Surprisingly Good Yet Easy Tube (Valve) Amplifier Build - PCL82(16A8)
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- Опубликовано: 6 сен 2024
- This is a build of a simple but otherwise excellent tube amplifier.
The unit is based on PCL82 - 16A8 Tubes (Valves), it's single ended and stereo and sounds amazing.
Construction is made easier by employing a cheap but effective boost converter and everything used in the build is easy to find on eBay etc.
There should be enough information in the video for anybody with moderate electrical skills to have a go at building one themselves.
Warning - contains high voltages so proceed with caution if you do have a go.
Leave a comment if you have a question and I'll try to answer it if I can.
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I made my first tube amplifier after watching this video. Worked perfectly and sounded very good, for a while. Then the HV boost converter failed.
Put in another converter and it failed after a few hours. Tried various Chinese boost converters from Aliexpress and other sources. They lasted from minutes to a few weeks. Then they all gave up the ghost.
Got a standard linear power transformer replacing the last failed boost converter, amp has been working perfectly for years.
Have since made 12 tube amplifiers, all using standard power transformers. None have failed.
If people have used a boost converter and it has lasted, then I'm happy for them. And a little envious.
I know a linear transformer costs more, but in my limited experience it's worth it.
If you have made this amp with a boost converter and it's still working, let me know here!
One recommendation for beginners that want to replicate this design; add a front-panel-mount neon indicator, and wire it across the B+ supply; not only does this act as an on/off indicator, it'll tell you if dangerous HV is still present; once the indicator goes out, then there's only about 60 volts or so (the breakdown voltage of a neon bulb) left in the capacitors in the boost converter. A 220 kilohm resistor in parallel will also help drain away the charge. :)
Yes, a light indicator is a good idea if only because it looks cool in the dark. Lol!
He used a power block from an old pc to lower & regulate his voltage. IMO, his amp doesn't need a resistance to bleed the capacitors, but that could be verified with a multi-meter & a chronometer as an experiment of bleed time.
Also they dont come in overly bright blue.
Great work! The kit companies will not be happy with this video, but us hobbyists are! Thank you.
That extra stereo imaging "thing" a decent tube amp and GOOD speakers provide is called "sound-stage", the wow that comes from being able to identify the exact location of each instrument. This design is a great practical new build approach. I love the elimination of the power transformer, when there are so many power bricks laying around everywhere. (I wish I hadn't thrown out all those old, dead big-iron receivers and amps years ago - they had gigantic PT!)
Fun project. One thing you may not be aware of, your original design to have the left and right output transformers placed at 90° to each other was ideal as it would have reduced the magnetic coupling between them. It appears you changed their orientation to fit the strip between them. Better probably would have been to cut the strip in 2 and orient up-down back-to-back on an L bracket inside the plastic box so you could accommodate the transformers at 90°. If you end up redoing any of it, something to consider as a small improvement. I suspect you didn't include bleed resistors on your series capacitors for simplicity and if they blow up, get the single required size. Thanks for sharing your build. It looks great !
Good idea, I always mount my output transformers at opposite ends of the chassis,never close together to minimise coupling between them.
The plastic box adds a lovely "factory look" to the amplifier. Thanks, really nice video. Greetings from sunny Jamaica.
There's a documented phenomenon of even order harmonics existing in abundance inside a vacuum tube. These are the natural harmonics that are most pleasing to the ears. This is the main reason tube amplifiers feel warmer n sound more natural
The PCL82 was a common audio output valve used in UK TV's during the 60/70's, the ECL82 with 6.3v htr was used in many a record player of the time.
I can hear its much clearer through the tubes. Love the old systems, made almost from raw elements. I think we have to face it - do we like the sound of electricity passed through rocks or a vacuum. I wonder if there is a third medium as yet untried. Tubes of the future?
Tube sounds better from high end of low pass all the way thru the audible limit. In comparison, the other two attenuate same frequencies, the transistor the better. I like how you approached the project; especially starting up. Thanks.
