, and will add. Then you're in business.

If you do put one together when you get home, maybe experiment with the caps - 470pF, .001uF  or .0022uF will change the low cutoff, I have yet to try this. Also, maybe try changing the two 100K resistors at pins 4 and 5 of the first pentode for higher values - 220K or 470K perhaps. I've an idea this might increase the gain and drive the second pentode harder.

The 6111 data sheet I have quotes 6.3 volts +/- 5%, therefore:

Minimum = 5.985 volts

Maximum = 6.615 volts

Yeah, I need to get some 4001 and 4007..........

Happy breadboarding !!

Rick
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frequencycentral

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I realised that the 100k resistor from pin 3 of the pentode to earth is completely pointless - don't know how that got there! So i have removed it from the schematic.

Rick

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soulsonic

Just use a freakin' "C" or (better) "D" cell battery for the heaters and it will last for a decade!

Use a 9 volt for the other stuff and you'll be 100% battery powered! Those little tubes with the 1.25 heaters are made for generic battery power.... that's the whole point of the puny votages and currents!
Check out my NEW DIY site - http://solgrind.wordpress.com

frequencycentral

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Just use a freakin' "C" or (better) "D" cell battery for the heaters and it will last for a decade!

Use a 9 volt for the other stuff and you'll be 100% battery powered! Those little tubes with the 1.25 heaters are made for generic battery power.... that's the whole point of the puny votages and currents!

Yeah you're right- these tubes are particularly suited to battery power, or even throwing onto a pedal board without worrying about the massive current draw that some other tube designs require. I think this circuit would probably work equally well from a 9 volt battery and a 'C' or 'D' cell for the heater.

I guess I didn't take that route because I'm building for my own requirements first and foremost. I don't use battery clips in any of my builds. One thing I regret about the learning process that is electronics is that I've built some tube pedals with pretty high current draw requirements - now I'm thinking that if I had used these 'little tubes with puny voltages and currents' from the start I would have a more power-efficient set of pedals. One case in point is my 'Vibracaster' - I used a 6111 drawing 300ma to build mine - I should redesign it using a 5672 really. Heyho - live and learn.
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cpnyc23

Is there a best source for these tubes?  Or is it an Ebay situation...

thanks
-chris
"I've traveled the world and never seen a statue of a critic."    -  Leonard Bernstein

frequencycentral

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Is there a best source for these tubes?  Or is it an Ebay situation...

thanks
-chris

I got mine from a Dutch Ebay seller.

I just changed the gain pot from 1M Lin to 1M Log for a more even sweep across the range.
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Jimmy-H

Is there a best source for these tubes?  Or is it an Ebay situation...

thanks
-chris

You come from America right?
Just google, and you will find some.

Some examples:
http://www.radiodaze.com/tubes-09.htm
http://www.vacuumtubes.com/price10.html
http://www.vacuumtubes.net/p5.pdf