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Post by jcgss77 on Jul 7, 2010 19:48:55 GMT -5
Greetings fellow Nutz, I am starting a build of a low-voltage tube preamp that I am going to mount into an old Daphon pedal I have laying around. The schematic is here: www.beavisaudio.com/projects/ValveCaster/I will be using a 12at7 that I salvaged from an old Zenith tube radio, and a 12 volt wall wart, and want to go from a wimpy 12 volts  on the plate to about 48 volts  (or so, depending on what info I get here). I have read about using a voltage multiplier for this, but can't seem to find a proper schematic for this. Can someone please share with me the proper way to accomplish this? Thank you for all assistance. |
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Post by sumgai on Jul 7, 2010 22:16:38 GMT -5
jc, Might I suggest that you Google for: "voltage doubler", and see what you get. I first searched on "voltage multiplier", and I didn't like the results - too technical for your needs. "voltage doubler" returns much more useful results, the first being one of my favorite sites, www.play-hookey.com, but the next four or five are also very good. There are even some YouTube videos, but I didn't check them out myself, so...... BTW, on that Beavis site...... some of those schematics make me go "hmmmmmm......" as I stroke the chin area of my bag while lost in thought. I'd be pleased if you kept us all abreast of your progress as you build this pre-amp. Pictures would be cool too, but if not, just a short essay once in awhile, if you please.  HTH sumgai |
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Post by jcgss77 on Jul 8, 2010 10:40:31 GMT -5
Thank you sumgai, it never occurred to me to try voltage doubler. I have been following a L-O-N-G thread on DIY stompboxes, and there are some awesome variations of this nice pedal. I have been doing research on this for about 2 weeks, and when I came to the voltage multiplier, I feel I have enough info to make a really nice pedal. I already drilled out my pedal, and will be building this pretty much from all salvaged parts, so I have a feeling it will be, well...unique. As I progress, I will post some pics and maybe some sound samples of my horrendous playing through this. I am pretty excited, as I have not really had much chance to tinker with tube sounds, and I am planning to use the experience I gain from this build to build a nice little amp from a schematic over on AX84. BTW, here is the link for the Matsumin Valvecaster on DIY stompboxes: www.diystompboxes.com/smfforum/index.php?topic=63479.0Enjoy, this is some heavy reading. |
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Post by sumgai on Jul 8, 2010 11:49:38 GMT -5
jc, That's pretty hefty alright! From the 5 minutes or so that I gave it, I have to agree with a couple of posters there who admitted "I don't know anything about electronics....." Beyond that - must..... keep.... mouth..... shut!  I've always said that it's silly to go buy parts if you already have them in your "junk box". Fortunately, particularly in tubes, component values are variable - there's a lot of room to experiment, without worries over damage to parts, tools, workbench, self, etc. Just keep the voltages low, and all should be cool. Looking forward to your results..... sumgai |
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Post by jcgss77 on Jul 8, 2010 17:24:21 GMT -5
After some browsing around on Play-Hookey...which I have to admit, I was doing just that during work today...*ahem*...it seems I have a lot of learning to do about diodes before I just start randomly soldering come caps and diodes together to create a 5x voltage multiplier...wait, I forgot about the resistors... Well, okay, my wall wart is 12 volts and 750 mA, so it seems I can only double it, and still have enough current to keep the 12at7 happy, as if I read it correctly, each stage of multiplication reduces current by half. Guess you can't get something from nothing  Anyways, if you have any suggestions of proper values, I am all ears. Do diodes have values other than wattage ratings? I DO need to learn more about them... the experimenting is the fun part. Wish I had one of those fancy breadboards...oh well! On to the soldering iron, Batman! |
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Post by jcgss77 on Jul 8, 2010 19:11:06 GMT -5
ooooo...just had a thought.
I was thinking about how I will be doing voltage multiplication, and was wondering...
