Step 8: Cathode Resistors And Bypass Caps

... and the Coupling Capacitor between the two halfs of the 12AX7. And other connections...?
Get these Parts:
2 4.7k Ohm Resistors
1 35v 2.2uF Cap
1 63v 0.47µ Cap

400v 10nF Cap
100k Resistor
<p>plsss. reply</p>
<p>how can connect this to guitar </p>
<p>Here's a newbie question. Is that a 60v AC or DC power supply.</p>
<p>Mine keeps squealing, tried different tubes, different power supplys nothing fixes it. Any ideas?</p><p>BTW Really good instructable very straight forward </p>
<p>Hi... random question here but I have a random ECC82 Tungsram tube kicking about and I am looking into making this.. I can follow the instructable with no probelms because of the images but I am not too hot on schematics when it comes to the transformers... What is the input voltage for them and would you be able to put a picture up so I can see what it is meant to look like? </p><p>Thanks in advance... </p><p>Craig :)</p>
<p>how dangerous is this build?</p>
<p>I am looking for more information on the step-up converter, is there a source for how to build it, a BOM or any other information available? Thanks</p>
can someone help me out with the switches, becouse I whant to solder it all on a pcb but dont know where the switches go on the schematic
<p>is there any way i could make this to run on a 9v power supply rather than making the step up/down transformers?</p>
<p>Thanks for sharing this simple tube amp circuit. I am new to diy amps so I have some questions with the build. </p><p>I just happen to found a power supply unit at home that gives 350mA on 12 volts, so Is it possible to make this preamp run on 12volts 350mA? i have reduced the resistorstors to the cathode to 50k&Omega;. Also where do I connect the ground to? Should I connect it to the negative end of the power supply?</p>
<p>Hey!<br>You should be able to convert the circuitry so it runs with your PSU; first, you should wire the filaments of the tubes in series and directly tie them to your psu, thus powering the filaments with 12V/150mA (as described in the tube datasheet); further, reducing the anode resistors is the right way, 47k sounds about right, if you're unsure just fool a little around. And yes, your psu negative goes to signal ground.</p><p>Have fun!</p>
<p>HI, Lenny24 ! Great work !!! Let me ask you some questions...Do you have a pdf version file for the PCB's step up/down converter ? I'm not a pro in electronics and I;m a little (dazed &amp;) confussed. (I don't speak English either...I'm doing my best so, sorry and thanks a lot !)</p>
<p>Hello, your project is very inspiring! Thank you alot.<br>Im having <br>questions about your psu, i havent built any smps and am researching the <br> chip you used. and your schematic seems different than all the examples <br> ive found( diode and inductor in different places) could you please help me with calculations for 9v 1% input and 60v(0,01a??? or what ever amps your anode eats?)0.01vripple out for the schematic like yours?(since you probably didnt use the datasheet example schematic for a reason)</p><p>also when using multiple regulators(notswitchingmode) in a single output, does the adding up of input filter caps do any harm to the regulators?</p>
<p>Hello, thanks!<br>The schematic used is just a simple boost-converter using an inductor, a switching-FET and the chip as switching regulator. The output Voltage is more or less independent of the input voltage as of the fact that its a regulated supply. The output voltage is set by the voltage divider R7 R3.</p><p>Do you want to connect multiple regulator outputs together? There may be some difficulties with that.</p>
<p>thx for explanation! is there a need to use a fet, couldnt the chip supply enough power by its own? are there any improvements for this kind of low current application? if there is, maybe you could help me with the calculations. i used an online calc for the mc34063 and it gave me these values in the schematic ive added. and i have access to 470uh coils that i could use both between the pins 1 and 8 and also the low pass on the output with the 100uf cap.<br>about the regs- no i do not want to connect the outputs, just the inputs and on the back of my mind i remember something about max input capacitance for regulators and for instance if id use 5 from the same power source and only one would be used at the occasion it would have 5 times the input capacitor, wouldnt it be problematic?<br><br>i am working on a 9v psu for my addac and the stuff that connects with it and the plan was to put 3 separate regulators for 3 outputs @9v and it would be nice to power a preamp like yours with this same transformer, so 2 extra regulators for 6.3and60v.<br>also how much current does the 60v line needs to supply?</p>
