Correcting voltages for DC jacked Valvecaster

[esdiezy28]

Hi all! I've been having trouble regulating my power supply for a valvecaster. I used an LM317 with about 13 unregulated Vin, used a 5k resistor (R2) from adjust to ground, and a 510ohm (R1). The equation for power out is Vo= 1.25 (1+ R2/R1). My power reads at around 12V (which I want approximately 12.6 for the heaters) UNTIL I connect the heaters and both plate resistors, then I lose all voltage at the output. Is it that my DC pack doesn't give me enough total current? I have no idea, any help appreciated, thank you!

[frequencycentral]

The Valvecaster heater (12au7) requires 150ma between pins 4 and 5 at 12 volts. The plate requirement is almost negligable in comparison. 200ma in total should do for both.

[slacker]

What are the specs for the power supply?
It should tell you the voltage and how current it can supply, usually in milliamps. If it's only giving 13 volts with no load it probably can't supply enough current. Even if it can if you want 12 volts out of the LM317 you need more than 13 volts in, you normally want about 3 volts higher than the output, especially for something like a valvecaster than needs a few hundred milliamps.

[esdiezy28]

Thank you both! I was trying to use a 9VDC plug rated at 300mA. I do have another plug around here, a 12VDC rated at 700mA but the positive and negative on the jack are opposite polarity of my 9V plug. Can I just switch the wires on my DC jack and try running it with the 12V DC and then into the LM317. I also have several other options to reduce my power supply hum, a 7812 positve 12V voltage regulator, and even got a TC1044, a DC-DC charge pump converter, in case I did need to provide for more voltage than I started with. So I guess my new question is, "Having all these options for PSU regulation, is there a "best" solution among them or are thier prospects equally opportunistic?"

[frequencycentral]

You can just switch the wires of the DC jack of your power supply, better to do that than switch the wire on the socket of the pedal. Test it with a meter before you use it though - it's easy to make mistakes!

People are generally using a 7812 and a 100uf cap to regulate/filter the voltage for Valvecasters.

The TC1044 you have (same as a MAX1044?) might come in very handy to boost up the plate voltage. Have a look at this:

http://www.diystompboxes.com/smfforum/index.php?topic=73317.0

.....and this:

http://www.diystompboxes.com/smfforum/index.php?topic=73222.0

Ok, they are amps, but same principle. The general consensus is that 12au7 really start to open up at voltages of 18v and higher, so just take the MAX1044 section of the circuits I linked to. I'm thinking of retrofitting a MAX1044 into my Valvecaster. As the MAX1044 has a maximum input voltage of 10.5v, you should maybe consider a couple of 1n4148 to drop the 12v into the MAX1044 to nearer what it likes. I'm just in the process of building my "Murder One", I've completed the voltage doulbling part, which uses a MAX1044, twelve 1n4148 and twelve 10uf caps to get a plate voltage of about 70 volts.

[esdiezy28]

Awesome, gonna try switching my positive and negative wires at the DC jack to get my 12V input. I'll give it a try with a 7812 and a 100uf capacitor for regulating 12V to run to the heater (pin 5). Then, use the Max1044 (mine is a TC 1044 but is equivalent) with diodes and 10uf 100V capacitors to boost my plate voltages up to around 18V to provide larger headroom (is that right?). Sounds totally awesome I just can't wait to get this pedal working!

[frequencycentral]

Awesome, gonna try switching my positive and negative wires at the DC jack to get my 12V input. I'll give it a try with a 7812 and a 100uf capacitor for regulating 12V to run to the heater (pin 5). Then, use the Max1044 (mine is a TC 1044 but is equivalent) with diodes and 10uf 100V capacitors to boost my plate voltages up to around 18V to provide larger headroom (is that right?). Sounds totally awesome I just can't wait to get this pedal working!

If you're only going up the 18v with the 1044 the 10uf cap only needs to be rated at say 25v. You should try a few more voltage increases though, making sure the caps are suitably rated at each stage.

[esdiezy28]

First of all, Sweet Valvecaster Success! That did the trick, as I finially got the polarity on the power source correct. Its a 12V 700mA DC Plug for my Yamaha Keyboard, and by regulating it with a 7812 Voltage Regulator its hum free.

Running my Dr.Distorto Module into the Valvecaster then my Amp makes a sound that's so fulfilling, rich, resonant, and controlable, that I can not explain how I ever lived without a Valvecaster before.

Further Tweaking....
As time went, as always for me, I got to wondering about tweaking some things in the circuit. First, I had only one Voltage increase stage coming from my TC1044 giving me 18V, I increased this one stage at a time, settling finially at around 36V.

Next, I wanted to add a smallish capacitor onto Lug2 of the gain control, and used a 0.68uF electrolytic cap, add's just a bit more bottom end though I still find the gain control has minimal effect for me.

It was very versatile, but I wanted to drive it harder still, but without having to wire in another tube (save that for another rainy day) and decided on using RoG's Fetzer Valve with a J201 calculated at 12V to place infront of the triode stages. Its not pure tube anymore, I know, but it can really drive a hot signal for the tubes for play with 

And just tonight, which sparked this comment, I realized I had a 12AT7 (mu of 60) laying around with identical pinout. Swapped it in and to my amazement it sounded very crisp and clean, I'll have to make more swapping comparisons and maybe some video clips or pics to share the wealth with you all! Let me know if anyone has any questions....

                                                                                                   ToNy