DIY EL84 SE Tube Amp // Building a stereo vacuum tube amp from scratch

[@PrinceWesterburg]

I just discovered your channel - I've worked in valve hifi so most valve amp videos on KZbin are difficult to watch at best but this is a solid amp. I'd recommend trying an EZ81 rectifier, routing the filament wires away from the chassis (though it is dead quiet) and definitely favouring wood and non-ferous metal chassis. This is kicking my backside to get on with projects! :o)

[@MikeFreda]

Thanks for commenting. Glad you like the built. Actually, the original plan was to use a EZ81 but when I was simulating the PSU in Duncan Amps PSU Simulator, the B+ was getting a bit too low for my liking with 33-35ma of current on each EL84 tube. Next time! The shielded filament wires works wonders. They can be a pain to strip , train and solder but it's worth it in the end especially if you have a tight/a lot of wiring. Cheers.

[@paulbrodie]

Looks good Mike! All the circuits are way above my head, but you know what your are doing I am certain. I did catch you using the drill press and belt sander without safety glasses, but we won't worry too much about that.... Safety Third!

[@MikeFreda]

Thanks Paul! Yes, you caught me being a little unsafe. I typically do wear PPE. It must have slipped my mind as I was pressing record! I'm not fortunate enough to have a Mitch! lol Cheers!

[@dans8287]

Wow, I am going to have to step up my game here. You weld up your own chassis? Amazing! The lettering on the chassis using the cricut stencils is a great idea as well! I decided to build my own stereo single ended output amp during the shutdown in 2020. It uses 6AQ5s instead of the 6BQ5s. Interesting feedback loop idea, I tried to implement global negative feedback in the one I built but I never got that to work so it still has no negative feedback. Apparently there is a lot of combined phase shift in the preamp and output stage and never figured out how to measure it or compensate for it. My ears are shot anyway so it sounds ok to me even though there has to be more than 10% thd at 4.5 watts. I just found your channel and subscribed. Your builds are top notch!

[@MikeFreda]

Thanks for commenting. I’m glad you like my content. Building tube amps is a fun hobby and realistically, if it sounds good to you then that all that matters! Keep on building! Cheers.

[@michaelwright1602]

I just bought a little Cayin EL84 tube amp and am so glad I did. WOW! The sound out of my Zu DW6 Supremes has never been better. I am really stoked to attempt to build my own tube amp after watching your video, actually been thinking about it for awhile now. Thanks for the work you do, very clear and concise, and yes, I subscribed.

[@MikeFreda]

Great to hear! Please let me know if you do make one and how it turns out. Cheers.

[@KleyDeJong]

Beautiful build, thanks for sharing!

[@MikeFreda]

Thanks for commenting. I did enjoy making this amp and that it worked right away made me even happier! As you probably know sometimes there can be issues! Cheers.

[@KleyDeJong]

@@MikeFreda Oh man a perfect first time startup is the best feeling!

[@MrJbhunter11]

Yessss! You’re back!

[@jimwilliams8858]

Mike, you are truly master of your craft with excelect attention to detail. Love the chassis build and look. I will suggest two things to others watching and building the same. 1) One can buy same Audio output transformer with attached insulated wires. it is a different part number in thei catalog... it's same transformer. In this way you don't need to build a bulkhead for transformer. Simply spary high temp flat back on it. 2) you are placing EL84 tubes too close to transformers. Radiant heat energy from tubes will contribute to temp rise of transforer in long listening sessions.

[@MikeFreda]

Thanks for commenting. I’m glad you like the build. Yes, I’m aware of the different versions of this OT. They do cost more and I had planned to cover it anyways for aesthetics. As for the temps, have a look at my community page. I post a pic of the operating temps. After 8+ hours of operation, the OT cover is at 26-28Deg C. I reached out to Edcore and they advised me that the normal operating temperature range is -40Deg C to 105Deg C. So I think I’m safe. But yes, it is a thing to consider for longevity. That’s why I used a 10w cathode resistor. A 3watt would work but it would get pretty hot. Cheers.

[@nikolaos9906]

Very good job and clean. It's good that you write high voltage.

[@MikeFreda]

Thank you. Cheers.

[@marknielsen8977]

Yet another terrific build Mike and as always, a very high level of finish. I do feel that you could make your video's into more parts, explaining some more theory and how the calculations are done and why.