<p>Hey there!</p><p>The chip itself could deliver enough power, thanks to the 1.5Amps switching current of the transistor, but: its only rated at 40 Volts Uce, which means it would definitly die because of overvoltage. If you have one on hand, you could surely use any transistor which is rated with Uce &gt; 80 Volts and switches enough current for your application.</p><p>Connecting the inputs of different regulators together shouldnt be a problem as long as the power source is able to deliver enough current for all circuits, including 10 - 20% buffer. In case one of your regulators then starts unwanted oscillation, you could try decoupling the regulators with a small inductor (eg. 2&micro;2H, depending on your current) and a 100nF ceramic (!) capacitor in front of the switching type regulators. </p><p>R4 is the gate pulldown-resistor, its used to switch off the mosfet, because only the 'on'-state is driven by the internal Transistor of the chip.</p><p>R5 creates a voltage divider with R7, which determine the output voltage of the regulator. It shuts off, as soon as the input voltage at pin 5 (which is connected to the tap of the voltage divider) reaches 1.25 Volts (Vref).</p><p>C2 should be used if your regulator is oscillating; if you double the resistance of the voltage divider, the capacitance should be roughly halved.</p><p>hope i could help!</p>
<p>thx ill try to put this together see how it runs :)</p>
<p>as i understand you had a 12v supply so ive changed the Vsense resistor to a one for 9v and also changed the coil and Ct accordingly. and do i have change some other values like R4,r5,c2? you think this schematic below would supply 60v?</p>
What about earthing the circuit? I mean the third wire (earth) of the plug, where have to be connected?
Most important, I normally tie my metal casing parts to ground. In cases of tube power amps, I <strong>do </strong>tie my circuit ground to the 3rd Powercord Prong (PE), but if you are using a two grounded pieces of electrical equipment,&nbsp; it is likely to cause hum because of two ground connections. In this case, you may want to consider tieing your Preamp-Ground to earth with a 10 Ohm resistor with two antiparallel diodes and a 0.1&micro; film capacitor.
Hi, sorry I am a newbie about amps construction, I am asking how to connect the power transformer. From the circuit scheme I'm not able to find the points where to connect the 6.3V output and where to connect the (100-200V ?) output. And, the 100-200V output have to be reduced to 60V? And where must I connect this 60V output. Sorry, probably those are stupid answers but I need a perfectly detailed recipe :)
Hey there, <br>At first, youll have to rectify your AC Voltage, coming from your transformer. Thats normally done with 4 rectifier Diodes ( eg. UF4007 or 1N4007) and then filtered with capacitors. With the rectified AC voltage, you are able to supply your circuit at the points, where that voltage is needed (if you take a look at the last step of this 'Table, youll find a supply-point named 'V+'). <br>The low AC voltage for the filaments is wired directly to the filaments of your tubes (hint: the Datasheet of a tube could be a really great helper!). <br>If the Capacitors and Resistors in your circuit are able to withstand the higher Voltages, there shouldnt be a reason to reduce your perfectly good 200V to 60V. <br>Stay safe and have fun!
is there any way i can make this thing run on 12v? i cant get a 60v PSU and i have seen videos of matsumins valvecaster running a 12AX7 valve on 12v. I have reduced the resistor values down to 1/10th of what they were on the power supply to the cathodes, and i have removed all resistors totally on the supply to the heater because i have read that to get a valve to work in starved cathode mode then the heater must be as hot as possible without causing it damage. I am not very good with resistor vaues, so can u get back to me asap on this please. <br>hazza
I am not sure how to do the emmiter follower stage, it just adds awful solid state distortion and lowers volume, causes &quot;dead battery in fuzz face&quot; style sag etc. I need some help
Hey there, Im glad it works out for you! <br>The emmitter-follower stage has to be DC-Coupled, meaning there should be no coupling-capacitors between the anode-connection of your last tube section and the base of your NPN-transistor. The collector is tied directly to V+ and the emmitter should be tied to ground with a 4.7k-22k resistor, depending on the type of your transistor. <br>otherwise, you could send me a schematic of your actual set up and I could try to fix it for you.
ok thanks for that, could that have been the reason for the distortion? It sounded more like a plain old overdriven transistor to me. I re-did the emitter follower (it still had the coupling cap between the valve and the transistor at this point) with some base biasing and it just acted way to sensitively to any input from the valve and caused this ugly, buzzy sort of clipping, that kind you get if you turn up a stereo or radio too loud and things get nasty. Thx for suggestion I will try with the emitter follower again although It sounds alright as it is. It seems as though, however, that the valve isn't driving my output stage hard enough for it to reach its maximum clean output (about 5 watts). I have been trying to fix this with a variety of different methods, but will the emitter follower resolve this situation?
