Hey everyone, I've recently ordered a bunch more 6J1 tubes from aliexpress to test in this circuit and I've found the results with them to be pretty inconsistent. Some of them seem to have much lower gain at these low voltages or much less headroom, leading to very quiet and/or very distorted output. Even though they all came from the same order they seemed to be just a bunch of random new old stock tubes from various manufacturers made at different times. The tubes that I have that work well say 北京 (Beijing, I think, I can't really read Chinese…) on them with stripes that run along the length of the tube with a star in the middle. The print on them seems to indicate they were made in made in September of 1980. I also have some earlier tubes from 1978 with the same logo printed widthwise across the tube but they don't perform nearly as well. Maybe they're just really inconsistent in general though? So if you wanna repeat this it'd probably be good to buy a bunch of the tubes (you can currently get 5 of them for $10) and just try them till you get one that sounds good…
The 2 watts in the datasheet for 6J1/EF95 tubes isn't output power, it's max plate dissipation. When biasing that tube, you have to make sure the voltage and current at plate are lower than the plate dissipation, or the tube redplates and eventually burns out. The actual power output for a tube like this is probably between 0,1w to 0,5w. If you want a cheap tube for an easy 1 tube amp build, try the ECL84/6DX8 and ECL82/6BM8. They're triode-pentode tubes, essentially a Preamp and Poweramp in a single bottle. The former puts out up to like 0,9w, the latter can push out 3w.
Oh yeah, I didn't explain that super well in the video I guess… It's more that having a plate dissipation rating of 2W at 120V indicates that the transconductance of the tube is probably pretty high, which is what really limits power output when using them at low voltages. So in this case the high-ish power rating is really just a quick indicator that the transconductance is probably decent.
I found this video cause im learning about tubes from an electronics standpoint and i wanted to see if they really are as simple as they seem. Good to know they are XD
Every few years I check prices of random tubes and always keep an eye out in the meantime. I was 58 seconds in and had to pause to look up some prices. I just ordered two for $15 and they will be here in 3 days. After waiting a few years for these tiny lil guys, the stars finally aligned. Thank you. Lol
Yes, it absolutely is! It really helps that most guitar cabinet speakers are very sensitive, so you get quite a bit of volume even with very little power!
Probably better as a preamp, it has good range and would work well set up as a pedal, you could even use a boost converter so you can run it off a 9v supply and get your 2 watts if you crank the voltage up......
I’ve honestly been looking for a channel like this for years. Glad I stumbled on this micro build. I’ve been taking old tube radios and converting them into guitar amps for years. Stoked to find this little tube amp. Gonna get started sourcing parts and building this TOMORROW! Just went to your build site and noticed an issue I’ll have here in the US. Our wall voltage is 120v. So if I got a transformer to step down to 12v it would only be 10:1. Would that work? Any solutions?
It might work, but the safest bet would be to get a lower voltage transformer. 6V transformers aren't very common though I think. You might also get lucky and find a center tapped 12V transformer which can be used on both 120V and 240V and wire that correctly.
@@miclairmiclair876 There are a lot of very different tubes with 6 and 7 pins that have wildly varying functionality and parameters. If you want to swap it for a different tube be prepared to do a bunch of research into what you're getting first.
I haven't yet built it but I did design a smaller stereo amp that is all valve! Christ, I should start a TH-cam channel. Forgive me for not passing on details of valves for this reason but I' like to thank you for joggin gmy memory!
I test your circuit with higher voltages. 48v from a canon printer, it works. I used another source for the heater. I also used 100v. With some thinkering and another pair of 6j1for a preamp this could be a very useful low power practice amp. Power amp distortion without getting ear damage.
@@KrisSlyka no, I just increase the input input capacitor from .1u to 4.7u it was cutting to much low end for me. for the heater I use one of those DC DC buck converter to reduce 12v from another PS to 6.3V. I could not find a 220V to 12V transformer so I used an american 110 to 12 with center tap. I use the center tap that is 110 to 6. Roughly 20:1.
I’m doing the same thing right now too… I have a 42 volt supply and separate heater supply as well instead of the biasing resistor of 100k I put in a 1 Meg pot…. And adjusted till it sounded good in my ears… looking for a more output/higher headroom..How was the sound at 100 volts..? What was your power supply for the 100 volts…? Any info would be great!
I've got a spare 6J1 that I'm *itching* to turn into a preamp to drive a solid state output stage (I have a spare LM3886 if I can find a decent size driver, or something smaller if I'm just gonna drive a 4" or 6" as a little practice amp). Can the 6J1 operate at a lower voltage than 24V, or would I have to give the output stage a bit of extra headroom and just jam the tube's full output right into it? :D (can you tell I've never done this before)
Yeah, it'll run at 12V or 9V probably, just with even lower headroom. But if you're only using it as a preamp you can skip the output transformer and bias it using a large-ish resistor instead.
@@utkukaya757 Sure! You can use two tubes in series to increase the gain, basically making the first one act like a preamp, or you could use two in parallel or in a push-pull configuration for more output power.
Nice clean schematic! 100K input pull down seems a little low for impedance it would be cool to add a lightbulb in series with that pull down to experiment further.... Cheerz!
Well, it's a "power" amp, designed to be driven by some kind of preamp or just any guitar pedal, so the input impedance isn't a huge problem. I'm kinda curious about the light bulb though, what would that do?
@@bigbasil1908 everything on this amp draws less than a milliamp (excluding the filament), that's not even enough to light a lightbulb, let alone burn anything out.
I'm able to built every known pedal effects you can have on any diy websites but I can't understand the meaning of the circuits that are used as you can do, that's quite very impressive how a true knowledgable person can do with that low number of components! 👍
I have a tone-EQ- and gain section from a 9V powered guitar amp, and it sounds good as is plugged straight into a guitar cabinet. I want to add this, just for some more tube goodness. If I added this before the amp circuit (order is guitar, tube amp, to 9V amp), would I hear less output? I feel like I’d have to run the tubes after, just so the 9V amp is pushing the tubes a bit more. What’s your thoughts?
You could go either way. You can probably get more volume from the 9V transistor amp plugged into the cab because transistors just work a lot better at low voltages. But it would feel like a bit of a waste to just use this as a preamp. And the output transformer really needs to be plugged into a low impedance thing like a speaker to work right. If you plug the tube amp into the cab and drive it using the 9V amp you're probably going to overdrive it pretty hard. It's hard to say, honestly. I'd just try both and go with what sounds better to you
@@KrisSlyka Thank you! Also, I greatly admire your patience for answering so many questions coming from people like me who have no clue what they’re doing. I’ve read through so many repeat questions on you channel 😭
@@KrisSlyka Also just a brain check, I'm in the US, so I'd have to find a power transformer that has an output of around 6.5V with our 120V input right?
Just checked the price for a pair of 6j1 they are a little under 5 dollars on ebay I haven't found the dollar tubes. Even so it's not as bad as 12ax7 tubes.
Thanks I never bought from them. Maybe this will help other viewers as well. I did find in quantities were each price was about a dollar. If you buy like 10 or 12. I do want to try to build a headphone amplifier using these tubes. Thanks
Thank you very much for sharing this project Kris ! Just a question, how many watt your speaker get ? Or can you give us the name of your blackstar combo ? Thanks !
@@KrisSlyka hey Kris… how would this design work at higher voltages..? Keeping a separate filament voltage and say run 90-100 vdc… would there need to be some change to resistors and capacitors… if this will work..? Found some power supplies I would like to try… thank you Kris for any input you may have, you have always been most helpful and informative. Thanks again Justin
@@justinj1359 Yeah, basically! Keep 6V on the heater and then adjust the plate voltage. You'd definitely need to re-bias it though since the transconductance of the tube will go up a lot at higher voltages, probably also add a resistor to the screen. I don't really have any experience with that though since all the tube stuff I've done was low voltage
How do you get more distortion without using pedals? I’m trying to figure out getting heavy distortion with a good crunchy bunt, what do I need a better resistors .?
