"V2" - 25% more gain for your Valvecaster sir?

[frequencycentral]

I've been playing about with the constant current source idea used in the MkII versions of the Pentaboost, PentaDriver and Red Star Drive. I breadboarded it using a 6111 (identical to a 12au7 but smaller) to see if I could achieve a higher gain Valvecaster. I did! MUCH MUCH meatier drive. Nice. 

The setting of the R1 trimpot is everything in this circuit. It's very sensitive, you have to get it just right, or no gain at all! But when you get it just right - boy it's another beast altogether from it's parent! I measured it at about 45K, I'm using a power supply of 11.94 volts.

Battery power is not recommended, as the trimpot will need to be tweaked as the battery loses power. I haven't tried it a 9 volts either. I think the general consensus is that the original Valvecaster is a 12 volt circuit anyway. Having said that, it should work at 9 volts with a little tweaking, and I probably will try it just to confirm that.

While I was about it I thought I'd change the one part of the original Valvecaster which always bothered me, the 'thunk' as you turn the Gain full up (as the cathode grounds), so I replaced the gain control with an interstage Gain pot instead. No 'thunk'! I changed the caps too.

I haven't included the Tone control, but that's easy enough to add in if you wanted to.

I'm building mine using a submini 6111 in a Hammond 1590A - when I can find one. Anyone want to trade me a 1590A?

Here's the schematic, I've done the pinout for 12AU7, but it's easy enough to adapt to 6111 if you want to.

[tranceracer]

Wow! Very cool Rick!  Just curious about the "thunk" you mentioned.  I'm not sure if it's because i'm running my Valvecaster at 9V but I don't recall any such noise.  Is this something that primarily happens on the 12V version?

Thanks for sharing!

[forsakenrider]

HEY!! thats what I was going to do, but just put it on the second stage instead, maybe I should put one on both! MUAH HA HA!
also, this mod will NOT work unless you change the gain pot like you did.

How do you find that sweet spot? just rock out while turning it?

My other question, why the two 1m resistors to ground (r4 and r5)?

[jakehop]

How about measuring the current from the transistors collector? Ain't that what we're looking for in regards as to how to adjust this thing?  

[frequencycentral]

Wow! Very cool Rick!  Just curious about the "thunk" you mentioned.  I'm not sure if it's because i'm running my Valvecaster at 9V but I don't recall any such noise.  Is this something that primarily happens on the 12V version?

Thanks for sharing!

I noticed the thunk on both the 9 volt battery version I built and the 12 volt wall wart version too, I assumed everyone has it?? Anyway, I prefer the interstage gain contol. As forsakenrider says. the mod won't work with the original Valvecaster gain control.

HEY!! thats what I was going to do, but just put it on the second stage instead, maybe I should put one on both! MUAH HA HA!
also, this mod will NOT work unless you change the gain pot like you did.

How do you find that sweet spot? just rock out while turning it?

My other question, why the two 1m resistors to ground (r4 and r5)?

Yeah, we did discuss it didn't we. Putting the tranny on the second stage would just boost the signal, whereas putting it on the first increases the drive.

Sweet spot - yeah, rock out and tweak!

1M - I'm paranoid about popping.

How about measuring the current from the transistors collector? Ain't that what we're looking for in regards as to how to adjust this thing?  

Yes, I'll get some more measurements together.

[forsakenrider]

Hmmm, it doesnt seem to be working out as amazing for me! i dont even notice a gain!! but  notice when the tranny isnt biased right, cuz then it like "bogs" down. does that sound about right? but i have like 10 turns to play with in the wear it seems good part.... hmm. i need to play louder, so tomorrow.

but still, not noticing much gain! if any, doesnt seem like 25%!!

[brett]

Hi
if it's fairly clean, 25% won't do anything noticeable.  You'll only detect extra dirt from that much gain if you're already clipping, and the boost is adding eaxtra distortion.  Also, to some extent the result will be dependent on the valve.  Gain in 12AU7s will vary from tube to tube when used at voltages this low.  It might be worthwhile trying this with a 12U7, too.
cheers

[forsakenrider]

... I just wish i could find some 12u7's!!
My valvecaster seems pretty meaty allready so maybe thats why. I will need to play it a bit loud and see if i can notice a difference.

[Renegadrian]

I am going to try this one soon, I have a bc307b, which should fit the bill, according to this file
http://www.ilmaurino.com/public/mws7/file/elettronica/carat_equiv.pdf

Rick, if you say those magic words "HIGH GAIN" you know you got me on...

[frequencycentral]

Had a chance to have another fiddle with this on the breadboard today. I added a cap between the transistor base and +ve, as i found that without I was getting a bit of unwanted compression/gain loss.

I recorded a very quick clip. The first part is recorded with the plate of the first triode receiving +ve via a 220K resistor (ie normal Valvecaster), the second part is recorded with the plate receiving +ve through the transistor. You can hear the thump as I change the connection on the breadboard!

My power supply measures: 11.94 v

Voltage at plate via 220K resistor (ie normal Valvecaster): 8.96v

Voltage at plate via transistor: 11.79 v

http://www.aronnelson.com/DIYFiles/up/V2_quick_demo.mp3



EDIT: I should stress that I'm breadboarding this using a 6111, so it might be slightly different with a 12AU7, though the principle is the same.

[frequencycentral]

An apology: I just tried this circuit with a 12AU7, and I can report that it sure does not work the same as with a 6111. Sheesh!



So, I've deleted the original schematics from Photobucket - if you can see any schematics above this posting ignore them.

This thread should correctly be named "V2" - 25% more gain for your Subcaster sir?

I once again apologise to the thousands of you out there who may have wasted fruitless effort on this one.

However - it does work with the 6111 very nicely!! So I'm continuing to experiment along that path. It should be considered a 'work in progress' at this stage. Here's the latest version:

[robizz]

 

i'm so sad, because today i have opened mi 12au7 valvecaster to make the experiment with the mod!

by the way, i'll be waiting for more news (and more gain!  )

[frequencycentral]

i'm so sad, because today i have opened mi 12au7 valvecaster to make the experiment with the mod!

by the way, i'll be waiting for more news (and more gain!  )

Sorry! 

I'm going to complete the 6111 version first - then I may move on to the 12AU7.

The 'rub' seems to be that the 'normal' plate voltage for the first stage of a 12AU7 Valvecaster is one quarter of the supply voltage, whereas with the 6111 Subcaster it is three quarters of the supply voltage.

Strange - because in other experiments I have done they perform very similarly. 

[frequencycentral]

Ok, I've soldered jumpers to a tube socket and plugged a 12AU7 into my breadboard. I've fiddled about with the constant currect source and come up with this:



I'm measuring just under 6 volts at pin 1, which is twice that of a stock Valvecaster.

I've been toggling between a 220K resistor and the constant current source to feed power to pin 1.

This seems a lot brighter and more crunchy to my ears. Would someone care to breadboard it for a second opinion?

[robizz]

i'll breadboard it as soon as possible, maybe with the right transistor, if i have one!

Thanks for the help! 

[Renegadrian]

I want to try it the next week...THX Rick. 
I appreciated your works and your words.

[mitzrecords]

thanx for this great post!

so does this work with 9V power or still needs tweaking?

if someone has a layout handy, could you post it pretty please? i always make so much mistakes reading schmatics.(maybe it might be time to practice reading better more)

[frequencycentral]

I would expect R1 would maybe need tweaking for a 9 volt supply. There is no layout yet. I'm hoping a couple of people will breadboard this circuit and compare their results with mine.

[esdiezy28]

It was over a year ago and I can't find my schematic anywhere, but I think I had a 12AU7 version working with a CCS. I remember tampering with using a N-channel JFET J201, and a MosFET, something like a 2N7000. I'll tinker around with what I have and see if I can get something verified and working.