[@MikeFreda]

Thanks for commenting. I’m glad you like the video. My goal is to make the video as short as possible, make it entertaining with byuld tips. I’ve made video in the past that do deep dives into the theory but people don’t really watch it. Too dry for most. There are some great videos that already do that so I really don’t want to duplicate videos that already exists. Is there something particular you want more clarity or more explanation on? I do plan to do a linestage video that focuses more on the circuit than the chassis build. Cheers.

[@kennethcoutinho4439]

Wow awesome build and beautifully explained.....

[@MikeFreda]

Thanks, I’m glad you found it helpful! Cheers.

[@dilbyjones]

Glad I found ya been wanting to build this way

[@MikeFreda]

Awesome. I hope it inspires you! Cheers.

[@mastopage3120]

Beautiful job. Love it.

[@MikeFreda]

Thank you! Cheers.

[@HolgerBarske]

Very nice. I really dig your building style 👍.

[@MikeFreda]

Thank you very much!

[@alanpecherer5705]

Nicely done! I used to build and enjoy building amps and other projects quite a bit, started as a teenager back in the 60's. I have more build skills than I had then, much better tools, but to be honest, I simply don't have the patience for it any more.

[@MikeFreda]

Thanks for commenting. I started my tube amp journey from reading a Leo Fender book. A few “older” men I worked with were into ham radios. This was before the internet and way before KZbin. They all laughed at me saying it was old technology. They did end up teaching me a few things. Funny enough, I never stop wanting to learn more and now I know more then they do. Lol. Never to old to learn or try new things. Cheers.

[@alanpecherer5705]

@@MikeFredaYeah, I think many electronics buffs our "our age" started on Fender amps. Either that or ham radio, either building from scratch or adapting war surplus radios that were available very cheap. The other factor that kind of sourced me on amp building was parts cost. Back when I started, tube sockets were 25 cents and the tubes were $1, maybe $3 for 6L6's. Now, if you develop a parts list for a Fender amp, you find you cannot build one for less than $400-$600, certainly not with a cabinet that can withstand dragging around to gigs. For a while I was buying carcasses of dead solid state guitar amps for $25 or even free, gutting them, and building a Princeton or Deluxe Fender. It's blastedly time consuming and the thing is, you can't quit at 95% completion. You have zero if you don't fully complete the amp. Yet, to buy the amp as a finished product will cost me $600-$700 but I can play it for 5 or 10 years and then sell it for $500-$600, so it only costs $100 to own.

[@josephcunningham8961]

My mind has been blown. Awesome job. Still stand by my statement. You should be working fir NASA

[@thomastubeworks]

Nice little amp! EL84 is a great sounding tube I really love the tone, I have a little single ended one myself, also have a 5 watt EL34 single ended amp another great tube and probably one of my favourites sound wise. Give the Soviet 6P14P a try in that thing!

[@MikeFreda]

Thanks for commenting. I’m planning on a 6L6 amp which is somewhat similar to a EL34. I’ll give that variant a try. Cheers.

[@josephcunningham8961]

Bloody Brilliant

[@rickg8015]

I really dig your chassis design/work👌🏼.. Well done.. Maybe you could sell some online one day..

[@MikeFreda]

Thanks. Not sure if there is a market for this sort of thing. It is labour intensive. Was thinking of just providing chassis like this. Cheers.

[@gee3883]

I wish I had the skills to build this. nice vid dude.

[@MikeFreda]

Thanks! Start small/simple and work up to something like this. Cheers.

[@dennycote6339]

@@MikeFreda Which build wou suggest i start with?

[@zdzisiek1979]

Ładny wzmacniacz :) 👍

[@MikeFreda]

Thank you.

[@KleyDeJong]

For your filament wires are you using shielded two conductor wire? That's pretty smart... Do you find that works better than a traditional twisted pair?

[@MikeFreda]

Yes, it's 2 wire, twisted pair, shielded. Only one end of the shield is bonded. I have 20 and 18 gauge depending on the current draw. I find that it works well for tight situations were other wires (B+/signal) may come close. Cheers.