Thanks so much for sharing this, the video, the clear schematic and the slow-start circuit, which is pleasure to watch. I used a BC557 as the pnp transistor- I see that the value of the 240 ohm transistor needs to be quite precise to get to the 15 volts. I do find that the sound is lacking treble on low volume settings. Great instructions - thanks again.
The Technics isn't a true Class A amplifier. It's what was called a non-switching circuit. They achieve this by putting the output transistors in what's called a linear state (not hard on). In a true Class A amplifier the transistors are switched hard on and generate lots of heat and draw lot's of current very inefficient but are said to be very high sound quality. The Technics system give you all the benefits of class A/B with just some of the benefits of Class A. Great video love to see people build equipment. My opinion is they do sound much better and warmer than transistors. I still have the two power amps and preamp my late father built in the late 50's. He rebuilt them and did some modifications on them when I showed an interest in the 1990's. They are still working perfectly today.
woah woah woah wtf. Picture at 1:45, Hayling Island bridge in winter taken from either the Royal Oak or Ship Inn. Really didn't expect to see my hometown in this random video!
I dramatically prefer the sound of a tube amplifier, particularly in the vividness of the midrange and depth of stereo image. I have solid state gear as well; its good and plays clean, but it just sounds "hi-fi" and not "lifelike".
Single ended tube rocks, back to the basics. 👍
The vintage solid state amp is a gem too.
Excellent build, big thumbs up! If I may suggest, using 11BM8 (LCL82) tubes with their heaters wired in series would simplify the project even more because each tube heater requires 10.7 volts and 2 of them would equate to the voltage output of the computer power supply, therefore eliminating the heater voltage regulator. Also, because these xCL tubes love to self oscillate, the addition of grid stopper resistors in line to each grid of the tubes very close to the socket pins (1k at pin 3, 22k at pin1 and possibly 50ohm at pin 7) would help if this phenomenon occurs.
I built an amp identical to this except I built a full dc/dc inverter to give me a 230v supply. Can't beat the sound. Love it, the imaging is stunning. Never heard sound this good.
"A lot of what is considered knowledge might just be in people's heads" Classic. No knowledge in my head I can assure you. I thought the tube amp had a pleasing distortion to it. I'm sold - I hope to find time to build my own version.
If you didn't know this, many variable voltage regulators can actually be used as an audio amplifier, simply by passing the audio signal to the adjust pin(plus as positive or negative bias you need to add to pull the voltage into the appropriate range).
Tube Amps are so much warmer and sweeter to listen to...Nice Job
You make it look so easy. Anyone who builds projects like this knows how much time and effort has gone into that.
Very impressive indeed.
Thanks, most of the effort went into editing the video, the build was easy in comparison.
Nice thing to add would be a grounded sheet of metal bent inside the chassiss as a housing for the power supply parts, so it covers the power supply from other componnents, power supplies tend to generate a lot of noise that you can hear and see on oscilloscope if the amplifier is inconveniently grounded. Wich is hard to tell before you get to test
Interesting design. Sounds excellent. Well done, mate.
I'm a bit of a sound freak and I believe there is an analogue and natural aspect to tubes, vinyl records and tapes. Not sure it means anything now as we would get a 99.5% true copy of what happened in the recording (if we care about the whole thing.)
I can’t believe this is your only video ! Please consider doing more this is the 1st tube build that seemed I could actually take on as a newbie.
I like old school analog audio VT designs even if an entirely different generation from digital signal processing, high bit rates AD/Cs and DACs it gives you a lot of skill with your hands and listening. I will certainly build one myself very soon. Of course everything will have some crossover hybrids between the old and the new somehow.Thank you Electrolack its inspiring to see the renaissance of the Tubes these days. Reminds me of old professor's textbook of Frederick Emmons Terman - Radio Engineering.
