How Amplifiers Work: Rectifiers and Filter Capacitors
HTML-код
- Опубликовано: 24 ноя 2013
- This video is a continuation of my previously posted Two Sources of Amplifier Hum Video, and explains (in very basic language) the different methods of rectification used in amplifiers and how the filter capacitors function to eliminate the 120 cycle/sec ripple (hum) that remains after the 60 cycle/sec current is rectified. In addition a comparison of commonly used guitar amp rectifier tubes is presented, and different types of diode (solid state) rectification are discussed.
PLEASE NOTE: There is an error in the diagram for Half Wave Rectification. The output should be labelled "120VDC (169VDC RMS)" instead of 60VDC. With half-wave rectification, you get approximately the same voltage out of the single diode that you put in, but only half the current, since the negative portions of the waveform (i.e. half the current) are blocked.
If you enjoy videos featuring classic vintage amplifiers, jukeboxes, and related electronic devices, and you are curious about how they function, then please subscribe to my channel. You will gain immediate access to over 70 more videos, and you will be alerted each time a new video is posted.
Thanks for watching !! 
Видеоклипы
I am a physician with absolutely no musical talent, but an endless thirst for knowledge on all fronts, including circuit design. I ended up here after searching for videos on how tube amps work. I've been up for hours watching your videos. Your patient and thorough explanations are incredible. Thank you for your time and effort in contributing these videos to the collective knowledge base that is the internet. The world is a better place because of them!
Wow.....thanks so much for your very kind words, ADW. We sincerely appreciate them, and are glad to hear that the videos are helpful and informative.
Uncle Doug needs his own t.v. show, he is truly one of the best contributors on RUclips. No doubt about that.
Thanks, SS, but only if Rusty can be my Ed McMahon :)
Oh absolutely! If you’re into vintage amplifiers this is like a technical education. So valuable. I know a younger fella here in New York that owns his own shop repairing and restoring these beautiful creations and cites Uncle Doug as his influence and inspiration. That’s how far this amazing work reaches!
the smartest people explain things in the simplest terms - thanks!
Thanks. I hope our explanations are always clear and concise, EA.
Thank you very much. I've tried so hard other the years to understand amplifiers and nothing stuck in my head. Your explanations just made it click for me somehow, very clear and concise. I feel like a complex subject finally fits inside my small brain 😁
I very much appreciate these videos. Subscribed. 👍
Glad to hear it, KW. Thanks for subscribing :)
Wow, I have watched a few of your videos in this series. You have totally demystified many of the questions I didn't even know how to formulate to ask. You have a teaching gift, Sir!
Thanks so much, John. Rusty and I really appreciate your kind words.
+Uncle Doug, thank you. Best time I've spent on RUclips lately. I learned more about tube amps from you in 2 hours than I did elsewhere in 10 years.
You're welcome, Don. It's great to hear that the videos are an effective learning tool.
Agreed. I built a few amps in the early 2000s and due to life interference dropped it a few years later. There were forums to learn from, and I learned a lot back then, but having the visuals makes the learning process so much easier to comprehend. It is inspiring me to pick up some of my old unfinished projects.
I’ve been binge watching your videos. You use great analogies to explain the concepts, yet keep enough of technical aspects to have plenty of aha moments. Keep up the great work!
Thanks, BGR. Glad you enjoy our methods :)
This is great. Clear, concise, and very helpful. You obviously have a lot of knowledge about tube amps and it shows in all your videos.
Thank you, DN. Over the years, I've found most explanations of electronic theory to be utterly confusing and overly complex.....even though the principles themselves are actually rather simple. After struggling to learn about these topics, I am now trying to "translate" them into basic language and make them more accessible.
I love your videos. Simple, to the point, and informative. Perfect for learning new things at home
Thanks so much, 1PM. We're glad you like them :)
I'm blown away by the wealth of information you provide on your channel. I'm just getting started learning about tube amplifiers and am very excited to start digging in here. Thank you SO MUCH for sharing, sir.
microcosm You're quite welcome. Rusty and I are glad you're enjoying our videos and sincerely appreciate your very kind words. Thanks for watching :)
The absolutely best presentation I have found! The best parts are the LARGE simple drawings and the physical
tubes and electronic components that mirrors, emphasis and tie everything together! Great work! Will continue
to watch more of your series!!!
Thanks so much, Jeff. We're glad to hear that our videos are easy to understand.