Getting really heavy distortion is gonna be tricky with an amp like this. You can drive it real hard but it's not gonna sound great probably. A lot of the "goodness" of a distortion sound depends on the EQ-ing and gain staging inside the amp.
Well, +/- 12V is the same as 24V, so that's gonna work just fine. Higher voltages might need a tiny bit of bias adjustment, but generally it should work quite well.
Audio transformers have an air-gap to help prevent saturation of the iron, the salvaged transformer does not. I guess maybe with guitar amps you don't care.
It's definitely not a drop in as far as the heater supply goes since it's only got a 1.2V heater voltage. As far as the other voltages and biasing goes… no idea. Just give it a try! Chances are good you'll get something at least since it's built to run at a quite low plate voltage.
I've been thinking of making a more "proper" version of this amp with a little PCB and small off the shelf mains transformer as output transformer. If there is interest I could look into that?
@@KrisSlyka yes I think people would be interested if the price not too high. Transformers are expensive as they are. using a wall transformer would cut cost if you sell just the amp parts less the transformer. Just an idea you can use 70 volt line transformers that are used on pa systems for single end amplifiers. Push pull need a center tap.
Hey Kris! Another milliamp question if I bring the voltage up to around 90-100 besides the electrolytic cap being raised to say a 350v rating or so what I need to change capacitance? I have the biasing as a 1 Meg ohm pot. I’m also running the heater off a separate power supply… could you help me figure out values… or would everything else work ok..? The way I have it now is real nice can even get clean tones but would like some more headroom/output have it now on an old 4inch alnico speaker sounds good just looking for a little more output. Thanks Kris! Look forward to any info or help you could give me
Hmm… the input capacitance is probably fine, the main thing you might want to play with is actually biasing the tube to a negative supply. As the plate voltage gets higher and the tube's transconductance goes up you need to bias the grid to a lower voltage to stay at an operating point that will give you the best headroom in either direction. Otherwise it'll clip the wave form either at the top or bottom. The grid naturally takes on a slightly negative charge just from electrons hitting it, so in my circuit the biasing resistor actually pulls the grid *up* towards 0V to get more idle current to flow. Once you increase the plate voltage though the idle current can get too high and you might need to pull the grid to a lower voltage, which will require a negative supply rail of maybe -12V or so. Aside from that, maybe adding in a screen resistor would be a good idea, maybe 100Ω or so. Aside from that, well, there isn't really anything else in the amp to tweak!
@@justinj1359 Maybe check out the chapter on biasing here: www.valvewizard.co.uk/Common_Gain_Stage.pdf The original version of the amp uses grid leak biasing, but both fixed biasing using a negative supply rail or cathode biasing (ideally with bypass) should both work.
Back in 1954, this and other (25 in total) tubes were tested with reduced power. Satisfactory performance results were achieved with an anode voltage of 26 V. However, talk of 1.5W output power remains only a pale blue dream! 🧐Feel free to divide by ten! 🤓
Are any of the output signals safe enough to run into an Hxstomp with IRs? I would like to capture and mix the tube and output transformer interactioms with emulated speaker IRs out through headphone out of the Hxstomp.
No, they have a different pin count and pinout and are also completely different kinds of tube. The 6J1 is a single pentode and the 12AU7 is a dual triode. But I do have a video on my channel about building a small preamp using a 12AU7.
I wired this up using a screenshot of the schematic. It has the 120R connected to Pin 3 and Pin 4 going to ground, but I noticed that those are reversed in the build in this video. It didn't work when it was wired per the schematic, and I caught the mistake while troubleshooting. Still isn't working now that I've swapped them around. Did that damage the tube? Sorry if this is a stupid question. I know quite a bit about building pedal circuits, but I'm just now starting to learn about tubes. I tried googling first, but I can't find anything addressing that specific question.
Nah, don't worry, that doesn't matter. The heater is just like a light bulb, so the polarity doesn't matter and you can connect it either way around, so nothing should be damaged.
@@KrisSlyka I built a small charge pump to get 24v from the 9v going into my breadboard. Works fine on its own, but when I connect the amp circuit, the output drops to 12v (measured where the 120r and 100r resistors connect). I'm getting 12v on the heater, and about 2v on pin 6 (the screen?). Everything else is zero. No output. Any idea what I might be doing wrong?
@@brainbonkk How much current can your charge pump output? Powering the heater from the charge pump is gonna be a problem most likely since it requites a lot of current. Also it's kinda pointless to step up the 9V to 24V only to use a resistor to drop it back down to 6V and waste the rest of the power. I'd recommend running the heater off of the 9V with a smaller dropper resistor instead of the 120Ω one and only use the charge pump for the plate voltage. Also, 12V on the heater is way too much for 6.3V heater. Make sure you haven't burned that out. (though I doubt the charge pump can deliver enough current to burn out the filament)
Sounds good if you consider the price and availability of these. I bought preamp kit few months ago and they work well with my speakers for PC. But I also got extra one (for tubes and other parts) so I am thinking about making this one. I have one question. Can I plug my passive bass guitar to this preamp and then connect preamp to my bass amp? Or maybe I have to make transistor preamp for this one as well?
You're going to need some kind of preamplification for this since it's technically more of a small power amp than a preamp. The input impedance is kinda low, so the tone isn't gonna be very good without some kind of buffering and there also isn't a ton of amplification. Though the second part might be less of a problem if you're running it into another power amp. And for buffering the signal any kind of pedal with a built in buffer will probably do.
@@KrisSlyka Thank you very much. I ve build this simple 1 transistor preamp so it should act as a buffer. Anyway I am looking forward to building this circuit so I will tell you if it works as expected
@@KrisSlyka I've made my prototype but it seems the filament isnt heating. I didnt have single voltage source of 24VDC so I used 2 sources of 12. One has max output of 1.5 amps and other of 3. I dont know what could be the problem
@@zazacraft2062 Start by checking the resistance of the filament to make sure it's nor burned out or something, then check how much current it draws when powered.
hi, thanks for sharing. i tried to do it but the transformer i used a 9 volt by 127 volt from an old AC source, and there was no sound. If I use a 12 volt by 220 volt transformer will it sound?
If there is no sound at all it's probably a different problem. Even with a suboptimal transformer there should still be some sound. I don't even know if the transformer I used is "optimal". It's just what I had. And the ratio of yours doesn't seem so far off of mine, so I'd probably look for the problem somewhere else first.
Hey there :) I was just about to start my first project with tubes. Is there any good source you could recommend, that has a little workarround or just good informations for the beginning? To be precise I wanted to "pimp" my marshall toy amp ms-2. And look what I can get out of it.
I don't really know of many. One very good, albeit also very technical, one is "Triodes at Low Voltages" by Merlin Blencowe which you can find here: valvewizard.co.uk/Triodes_at_low_voltages_Blencowe.pdf It only covers triodes for preamps but lays out all the basics to keep in mind and is a good starting point. If you want to learn how different tubes work in general check out this video by Mr. Carlson's lab maybe: th-cam.com/video/oHjZs0bNwEs/w-d-xo.html Generally though I've found the best way to get to what you want to build is just do to a bunch of experimentation. The good thing is that at low voltages aside from burning out the heater tubes are pretty much impossible to kill :D
@@KrisSlyka Thank you for your answer :) I didn't necessarily meant TH-camrs. But I couldn't find a book covering that topic as well. But I guess to find out about the sound of different tubes i need to experiment anyway 😄
Sure, but you're gonna have to add in a plate resistor and probably change the biasing a little. Or you can also just use it as a preamp with the transformer.
Total rookie question... What watt rating is the 100 ohm power filter resistor? Also the watt rating of the 100k biasing resistor? Is a 24 Vdc at 2 amps power supply sufficient?
@@KrisSlyka I’m pretty novice and always looking for low buck solutions I think it will be nice with my behringer tm300 pedal as an input. I would like to also build a tube preamp which I would guess I could input into the “milliamp” ...? Also in the milliamp I’m gonna try some GE 5654w tubes, hoping for good results!