[@stephenfoster225]

Mike, why do you use steel for the chassis, not everyone has a welding set available, Steve

[@MikeFreda]

You don't have to. That's just the way I decided to make this one. You could get a preformed Hammond project box or as mentioned in the video, you can use s aluminum top plate with a wooden base. They all work well. Cheers

[@regscheuber1083]

Would benefit from some NF but you don't have enough gain as is. I'm not a fan of having the gain pot being connected directly to the grid, the pot will get noisy very quickly.

[@MikeFreda]

Thanks for commenting. This amp does have some NFB. It’s plate to plate (aka Schade feedback). It does make a subtle difference. I’ve yet to try global. Perhaps one day. Cheers.

[@scottstrange5389]

I have a 6 tube amp I was needing a high low power switch in it.. is it possible? If so how? Thanks

[@mer9706]

Cool! I'm giving this a go. Two questions: Can this be bridged like a Decware, and how? What is the total mains power consumption?

[@MikeFreda]

Thanks for commenting. I do believe it is possible to bridge the output but you "may" have to omit the NFB loop. I've never done it. I think you just need to put the speaker output in series. Left negative to right positive and connect the speaker to left positive and right negative. Then use a 2-1 Y connector for the RCA input. This amp is not biased that hot and uses solid state rectification (no Rectifier tube) I suspect is draws around ~55-60 watts. I'll have to plug the amp in and measure. I can report back! Cheers

[@mer9706]

@@MikeFreda Great, thanks for the info. Parts are on the way and having an economical path (trafos) is much appreciated!

[@ColocasiaCorm]

great build! do you find sonic differences/characteristics to SE el84? vs SET or anything else? I'm looking for crystal-clear sound but with tube magic.

[@MikeFreda]

Thanks for commenting. This amp can be wired SEP (Single End Pentode) or SET (Single End Triode) by strapiing the grid. Triode mode has less power but also sound good. Not much of a difference but it can be noticeable. When running in triode, I find the bass not as deep but the vocals/mid range a bit more pronounced. You really have to do quality listening and A/B them to really hear a difference. To be honest, EL84 are good tubes, they are affordable and widely available but if you are looking for that "tube" magic you may want to look at my 6DN7 SET amp build. It's a low cost tube that sounds amazing! If you are looking to take a big leap into SET, another great sounding tube is the 2A3. These tubes do cost a bit more and the build process is a bit more complex but they are magical when paired with a higher efficacy speakers. I will be doing a build video using a 2A3 tube. Cheers

[@alexdokic5567]

Hi Mike, I’m getting the components to construct this Amp, but will use a tube rectifier, can you confirm which Capacitors are polarised for this circuit , I’m thinking all except C5? Any help appreciated. Alex

[@MikeFreda]

Wonderful! Yes, you can use a tube rectifier but you will need to adjust the components a bit. The first PSU cap will need to be lowered to align with what the rectifier will play nice with. You should be able to get that max value from the tube data sheet. You should also use a higher voltage transformer. A tube rectifier typical has a 15-35V drop across it (depending on the tube) The only cap that doesn't need to be polarized is the 0.1uf coupling cap (C1) the rest should be. You could use film caps in the PSU but those values and voltage are HUGE and cost a lot. Cheers

[@alexdokic5567]

Thanks for taking the time to reply to my question, much appreciated Mike, I’ve built a couple of SE KT88 amps from Blue Glow Electronics, and am pleased by the sound coming to my warn out ears! For you build, I am intending to use a Hammond 370 EX power Transformer and Hammond 125 CSE output Transformers with an EZ81 rectifier Tube . I just need to work out what components need changing, don’t know if there is any tool on line to give the correct values needed for the Circuit? I forgot to mention the choke, I have a Hammond 158 M, 10H, 100ma 262 ohms DCR Any comments welcome, good or bad, haha! If I get stuck, I may have to pick your brains again Mike, and buy you a beer 🍺

[@MikeFreda]

The 370EX will work great but it is a bit overkill. A EZ81 will also work BUT it has a 6.3v filament and its not ideal to have that on the same filament circuit for the other tubes. It will work but it is frowned upon by many tube amp builders. I'd suggest using a 5V rectifier like a 5Y3 or a 5U4. The transformer you want to use as a 5V winding. The OT are fine and the choke will work great as well. Buy me a few coffee's and I'll sketch up a schematic for you with those changes and expected voltages. Cheers

[@liamclauti2876]

Hi, do you think i need to modify anything if i wanted to use a 270-0-270 transformer? I’m trying to figure out how to use it in a circuit with 12ax7/at7 and el84 but not too sure on how to adapt the circuit. Is a voltage divider enough to drop the extra B+?