I am using a Zoom505 effects pedal, and really think the tube overdrive should be first, but is there a such thing as having too much voltage running into a sensitive pedal? Is there a name for this? Or am I worrying about nothing, since the tube will be using up most of the signal...I am still quite green at this. Aside from shielding my guitar, doing the tone bleed mod, and some small circuitboard repairs on the occasional electronic, I really have no experience at higher voltages, I just know to discharge caps before I go shaking hands with them. Some advice please? Do I also need to worry about the signal into my amp too?
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Post by sumgai on Jul 8, 2010 22:59:07 GMT -5
I am using a Zoom505 effects pedal, and really think the tube overdrive should be first, but is there a such thing as having too much voltage running into a sensitive pedal? No, not really. I suppose if you somehow managed to run a connecting wire from the input to a wall outlet, there might be some repercussions, but for the most part, nope. For what, over-driving the input? Yep - it's called "too damned much distortion!" In a nutshell, yep. But keep in mind that the tube isn't "using up" anything. In fact, you're putting it in to do just the opposite! HTH sumgai |
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Post by jcgss77 on Jul 11, 2010 17:14:27 GMT -5
OK. Seems I need to work on my technique.
I "finished" soldering up everything in my pedal, and assembled it all. And I just got buzz through it, and the tube did not get warm. I also apparently wired the volume pot backwards, as the hum got louder as I turned it counter-clockwise. I will be seeing if Radio Shack has any of the parts. Heh, I'll keep you updated as I make progress with this project.
By the way, is there a way to test a tube? I am asking this before I google. I am heading there next.
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Post by sumgai on Jul 12, 2010 14:31:51 GMT -5
jc, There are tube testers still on the market, some used, some new. But since your tube didn't light up, I'd say that first thing to do is not test the tube, but to make sure the filaments (heaters) are getting voltage on the correct pins. Fortunately, it's hard to damage a tube if it's wired incorrectly. About all that could happen is if you put the high voltage on the filaments, they'll burn out. But in your case, that's not easy to do - no high voltage! If you can't "see" what's wrong, then my best suggestion is to have a friend look it over, comparing your diagram of what you were supposed to do against what you actually did. Often a fresh set of eyeballs will detect something that you keep passing over..... it's happened to me, as ash will testify.  Keep plugging away! HTH sumgai |
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Post by jcgss77 on Jul 12, 2010 18:38:59 GMT -5
Ok, so here is the scoop.
In my schematic, the pins were not numbered. I think you can see where this is going. Since this is my first tube project, my hands were shaking to plug in this baby and see what all the fuss is about. So, in my haste, I did not count pins with nothing soldered to them, and since I am using over 12 volts, I left pins 4+5 empty, but also then left pin 9 empty, as in the schematic it has a varying B+, so they left the heater line out as the resistor will all the same vary.
It seems the only thing varying was my brain and my eyes.
As soon as the kids are asleep, the iron is getting warmed up and we shall see if I can fry some components tonight! I just hope I have 2 30 Ohm resistors, as I need 54 Ohms to keep the heaters happy.
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Post by jcgss77 on Jul 22, 2010 15:41:46 GMT -5
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Post by sumgai on Jul 22, 2010 21:54:50 GMT -5
jc, No, you don't use pin 9 if you're gonna feed 12vAC to the filaments. Note that there's a plural there..... There are two heater elements inside that glass envelope, one for each cathode (each triode half of the tube). Each element can be powered separately by 6.3vAC, using pin 9 and either pins 4 or 5, depending on which half you want active. (Presumably you want both active - no point in wasting half a tube, eh?) If you intend to use 12vAC to power the heater elements, you will connect it to pins 4 and 5 only, and leave pin 9 unconnected to anything. That is, if you want the tube to operate without blowing up.....  HTH BTW, your links are actually fine the way they are. It's never a bad idea to let our readers see what's happening on other forums..... a broader exposure and all that. sumgai |
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Post by jcgss77 on Jul 25, 2010 10:28:24 GMT -5
I think that my tube is bad. With a functional wall wart, I measured voltages to the pins of the tube socket. The wart is putting out 14.67 volts and says that it is 1 amp. Is there a way to measure the actual current?