@@justinj1359 Yeah, this thing goes great with a little tube preamp. You could probably even adapt the circuit from my preamp video to run on 24V and built it right into the same chassis with this one to make it a "full" amplifier!
@@michaellundsrensen2292 The transformer is part of the biasing of the tube and it's plate current supply, so DC current has to flow through it, otherwise the amp won't work. It's the usual setup for an output transformer on a tube amp. Tube amp output transformers are specifically built to handle quite high DC currents without saturating for that reason, but the currents here are so small that it really doesn't matter.
I've built this amp and can't seem to get any real volume at all, just incredibly quiet. I've even tried it with 110v input, which is louder but still super quiet. Any tips to increase the volume? I'm using a 20:1 OT.
What are you driving it with on the input? It's only a power amp, so it's gonna need some kind of preamp stage if you wanna get any real volume out of it. Even a guitar pedal that allows you to turn up the volume will do
I'm using a 10db tube preamp which doesn't saturate the tube, so nice & clean. I've tried a more powerful solid state pre-amp but it just over-saturates the 6j1. Was just wondering if there's any component changes which might boost the output. I'm running it through a 30w 8 ohm speaker, maybe that's too big for it to drive? I'm using a 470k pot for the bias resistor, set at the full 470k. Sounds super sweet, just very low volume. In your demo it seems to produce decent volume.
@@rogerlightbown what's the efficiency of the speaker? A guitar cabinet speaker will give you something like 90-100dB per watt, whereas normal speakers are probably more in the 20 to 30-ish range
@@KrisSlyka It is a guitar speaker, but suspect its not that efficient. Could of course be a poor output transformer which is from a 240vac to 12vdc PSU, so in theory should be ok as it's 20:1. Think I'll just try a couple of different speakers.
Well, it's gonna be a very different amp at that point. That's gonna need different tubes, much higher supply voltage, more complex biasing, most likely a proper output transformer… That's not impossible of course, there are plenty of plans for higher power tube amps out there or you could always design your own from scratch if you feel like it.
@@KrisSlyka I was thinking of using these 6J1 tubes, similar to how EL34 or 6L6 tubes are used in the big 100w amps. I may have gotten the output wattage of this tube wrong (been hearing about a lot of different tubes today).
@@KrisSlyka okay, so an 8 watt amp. Since there are 5 and 10 watt high gain amps that are great for recording and practice, that's still in the ballpark.
Hey kris! Quick question for you if you don’t mind..? If I raised the voltage say I have 42 volts would this increase my output..? Would I need to change caps and resistors..? Just a thought... I am still learning. Thank you for any input you may have! Have a good day!
Yeah, that would definitely work and probably give you quite a bit more output power. You might have to play with the bias resistor (R1) a little, but you can just replace that with a potentiometer and turn it until it sounds good. For a higher voltage you might need a higher valued resistor. I don't think any of the other parts would need to be changed aside from making sure that the capacitors are rated for the higher voltage.
@@KrisSlyka hey kris! Once again thank you for your reply! I have put in a 50v electrolytic capacitor in... and turned on the power got good sound very momentarily then nothing... is that to be expected with the bias way off? I am really trying to read more on biasing with mixed results.. would putting a 250k pot and finding a sweet spot restore and hopefully significantly improve my output.. again any insight would be so much greatly appreciated! Thanks from Wisconsin, USA by the way as well! (Also if I could direct message you in any way besides TH-cam would be great if that would be ok with you?)
@@justinj1359 Ohh no, I just realized that I forgot to mention something super important. The heater of the tube still needs to be run at 6V and since this build just relies on a resistor from the plate voltage to limit the heater current my dumb advice might have just burned out the filament in your tube. :( I'm super sorry, I completely forgot to mention this since that's not how you usually do it. If you change the voltage to the tube it's super important to keep the heater voltage the same! Either by putting in a larger resistor (which becomes very inefficient at higher voltages) or running the heater off of a separate power supply. Again, I'm super sorry I forgot to mention that…
@@KrisSlyka LOL it’s totally ok, at least it was one of my Chinese 6j1s that I have numerous of, but if it would have been one of the GE 5654’s that I have a pair of I would have been a little bummed 😉.. but anyway all good! Gonna change up and run a separate 6 volts for the heater and try again, what would you recommend on the value of the pot to find what sounds good for biasing..? 250k A or what would be in the range..? Once again thank you so much for all your help and loads of information! I really appreciate it! And it’s a learning process so I expect to burn up a few things a long the way lol... just found a lead for some more 6j1s cheap on aliexpress 😉
@@KrisSlyka I also realized a huge mistake I had the power filter and bias resistors switched! 🙄 another rookie move. But fixing that has got me a proper amp going. So grateful!
@@KrisSlyka thanks for the answer :) how to you measure the output impedance of the tube? I want to check if I can keep the same 20:1 ratio for the transformer in this push pull experiment
@@piringuabiroslau3769 Well, I never measured the output impedance to begin with and the 20:1 ratio was just based on what I had lying around. Though most commercially available output transformers also seem to be in the same ballpark. One simple option if you don't have a center tapped 20:1 transformer is to just use two separate ones, one for each tube, with their outputs connected in series and phases inverted.
Hi Kris. I just finished prototyping this amplifier, but the output volume is quieter than speech level. In your video, it seems to be louder than speech level. Is this correct? I'm using it with a Celestion Seventy 80 speaker. Thanks
Yeah, mine definitely is. I mean, might depend on how loud you speak? I don't own a sound level meter, but a quick measurement with 4 different (albeit totally uncalibrated) apps on my phone gave me levels between around 68dB and 75dB around a meter from the amp, which is in line with what I expected. Definitely louder than a conversation, but not overwhelmingly so. Take those measurements with a healthy pinch of salt though. As far as the low output volume of your amp goes I'm not really sure. I think the biggest variable here is the tube. Since they're meant to run at higher voltages they're often not really well specified at low voltages. I've had very different experiences with 12AX7 tubes from different manufacturers, with some working really well at low voltages and others not at all. With the 6J1 in this build it could be similar. I've had some Chinese 12AX7s work great in low voltage builds, which might partially be cause these tubes are made specifically to run in low voltage headphone amps and preamps. Maybe it's similar with my cheap noname chinese 6J1s? I'm really not sure…
@@KrisSlyka My speech level is very low. Just to have an ideia about how low the volume is: if I connect the guitar straight to the amp, the speaker doesn't even make a sound. I have to dime an overdrive or a booster in front of it to have any sound coming out (and even with that, it sounds almost as low as the sound of the guitar when it is unplugged). It is good to know that it is supposed to be louder than a typical conversation level. Maybe I have some loose coonection in the circuit that is causing this low output volume. By the way: is it normal for that 120 ohms resistor for the filament to heat up? Mine gets very hot, I can't even touch it for more than a second (even being a proper 5w resistor). Thanks again :)
@@pauloscabeni5277 Yeah, that resistor getting hot is normal. I strapped mine to the chassis of the amp to dissipate some of the heat. It's dissipating around 3.5W, so it's well within the spec of the resistor. What kind of tube and transformer are you using in yours?
@@KrisSlyka The tube I'm using is supposed to be a 6J1, but it is really hard to read what is printed on it. Looks like it's "6ж1п 8704". The transformer is a 127v/220v to 12v, 100mA transformer (which I use the 220v terminal of the primary)
@@pauloscabeni5277 Hmm… 100mA isn't a lot, but that shouldn't make a huge difference… And that should be the right kind of tube too. It's hard to say how it compares to the china made ones though… Can you measure the idle current you get through the transformer when there is no signal applied?
@@lisentzudir1087 I can't really help with that since I've never use a 6N7 before. But you could start with a circuit similar to the one I show in this video th-cam.com/video/TllEAf0Hgnc/w-d-xo.html It will require you to do a whole bunch of your own research and experimentation though.