I'm prepping for my General-class ham radio license and finally found someone who can explain this in a way that makes sense. THANK YOU UNCLE DOUG!
You're welcome, Mason. Good luck on your test.
Thank You, Uncle Doug and Rusty. I was thinking I needed to go through all your videos, several times, to "wrap my head around" "IT". I am finding once or twice is clearing up so much that I didn't exactly understand. You (and Rusty) are excellent teachers. I Thank You again, dear Sir.
You are quite welcome, JL. We're glad to hear that the videos are helpful and easy to digest (Rusty's favorite word). Speaking of whom, Rusty is actually the "brains" of the operation, I am simply his servant and provider of ear scratching.....in fact, that's my official title in our partnership agreement :)
Thank you for the effort . Your videos are very instructive for us who are just learning about the old amplifiers. Greetings from Croatia.
You're welcome, Robert. It's great to hear from our international viewers. Best regards from Texas, USA :)
I'm a huge fan of this channel. You're like the teacher I never had. Great video!!
Thanks so much, Matt. I sincerely hope my videos are helpful and informative.....thanks for watching!!!
I know this is an old video but....AWESOME video! MORE! MORE! I learned a ton so quickly....I am 56 years old, with 9 vintage tube amps, and have been wanting to apprentice at a repair shop for years to try to learn more about circuit analysis on tube amps. There just arent any shops within a few hundred miles of me, so I try to pick up what I can on here. Great explanation! Cant thank you enough and really want more. ALL my amps need attention, but shipping a 65 lb tube amp costs a small fortune. So I'm trying to learn more myself.
Thanks for your very nice comments, B. You have the right attitude.....It's always better to pursue independent ability than it is to rely on others. Best of luck with your self-education.
I find this gentleman an excellent teacher, I have learnt more watching these videos than any book that I have read. I would like to see how to use an oscilloscope and what voltage you can put into the oscilloscope with out damaging the scope or my self. Please keep these splendid lectures up and thank you. Lionel (uk)
You're quite welcome, Lionel. I appreciate your kind appraisal. I haven't made a video featuring the oscilloscope, mainly because I'm not sure how many viewers own one, but I will definitely consider your suggestion. Thanks for watching and commenting.
I know I'm popping all over your videos like the popcorn electrons on a cathode, but I was in a complete fog about rectification tubes etc. and their use of and filtering..! I spent the last 13 or so minutes with your video and the 'Fog' has cleared Doug. Fab explanation. Thanks..Ed U.K.
That's great news, Ed. Thanks for making our day :)
High quality teaching Doug. Simple, well thought out lessons. Camera play and editing are straight. I dropped out 30 years ago because I could not visualize what circuits do. This is so plain to me now, thanks Doug for taking the time and effort. Time for me to build an amplifier...
You're welcome, CN. Thanks for your very nice comments. Best of luck with future projects.
Actually, I have an odd question. I have a reason why for this train of thought other than purely electronic, so bear with me sir. I want an AC power supply at 108V @ 54Hz. Could I achieve that with an AC to AC transformer and/or some sort of oscillator? I have no idea except a circuit I presume changes 110V@60Hz to 230V@50Hz?, or is that a simple switch? Is this even do-able? Thanks for any input.
You don't mention the current capacity of his power supply, CN, but it's an important factor. As far as the 108VAC, this would be easily achieved with good accuracy using a Variac. You can also use an inverter to convert DC into AC of varying frequency by altering the frequency of the oscillator withing the inverter. Here is an excellent source of info: electronics.stackexchange.com/questions/148023/how-to-change-the-frequency-of-ac-supply
Wow, what a good teacher you are! I understood and you made it seem simple and easy as well as provide practical advice. Now when I see a board, I know what the parts do! Thanks!
You're welcome, Bruce.
You are such a great teacher. I feel smarter after every video 🙏
Thanks, George. That's great to hear.
Thanks Uncle Doug. your sharing is a gift, stay with it, Your production is straight forward and professional. many Thanks!
You're welcome, DN, and thanks for your very nice comments :)
Hey, No charge, I should be paying you and the Carlson lab guy, words are nice ,but sharing the knowledge base that has taken you years to develope, and to point blank share it depicts great character, You are a valuable tech. and part of what makes America great, down the road I may ask you on certain test gear, I have more than whats needed for my analog world , and a newbie i Iz. many Thanks Uncle Doug!!! P.S.
gotta brag on my latest find, Stopped in at a garage sale cuz traffic was at a stand still and noticed a very familiar looking brief case.
a barley used Sencore MU-150 with all the original tags, power cord still factory wrapped. they wanted it gone, and $5 made it land on my bench. replacing all the electrolytics (ESR thru the roof), as I write this.
be well.....
