As usual, great video. Well explained for any novice getting into electronics. One point I think we need to make here is just like the capacitor, the choke stores energy as well. And just like the capacitor, it releases that energy when the voltage feeding it falls. One reason chokes were used in tube circuits was cost. Today that seems absurd as a choke costs many times even a large high uf/high voltage capacitor. But it wasn't that way in the 1920s through the 1950s. Large caps were quite expensive if not outright unobtainable prior to the 1940s. A choke was actually cheaper to manufacture at the time. Solid state circuitry also made the power supply choke mostly obsolete. As SS circuits use lower voltage, higher current, the required size (Henry's) of the choke becomes impractical at 60hz. And by that time we fortunately mastered the dry electrolytic capacitor. But then in switch mode power supplies that are universal today, we once again see a choke power supply. This is because the high frequency AC at 50khz or higher is easily filtered by a small choke (very low Henry's, in fact just a few micro Henry's). So in a sense we have come full circle in power supply design basics. But also note in a switch mode power supply, the primary input rectifier filter is still a moderately large electrolytic capacitor typically in the hundreds of uf range. This is because at this point we are still at 50 or 60hz.
I dont know much about electronics but I have always had a great curiosity . You are a great teacher your digrams help greatly in understanding. Thank you for explaining.
My new hero!!! WHERE HAVE YOU BEEN all this time I’ve been trying to learn electronics?! Every other YT channel I’ve found shows but doesn’t explain, explains but doesn’t show, goes way under my current knowledge level, or goes way over it. You should have a million subscribers. BEST video explanation of this I’ve seen YET! Subscribing and watching ALL your videos! As an aside, I’d love to know how you learned electronics. I’m fascinated by discovering what got other people to where they are... If you haven’t already made a video about your background, PLEASE DO! Thanks! 😊😊😊
Another great video, I'm not a sound guy but a radio ham... never the less, I'm learning loads and really appreciate you quiet, sensible delivery style. I might have to learn the guitar now! LOL
Great tutorial ! I started out watching D-lab and M.Caldeira which raised my interest but also raised questions such as the "choke". Visualizing the explanation helps out a lot for us who don't have english as the first language. Thanks ! And yes that is my real name, it's Swedish.
Nice video, thanks. I find it helpful to add a load when testing for ripple. Switching between 2 loads can also help provide details on what kind of output impedance you can expect from your power supply design.
Amazing explanation. I'm a newb and am having a hard time wrapping my head around things. But this cleared up a lot of questions. easy to understand. Thank you
YOU TUBE GOLD...as far as I am concerned...! Thank you so much...now I don't have to search some university library for a EE textbook to sort this out...! Very cool tip with the duncan amps software as well...! Thanks again...!
4 minutes into this video, and you have already taught me (in a manner that I will remember!) more about tube amps than almost 6 months of reading books/blogs/articles and even watching other content creators. I mean Rob Robinette has a invaluable reference site, but it kind of assumes that you are already fairly familiar with tube amps and schematics. When you buy a B-52 AT100 that is already infamous for electrical issues sight unseen, and the seller swears up and down that it was working when he sent it, but the 20 year old masking tape has markings that highlight the one tube that shows scorch marks on the board... well, lets just say, I'm out of my depth after replacing 3 bad resistors, 2 blown fuses, all of the tubes. Still will not power on. I Love the B-52's, but I might as well have gotten a Mesa-Boogie for the amount I'm spending to repair a $500 amp.
That's a really good demonstration and explanation. I would have also liked seeing the effect of the capacitor that follows the choke. It looks like it's shunting an even higher frequency to ground to smooth out the plate voltage even more. Thanks again.
Many early radios, and guitar amplifiers used the speaker's field coil as a filter choke for the power supply. Including the early 31H Leslie speakers.