I got around to building something like this (with a second tube for preamp) but the output is extremely quiet, as in I have to hold my ear to the speaker to hear it. Do you have any idea how much output power you were able to get? Thanks for the video!
I don't really know how much mine delivers… Did you use the same kind of tubes for your amp? The kind of speaker also makes a big difference. Guitar cabinet speakers are a lot more sensitive than normal speakers.
@@KrisSlyka I'm using a regular 3 inch speaker. I suppose that's the main issue then. I'm not sure how sensitivity varies with size though. My transformer is also physically smaller than the one you show. I used two 6J1s, and I've ordered a couple more to swap out in case they are defective or something. I tried different transformers, but the maximum DC plate current I could get was about 2mA. Anyway, I'll keep troubleshooting. Thanks for the reply :)
@@RijuChatterjee Yeah, that's probably the problem there. Large guitar speakers can usually deliver somewhere from 95dB to 100dB at 1W, which is a lot compared to other speakers. Maybe give it a try with some headphones since those also tend to be quite sensitive. The size of the transformer probably doesn't make a huge difference since the power is so low anyways. And the tubes low transconductance is probably the bigger limiting factor than any internal resistance of the transformer. Of course there is also the chance that the tubes I used were just better suited for low voltage operation. Running them with such a low plate voltage is kinda out out of spec, so they're not usually well characterized at those voltages.
@@KrisSlyka 100dB at 1 watt... that's almost hard to believe. Although to be fair I don't have much experience with sound dB levels, I'm just thinking of numbers you hear such as "a jet aircraft at takeoff is 80dB". I just tried it with headphones, and it's on the quiet side but usable. It sounds quite nice too; I suppose using it as a headphone amp might be the best option atm.
@@RijuChatterjee Sounds like a lot, but isn't uncommon. Guitar amplifiers are loud! A Celestion greenback has a sensitivity of 98dB. celestion.com/product/g12m-greenback/ Sensitivity for speakers is measured with a 1khz test tone with 1W RMS power at 1m from the speaker.
@@KrisSlyka So I would like to build amp like this i got 6j1 tubes, can I just plug it to pc and play it like regular amp? Because PC audio output can act like preamp... is it posible or I need to build real preamp, and can I use same tubes for preamp? Thank you!
@@upside-down6211 What do you mean? The amplifier itself runs off of 24V because that was just a good voltage to run it at. The transformer on the amplifier itself is just there for output coupling.
@@upside-down6211 The power rating of the transformer doesn't really matter. This was just from a small wall wart that was rated maybe 1A. You can try running it on 12V, but it's going to severely limit the output power. (More than it already is)
It's built from scrap, so as long as you got scrap lying around you got your kit. On a more serious note, sadly those super cheap 6J1s don't seem to be available anymore…
@@josephforrest3713 I'm not sure! I haven't tried any other ones, but a similar small pentode might be a good start. Or just look for an EF95 or any of the other names this same tube goes by
I've been wanting to make a single tube 6gw8 guitar amp. There were some from Australia a long time ago. I am an American, so I'm internationally challenged. I have some schematics but am lost. Any ideas?
Hey everyone,
I've recently ordered a bunch more 6J1 tubes from aliexpress to test in this circuit and I've found the results with them to be pretty inconsistent. Some of them seem to have much lower gain at these low voltages or much less headroom, leading to very quiet and/or very distorted output. Even though they all came from the same order they seemed to be just a bunch of random new old stock tubes from various manufacturers made at different times.
The tubes that I have that work well say 北京 (Beijing, I think, I can't really read Chinese…) on them with stripes that run along the length of the tube with a star in the middle. The print on them seems to indicate they were made in made in September of 1980. I also have some earlier tubes from 1978 with the same logo printed widthwise across the tube but they don't perform nearly as well. Maybe they're just really inconsistent in general though?
So if you wanna repeat this it'd probably be good to buy a bunch of the tubes (you can currently get 5 of them for $10) and just try them till you get one that sounds good…
bro you should sell these
like the amp
The 2 watts in the datasheet for 6J1/EF95 tubes isn't output power, it's max plate dissipation.
When biasing that tube, you have to make sure the voltage and current at plate are lower than the plate dissipation, or the tube redplates and eventually burns out.
The actual power output for a tube like this is probably between 0,1w to 0,5w.
If you want a cheap tube for an easy 1 tube amp build, try the ECL84/6DX8 and ECL82/6BM8. They're triode-pentode tubes, essentially a Preamp and Poweramp in a single bottle. The former puts out up to like 0,9w, the latter can push out 3w.
Oh yeah, I didn't explain that super well in the video I guess… It's more that having a plate dissipation rating of 2W at 120V indicates that the transconductance of the tube is probably pretty high, which is what really limits power output when using them at low voltages. So in this case the high-ish power rating is really just a quick indicator that the transconductance is probably decent.
can you use the same circuit and just swap the tube for that?
A good way to people into electronics and get familiar with all the bits and what they do. Sounds is interesting and bubbly.
That rug really ties the room together.
Thank you so much for this!!!!! I have really wanted to build this sometime like this but have yet to see something so simple
Looking forward to it!!
I found this video cause im learning about tubes from an electronics standpoint and i wanted to see if they really are as simple as they seem. Good to know they are XD
Every few years I check prices of random tubes and always keep an eye out in the meantime.
I was 58 seconds in and had to pause to look up some prices. I just ordered two for $15 and they will be here in 3 days. After waiting a few years for these tiny lil guys, the stars finally aligned.
Thank you. Lol
Cool little amp! I'm working on a 'germanium/silicon' based (250-500mw) amp.I like the lower-voltage and the sound is still nice/raucous'.ha!🥂
Excellent! I also like the use of iconography on some of your pedals…. very “Orangey’!
This thing is amazing!!! I love it!!! I want to build one so badly!
Sounds very good! It seems to be very loud for such a tiny amp
Yes, it absolutely is! It really helps that most guitar cabinet speakers are very sensitive, so you get quite a bit of volume even with very little power!
@@KrisSlyka and a fair sized little transformer for a palm sized amp!
Thanks for this video Kris
Thanks!
Probably better as a preamp, it has good range and would work well set up as a pedal, you could even use a boost converter so you can run it off a 9v supply and get your 2 watts if you crank the voltage up......
Very good project, is there the possibility of adding a potentiometer to control the volume?
sure! you could probably add a 1MΩ or so pot before the input
Ooo, i dreaming of a hexaphonic amp with six of these cute little dudes.
Wow this sounds amazing!!!
I’ve honestly been looking for a channel like this for years. Glad I stumbled on this micro build. I’ve been taking old tube radios and converting them into guitar amps for years. Stoked to find this little tube amp. Gonna get started sourcing parts and building this TOMORROW!
Just went to your build site and noticed an issue I’ll have here in the US. Our wall voltage is 120v. So if I got a transformer to step down to 12v it would only be 10:1. Would that work? Any solutions?
It might work, but the safest bet would be to get a lower voltage transformer. 6V transformers aren't very common though I think. You might also get lucky and find a center tapped 12V transformer which can be used on both 120V and 240V and wire that correctly.
@@KrisSlyka can the be used for headphones
@@miclairmiclair876 Sure
@@KrisSlyka will any other 7 pin or 6 pin tubes work? I found a bunch on AliExpress
@@miclairmiclair876 There are a lot of very different tubes with 6 and 7 pins that have wildly varying functionality and parameters. If you want to swap it for a different tube be prepared to do a bunch of research into what you're getting first.
You havent seen cute tubes until you held some 6021s
Hah, yes! Those are indeed very cute :D
I haven't yet built it but I did design a smaller stereo amp that is all valve! Christ, I should start a TH-cam channel. Forgive me for not passing on details of valves for this reason but I' like to thank you for joggin gmy memory!
Do it, before somebody steals your secret tube information!
I test your circuit with higher voltages. 48v from a canon printer, it works. I used another source for the heater. I also used 100v. With some thinkering and another pair of 6j1for a preamp this could be a very useful low power practice amp. Power amp distortion without getting ear damage.