[@MikeFreda]

Thanks for commenting. You can use slightly larger B+. You can just increase the PSU dropping resistors a bit. I would not use a 12AX7 in this amp. The gain is way too high. It probably won’t sound as good and would clip much sooner. Plotting the load line will show you the much larger voltage swing. Would be okay for a guitar amp, not a hifi stereo. Cheers.

[@ritchardbookergrieco7872]

great job 👍🏻👍🏻👍🏻👍🏻👌🏻

[@MikeFreda]

Thanks! Glad you like the build. Cheers.

[@ritchardbookergrieco7872]

@MikeFreda you are welcome dear 👌🏻👍🏻🌹

[@arthurbatera2011]

Hello my friend, how are you? I really liked your project! I got some ultralinear Wilson transformers, and I would like to build an amplifier with them. It would be my first valve. Do you have any projects you can share for ultralinear transformers that use 12ax7 and el84? Thank you very much and success!

[@MikeFreda]

Hello, thanks for your comment and question. Unfortunately, I'm not familiar with those transformer so it's difficult for me to recommend something for you that would work. That being said, a 12AX7 is not an ideal input tube for a EL84 SE amp. The mu of that tube is high and it may be difficult to tame the noise. I know the Budgie circuit uses a 12AX7 but I've never heard it. To be honest, in this amp I made, the 12AT7 i'm using is hardly being utilized but it sounds pretty good, its affordable, easy to get and they last a very long time. You may want to ask over at the Audio Asylum or DIY Audio for some advice. Cheers.

[@kubockferre5532]

Hi i made a single end with 6sl7 and kt66 ,id like to know if i put a potentiometer do i need 1 meg ohm paraalel with that to input !.i see in your shematic you have only 100k potentiometer .thanks

[@MikeFreda]

You typically don’t need the additional resistor. I’m not familiar with the circuit you are referring to but a 1meg is pretty high to serve as the ground reference in the input tube. It’s typically much lower than that. I hope that helps. Cheers.

[@kubockferre5532]

thanks @@MikeFreda

[@stevecousins4441]

Great job on this. I've been interested in this for quite a while. I'm curious what the cost for the parts comes to. Do you have an estimate? Thanks.

[@MikeFreda]

Thanks for commenting. Building tube amps is not a cheap hobby. Lol. Prices for tubes and transformers have gone up a lot in the last 10years. The transformers and choke where $200. The three tubes are $70. Chassis material and paint are $40. All the other parts are approximately $150. You are probably looking around $500 to make something like this. Could you make it cheaper, sure but you may have to scavenge parts from other devices or downgrade some components. For me, I wouldn’t change a thing. Well, perhaps the coupling caps, I may upgrade those in the future. Cheers.

[@vespass225]

Hi , supeer nice build. Those EL84:s though, put out rather about 2.5-3W/ch at reasonable THD

[@MikeFreda]

Thanks for commenting. I will do some testing and do a follow up video. I’m curious myself on how this amp “really” performs. Cheers.

[@ManMartin]

Thanks, maybe you can go deeper into the components soldering the next time. Good job 😊

[@MikeFreda]

Thanks for commenting and for the feedback. It's always a fine line to what to focus on. If I make the video too long, people will not watch. I will keep it in mind though. My next tube amp video will be more about the circuit/wiring and less about the chassis. I figured that people who are watching my build videos know how to solder and install components, but I could be wrong. I guess I could do a seperate video just on that. Cheers.

[@hpfctif7tx7t]

Hello do you have like a discord channel? i need help with a 6h8c,6l6gc otl amp i just finished the schematic but i still need help with some resistor and capacitor values.

[@MikeFreda]

Thanks for leaving a comment. No, I do not have a Discord Channel/account. Just a email. Your best option is to post the schematic at DIY Audio or Audio Asylum and let that hive help you out. What you are making is not that normal and people will their opinions. Cheers.