Great video but I must politely point out a small yet important detail you missed. All the voltages you refer to in this video are RMS and those are not the same as peak to peak. For example common household voltage is well known as 120 V but that is RMS, the peak of this sine wave is actually the RMS voltage multiplied by the square root of 2 which turns out to be around 170V peaks. This is important as this peak voltage is what is actually rectified and stored in the capacitor which is why your DC voltage is higher than the RMS voltage when rectified. Same for the transformer secondary voltages. The rectified voltage will be 380 times square root of 2 or 1.71
Hi Jacob, the square root of 2 is 1.414 not 1.71, hence the 380 volts RMS when rectified becomes 537 volts DC. You are correct about house peak to peak voltage in North America is very near 170 Vpp or 120 x 1.414. :-)
@@garybevis8691 You are right! I don't know where I got that number from. I think I was thinking of root 2 and root 3 simultaneously root 3 is about 1.73. I use root 3 more at my job for 3 phase conversions.
Kudos ur schematic is very good in order for ur choke to do its job thebinput C should be relatively low and the C after the choke should be 20 or so times higher good power supply design
You took me back to 1969 when I went on an evening course called the fundamentals of electronics and i built a TRF or Reaction radio. My tutor never went into so much detail, so thank you.
The voltage of the high voltage secondary of the xformer is 780 VAC RMS. The P2P voltage will be 1074.8 V. The P2P voltage of each half of the secondary will be 537.4 V.
Also called a Pi filter? The choke opposes a change in current by storing and releasing the energy in an electromagnetic field. The capacitor opposes a change in voltage.
Nice videos. I'm a ham operator who plays with old AM "Boat Anchors" and have found a lot of overlap with your toys. If you are not already you should think about getting a ham ticket and getting on AM with some old tube gear. I will be watching. Thanks, George
Great video! Maybe you should put the fuse and switch inline in the L channel of the power input though. As a best practice, because whether the fuse goes or when you switch, in both cases you want the live input connection to be interrupted, and not the neutral.
I replaced all the filter caps in a customers 70s Fender Twin Reverb guitar amp. The amp still had more hum than normal. The problem was a shorted choke. I've probably had maybe 5 or 6 chokes fail in 30 years of servicing tube guitar amps.
Hi Mark, thanks for great explanations, Im a newbie, and have learnd a lot with your videos! If possible, would you make a video explaining how to design a real LC - Choke input filter (not a CLC or Pi filter...) considering critical inductance as well as minimal current for bleeder resistor calculations? I have read a lot about inductors efficiency for ripple smoothing, and also saw many rectifiers tubes datasheets with differences in operating characteristics between Choke Input and Capacitor Input (Pi) filters... Thank you very much!
I have been using the 1N4007 for a replacement for tubes for ten years now I know of and have dealt with are flash over and the turn on transient the coil stuff is fight on
Great video. Thank you for the excellent video. I have a question or two. I noticed in your schematic the neutral is switched. In my jurisdiction that is not allowed. The neutral must NEVER be open. Only the line side of the AC. When the neutral open the chassis is always live with a potential of 120v to ground and the could be you if the earth-ground (green) is not, for whatever reason, present. All fuses/CB must be on the line side for this reason. Again, that is my local code but maybe not yours. Next, I have a few old original Dynaco ST-70 amps. One was functioning perfectly when I decided to install a three-pronged "earthed" plug. The green went to the metal chassis. When I plugged it in the resistors on the rectifier board exploded, I assume due to high current ground as this amp has one lead from the power trans to the star ground along with the electrolytic capacitor can tab and other leads from the rectification board. I'm just in the process of replacing the caps and the board, I have read other have earth grounded that chassis w/o issues other than some hum (which makes me crazy why the chassis should have ever had anything to to with carrying current). My first thought is that it/s a polarity issue. Any thoughts would be greatly appreciated. Many thanks.
The circuit with the respective load of el34 has been simulated on multisim, with the choke and with the gyrator and actually seems that the choke and the gyrator identical same
I'm glad you posted this David Fuller. You are correct. I'm really surprised how many people have worked in electronics for years and don't know that the 120 VAC (or 117 or whatever) wall voltage is RMS not Peak to Peak. It makes me wonder if they have never looked at the wall voltage on an oscilloscope.
Maybe the name "choke" comes from the fact that you push all the current needed by the amp through this component while wanting to ensure there's enough steady breathing material available for the amp.