Ohh, that's great to hear! Did you have to mess with the biasing to get it working?
@@KrisSlyka no, I just increase the input input capacitor from .1u to 4.7u it was cutting to much low end for me. for the heater I use one of those DC DC buck converter to reduce 12v from another PS to 6.3V. I could not find a 220V to 12V transformer so I used an american 110 to 12 with center tap. I use the center tap that is 110 to 6. Roughly 20:1.
@@ot4kon Ohh, that's really cool! I'm super happy to hear it works so well. :D
@@KrisSlyka I uploaded a video. I used two 12v transformer back to back to get 100vDC. th-cam.com/video/Q9wokhP1A7w/w-d-xo.html
I’m doing the same thing right now too… I have a 42 volt supply and separate heater supply as well instead of the biasing resistor of 100k I put in a 1 Meg pot…. And adjusted till it sounded good in my ears… looking for a more output/higher headroom..How was the sound at 100 volts..? What was your power supply for the 100 volts…? Any info would be great!
Sweet built it, works, well done!
Do you know how to eliminate hum? For some reason all I can hear is buzz like it's not detecting anything from my input.
Can you make a kit for this one?
As soon as I see all your mouse-traps on the floor, I split from watching the rest of the video. Nice job on the construction of your little amp….👍
I agree. The clean sound is what we care about.
Fun stuff. Thanks 🤙
I've got a spare 6J1 that I'm *itching* to turn into a preamp to drive a solid state output stage (I have a spare LM3886 if I can find a decent size driver, or something smaller if I'm just gonna drive a 4" or 6" as a little practice amp). Can the 6J1 operate at a lower voltage than 24V, or would I have to give the output stage a bit of extra headroom and just jam the tube's full output right into it? :D (can you tell I've never done this before)
Yeah, it'll run at 12V or 9V probably, just with even lower headroom. But if you're only using it as a preamp you can skip the output transformer and bias it using a large-ish resistor instead.
Thank you very much. Can I use 12ax7 instead?
You can try, but it's transconductance at low voltages is probably too low to work as a power output tube.
Thanks. İs it possible to get more gain by using two 6j1?
@@utkukaya757 Sure! You can use two tubes in series to increase the gain, basically making the first one act like a preamp, or you could use two in parallel or in a push-pull configuration for more output power.
can it Pre amllifier a guitar or a dinamic mic with distortion controll? do you havebthat project?
I don’t play the guitar, but I think I might still build one!
Hey, could you do a complete build video for a sub miniature tube high gain pre amp pedal kinda like the Seymour Duncan mayhem
Nice clean schematic! 100K input pull down seems a little low for impedance it would be cool to add a lightbulb in series with that pull down to experiment further.... Cheerz!
Well, it's a "power" amp, designed to be driven by some kind of preamp or just any guitar pedal, so the input impedance isn't a huge problem.
I'm kinda curious about the light bulb though, what would that do?
@@KrisSlyka I think it limits the amperage or something like that. It can be a way to experiment without risking burning something out lol
@@bigbasil1908 everything on this amp draws less than a milliamp (excluding the filament), that's not even enough to light a lightbulb, let alone burn anything out.
What are the specs of the transformer? What size power supply did you pull it out of?
it came from a small 230V to 12V wall wart power supply rated to maybe 250mA or so
Hi, nice job!!!! Excuse-me, how can i use in 127v?
how can i learn to build guitar amps from scratch?
I'm able to built every known pedal effects you can have on any diy websites but I can't understand the meaning of the circuits that are used as you can do, that's quite very impressive how a true knowledgable person can do with that low number of components! 👍
I have a tone-EQ- and gain section from a 9V powered guitar amp, and it sounds good as is plugged straight into a guitar cabinet.
I want to add this, just for some more tube goodness.
If I added this before the amp circuit (order is guitar, tube amp, to 9V amp), would I hear less output?
I feel like I’d have to run the tubes after, just so the 9V amp is pushing the tubes a bit more.
What’s your thoughts?
You could go either way. You can probably get more volume from the 9V transistor amp plugged into the cab because transistors just work a lot better at low voltages. But it would feel like a bit of a waste to just use this as a preamp. And the output transformer really needs to be plugged into a low impedance thing like a speaker to work right.
If you plug the tube amp into the cab and drive it using the 9V amp you're probably going to overdrive it pretty hard. It's hard to say, honestly. I'd just try both and go with what sounds better to you
@@KrisSlyka Thank you! Also, I greatly admire your patience for answering so many questions coming from people like me who have no clue what they’re doing.
I’ve read through so many repeat questions on you channel 😭
@@KrisSlyka Also just a brain check, I'm in the US, so I'd have to find a power transformer that has an output of around 6.5V with our 120V input right?
@@jtmotenz Yep!
@@KrisSlyka Thanks!
Just checked the price for a pair of 6j1 they are a little under 5 dollars on ebay I haven't found the dollar tubes. Even so it's not as bad as 12ax7 tubes.
Searching for "6j1" on AliExpress brings up a bunch for $1-2 on the first page.
Thanks I never bought from them. Maybe this will help other viewers as well. I did find in quantities were each price was about a dollar. If you buy like 10 or 12. I do want to try to build a headphone amplifier using these tubes. Thanks
Hello. How many volts of Input and Output did the Transformer you used as the Output Transformer have ? 😊
it's a 240V to 12V transformer
Hey Kris what cabinet are you running through? What’s the speaker impedance? Single or twin? Thanks!
Justin
It's an 8Ω 1x12"
Thank you very much for sharing this project Kris ! Just a question, how many watt your speaker get ? Or can you give us the name of your blackstar combo ? Thanks !
@@hagro71 It's a Blackstar HT-5
@@KrisSlyka hey Kris… how would this design work at higher voltages..? Keeping a separate filament voltage and say run 90-100 vdc… would there need to be some change to resistors and capacitors… if this will work..? Found some power supplies I would like to try… thank you Kris for any input you may have, you have always been most helpful and informative. Thanks again
Justin
@@justinj1359 Yeah, basically! Keep 6V on the heater and then adjust the plate voltage. You'd definitely need to re-bias it though since the transconductance of the tube will go up a lot at higher voltages, probably also add a resistor to the screen. I don't really have any experience with that though since all the tube stuff I've done was low voltage
How do you get more distortion without using pedals? I’m trying to figure out getting heavy distortion with a good crunchy bunt, what do I need a better resistors .?
Getting really heavy distortion is gonna be tricky with an amp like this. You can drive it real hard but it's not gonna sound great probably. A lot of the "goodness" of a distortion sound depends on the EQ-ing and gain staging inside the amp.
Haha yes glad to see this video!
Hi, can i use directly pull push on this shematic? like +/- 12v? or little higher maybe +/- 15v?, or increase single supply to 36v? Thanx.
Well, +/- 12V is the same as 24V, so that's gonna work just fine. Higher voltages might need a tiny bit of bias adjustment, but generally it should work quite well.
Audio transformers have an air-gap to help prevent saturation of the iron, the salvaged transformer does not. I guess maybe with guitar amps you don't care.
Yeah, and in this case the bias current is so low that there is really no way to saturate the core anyways
@@KrisSlyka with a 24 V power supply, and 20:1 transformer reflecting an 8 ohm speaker o calculate about 250 mW RMS!
Goods, Are output transformers and power transformers common?
Pretty sure you can salvage them from power bricks
Would this work with 1J24b subminiature tubes?? Would it be just a drop in replacement for the 6J1 tube?
It's definitely not a drop in as far as the heater supply goes since it's only got a 1.2V heater voltage. As far as the other voltages and biasing goes… no idea. Just give it a try! Chances are good you'll get something at least since it's built to run at a quite low plate voltage.
8:10
whoa wait, i can just write a song about an ex drowning on drugs and we are the new Deftones!
You should add this one as a kit on ETSY page, I would buy one
I've been thinking of making a more "proper" version of this amp with a little PCB and small off the shelf mains transformer as output transformer. If there is interest I could look into that?