Congratulations on a major score, DN. I guess traffic jams are good for something :)
Whenever I learn something new, I realize just how far Id like to go, thanks!
You're welcome, Michael.
and then there's kirchoff's laws and quadratic equation. backin' up, backin' up.
in another video you mention the 12ax7 tube being two tubes in one. is this why the 12ax7 is more gainy than others further down the list such as 12at, 12ay etc? and also the reason why it uses less current?
I love your handwritten and hand sketched tutorials. Your drawings are very clean and to the purpose. I would only like to express that if you are using two-diode setup, your transformer will have 2×V output, whereas bridge rectification requires only V output from the transformer, V being the desired output voltage. Since 2×V capacity transformer will have double the secondary windings of a V capacity transformer, it contains more copper and therefore it tends to be more expensive than the latter. Very informative video as always and thank you very much for it.
Thanks for the nice comments and info, LS.
@@UncleDoug thank you uncle. One stupid question: do tube rectifiers have voltage drop characteristics like diodes have?
Not stupid at all, LS. Yes, they do.....because rectifier tubes contain two diodes, so all the same rules apply.
Uncle Doug, . . . your videos are so educational and clear. Thank you for sharing your knowledge. Great Deal for us All.
Thanks so much, RD :)
excellent explanation. especially appreciate your run-down on tube categories and models.
Thanks, Jex.....glad you enjoyed the video.
finally I understand rectification, Uncle Doug your the BOMB!!! give rusty a treat for me!
+jeff b Thanks, Jeff. Rusty and I are glad the videos were informative :)
Thank you, Uncle Doug. Just...thank you. This stuff is the bomb. I'm learning a great deal because you're a great teacher - clear and direct. Lovin' it! Thanks to Rusty, too.
You're welcome, Shaun....from all of us :)
I love to hear uncle Doug explain things even some very basic stuff.
We're glad you do, Moses. Thanks :)
Thanks again Doug....fantastic video, and thorough explanation. And thank rusty as well.
You're welcome, Bryan. Rusty and I send our regards and sincerely appreciate your time and interest :) ^. .^
thanks Doug. your part 1 amp video explains it perfectly . I don't how I missed it!!
+Barry Davison You're welcome, Barry. I'm glad the video was helpful.
8:03 - those two really don't look happy... ;)
Great clarification, as always, Doug!
Thank you so much for all your work!
Those cathodes are definitely displeased about something, JT :) You're welcome.
Thank you Professor Doug for this rectifier lesson.
It was a pleasure, John.
Great work Uncle Doug!! Best subscription I've done EVER in YT!
I'm hungry for knowledge, keep those awesome vids coming!
Greetings from Greece!
Wow....Thanks, Foibster. Rusty and I really appreciate your kind words of support, and hope that all is well in Greece !! :) ^. .^
Hey Doug! Love your vids, I know about these concepts and watching your vids just makes all my doubts go away!
Glad to hear it, Sam. Thanks !!
This is a superb explanation! Really made everything simple and easy to understand : )
Thanks, Zach.....glad it was helpful :)
Thanks for posting this. I've always enjoyed the sound of tube amps, and tinkering with electronics. Recently, I've been itching to building my own tube amp (but I don't play guitar ... weird, I know). Before I pull out the soldering iron, I want to understand more about what is actually happening inside the amp. It looks like I'll be spending a bit of time on your channel in the coming days.
You're welcome, Jon. Hopefully the videos I have posted will give you a basic understanding of amplifier circuitry. Best of luck with your pursuit of knowledge.....and your project.
Best explanation I’ve ever seen. Bravo. Thank you!!!
You're welcome, Michael. Thanks !!
I just wanted to let you know that you answered all my questions about the inner workings of an amplifier - this is true after I read the "Inside Tube Amps" by Dan Torres. Thank you so much! I'm ready to put my amp together now (I've had the parts for about three years, but I hate to attempt things I don't fully understand.) PS: Don't worry, I've built PSUs before and know about safety measures for high voltage high current, and cap discharge etc. Thanks again, excellent videos in layman terminology.