It could totally have been the reason for the Distortion, if the transistor stage's bias current was near 0 and the output voltage was driven of of near GND-Potential, one half of the sine wave is completely cut of! This type of clipping is very similar to what your are describing, its very fuzzy with cut sustain and so on. <br>If it isnt driving your power stage enough, you might try to put another amplifing transistor stage after the tubes, as they normaly put out only a relatively small potential at the output. That amplifing stage should have a gain no higher than 2 or 3.
I can give you a schematic of my output stage, which is a slightly modified version of a very popular low power class a/b design.<br>here is the original: http://hackaweek.com/hacks/wp-content/uploads/2011/08/class-ab-amp-schematic.jpg<br>My modifications include: output npn to bc337, output pnp to bc327, driver npn to bc547, as well as a couple of small resistor changes. This was to accomodate for me not having exact resistor values and transistor types. The output stage itself is sensitive enough to amplify a guitar signal. Is this sensitive enough to amplify the high impedance signal from my 12ax7 preamp's output?
hey! Sorry for this late reply, I've been occupied lately. <br>Yeah, Sure you are able to get this running on 12V, at first, you may want to consider using a 12AU7 as the Tube as of its lower internal resistance. Further, the resistor values stay pretty much the same, but its best to use 2 Preamp Tubes for 3 Gainstages and 1 Cathode follower. On the other hand, you could use a single Tube and a NPN-Emitter follower for a low output impedance. Otherwise you may loose some of your tippy-top highs. I would use a 220k (a) and a 4.7k bypassed with 0.47&micro; (c) on the first stage an maybe a 100k (a) and a 3.3k on the second.
hey ya thanks I managed to get a 12ax7 running on a 12v plate voltage and it is now inside, believe it or not, a hybrid battery amplifier using six of those humungous D cells as power supply and a pnp/npn push pull power stage. I will add an npn emitter-follower between the valve and the power stage, and an npn signal booster in front of it as it is the cleanest valve pre amp I have ever heard. The whole thing is inside a Chateauneuf Du Pape box lol.
Very good job!! I have a question can you wire two of these together to make a two stage pre amp because if you could i can use the Hammond 262B12 transformer to wire the tube filliments together in series and that remaining 60v in series to use the 120 from the secondary
Thanks!<br>Yeah, you could easily do that, just leave out the Gain pot, from that point the Volume Pot would be the Gain pot.<br>With two additional Gain stages you are able to get some Rock tunes and maybe some High-Gain distortion, depending on how exactly you combine the two stages.<br>The 262B12 is a pretty neat Transformer for this application, Just make sure you use Capacitors with a voltage rating thats high enough to take the 170 or more Volts DC. But that shouldnt be a problem.<br><br>Have Fun Building it!
I am having trouble reading the values on your schematic, could you post a better image of it please? Really want to try this one out!
Well, here you go, check out the last step for the Schematics!
Hey there, I'm just starting to get into this kind of stuff and im a little bit confused on your power supply set-up. I'm mostly getting confused with how to make the transformer/ power supply. Would you know of what kind of power transformer I could buy so that I can bypass the making of one right now?
You could use a Preamp- Power Transformer. You should be able to get them at your local electronic shop.<br>It should have something around these Values:<br>Primary: 110 or 230V Input (Depending on where you live)<br>1. Secondary: 6.3Volts @ 1 Ampere<br>2. Secondary: 100 - 200 Volts @ 50 mA (Note: the DC-Voltage will be multiplyed by the Factor 1.41, If you have a Output of 100 Volts AC, youll have a DC Output of<br>141 Volts)<br><br>
Would I need to add anything different to the circuit like a choke or something? Also would I just connect the transformer to an IEC socket for power, and where in the circuit would be a good place for a fuse to be put in?