Thanks for this. Only because I watched a video this morning, the LM317 is a good VR, but using a buck converter is much safer. If, for some reason, the 317 gets too much voltage, it will get hot and possibly exceed it's threshold of 125 degrees C (app. 250 degrees F), though this is a high value. Once this happens, it will shut down, then come back on when it cools enough. Just food for thought. Great job.
This is a marvellously clear demonstration video! Very interesting even though I may never build one myself.
I don't know what it is with the tube sound... But on a cheap 10w output amp, I could clearly distinguish guitar mistuning in Rammsteins music 😲 I have a blaupunkt Arkansas 58 at home. Mono only and not much power, but the quality is incredible. Never restored anything, only removed webs and dust inside a bit. The whole case is part of the speakers resonator. Also the speakers are high reluctant. Mono only, I need a second Arkansas! 😍
Hmm nice idea to use a buck-boost converter for the HT. I was thinking of making a guitar practice amplifier using valves, but decided not to when I looked at the price of a suitable 200 - 0 - 200, 0 - 6.3 volt mains transformer !
Try triode connection on the output tubes, just tie screen grid to the anode (some use 100 ohm resistor). You will drop distortion to a much lower level and power will drop to under 2W...But you don't notice, it sounds subjectively more powerful - and twice as amazing - to us nutters? Anyhow its so easy to do it's worth a try.
Sorry to be off topic but does anybody know a method to get back into an instagram account??
I somehow lost my password. I love any assistance you can give me
@Finnegan Zahir Instablaster =)
@Maximus Samir thanks so much for your reply. I got to the site through google and I'm waiting for the hacking stuff now.
Looks like it's gonna take a while so I will reply here later when my account password hopefully is recovered.
@Maximus Samir it did the trick and I actually got access to my account again. Im so happy!
Thank you so much, you saved my ass !
@Finnegan Zahir Happy to help :D
This was a wonderful video to watch, well spoken, intriguing to follow too.
Thank you.
I second Dave K's sentiment!
Electrolark the valve amp does sound awesome
Sound is always most affected by the output transformer. Buy the best one in your budget.
Next are the caps and resistors in the direct positive voltage signal path.
Go big with the mug size $100 polypros.
Build your own speakers next.
Commercial speakers spend most on marketing and the cabinet.
The drivers are 20% of the retail price at most.
A $300 full range on an OB is better quality than any speaker under $20k.
Of course anything analog is going to sound better than digital. Every musician knows this. Cathode tubes rock! The best rigs are point to point wiring. Sending your sound signal through some tiny wafer of copper on a printed circuit board kills the reproduction at the speaker end. Take apart an old Marshall plexi and you will see, and they used el34 pentode tubes which are meh on a good day but powerful. 6L6's or 6550's really sound good. Interesting vid. Thank you.
Great I've been looking for something like this to build. My Klipsch Forte speakers don't need much power.
what an excellent video,thank you. and be assured the sound quality and clarity is not an illusion.i recently built one of those single ended valve kits from china and made a few upgrades (,better valves,connectors,and a diode full bridge rectifier). and got similar pleasing results. thanks again and happy hi-fi
I built my own tube amplifier using an ECC83 and a couple of Russian 6L6 clones, it sounds great but since I dont have the proper output transformers I just had to settle for using a couple of mains step down transformers instead so it doesn't output anywhere near the amount of power it could do mainly as the impedance is way out (especially if I use 8 ohm speakers) but it still works well. If I ever find any proper output transformers, I'll then go though the process of setting the bias correctly along with the plate voltage and current.
I image ECC83 and EL84 would adapt. I like the boost converter. R4 I guess is shunt feedback. ECC81 might work as higher Rp. R6/5 unusual as no bypass. The latter might give it better than average sound.
One word stands out : REALIRTY ! "
And at leat being skeptic is not the same as believers in measurements ....you can NEVER argue with beliefs ....but you can trust you rears and your soul..
Reality means you can perceive and identify ..so you feel and understand the music.
Nice job man. Nice to see those high voltage modules in a working environment. Jack Ma would be proud!