Alexander Brevig You're quite welcome, Alexander. It's great to hear that the videos are helpful. Best of luck with your amp project :)
Another great video. Great explaination and teaching style, thanks so much!
Thanks, Scott.
very informative and appreciated, you are a good teacher. thank you
Kevin Courtney Thanks, Kevin. I'm glad the videos are helpful.
Wow. I'm amazed and informed with every video!
Glad to hear it, Ed :)
Thanks for all your time in the information we definitely appreciate it
You're welcome, Robert
Great video, very concise. Thank you so much Uncle Doug for posting. Subscribed.
You're welcome, Rudy, and thanks for the kind words. Welcome aboard :)
Absolutely brilliant explanation, thanks for the video!
You're welcome, WW. Thanks for the nice comment :)
Very good explanation of rectification.
Thanks, Mark.
Really great video. You made this very easy to understand.
Thanks, Don :)
Thanks Doug - useful insight here - never thought about how an indirect cathode on a rectifier gives a more gentle HT switch on to the rest of the valves (tubes!) in the circuit eg allows the heaters to get working first...clearly a better option than a direct one!
You're welcome, David. The difference is quite evident when using an indirectly-heated rectifier vs a directly-heated one. The first time I used a GZ34, it took so long to come on that I initially thought that the amp circuit was faulty :)
You sir are an excellent teacher!
Thanks Ben :)
Thanks Uncle Doug!
You have a eliminated so much of my ripple lol
GREAT VIDEO LESSON!!! (I will be watching this repeatedly)
Rob Valdivia You're welcome, Rob. I'm glad that Rusty and I could smooth out your B+ :) Thanks for the kind words and best of luck.
A very thorough explanation, thank you. After running some simulations in LTSpice, I completely understand your preference for the soft start of the GZ34.
Thanks so much, BT. I'm glad that the GZ34 distinguished itself.....it's a great rectifier.
You are doing the world a diservice if you are not teaching electronics / electrical engineering at the college level. I've take course work that I didn't understand until finding your channel. Just becuase you can pass tests doesn't mean that you "get it". NOW, I get it... ; )
Thanks so much, TJ. That's great news.
keep it up Doug. I am learning so much .Thank You.
I will, Edwin. Thanks for watching !!!
Thanks Doug! Your videos are excellent
You're welcome, PDE.
Super explanation! Thank you for posting.
Glad you enjoyed it, WW :)
Thanks so much. Explained so well!
Thanks, Kevin. I'm glad the video was helpful.
This is a great video! Thank you for your explanation.
+Michael Martinez Thanks, Michael. I'm glad you liked it :)
Such a beautiful explanation.
Thanks, Christoph.....I really appreciate your kind assessment. I have several other technical videos that may be of interest. Please check my most recent posting on Output Tube Biasing.
Dirty uncle Doug! Thanks for the video. MY kx15 crate amp was buzzing really loud, and there was something loose inside.I resodered the loose part, but I forgot which wires went where... now trying to learn a lot.thanks again, peace
+alex thefakest You're welcome, Alex. It's good that you are trying to learn as much as possible to enable the repair of your own amps. That's always the best place to start. Best of luck with your project :)
Always take a photo before dismantling a circuit.
I've watched this before..its Good to refresh my memory..
Repetition is good for recall. Thanks for watching.....twice :)
uncle doug you kick ass. thanks!
John Brown You're welcome, John :)
Awesome. Excellent presentation. Thank you.
You're welcome, Joe.
Another great video. Thanks!
You're welcome, James.
I'm working my way through all your videos UD&R. You are hitting on all the topics I have questions about. It's like you're reading my mind. I understand the electronics from a numbers side, but never understood why "filter caps" were in audio circuits. This video filled in some big gaps for me. THANKS!
You're welcome, Greg. I try to cover all the topics that puzzled me when I started out with tube amps.....and, apparently these topics coincide with other people's areas of uncertainty. Rusty and I are glad the videos are helpful :)
Doug, this is a great explanation, best I've seen yet. If you get a chance to make another video, could you please go further into depth on tube rectifiers and how is it that we get the B+ off of the cathode. Also, how does the current flow through the anodes since it appears to be a seemingly open circuit. I'm assuming the anodes don't touch.
Please check our more recent videos on rectification and power supplies, Maddox. They contain the information you seek.
Thank you Sir, don't stop doing the good work you do!
Very Good explanation. Tank you very much.