@@KrisSlyka yes I think people would be interested if the price not too high. Transformers are expensive as they are. using a wall transformer would cut cost if you sell just the amp parts less the transformer. Just an idea you can use 70 volt line transformers that are used on pa systems for single end amplifiers. Push pull need a center tap.
Hey Kris! Another milliamp question if I bring the voltage up to around 90-100 besides the electrolytic cap being raised to say a 350v rating or so what I need to change capacitance? I have the biasing as a 1 Meg ohm pot. I’m also running the heater off a separate power supply… could you help me figure out values… or would everything else work ok..? The way I have it now is real nice can even get clean tones but would like some more headroom/output have it now on an old 4inch alnico speaker sounds good just looking for a little more output. Thanks Kris! Look forward to any info or help you could give me
Hmm… the input capacitance is probably fine, the main thing you might want to play with is actually biasing the tube to a negative supply.
As the plate voltage gets higher and the tube's transconductance goes up you need to bias the grid to a lower voltage to stay at an operating point that will give you the best headroom in either direction. Otherwise it'll clip the wave form either at the top or bottom.
The grid naturally takes on a slightly negative charge just from electrons hitting it, so in my circuit the biasing resistor actually pulls the grid *up* towards 0V to get more idle current to flow. Once you increase the plate voltage though the idle current can get too high and you might need to pull the grid to a lower voltage, which will require a negative supply rail of maybe -12V or so.
Aside from that, maybe adding in a screen resistor would be a good idea, maybe 100Ω or so. Aside from that, well, there isn't really anything else in the amp to tweak!
And how would I go about this? I’ve been reading on negative supply rails, just still learning
@@justinj1359 Maybe check out the chapter on biasing here: www.valvewizard.co.uk/Common_Gain_Stage.pdf
The original version of the amp uses grid leak biasing, but both fixed biasing using a negative supply rail or cathode biasing (ideally with bypass) should both work.
Back in 1954, this and other (25 in total) tubes were tested with reduced power. Satisfactory performance results were achieved with an anode voltage of 26 V. However, talk of 1.5W output power remains only a pale blue dream! 🧐Feel free to divide by ten! 🤓
Are any of the output signals safe enough to run into an Hxstomp with IRs?
I would like to capture and mix the tube and output transformer interactioms with emulated speaker IRs out through headphone out of the Hxstomp.
Yeah, the output voltage from the transformer should be low enough to run into a mixer or effects pedal without problem
@Kris Slyka Awesome 👌. Real slick design Kris.
Love this
So interesting. Is the socket an ecc83? In that case… may i simply put a 12au7 on this circuit without any modification?
No, they have a different pin count and pinout and are also completely different kinds of tube. The 6J1 is a single pentode and the 12AU7 is a dual triode. But I do have a video on my channel about building a small preamp using a 12AU7.
@@KrisSlyka nice.. so it would be possible to build a “complete” tube amp with that preamp and this power one..
@@matteol.9688 yep! That's what I'm mostly using to play right now
I wired this up using a screenshot of the schematic. It has the 120R connected to Pin 3 and Pin 4 going to ground, but I noticed that those are reversed in the build in this video. It didn't work when it was wired per the schematic, and I caught the mistake while troubleshooting. Still isn't working now that I've swapped them around. Did that damage the tube? Sorry if this is a stupid question. I know quite a bit about building pedal circuits, but I'm just now starting to learn about tubes. I tried googling first, but I can't find anything addressing that specific question.
Nah, don't worry, that doesn't matter. The heater is just like a light bulb, so the polarity doesn't matter and you can connect it either way around, so nothing should be damaged.
@@KrisSlyka gotcha! that's good to know. now on to finding the actual problem 🙃
@@KrisSlyka I built a small charge pump to get 24v from the 9v going into my breadboard. Works fine on its own, but when I connect the amp circuit, the output drops to 12v (measured where the 120r and 100r resistors connect). I'm getting 12v on the heater, and about 2v on pin 6 (the screen?). Everything else is zero. No output. Any idea what I might be doing wrong?
@@brainbonkk How much current can your charge pump output? Powering the heater from the charge pump is gonna be a problem most likely since it requites a lot of current. Also it's kinda pointless to step up the 9V to 24V only to use a resistor to drop it back down to 6V and waste the rest of the power. I'd recommend running the heater off of the 9V with a smaller dropper resistor instead of the 120Ω one and only use the charge pump for the plate voltage. Also, 12V on the heater is way too much for 6.3V heater. Make sure you haven't burned that out. (though I doubt the charge pump can deliver enough current to burn out the filament)
@@KrisSlyka current didn't even occur to me 🤦 that's definitely the culprit. thanks for your help, kris!
Cool project, I love it.
can i use a 25l6 or a ef184 in this project? Thanks man
I've built similar setups using EF183 and PL81 tubes, so as long as it's kinda in that general ballpark it'll probably work
How many ohms does the speaker have?
it's an 8Ω speaker
Thank you
Great project. Might a capacitor dropper be better than just the big block-shaped resistor, to reduce the voltage?
I'm running the heater on DC, so a capacitive dropper won't work. Might be an option when running it on AC though
@@KrisSlykaI forgot what type of voltage powers the plate Ac,or dc?
@@MichaelConnell-zb8me DC
Do those valves come with sockets or do you have to source those somewhere>
Usually not. But they're easy to find as replacement parts on guitar amp repair sites or ebay.
Sounds good if you consider the price and availability of these. I bought preamp kit few months ago and they work well with my speakers for PC. But I also got extra one (for tubes and other parts) so I am thinking about making this one. I have one question. Can I plug my passive bass guitar to this preamp and then connect preamp to my bass amp? Or maybe I have to make transistor preamp for this one as well?
You're going to need some kind of preamplification for this since it's technically more of a small power amp than a preamp. The input impedance is kinda low, so the tone isn't gonna be very good without some kind of buffering and there also isn't a ton of amplification. Though the second part might be less of a problem if you're running it into another power amp. And for buffering the signal any kind of pedal with a built in buffer will probably do.
@@KrisSlyka Thank you very much. I ve build this simple 1 transistor preamp so it should act as a buffer. Anyway I am looking forward to building this circuit so I will tell you if it works as expected
@@zazacraft2062 Awesome!
@@KrisSlyka I've made my prototype but it seems the filament isnt heating. I didnt have single voltage source of 24VDC so I used 2 sources of 12. One has max output of 1.5 amps and other of 3. I dont know what could be the problem
@@zazacraft2062 Start by checking the resistance of the filament to make sure it's nor burned out or something, then check how much current it draws when powered.
hi, thanks for sharing. i tried to do it but the transformer i used a 9 volt by 127 volt from an old AC source, and there was no sound. If I use a 12 volt by 220 volt transformer will it sound?
Or use this 0+6 volts 220volts, look it please here www.multcomercial.com.br/transformador-de-tensao-127-220v-para-0v6v-200ma.html
If there is no sound at all it's probably a different problem. Even with a suboptimal transformer there should still be some sound. I don't even know if the transformer I used is "optimal". It's just what I had. And the ratio of yours doesn't seem so far off of mine, so I'd probably look for the problem somewhere else first.
@@KrisSlyka Thanks for reply, I will ivestigate the problem and report later
Hey there :)
I was just about to start my first project with tubes. Is there any good source you could recommend, that has a little workarround or just good informations for the beginning?
To be precise I wanted to "pimp" my marshall toy amp ms-2. And look what I can get out of it.
I don't really know of many. One very good, albeit also very technical, one is "Triodes at Low Voltages" by Merlin Blencowe which you can find here: valvewizard.co.uk/Triodes_at_low_voltages_Blencowe.pdf
It only covers triodes for preamps but lays out all the basics to keep in mind and is a good starting point.