[@hpfctif7tx7t]

​@@MikeFreda update I managed to make it, now I'm dealing with lots of noise and very muddy sounds coming out of it, is it ok if I send my schematic and photos to your email to check it out?

[@MikeFreda]

@@hpfctif7tx7t You can and I can have a quick look but if this is a scratch build of your own design it will be difficult for me to determine what the issue is over the internet. I'll need to know what your voltages are and what you expected them to be.

[@hpfctif7tx7t]

@@MikeFreda ok2x 👍 I'm currently in school but I'm gonna be home in 2 days I'll test out my voltages again and make it as detailed as possible, I did join a discord group but I didn't understand some things that they are saying I'm really new to this hobby I don't know some specific terms that they said

[@hpfctif7tx7t]

​@@MikeFreda I got the bias voltages and the schematic here drive.google.com/drive/folders/1lBohg04IZE7-iso2Jca-QozYISXILS24

[@moodyga40]

tig welding is fun

[@MikeFreda]

Yes, it sure is! Cheers

[@randellhenry2603]

Would you build for someone?

[@MikeFreda]

I have before but I would prefer not the ship. Since I have to purchase everything at retail costs and when you add the labor, most people underestimate how much and amp like this can cost. That's why I recommend the DIY route. Cheers

[@ladronsiman1471]

I think is way much better to do tube amps chassis in Aluminum .. Sheet metal rust very easy .And aluminum is more conductive anyways .. No need to TIG, pop rivets are simple and look great

[@MikeFreda]

Thanks for commenting. I've made a few amps that way and it works. I have all the tools to make a "polished" looking amp so why not. Ken Fisher from Trainwreck amps felt that aluminum chassis provided better tone but that is with a Guitar amp, HiFi are a bit different. I'd like to see the proof/math on that! lol I also bond and ground all my nodes with wire so I don't find that is an issue for me. At the end of the day, I just want the amp to be quiet (no hum, buzz of hiss) whatever that takes. Cheers.

[@lnglng6961]

❤❤❤🎉

[@MikeFreda]

Thank you.

[@ИгорьДенисов-ц8к]

Автор дизайнер... Уважаемый автор,трансформаторы должно располагать под углом 90° сердечники,что б подавить взаимную индукцию,которая вызывает наводки и искажения"кашу" в сигнале.

[@MikeFreda]

Correct. The Power Transformer and the output transformer are 90deg from each other. Furthermore, the Output transformers are inside an iron/metal enclosure. It is misleading due to how the power transformer is mounted (through chassis). Thanks for commenting. Cheers.

[@moodyga40]

tech tip you have your fuse holder wired the wrong way around

[@MikeFreda]

Thanks for commenting. Interesting, I always thought the HOT goes to the barrel first. What's the rational? Safer to pull the fuse out when its still plugged in?

[@petercornell2002]

Thanks for the vid Mike. If I can offer some constructive feedback, please do not cut out all the gaps in the voice recording, it is very distracting and confusing. Everything you say is important, but with this type of edit, what we hear is one 20min long sentence. Could you listen to a lecture for 20 mins with no gaps? No one can. I know it is not hip n cool, but man it is hard to follow. Just my opinion. Thanks again, Peter

[@MikeFreda]

Thanks for the feedback. I do try to break things up with some action shots and b-roll. I’ve been told that I say “umm”, “and” , “so” a lot. I try to cut that out and get right to the point. Which is what most people want unfortunately. Thanks for the insight and will try to find a balance in my upcoming videos. Cheers.

[@bussi7859]

This is crappy, I made tube amps 60 years ago class AB and class A. Today I use semiconductors and class D

[@MikeFreda]

That's pretty cool that you are making amps like that in your late 70's. My father is just a bit older and all he wants to do is fish, watch TV and nap. I've made a few chip amps and they sound okay but they just didn't do it for me and they weren't as gratifying to build. I'm curious on what makes this build crappy? Tube amps are becoming a lost knowledge and I'm just sharing my hobby and knowledge with others. Cheers.

[@johnny_fomo]

@@MikeFreda classy reply sir. I hope people are as kind to me when I’m old, grumpy and deaf.

[@kenturmon3660]

Dont like it don't watch. Nothing better to do ?

[@yuriarnautovValgur]

Excellently!!!😀

[@MikeFreda]

Thanks!