Excellent explanation but the modeling experiment even better. Would you provide a schematic and parts list for your test? What did you use for a load on the rectifier circuit?
I came across a place that sells lots of transformers and Chokes that are relate to tube amps. Often there is no writing on them. Could you make a video on identifying such components? Especially estimating or measuring the current limits of these hunks of metal... Thanks !
Watching this with my DIY tube amplifier. One question, suppose I have an unused supercap (1.2 mF 400 V), is it OK to connect it parallel to the rectifier output and eliminate the use of a choke? Since a bigger capacitor will smoothen the ripple even more as well.
Liked most of the video but the rectifier doesn't "flip" half of the waveform negative to positive. You have two diodes alternately conducting around a common center tap. Each diode adds its pulse when its side of the HV winding goes positive with respect to the center tap.
This was a really nice, informative video. I would like to mock something like this up so that I can add a choke to an amp that was not originally designed with a choke. I've added a choke to a Princeton Reverb and had to install a lower than spec resistor after the choke to drop voltage to the next node in the chain. The choke alone dropped me 3v., I needed to drop 20v. I'd like to add what you did to a build board. Do I need a load on the power transformer to do what you just did? I always put a 4, 8, or 16 ohm load on output transformers to run diagnostics so I don't have to listen to signal coming out of a speaker. Does the same methodology apply to power transformers? Can they be powered up open ended?
Howdy. Chokes try to uphold the current. This causes the anode voltage to drop in suddent current demands. For instance a kettledrum is hit. When the current demand goes down the anode voltage will rise. This can cause a pumping effect on the sound. Chokes were used earlier when there were no large high voltage capacitors available or they were crazy expensive.
Why aren't there center taps on the rectifier filament windings? The connection of the load to one side, as is common, introduces significant 60Hz ripple.
In filament rectifiers, the filaments in the 2 halves are in parallel. You can choose either pin 2 or 8, and there will be no difference in plate voltage due to filament voltage.(5Y3, 5AU4) If you have a unipotential rectifier, it is necessary to draw positive from the pin #8, which is connected to the cathode sleeves.(GZ34, 5AR4)
Nice video explaining the power supply and purpose of filter chokes. Why does Paul Carlson refer to them as reactors? On your schematic L on the IEC connector is shown connecting to the 2 amp fuse and then to the transformer primary. N is connected through the switch to the other end of primary. Switch should be on L side between fuse and transformer.
"Reactor" is an older term, it refers to the effect of "reactance". But it was always ambigious because reactance is not unique to coils, it also happens inside capacitors (capacitive reactance/inductive reactance), so it was never clear wether you are talking about an inductor, a capacitor (or sometimes also combinations of both were called a "reactor"). Paul Carlson seems to use the old terms on purpose when he talks about vintage gear.. you also hear him saying "megacycles" or "kilocycles" very often ;)
Are you familiar with Matt Renaud's power supply design article where he uses a 2 stage filter scheme using 1.5 H chokes instead of a single stage using the 10 H. Better ripple figures and a lower cost. Very interesting topic. Thanks for your video.
Such a scheme will also result in lower resistance losses, and higher core saturation currents, allowing the power supply to handle higher peak current, with less voltage drop. It just means a few more components to mount, despite their smaller sizes.
Excellent! I know now not only what i wanted to... but much more. Only $40 for that choke? Worth every cent regarding the fine performance and most likely long life it probably has.This kind of stuff as you would know is getting scarce today. BTW, do you know if the newly manufactured Mullard tubes are anything near the superb originals for HI FI use ? Thanks for your valuable opinions and superb videos.
Thank you very much for this video! This is the explanation I have been looking for. You make my day! If I understand correctly, tubes are all about voltage amplification at relatively low current, as opposed to transistors who are about current amplification at relatively low voltage. I guess rectification of a high voltage B+ simply can not be done with reasonably sized capacitors. Is it correct to say a choke filters a high voltage sinus by topping off its peaks, as opposed to caps who filter low voltage DC by filling in the 'gaps' between peaks? So, inductive filtering is the best way for high voltage, low current and capacitive filtering is suited for low voltage, high current.