If you want to learn how different tubes work in general check out this video by Mr. Carlson's lab maybe: th-cam.com/video/oHjZs0bNwEs/w-d-xo.html
Generally though I've found the best way to get to what you want to build is just do to a bunch of experimentation. The good thing is that at low voltages aside from burning out the heater tubes are pretty much impossible to kill :D
@@KrisSlyka Thank you for your answer :)
I didn't necessarily meant TH-camrs. But I couldn't find a book covering that topic as well. But I guess to find out about the sound of different tubes i need to experiment anyway 😄
Kris what’s your opinion on el34 tubes ?
Don't know, never tried one
Can I omit the transformer and use just as a preamp?
Sure, but you're gonna have to add in a plate resistor and probably change the biasing a little. Or you can also just use it as a preamp with the transformer.
Total rookie question... What watt rating is the 100 ohm power filter resistor? Also the watt rating of the 100k biasing resistor? Is a 24 Vdc at 2 amps power supply sufficient?
Anything is fine, really. They barely pass any current so a normal 1/4W resistor will do fine
@@KrisSlyka thanks so much I really appreciate it! I look forward to get started on this little guy!
@@KrisSlyka I’m pretty novice and always looking for low buck solutions I think it will be nice with my behringer tm300 pedal as an input. I would like to also build a tube preamp which I would guess I could input into the “milliamp” ...? Also in the milliamp I’m gonna try some GE 5654w tubes, hoping for good results!
@@justinj1359 Yeah, this thing goes great with a little tube preamp. You could probably even adapt the circuit from my preamp video to run on 24V and built it right into the same chassis with this one to make it a "full" amplifier!
@@justinj1359 Try "Banana booster". f I remember correctly, 7 components besides the hardware and the tube.
You have DC running through the transformer, is that a good thing?
well the police hasn't caught me yet
@@KrisSlykaSorry, but I thought that a capacitor would do well between R1 and trafo pin 1.
Nice little amp!
@@michaellundsrensen2292 The transformer is part of the biasing of the tube and it's plate current supply, so DC current has to flow through it, otherwise the amp won't work. It's the usual setup for an output transformer on a tube amp. Tube amp output transformers are specifically built to handle quite high DC currents without saturating for that reason, but the currents here are so small that it really doesn't matter.
You can build a guitar headphone amplifier by using a lm - 389 ic - chip the lm -389 chip is a amplifier. 🎸🎛🔈
what type of tube do you use, and what does the 20:1 transformer mean
As I mention multiple times in the video it's a 6J1 pentode. And a 20:1 transformer is a transformer with a 20:1 turns ratio between the sides
means a transformer with a primary of 20 turns and a secondary of 20 turns like that
@@reganaudiochannel No, a primary of to secondary ratio of 20:1. So maybe 2000 turns on the primary and 100 on the secondary.
Good job!!!
Sorry for being a noob ,but the 24 v power adaptor is ac/Ac right?
Nope, just a normal DC brick thing.
@@KrisSlyka so you’re running dc to the plate ? And the output transformer is just the ac/ac part of a normal power brick right ?
@@christianpucciarelli Yep!
@@KrisSlyka thank you 🙏
That would be sweet if you could design a battery powered tube amp.
You could probably run it as it is off of a 24V lipo pack…
You use Jfets for such low voltages.
I've built this amp and can't seem to get any real volume at all, just incredibly quiet. I've even tried it with 110v input, which is louder but still super quiet. Any tips to increase the volume? I'm using a 20:1 OT.
What are you driving it with on the input? It's only a power amp, so it's gonna need some kind of preamp stage if you wanna get any real volume out of it. Even a guitar pedal that allows you to turn up the volume will do
I'm using a 10db tube preamp which doesn't saturate the tube, so nice & clean. I've tried a more powerful solid state pre-amp but it just over-saturates the 6j1. Was just wondering if there's any component changes which might boost the output. I'm running it through a 30w 8 ohm speaker, maybe that's too big for it to drive? I'm using a 470k pot for the bias resistor, set at the full 470k. Sounds super sweet, just very low volume. In your demo it seems to produce decent volume.
@@rogerlightbown what's the efficiency of the speaker? A guitar cabinet speaker will give you something like 90-100dB per watt, whereas normal speakers are probably more in the 20 to 30-ish range
@@KrisSlyka It is a guitar speaker, but suspect its not that efficient. Could of course be a poor output transformer which is from a 240vac to 12vdc PSU, so in theory should be ok as it's 20:1. Think I'll just try a couple of different speakers.
@@rogerlightbown Yeah, maybe also give it a try with some headphones. At 110V this tube should give you 1-2W, which should definitely not be quiet.
Is that a rectifier tube?
No, the 6J1/EF95 is usually used as a general purpose low power HF amplifier tube.
Might be a stupid question, but how hard would it be to scale this up to a 45w, 4 tube power amp?
Well, it's gonna be a very different amp at that point. That's gonna need different tubes, much higher supply voltage, more complex biasing, most likely a proper output transformer…
That's not impossible of course, there are plenty of plans for higher power tube amps out there or you could always design your own from scratch if you feel like it.
@@KrisSlyka I was thinking of using these 6J1 tubes, similar to how EL34 or 6L6 tubes are used in the big 100w amps. I may have gotten the output wattage of this tube wrong (been hearing about a lot of different tubes today).
@@KrisSlyka also, I'm planning on coupling this power amp with a preamp that uses two 12AX7 tubes.
@@insidethestudio3886 The 6J1 tubes are only rated to 2W, so if you want something like 45W you're gonna need a lot of them!
@@KrisSlyka okay, so an 8 watt amp. Since there are 5 and 10 watt high gain amps that are great for recording and practice, that's still in the ballpark.
Can you make a high gain tube stage pedal from sub miniature tubes
sure, I don't see why not
No, I mean can "you" make one with an assembly video?
@@paigdyll ohh, lol. Nah, that's not really something I'm planning to do at the moment, sorry
Where did you get the schematics
I designed the amp, so I drew them myself. In KiCAD to be specific.
Hey kris! Quick question for you if you don’t mind..? If I raised the voltage say I have 42 volts would this increase my output..? Would I need to change caps and resistors..? Just a thought... I am still learning. Thank you for any input you may have! Have a good day!
Yeah, that would definitely work and probably give you quite a bit more output power. You might have to play with the bias resistor (R1) a little, but you can just replace that with a potentiometer and turn it until it sounds good. For a higher voltage you might need a higher valued resistor.
I don't think any of the other parts would need to be changed aside from making sure that the capacitors are rated for the higher voltage.
@@KrisSlyka hey kris! Once again thank you for your reply! I have put in a 50v electrolytic capacitor in... and turned on the power got good sound very momentarily then nothing... is that to be expected with the bias way off? I am really trying to read more on biasing with mixed results.. would putting a 250k pot and finding a sweet spot restore and hopefully significantly improve my output.. again any insight would be so much greatly appreciated! Thanks from Wisconsin, USA by the way as well! (Also if I could direct message you in any way besides TH-cam would be great if that would be ok with you?)
@@justinj1359 Ohh no, I just realized that I forgot to mention something super important. The heater of the tube still needs to be run at 6V and since this build just relies on a resistor from the plate voltage to limit the heater current my dumb advice might have just burned out the filament in your tube. :(
I'm super sorry, I completely forgot to mention this since that's not how you usually do it. If you change the voltage to the tube it's super important to keep the heater voltage the same! Either by putting in a larger resistor (which becomes very inefficient at higher voltages) or running the heater off of a separate power supply. Again, I'm super sorry I forgot to mention that…
@@KrisSlyka LOL it’s totally ok, at least it was one of my Chinese 6j1s that I have numerous of, but if it would have been one of the GE 5654’s that I have a pair of I would have been a little bummed 😉.. but anyway all good! Gonna change up and run a separate 6 volts for the heater and try again, what would you recommend on the value of the pot to find what sounds good for biasing..? 250k A or what would be in the range..? Once again thank you so much for all your help and loads of information! I really appreciate it! And it’s a learning process so I expect to burn up a few things a long the way lol... just found a lead for some more 6j1s cheap on aliexpress 😉
@@KrisSlyka I also realized a huge mistake I had the power filter and bias resistors switched! 🙄 another rookie move. But fixing that has got me a proper amp going. So grateful!