Nifty amp, I'm in the process of building a stereo amp but with some 6SN7 and 6V6 tubes from parts sourced from a old Radio and a few Oscilloscopes. At first I was going to just build a preamp and use solid state for the main power amp but after looking at my inventory stock I'll just build it all tubes. I just need to order two matched output transformers.
Um ótimo trabalho, inspira tentar confeccionar um igual, de tão bem detalhado .
Um amplificador assim ligado a caixas de alta sensibilidade é um deleite , ainda mais com mídias analógicas
Parabéns e saudações do Brasil
Hi I have a question about the value of R4--the anode to anode feedback. The first schematic you showed, its value was 3.3 Mohms. On your final schematic it's listed value is 330k. Is this a typo? And if not, why did you change that value? Thanks!
Loving Your approach, and I've just bought pretty much the same components for My project. Aww Maplins, what a shame they've gone. Anyway Best Wishes Dee : - )
To me tube audio sounds clearer in the highs. While solid state sounds a small amount muddied in the highs. However, neither sounds bad at all.
I love tube audio, it's warmer
not too distorted? with this level, the distortion may be too high for my taste
A nice idea to simply use a power brick, and some regulation circuitry. Surprised you only needed 2 amps though. Must only be using 20 V rails or so, and 8 ohm speakers.
Thanks for this! The quality of sound from any amplifier is purely subjective. Measurements (frequency response, IM distortion, harmonic distortion, and damping factor) can prove which amp more accurately drives a *specific speaker* to reproduce a given input signal. That isn't subjective. I find that tube amplifiers often correct (or hide) terrible recording quality. I suspect most recording engineers went deaf 10 years ago, and most of them produce pure crap.
I find that pro speakers (big JBLs, EVs, Wharfdale, older Klipsch, etc) provide the most consistent grins from listeners, but Wife Acceptance Factor of such systems is inversely proportional to sound quality.
Carmina Burana is a good test. Tracy Chapman's first album is well recorded. The Voice Squad is a good test.
Excellent video on your build. Interesting using buck regulator for the 220v section . Think that type valve was sound in TVs , Thankyou for posting. I would love a valve amp again might copy your ideas , deffo easier to source the parts you used rather than trying to find an old mains transformer
Excellent video, many thanks. I recognise the PCL series of valves as the ones traditionally used in TVs. They have unusual heater voltages, so have been unpopular for hobbyists. Now with the availability of cheap DC power supplies from China this is no longer an issue. So when I searched Ebay I was expecting the find the PCL82 going for 50p or a quid. Much to my surprise even these valves have asking prices of £5 - £10. Anyway I have a small stash of valves so I will see if I have any ECL82s and I will have a go at building a mono channel. BTW I recognise the schematic (the style is quite obvious) from a magazine called Radio and Electronics Constructor. Also thanks for making me aware of the HV switch mode PSU. £4 - what a bargain!
Thanks for the comment. You might like this archive if you haven't already found it-
www.americanradiohistory.com/Radio_Constructor_Magazine.htm
They have several other British magazines such as PW and WW.
Nice build ..... I built a single ended valve amp (for guitar) from scratch last year which was fun and I am pleased with the tone quality. The parts for mine were a lot more than £100, although I did use a PT + a valve rectifier circuit and also had to buy a speaker.
I think that's a good choice for a guitar amp because they are usually driven hard into limit which inevitably brings the rectifier into the picture.
The only issue I see is safety. Wiring direct through a bridge rectifier leaves the chassis connected to one side of the incoming power (neutral). If somebody were to connect the plug incorrectly, or into an incorrectly wired outlet, the chassis will be full live AC voltage. Switching power supplies get away with it because there's a high freq. transformer isolating from the source AC.
This is lovely. I am planning my first valve build and this really helps thanks.