You're welcome, Nelson.
very cool video, thanks uncle
What a great YT channel
Thanks, P.
Great video, thanks for posting!
You're welcome, Tyson :)
Very well done!
Thanks, BB :)
Great teaching!
Thanks, Stephen :)
Thanks Uncle Doug! Well done!
You're welcome, T :)
Great video!!
Thanks, Jimmy
Thanks! This helped a lot.
Great video.
Thanks :)
Great video, learned a lot!
That's great to hear, DD. Glad you liked it :)
Excellent - helped me a lot!
Thanks, Lorne. I'm glad :)
Way less rippled! Thanks a lot.
Yago Bolívar You're welcome, Yago :)
very usefull video! thanks Uncle Doug
You're welcome, El :)
Very nice video Uncle Doug.
Thank you, ST. I really appreciate your favorable input.
great stuff!
Thanks, Steven :)
Hi, Unclr Doug, here's a good one.
I'm rebuilding a Newcomb AV-7 phonograph with a Widow Maker circuit. It has a a 12av6, with dual diode and a triode in the same glass envelope. The diodes are connected in a half-wave configuration, and a solid state diode is connected in the heater section. I've seen a similar circuit using a single diode tube, and a SS diode in the heater section.
I tend to avoid the series-filament circuits, Stephen, but this one sounds rather unusual. Thanks for sharing it with us.
@@UncleDoug Thanks for all of the Videos, and for your reply. After weeks of study, and searching for an isolation transformer that never existed, I tend to concur. Current draw on a 'Widow Maker' is enormous. But it was a great case study in archaic engineering (and finding obsolete parts), and I did find an excellent source for schematics:
''Practical Amplifier Diagrams'' (Robin & Lippman, 1947).
You, and your fan base, can download a PDF copy for free.
Awesome video! I love it!
Thanks, JS2. I'm glad you enjoyed it :)
very informative, thanks!
You're welcome, LW :)
Uncle Doug great lesson!
Glad you liked it, V :)
there are many great videos here that help tremendously. But what about repairs and identifying distortion and other enomolies in existing new and vintage amps?
I have posted quite a few videos demonstrating diagnostic and repair techniques, Francis. Please check out my video list.
I always knew what filter caps did, now I know how they do it!
I'm glad the video was informative, James.
SUBSCRIBED! Amazing explanations!
Thanks, KA. Rusty and I welcome you to our channel.
thank you made it much easier for me !
+Duche Khutsishvilii That's good news, Duche. We're glad the video was helpful :)
pardon my ignorance, but in a case of mesa dual or triple "rectifier", does it even have anything to do with rectifying AC in those particular amps?
Yes, it does. 100W and above tube amps require more high voltage DC current than a single rectifier can provide, so two or three rectifiers are necessary.
Uncle Doug, I have a few questions for you and please explain them :
1. What is 169VDC RMS !!!!?
2. What is pulsating D.C.?
3. If I need +270VDC, using a two-diode full-wave rectifier, how many volts should the transformer secondary be?
4. What is the P.I.V. of a diode?
5. What is 120Hz hum!!!!?
6. Why is a computer power supply so special that deserves a mention?
Looking forward to hearing from you, Uncle Doug.
Paul Cheung
I started to answer all of these, but realized that the answers are all readily available either in my videos or via internet searches. Good luck.
Great explanation Uncle Doug! Thanks.... And as I like to joke abit, back in the day I had a bad bottle of "Ripple" and the next morning my head had a very large hum!! Ok, ok. I'll stop! Seriously though, Ive learned alot from you and greatly appreciated it!!🎼🎛
Ripple was the nectar of the gods back in the old hippy 60's, Wayne. I downed many a bottle of it while listening to Iron Butterfly and Vanilla Fudge albums ;)
@@UncleDoug Remember it well!!! Matuse White...
Awesome video! I have learned a lot from your channel Uncle Doug. I have recently purchased an all original (including the two prong plug) Traynor YBA 1A. I have been researching how to install a three prong plug but am still a bit lost on how to wire it up. if it's not too much of a hassle, could you and Rusty do a video on it or at least answer a few questions? Thanks!
I have shown the proper method for installing a 3-wire power cable in quite a few videos, Samuel. You might want to watch the recent Supro Tremo-Verb wiring video.
Hello uncle doug.
thank you for your excellent didactic videos.
I'm learning a lot.
I wonder what differs in the eletric design a guitar amp and a hi-fi amp.
thank you
Greetings, Bruno. I'm glad the videos are helpful and informative.