Thank you.
this is so cool! Is it possible to configure this for a push pull setting by adding another 6j1?
Thanks! And yes, kinda. You'll need some kind of phase splitter to drive the second tube and a center tapped transformer.
@@KrisSlyka thanks for the answer :) how to you measure the output impedance of the tube? I want to check if I can keep the same 20:1 ratio for the transformer in this push pull experiment
@@piringuabiroslau3769 Well, I never measured the output impedance to begin with and the 20:1 ratio was just based on what I had lying around. Though most commercially available output transformers also seem to be in the same ballpark. One simple option if you don't have a center tapped 20:1 transformer is to just use two separate ones, one for each tube, with their outputs connected in series and phases inverted.
@@KrisSlyka
Is it possible to bridge them say two identical circuits and get twice the wattage output?
Hi Kris. I just finished prototyping this amplifier, but the output volume is quieter than speech level. In your video, it seems to be louder than speech level. Is this correct? I'm using it with a Celestion Seventy 80 speaker. Thanks
Yeah, mine definitely is. I mean, might depend on how loud you speak? I don't own a sound level meter, but a quick measurement with 4 different (albeit totally uncalibrated) apps on my phone gave me levels between around 68dB and 75dB around a meter from the amp, which is in line with what I expected. Definitely louder than a conversation, but not overwhelmingly so. Take those measurements with a healthy pinch of salt though.
As far as the low output volume of your amp goes I'm not really sure. I think the biggest variable here is the tube. Since they're meant to run at higher voltages they're often not really well specified at low voltages. I've had very different experiences with 12AX7 tubes from different manufacturers, with some working really well at low voltages and others not at all.
With the 6J1 in this build it could be similar. I've had some Chinese 12AX7s work great in low voltage builds, which might partially be cause these tubes are made specifically to run in low voltage headphone amps and preamps. Maybe it's similar with my cheap noname chinese 6J1s? I'm really not sure…
@@KrisSlyka My speech level is very low. Just to have an ideia about how low the volume is: if I connect the guitar straight to the amp, the speaker doesn't even make a sound. I have to dime an overdrive or a booster in front of it to have any sound coming out (and even with that, it sounds almost as low as the sound of the guitar when it is unplugged).
It is good to know that it is supposed to be louder than a typical conversation level. Maybe I have some loose coonection in the circuit that is causing this low output volume. By the way: is it normal for that 120 ohms resistor for the filament to heat up? Mine gets very hot, I can't even touch it for more than a second (even being a proper 5w resistor). Thanks again :)
@@pauloscabeni5277 Yeah, that resistor getting hot is normal. I strapped mine to the chassis of the amp to dissipate some of the heat. It's dissipating around 3.5W, so it's well within the spec of the resistor.
What kind of tube and transformer are you using in yours?
@@KrisSlyka The tube I'm using is supposed to be a 6J1, but it is really hard to read what is printed on it. Looks like it's "6ж1п 8704". The transformer is a 127v/220v to 12v, 100mA transformer (which I use the 220v terminal of the primary)
@@pauloscabeni5277 Hmm… 100mA isn't a lot, but that shouldn't make a huge difference… And that should be the right kind of tube too. It's hard to say how it compares to the china made ones though…
Can you measure the idle current you get through the transformer when there is no signal applied?
Can i use AC-AC transformer or must use AC-DC ?
The amplifier needs a DC supply if that's what you mean. The output transformer is just a transformer. No rectification involved.
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Will a 6N7 tube work for this??
The 6N7 is a double triode. You might be able to build a small amplifier with it but it's gonna need a very different circuit.
I have this one 6NV tube and really wanna use it to make a small amp. Would u be kind enough to help me out?
@@lisentzudir1087 I can't really help with that since I've never use a 6N7 before. But you could start with a circuit similar to the one I show in this video th-cam.com/video/TllEAf0Hgnc/w-d-xo.html
It will require you to do a whole bunch of your own research and experimentation though.
Cool thank u so much for your videos and replies. Keep up the good work 🤟
I got around to building something like this (with a second tube for preamp) but the output is extremely quiet, as in I have to hold my ear to the speaker to hear it. Do you have any idea how much output power you were able to get? Thanks for the video!
I don't really know how much mine delivers…
Did you use the same kind of tubes for your amp? The kind of speaker also makes a big difference. Guitar cabinet speakers are a lot more sensitive than normal speakers.
@@KrisSlyka I'm using a regular 3 inch speaker. I suppose that's the main issue then. I'm not sure how sensitivity varies with size though. My transformer is also physically smaller than the one you show.
I used two 6J1s, and I've ordered a couple more to swap out in case they are defective or something.
I tried different transformers, but the maximum DC plate current I could get was about 2mA.
Anyway, I'll keep troubleshooting. Thanks for the reply :)
@@RijuChatterjee Yeah, that's probably the problem there. Large guitar speakers can usually deliver somewhere from 95dB to 100dB at 1W, which is a lot compared to other speakers. Maybe give it a try with some headphones since those also tend to be quite sensitive.
The size of the transformer probably doesn't make a huge difference since the power is so low anyways. And the tubes low transconductance is probably the bigger limiting factor than any internal resistance of the transformer.
Of course there is also the chance that the tubes I used were just better suited for low voltage operation. Running them with such a low plate voltage is kinda out out of spec, so they're not usually well characterized at those voltages.
@@KrisSlyka 100dB at 1 watt... that's almost hard to believe. Although to be fair I don't have much experience with sound dB levels, I'm just thinking of numbers you hear such as "a jet aircraft at takeoff is 80dB".
I just tried it with headphones, and it's on the quiet side but usable. It sounds quite nice too; I suppose using it as a headphone amp might be the best option atm.
@@RijuChatterjee Sounds like a lot, but isn't uncommon. Guitar amplifiers are loud! A Celestion greenback has a sensitivity of 98dB. celestion.com/product/g12m-greenback/
Sensitivity for speakers is measured with a 1khz test tone with 1W RMS power at 1m from the speaker.
Can you plug it to pc? But I would install pot also...
The input or the output?
@@KrisSlyka Input, thank you for responding :)
@@KrisSlyka So I would like to build amp like this i got 6j1 tubes, can I just plug it to pc and play it like regular amp? Because PC audio output can act like preamp... is it posible or I need to build real preamp, and can I use same tubes for preamp? Thank you!
@@vukiss-su7hn Using a normal line level output from a PC or similar is fine for driving the amp, no separate preamp needed.
@@KrisSlyka Thank you
This is super simple. how much power ?
Hard to say, really. Maybe 0.1W? I haven't measured it.
@@KrisSlyka Please tell me about the transformer. Why does it work off of 24V?
@@upside-down6211 What do you mean? The amplifier itself runs off of 24V because that was just a good voltage to run it at. The transformer on the amplifier itself is just there for output coupling.
@@KrisSlyka how much ampere of the transformer ?and can i use 12v power suply?
@@upside-down6211 The power rating of the transformer doesn't really matter. This was just from a small wall wart that was rated maybe 1A. You can try running it on 12V, but it's going to severely limit the output power. (More than it already is)
Is this available as a kit??
It's built from scrap, so as long as you got scrap lying around you got your kit. On a more serious note, sadly those super cheap 6J1s don't seem to be available anymore…
@@KrisSlyka Is there an alternative tube you can use with the same circuit?
@@josephforrest3713 I'm not sure! I haven't tried any other ones, but a similar small pentode might be a good start. Or just look for an EF95 or any of the other names this same tube goes by
You need to get some sunlight bro.
My nut sack
G R E A T !!!
Very cool amplifier. Would you be interested in selling me one.?
sorry, don't really have the capacity for that right now
Headphone amp at best
Play some music on it please :D
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I've been wanting to make a single tube 6gw8 guitar amp. There were some from Australia a long time ago. I am an American, so I'm internationally challenged. I have some schematics but am lost. Any ideas?