The tube sound is much richer, even in your short test example.
well done sound much better than the transistor amp The PSU design great idea those valves were mainly just used in black and white tv's from 1960's and still produce great sound.I recommend William's mods
William's mods? you mean a lamp and bleed network?
I would love if you put in the parts list and the schematic maybe on the next build great video
A really nice build. Kudos! It had to be a very enjoyable process and most satisfying result. I really enjoyed watching your video.
Nice project and well documented. I can tell you have a technical background in electronics. I know tubes sound good for guitar amps. I would like to build a minimalistic stereo amp like this one.
Enjoyed the video. You should make more.
It seem a very dangerous because the ground of input jack may be on high voltage phase of 220V. I recomended a separation trafo 220/220 on supply input between socket and device.
No. The power supply in the computer brick he uses is totally separated from the 220v live, no danger
Great, awesome build, I’d love to see some more of your videos. Shame this is the only one on your channel 😊
Man! THANKS! You rock! Super detailed and useful video, hope the YT community learn with you how to do a DIY project
A great video! I suspect many will follow your example. I think I can hear the difference - the valve amp sounds sweeter. I wonder if that's a shortcoming of that particular transistor amplifier? Only the better solid-state amplifiers are normally referred to as sweet-sounding...
I got excited when I saw my class a technics amplifier and I must say, sounded good! Thanks for the tutorial!
I think I had that same Technics receiver or one very similar back in the day. Early 80s (a/k/a GREATies) vintage. Not great, not terrible. Think it cost me $20 at a garage sale, and I picked up some Infinity bookshelf speakers with it as I recall for a few bucks more.
Since it's a class A amp, the plate voltage should be biased to half the supply voltage. Both sides should be the same. Did you check?
Datasheets shows PCL82 170v plate max.
Nice and detailed construction :)
ABC
Brilliant video - what is the spec of the o'/p transformers - Thx
The schematic shows R5 and R6 as being in series between pentode cathode and ground, with a connection between the two going to the triode cathode.
In the video, the author connects R5 to the pentode cathode and earth, and R6 between the pentode and triode cathode, with no connection to R5, apart from the socket terminal (16:10 on the video).
Can anyone enlighten me as to which is correct?
Interested to know how you printed the plastic in an ink jet. It could be a useful thing that.
I am really impressed.
Wow for youtube I was surprised. The first time I could here a difference between the tube and the techniques amp. The tube had distortions on both the outer limits of the frequency band but also had some great tones inside the mids. Would love to try this in person. don't tell me Im biased... I was hoping for better sound from the tubes. Bad joke... biased...lol.
Unfortunately with all the compression on RUclips videos, it was very difficult to tell the difference. A lot of people comparing tube amps to solid state have similar experinces to your verbal explanation, but as you said, music is a subjective thing and everyone has their own preference, and plecbo effect has a huge influence. I don't understand why people talk about "soft start" power. Tubes/Valves use to run AC heaters, the heaters got the power immediately when turned on, and there were numerous directly heated rectifier tubes. Soft start is not needed for Tubes/Valves at all. They really are not that sensitive. The indirect heated tubes don't conduct until they are warm so they do their own soft start anyway. The only thing is to make sure your filter caps can take the voltage of the unloaded power supply.
Hi.. Kindly help me with the output transformer details.
To upgrade this search out Telefunken, Mullard, or Amperex bugle boy tubes in that order of quality. They sound better.
It might be better to start using TELEFUNKEN Space Charge Vacuum tubes that use a B+ of 12-90V and a H+ of 1.5-3V
Cool built. You should add a wireless chip to your amplifier so you can play music from any iPhone. Those chips are small & cheap and its a good, modern upgrade to have.
The tubes attenuate the "ringing highs"?
it is advised to use linear power supply's whit analog amplifiers, but I was surprised how not noisy the audio was!
I like both solid state and tube amplifiers. And honestly, the tube amp sounded fat and thick. The solid state amp sounded a bit thin in comparison to my ears.
Great video and build. At first I was all set to get all upset by the absence of a PT. But the boost converter seems to run well! What current do both channels draw including heaters? And what's the output. Do you need really high efficient drivers? I really love this build. Well done!
I understand what your say about the transformer and had this been a guitar amp then I would have been a lot more concerned myself but as it was for "HiFi" and nothing was been pushed I thought the converter was worth trying.
The total draw is 1.7A at 20.5V the heaters are 0.6A for both and each channel is biased at 35ma. I think the speakers are 88dBm so not particularly efficient.
Many thanks for taking the time to watch the video and comment - I'll really appreciate that.
Electrolark ha! I can't stop watching the video! I'm very new to all of this having just started down the road of learning any of this a year or so ago. Approaching the design this way seems brilliant to me. I suspect it's not the first time anyone's done this but it still kind of blows my mind in it's bucking convention. Not only that but having watched simply 100's and 100's of hours of tube amp building/theory videos I can say that the video itself and the illustration of the actual build is incredibly unique. No one goes into this much detail. It's as if there's an unspoken agreement to hide certain steps from beginners. Hell, I've already ordered three of the converters from EBay.
Great build! Thanks!
Hello, I would like to know from you very important point, so please answer :) You employed step up SMPS in your project. How is the reliability of this particular board/module you used? You build it 4 years ago if I see correct. Does the step up SMPS still work? I heard from couple people they are so low quality to survive only few weeks...
I've built several tube amps using SMPS and I can report they don't last long, from minutes to weeks. I only use transformers.
I think this is a wonderful project, and guess what? Going to give it a go....I often pondered about power supplies and this seems to have an answer to the vexing problem of huge PSU supply transformers....I listened to the track by 126ers on youtube and through halfway decent speakers and then your the demo....by comparison between the solid state and tube and even after consideration of Mic placement noticed far more depth in the tube amp.! Very nice job...Ian
Good luck if you do give it a go.
Beautifully done!
Very neat work and layout.. If I lived near your area I’d pay you handsomely for some valve preamp/amp projects I have in mind.
고맙습니다
thanx a lot
Great video...thanks for posting!
Hi there. I’m still watching this. Please build something else and film it. Anything! This is easily, hands down the best start to finish amp build video on the net. But one question....
I’m just about to try building this just as you’ve shown. Just waiting on the OTs. My question..
Why is the slow start circuit on the heater supplies? Maybe I’m missing something but don’t tubes want to be warm before the B+ hits them? wouldn’t any slow start be there with the heater voltages working right away?
Anyway, thank you again. Truly.
Thanks for the comment and good luck with the build.
The slow start heater circuit is there to reduce thermal shock and prevent hot spots in the heater by limiting the heater startup current.
Because some sections of the heater filament are exposed whilst other sections are inside the cathode there are significant variations in the effective thermal mass along its length. The short exposed sections heat up quickly whilst largest part take much longer to get to temperature. Because the overall resistance of the heater at startup is low due to Tungsten's positive temperature coefficient a higher than normal current will flow until the all the heater has reached the correct operating temperature. The short exposed sections will reach then overshoot the correct operating temperature due to the excess current and will not drop to the required operating point until the rest of the heater has reached its operating temperature and the heater current drops to normal.
Your video shows 560 k&R resistors when the circuit shows 470 and the 330K (R4) ?
Great amp project. For some reason, I've ended up with loads of ECL82 valves, similar to the PCL82 but with a different filament voltage. My L8 partner had an electronics shop in Hainault, near London. When we moved to the south coast, we took all the contents from his storage facility. They're now in the basement. I've built a similar amp to this many times in the past. One problem with these single ended small valve designs is limited output power. One way to get around this is to use ALNICO magnet speakers. Newer ones have the ferrite magnets that are cheaper to produce but they aren't as sensitive. Love the plastic box solution to housing the output transformers. One thing found, is it's possible to used scalectrix (wall wart)transformers to match the speaker to anode load of XCL82. However, a 15 - 16 ohm speaker must be used. Thanks for the upload. (o:
Wall wart power transformers are no good for the tube output, but you can use 100v line transformers used for large multiple speaker installations such as shopping malls. They are cheap, and perfect for this situation. Google "M1112 100v line transformer" for more info. Im using two M1120's for a 10W stereo build with 6BM8's.
Direct cut is the best.
Do you have a source or specs for the output transformer, please?
Thank you for sharing your little project. I just finished the left channel and tested it; it works! I used the original 3.3M R4 resistor because I did not see an explanation for the change in your schematic
I do have 2 issues. R6 and R7 (both 1 watt resistors) are overheating. R7 is the worst and I do not understand why. I would not think that much current would be flowing through R7. Any suggestions?
I think I solved my own problems. For R6 I had used a 1/2 watt resistor. I replaced it with a 490R 1 watt and all is now good.
For R7, it stopped over heating once I changed out the 3.3M feedback resistor for a 330k resistor. I believe the 3.3M was creating a strong oscillation through the transformer RC shunt and the AC current was fairly high. My best guess right now but I did not try to over analyze it.
Anyhow, left channel is playing great, clean amp, no hums, no hot components. Time to duplicate for the right channel.
Update: Completed the right channel today and I have been playing the amp for over an hour now. No issues and it sounds full, warm and clean. Plenty of volume for my Den and actually much louder than I expected through a pair of old Realistic MC-1201 bookshelf speakers. I have the volume set to 3-4 using 150K pot and feeding it with a CD Player.
Today I added VU meters. Mini analog meters off Amazon or EBay. Work great and look cool.
@@brucewinterstine9582 Hi Bruce, please help me with important question - I am going to build such amp but literally nowhere in whole movie HT voltage value is mentioned (I mean at the point of R7 and transformer connection). Which voltage did you employed? Please answer
@@wodzimierzwohn114 I will try to look it up tomorrow. I did measure it but I do not remember. I used the tube specs to set it. By the way, I am still using the amp. :)
@@brucewinterstine9582 please do! I will highly appreciate your support. PS if I understood correctly you finally stick to resistors values as on the schematic given in the movie, didn't you?
Great video, am collecting the parts to build one myself. Just wondering what value of potentiometer did you use for the volume control?
Thanks
I was wondering how can i get the schematic for this amplifier?
Just looking at your circuit description, where you say the triode is getting 'positive'feedback from the resistor divider in the pentode cathode circuit. This is negative feedback for both the triode and pentode. The signal on the triode anode is out of phase(with input), therefore in phase on pentode anode and reversed again on cathode so pentode cathode out and triode in phase - you generally never want any positive feedback in an amplifier, as it can make it an oscillator. Very unusual circuit though and you normally never see that 'bootstap' style R4, in simple valve designs which is maybe where the positive thought came in? (Bootstrapping was a small amount of positive feedback to improve impedance matching, usually over two stages (of similar type) so it was positive).
I may be wrong, I often am, but I can't see any positive feedback at a quick glance.
British valve (Mullard Philips) nomenclature had the first letter give the heater voltage/current, 'P' 300mA. Second internal construction of valve 'C' for triode and next same 'L' for pentode (and so on for valves stuffed with bits, EABC80) and then the specific number in a range of valve base identifiers 82 - B9A for this example. 30s for international octal - You can look up the system.
PS I note the original design had a 3.3 M (dropping to 330K is pushing it somewhat)) But.. it seems to work OK and has enough gain.
Good morning friend! I congratulate you on this project! is it possible can you share the diagram? I'd like to do it! since I have the valves PCL82!
Just wondering if there should be a chassis protective earth when using a double insulated stepped down supply but then bumping the volts back up again inside the enclosure?
If not for shock protection, perhaps for EMI?
Great video and build by the way.
May I know , what speaker you use to play that music for amp test?? :)
Now you can add a fancy English walnut base, call your creation the Lark mark I and sell it for... a tidy profit.