Here are my measurements:
1- 11.68
2- 1.41
3- 0.04
4- 14.67
5- 14.67
6- 13.26
7- 11.08
8- 0.09
9- 14.67
It definitely seems that my filament resistor is bad. I took these measurements with the tube in, no input cables, and I am not sure where I had the gain and volume knobs. Do these measurements seem okay? Or do I need to re-take them with the pots full open or closed or something? Sorry, I feel like I need to be led by the hand here.
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Post by jcgss77 on Sept 13, 2010 20:22:23 GMT -5
I think I know what is wrong.
I have just received my breadboard to work on my Valvecaster build-yeah, I know that was a while since I started it- in order to troubleshoot it. So, as a status report, I boarded it and found that the tube lights up, however, no output, just BZZZZZZZZ. I have torn the board bare and rebuilt at least 4 times.
So here I am, scratching my head. Then, I notice and actually read the whole thing on my PSU. Wouldn't you know it, it is only a step down AC converter. So I look through all of my supplies, and lo and behold, they are all just AC!
So, now what I need to know is-do I need to convert to DC? And if so, how? Is this why I have gotten nothing out of it?
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Post by sumgai on Sept 13, 2010 23:49:08 GMT -5
......
Is this why I have gotten nothing out of it? Yep, you got it. The proper term is "rectify". You rectify AC into DC. This takes at minium one diode, either solid-state or vacuum, doesn't matter. In your case, you need to build a rectifier circuit, which can comprise the whole of a power supply, or only a part of one. Let me suggest that you google for "diode rectification", and see what turns your crank. I just did that, and the first few entries are kept at a basic level, so I'm sure you can follow them easily, since you said that "voltage doublers" made sense to you. As usual, you know where to come, if you have any further questions. HTH sumgai |
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Post by jcgss77 on Sept 18, 2010 13:52:42 GMT -5
Pedal update-The good news is I have a tube pedal that works! The bad news is, there is so much noise it is unuseable. I can hear the signal through my amp, but there is lotsa white noise. I used a 12vAC/1A psu into a bridge rectifier, with an electrolytic capacitor to ground right at the input. I also used a 19v DC pedal with the same electrolytic cap to ground. Both yielded the same problem. I checked and double checked the build on the breadboard, and it is right. The schemo I am using is here:  I am omitting C4 and VR2 for more gain. Now, the nutz part. I am using a B250K for the gain pot, and a B1M for the volume. They are just what I had laying around, that were closest to the values called for. I will be experimenting more with those values once I get this thing cleaned up. The cap I am using for filtering is a polarized 10uF 50V. Can you please tell me what I am doing wrong, or what the source of the noise is? EDIT:I ran the circuit with a 9v, no filter, no regulator, and it was the most clean signal I have heard yet, but there was still a lot of noise, more than is acceptable. |
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Post by JohnH on Sept 18, 2010 16:09:19 GMT -5
OK, that looks interesting! We will probably have to await Dr sumgai for prognosis and diagnosis. In the meantime, it might be informative to test as follows:
1. If you ground the input, does the noise remain or go away?
2. What are the in-service voltages of the power supply and at points 1 and 6?
3. Through what range does the voltage at point 1 vary as you sweep the gain pot?
4. Does the gain pot work to control gain?
Most of that is related to checking whether the tube sections are biased rightly
cheers
John
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Post by jcgss77 on Sept 18, 2010 16:22:09 GMT -5
Thanks, JohnH. Voltages will have to wait till tonight, as the kids are up and electrical shop stays closed while they are up. I don't have a workshop  There is too much noise to tell if the gain pot is working, but it does sound like it is. I am thinking that there is some source of interference coming from somewhere in here or next door. Also, the house is not properly grounded, so I am thinking that I am picking up noise from every other electrical device in the house. I have always had a little noise with my guitar equipment here. I can report that I think that the high resistances of my pots are causing squealing when I touch the guitar strings. I turn the volume pot down, and the squealing stops. |
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on the plate to about 48 volts 
(or so, depending on what info I get here). I have read about using a voltage multiplier for this, but can't seem to find a proper schematic for this. Can someone please share with me the proper way to accomplish this? Thank you for all assistance.