The first Fuse should be in series with the Primary of the Transformer, the second Fuse in series with the 100 - 200 Volt Secondary.<br>You should use Fuses with a Value twice the Amperage,which you drain through it. Otherwise, it will blow, even if theres no Failure.<br><br>Youll need a CLC or CRC filtering supply. I Prefer CRC, they are easier.<br>For a simple preamp, you should use a Bridge rectifier, after that a charging Capacitor (the first C), that one should be around 47&micro;F and rated 1 and 1/2 Volts more than your Filtered DC Voltage. <br><br>Example:<br>You got a 100 Volt AC Secondary.<br>After the Rectifier you got very Unsmooth 141 Volts, the next Voltage-rating on Caps should be 200 Volts, so use one 47&micro;F @ 200 Volt Type.<br><br>After your Charge-Cap, youll need a resistor and another Capacitor, to complete the CRC - supply.<br><br>The Resistor should be a 2 Watt type and should have a value around 10 - 22 Kilo Ohms.<br>After that, use another cap to finally smooth out any spikes, that are in the Supply voltage.<br>For that, you can use another 47&micro;F @ 200 Volt type.<br><br><br>
Thanks for being so helpful with questions! But I do have a problem with finding a transformer. The local radio shack doesn't have what I need, and I've looked through a lot of different transformers online trying to find one with the right specifications. I don't know how far off the numbers can be from the specs you gave me. I've found some that are close, but Im not sure if they're usable-<br><br>http://www.bottlehead.com/store.php?crn=221&amp;rn=439&amp;action=show_detail<br><br>http://www.tubedepot.com/tr-pw-13.html<br><br>http://www.hammondmfg.com/261.htm <br><br>If you could look through these and let me know your thoughts on them, it would be much appreciated!
No problem, man!<br><br><br>The first one looks pretty Solid, the second one looks a bit Underpowered for me (It could get very warm in use).<br>And with Hammond-transformers, you can do nothing wrong.<br>You could use the Hammond 262B12, but then youll have to connect the Filaments of the 12AX7 in series instead of parallel, thats just one Wire less, so easy to do.
out of curiosity, how much did it cost you to do this build?
Pewh, Well, I had a lot Parts laying around, I think about 10 - 20 &euro;.
Thanks for the schematic, it really helped me with another project :)<br> With what values have you actually ended up using for the inductors?<br> Would one of those <a href="http://stores.ebay.at/TRADINGHOME-ELEKTRONIK/Induktivitat-/_i.html?_fsub=19740432&_sid=31569152&_trksid=p4634.c0.m322">here</a> work?&nbsp;
Hey!<br>Sorry, I have no Exact values of the Inductor. I winded it myself, I think 50 Turns of 25AWG Copper Wire... I would use a 330 &micro;H Type, just to be Safe.<br><br>Which kind of Project is it? Normally, they should work.
Great job! I've been waiting for something like this since i read gmoon's amp 'ible and wanted to do it small scale first. You probably know this but for anyone else to whom this might not be clear, this preamp (or any) will not perfectly replicate an overdriven all-tube amp, because the power stages also affect the tone. Also, based on my research, good iron(transformers) can make a really big difference, so as a mod someone could do this using trannies instead of the regulated switchmode Power supplies.
Thanks! Yeah, thats right.I think my next 'ible will be a 5 Watt All-Tube Amp. Ive ordered some 12AX7 and EL84 Tubes, and I want to try that.<br>But If you only have got an Transistor Amp (Like me, until I finished my Tube Amp) this is a good option to bring some soft drive in your Songs.<br><br>Well, I dont have big Transformators at home, so now Im' thinking of Building the 5 Watt amp with a Switchmode, too. But in that case, I would build myself a step up transformer or I have to look for an ooooold TV. Otherwise, the big advantage of SMPS is, they have a much higher Frequency, which means you have no 50 - Hertz humming in your Powerline. SMPS handle frequencies, which are muuuuuch higher than the Human ear could Recieve.
yeah, i've just been drooling over all the guitar instructables. I moved and couldn't bring my guitar with me, so now all i have to play is some old classical guitar i picked up. Plus, i'm kinda broke too (studying hard with no time to work) so it'll probably be quite awhile until i can afford a guitar, let alone decent amp. I've been thinking of using a preamp like yours going into my computer. Using audacity (freeware)and headphones i can monitor myself and record loops to jam with...
Cool Idea! For use with Computer, you could just put in a 3.5mm Stereo Jack as the output Jack in this design and mess around with it.But maybe you have to make some changes in the Input and Output stages. Use a 100 Ohm instead of a 10k ohm resistor in series with the 1M ohm resistor to make clean sound Possible and Use a 100k insted of a 10k series with the 100k output pot. That will decrease the outputlevel and makes it easier to handle with a Computer sound card.
I'll definitely keep this in mind for when I can finally get my guitar back. Thanks.<br>

About This Instructable




More by Lenny24:Guitar Tube Pre Amp How to Make a Voltage Inverter 
Add instructable to: