I've built a Valvecaster for someone but now they've asked if I can make it run off 18v. If I throw a LM7812 voltage reg in there, is it likely to introduce noise into the circuit? Or would I be better off just getting a large ceramic resistor (of appropriate value) to drag the voltage down?
I've built a Valvecaster for someone but now they've asked if I can make it run off 18v.
What voltage is it running at now ?
If I throw a LM7812 voltage reg in there, is it likely to introduce noise into the circuit?
No, but you may want to use the suggested output filter component[s.
Or would I be better off just getting a large ceramic resistor (of appropriate value) to drag the voltage down?
If you're dropping from 18v to 12v using a 7812, it might get warm/hot, I've never made that V-drop/current with one though, I'm sure others have. the V-reg has the advantage of providing a smooth regulated voltage. Another option would be a zener diode.
The V-reg is pretty easy to work with, make sure the chip drawing has the pins labeled right under it, even if you have to de-code and redraw it off the data sheet.
I'm well familiar with the use of 78* series regulators, just wasn't sure if it would introduce noise. I'm running it off 12v at the moment but this guy is wondering about running it off 18v as it would make his life easier (apparently ???). A 7812 just seems the easiest option as I can heatsink glue it to the aluminium enclosure, right near the dc jack
What is or would be behind the regulators, a wall wart ?
The reg's need ~2vdc 'extra' to work with, pick your output voltage [say 7818, and add at least 2volts to that for it's input voltage.
For 18vdc supply, >20v, say 22v [a little extra elbow room] into a 7818 [18v regulator] would work.
He wants to use an18vdc supply but the circuit is 12v so I figure I can internally regulate it. Problems would only arise when he tried to run it off a 12v supply somewhere down the track
Surely someone can answer the question "Do voltage regulators introduce noise into effects circuits?"
No
If anything they take away noise.
just remember to filter it properly so that you don't introduce HUM (not noise) into your circuit.
Quote from: runmikeyrun on December 07, 2009, 07:49:59 PM
just remember to filter it properly so that you don't introduce HUM (not noise) into your circuit.
Caps to ground?
You must have two voltage inside - 12V to power the heaters (and that's unchangeable) and B to the plates.
B can be 12V too (and it simplifies things) or higher (so you have to separate it from the heater supply)
If I'd be in your shoes, I'd go with a power in of 18V - then one wire to the heatsinked 7812 to provide 12V for the heaters and another wire with the 18V going straight to the plates.
Maybe it helps...That's how me and some other men do...
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=39755&g2_serialNumber=1)
Thanks Adriano, that's very helpful!
I realize I'm necrobumping this, but it's the first google hit for "regulator circuit valvecaster."
IME, a regulator is unnecessary. Simply using a 36 Ohm, 2 W resistor to drop the 18 V input to 12.6V for the heater circuit is adequate. It's simpler, it doesn't generate more heat than the circuit can handle, and it's plenty quiet.
Another option, if you're interested in increasing headroom, is to use a 12V adapter, run the power directly to the heaters, and use a voltage doubler to supply 24 V to the plate.
Quote from: suncrush on February 08, 2017, 11:52:25 AM
I realize I'm necrobumping this, but it's the first google hit for "regulator circuit valvecaster."
IME, a regulator is unnecessary. Simply using a 36 Ohm, 2 W resistor to drop the 18 V input to 12.6V for the heater circuit is adequate. It's simpler, it doesn't generate more heat than the circuit can handle, and it's plenty quiet.
Another option, if you're interested in increasing headroom, is to use a 12V adapter, run the power directly to the heaters, and use a voltage doubler to supply 24 V to the plate.
Good call.
Bearing in mind to measure the adaptor output and consider its rating and voltage before you connect it to the heaters (could be unregulated). IE, "12V/500mA" could be quite a bit higher voltage at 150mA (or 300mA if you go that route) if it is not regulated, requiring more 'resistor tricks'.
Yes, and a tube breadboard device is a good way to do that.
I made my own:
(http://img.photobucket.com/albums/v481/suncrush/d68d1c6b-d908-4bc1-b71b-615839dfa928_zpsoip3wjgu.jpg)
Hey, that is definitely cool - simple, don't have to buy anything! I like it!! :)
> a tube breadboard
An HONEST BREADBOARD !!
I can almost smell the crumbs!
Thank you for saving our traditions.
___________________
For ultra-traditional, use Fahnestock clips (https://en.wikipedia.org/wiki/Fahnestock_clip). They are going out of style since I was a pup, but they are around if you hunt. HH Smith is very good and very over-priced (>$1 each). Cheap no-names seem to sell for more in tiny lots.
Quote from: suncrush on February 08, 2017, 11:52:25 AM
I realize I'm necrobumping this, but it's the first google hit for "regulator circuit valvecaster."
IME, a regulator is unnecessary. Simply using a 36 Ohm, 2 W resistor to drop the 18 V input to 12.6V for the heater circuit is adequate. It's simpler, it doesn't generate more heat than the circuit can handle, and it's plenty quiet.
Another option, if you're interested in increasing headroom, is to use a 12V adapter, run the power directly to the heaters, and use a voltage doubler to supply 24 V to the plate.
+1 to that, tubes sound better with higher plate voltage.
Quote from: sajy_ho on February 09, 2017, 02:03:01 AM
+1 to that, tubes sound better with higher plate voltage.
They're made to operate at MUCH higher voltages, so running them down here makes their load lines basically useless...no headroom...little dynamics...so yes, getting them over 100V is much better, IMO! Unless of course we can get some tubes meant for 12V operation :)
That would be the 12U7...
Quote from: GibsonGM on February 09, 2017, 09:36:24 AM
Quote from: sajy_ho on February 09, 2017, 02:03:01 AM
+1 to that, tubes sound better with higher plate voltage.
They're made to operate at MUCH higher voltages, so running them down here makes their load lines basically useless...no headroom...little dynamics...so yes, getting them over 100V is much better, IMO! Unless of course we can get some tubes meant for 12V operation :)
You might be surprised how good a Valvecaster actually sounds. They're quite nice in their intended application--a boost with a little breakup at high gain. It's not a preamp pedal by any stretch.
Quote from: suncrush on February 09, 2017, 10:23:38 AM
Quote from: GibsonGM on February 09, 2017, 09:36:24 AM
Quote from: sajy_ho on February 09, 2017, 02:03:01 AM
+1 to that, tubes sound better with higher plate voltage.
They're made to operate at MUCH higher voltages, so running them down here makes their load lines basically useless...no headroom...little dynamics...so yes, getting them over 100V is much better, IMO! Unless of course we can get some tubes meant for 12V operation :)
You might be surprised how good a Valvecaster actually sounds. They're quite nice in their intended application--a boost with a little breakup at high gain. It's not a preamp pedal by any stretch.
MMM, I've made them. Several of them. I can't tell the diff between that and say, a Timmy (opamp based), when pushing the front end of a tube amp. To get some 'tube sound', I agree low voltage circuits like this can make a difference, say before a solid state amp; and esp. to get your foot in the door with tubes.
But having built them, I find you then want to move on to more complex preamp projects, maybe even entire amps. They are a gateway circuit! :) I'm not knocking the V.C. by any means. I might build one again some time, for someone else perhaps. I hope people DO make their own.
Everyone's preference varies - some ppl love low voltage tube, some high voltage, and some people love semiconductors! Maybe not even for the sound, but for having made something 'vintage', complex, 'dangerous' (at least in that 1/2 your build might go up in smoke on first power-up, LOL). The challenge, the experience.
One little-known tube that should have been more popular was the 20EZ7 which is a 12AX7 with a 20 volt 0.1 amp heater. I have three 24 VDC wall warts that could be regulated down (or just supplied with a resistor in series) for the heater that would operate the tube with a bit more gain and linearity but still achieve breakup as required. I was using the wall warts in series for a 24/48/72 volt supply for old 1920's battery operated radios.
I wonder if anyone has ever tried a 12U7 in a VC. I'm sure someone has.
I found a site a while back where someone was using 12U7's. It would be neat to see more low-voltage tube projects like this.
Have you seen this, Brian, Ron?
http://www.sophtamps.ca/mambo/index.php?option=com_content&task=view&id=25&Itemid=37 (http://www.sophtamps.ca/mambo/index.php?option=com_content&task=view&id=25&Itemid=37)
Yes, I have seen this site and it is excellent! Originally these tubes were used in car radios that had a germanium power transistor as an output, so no one tried to make a power tube that could do much more than drive the relatively low impedance of a power transistor. This allowed a radio to be designed without a vibrator power supply to generate high voltage. The driver stage was usually a 12K5 space-charge grid tetrode that was rated to drive 40 mW. The small dynamic range guarantees that you can drive it into distortion easily.
The 12U7 only has a ยต of 20 so you don't get the gain you would from a 12AX7, but with enough stages, you could always get distortion. The plate characteristics are here:
http://www.mif.pg.gda.pl/homepages/frank/sheets/137/1/12U7.pdf
It shows you don't need to drive it hard to get the appropriate levels of distortion for a guitar amp.
It doesn't have the gain of an AX7, but the Valvecaster/Valvemaster runs an AU7...shoot, I need to try one myself! ;D
Quote from: rutabaga bob on February 10, 2017, 07:39:53 PM
It doesn't have the gain of an AX7, but the Valvecaster/Valvemaster runs an AU7...shoot, I need to try one myself! ;D
Often times, I find myself using an AU7 instead of an AX7 in a "V1" position, no matter WHAT the amp topology. Maybe I'm dreaming, but I think the lower gain makes them warmer, at least for the input stage. Here is where I set my min. gain for the whole thing, and I find them to be better candidates than the AX7. And if you've built your preamp right, you should have MORE than enough distortion available in other stages to 'let some go' this way....maybe a total thrash freak would disagree, but that's my experience.
It's not about how much you can amplify in one stage, after all - it's about what you get at the end of (2 or more) several stages....
Cool would be to find the 12V equiv. of the 12AX7, and the 12AU7, and see if that holds true for those guys too!
You can get as much distortion as you can stand by cascading stages. If you "only" had gain of 10, four stages is gain of 10,000, way more than audio needs.
If you run lower supply voltage, you do not need as much gain to distort a given input.
> find the 12V equiv. of the 12AX7
Does not exist. In the intro-puff for one of the 12V tubes they cited a rule (apparently known but not written) that Mu should be less than supply Voltage. Alternatively, if bias will be less than 1V, contact voltage grid ions and other hard-to-control stray effects will vary too much to be "producible". (And no tube maker caters to the one-off crowd.)
12U7 "beats the rule" 2:1 by very elaborate processing. This is the finest 1959 car-market technology; you won't beat it.
Merlin and others have written on bias techniques, sometimes using positive grid (low grid impedance) to force "some" current to flow at pathetic plate voltage.