The main difference is that guitar amps (particularly those with tubes) are designed to provide distortion at moderate volume levels, while Hi-Fi amps avoid distortion and provide absolutely clean tones, even at high volume.
You are so cool Uncle Doug!
You are so kind to say so, William. Thanks :)
Great info, thank you. I am trying to fix a home audio amplifier and was hoping you could help me troubleshoot it. The bridge rectifier on the power supply board emits a large spark when I power it up though it continues to work. I replaced the bridge rectifier and 2 small caps next to it and the problem remains!
Since bridge rectifiers are generally sealed blocks, I'm not sure where the sparks could be coming from, MT, but it sounds like the start-up voltage spike exceeds the rating of the BR. If the BR worked fine for a long time and suddenly began to act up, perhaps your filter capacitors are drawing more current than they should. You need to evaluate this before sacrificing another BR. It may be time to change the filter caps.
Are the filter caps the large ones (6800uF 80WV)? The spark seems to originate at the + lead of the bridge. You can see photos and video at this forum post: forum.allaboutcircuits.com/threads/home-audio-amplifier-repair.128825/
turned out to be a bad solder joint at the smaller "in-line" rectifier on the board. Working great again!
that 5u4 looks just like my 5z3p- cool, man i am hooked, long live the tube!!!!
+jeff b The two tubes are quite similar in design, but have different numbers of pins and different pin-to-component internal connections, Jeff. The 5Z3 was a popular rectifier with early jukebox amplifiers.
cool, did not know that, using the 5z3p in the Hifi with 2- 6N9P'S and 2-EL34-B'S, going to correct all my mistakes after watching some more of your videos 2 or 3 more times as to absorb all the info, happy holidays to you and rusty- sorry forgot your cat's name him too, take care
Happy holidays to you too, Jeff, and best of luck with all your projects in the new year :)
thank you, you are a class act my friend
You're welcome :)
Thanks so much for these videos Uncle Doug. I'm hoping to get a better understanding of how to select the capacitance of the Filter caps when using rectifier tubes. Is there any chance you have any videos that talk about that? I've been told that you need to be concerned about the in-rush current because the Rectifier tubes can't handle too high and that's why the capacitance needs to be low. I can't say that I understand why higher capacitance would increase that current (but I am just learning).
When an amp circuit is first energized, the filter caps have to charge up, so for a second or two, they are like a dead short....the higher the capacitance, the longer the short lasts. The maximum value for 1st filter cap is given for each rectifier tube in tube handbook(s).
@@UncleDoug That makes sense. Thank you. I'm reading Megantz's book and he mentions that the final stage of filtering is the preamp section and that is because you want to filter it more. So is there a reason that we usually see all low capacitance caps in a row? Why not just the first cap low and then all the rest higher?
Doug, thanks for all the excellent videos. I have a question regarding hum as well. There's hum in my amps that does not increase much whenever I increase the preamp volume, only when the master volume (PPIMV) is increased. Where could the (50Hz) hum come from? Thanks!
+Cue Zephyr It's impossible to tell without personally testing the amp, however your observation implies that it is coming from the stage(s) between the pre-amp and master volume control. As to possible causes, you can do a Google search for suggestions and solutions. Good luck.
Have a question. How to choose a rectifier tube for the scheme? Indirect heating for the slower warm up - done. But all other parameters? Heater current(HC). Peak inverse voltage(PIV). Max rectified current(mRC). Plate current. What they should be?
I'm choosing between GZ30 = 2A (HC), 125mA (mRC), 1400V (PIV) and other tube with 3A (HC), 190mA (mRC) and 1700V (PIV).
You said you like GZ34 the most. Why? I can see that it can output more current. has less heater current and has average PIV in comparison to the above mentioned. Are these critical parameters?
Thank you.
Best regards,
Yury.
Good question, Yury. I would say that an ideal rectifier should exceed circuit requirements by a "comfortable margin". If total voltage and current requirements (either directly measured or accurately calculated) were 90mA and 350VDC B+, then the GZ30 would be a good choice, and it's lower heater current would be less burden on the PT. If the V & C requirements were 115mA and 475VDC B+, then I would probably go with the 3A tube. I personally have no exact formula, but simply rely on common sense. In most sub-30W amp circuits, the efficiency, slow startup, and low PT demands of the GZ34 make it an obvious choice....at least to me.