Yes. As the voltage peak hits the choke, the inductive field in the coil builds up and prevents the full peak from passing. As the voltage starts to drop the field starts collapsing and supplying current.
@1959Berre ~ not exactly, you need a low pass filter to reduce the ripple in AC to a theoretical 0% of the signal or 0.00 Volts RMS and some potential either above or below 0 Volts or Ground, which is your DC voltage no matter the voltage potential, high or low. Low pass filters consist of two or more components designed to allow a signal of a specified frequency to pass. Ideally you only want DC to pass into the tube circuit for powering vacuum tubes. The two components of the pass filter work together to smooth out the ripple of rectified AC. The inductor (choke) resists being charged in response to an increasing magnetic field strength inside the coil. The capacitor tries to fill in the dropping ac voltage by supplying current stored on the rising AC sine wave, which it then discharges on the falling AC sine wave. Simultaneously the inductor also adds current to the circuit as the magnetic field induced in the coil windings collapses on the downward side of the sine wave. This is what gives you that smooth, flat signal on the oscilloscope display. You can increase capacitor voltage by connecting them in series, which adds the rated voltages. For example if you connect two 450 VDC capacitors in series (for polarized caps +_-,+_-) you get 900 VDC of rated voltage capacity. There are capacitors (large oil filled) rated at thousands of volts, the same goes for inductors as well. So both inductive/capacitive and resistive/capacitive are used in all power supplies high or low voltage.
Also yes, vacuum tubes are like Field Effect Transistors they are voltage driven devices and Bipolar Junction Transistors are current driven devices. Hope this helps.
Choke filters the Ripple like Capacitors , but does so much better because magnetic field is a lot stronger then Electrostatic that is weak , good only for Voltage , no current , while Coils are good for current no voltage . So that is why combo of those is the way to go
Question about current in the choke? Chokes always say working current rating. Higher current you'll have less inductance and lower you'll have a higher inductance. Is the current rating the maximum rating, or can it be exceeded some? Thanks again!
Do nodal resistors basically do the same thing that the choke is doing? I believe that's what they are called, but they are basically votage dropping resistor(s) that go in series in-between the filter caps. It's something that you'd typically see in a guitar amp.
An 'internodal' resistor serves two purposes. It drops DC voltage and also works in conjunction with a following filter capacitor to form a low pass RC filter to reduce ripple. A choke, due to the low DC resistance of its coil, has little effect on the DC voltage but it forms low pass LC filter in conjunction with the following capacitor which reduces ripple more efficiently than an RC filter.
Hi so i just watched your video on how chokes work and was hoping you could come with a answer for me. I'm building a amplifier that is going to use 6 KT88 tube witch will draw around 842 ma and 6 smaller preamp tubes that will draw around 2 ma so lets just round it off at 845 ma I'm going solid state on my power transformer using 8 N14007 and this will be a filter input not choke input amplifier. the capacitors will be 50uf @ 500v the first 2 at the power supply wired in series parallel followed by 2 at the screens of the kt88 also wired in series parallel and 4 more cap in the preamp section all 50uf @ 500v. I'm having a power transformer made that will be 500 0 500 at the H.T how many hennery do i need ? I've gotten different answers like from 4-8 hennery but o more than 10 also would you know how many ohms it would be thanks Jack
The best chokes made were speaker magnets before they invented permanent magnets. Then then they also had humbucking coil beside the speaker magnet to suppress hum from the choke.
Actually, it’s 760 RMS from one end to the other, ignoring the center tap, as all the other specified transformer voltages are RMS. Therefore the P-P voltage is twice the peak voltage, which is: 380 (V RMS) times sqrt(2), or roughly 537 volts peak, so the P-P is twice this, or roughly 1,074 volts peak-to-peak. This is important, as you need to make sure the capacitors have a higher voltage rating than the pulsating, full-wave rectified DC peak (here, 537 Volts), so the 630 volt rated, 10 uF capacitor is good!
Hi William can you help me I'm building a amplifier that is going to use 6 KT88 tube witch will draw around 842 ma and 6 smaller preamp tubes that will draw around 2 ma so lets just round it off at 845 ma I'm going solid state on my power transformer using 8 N14007 and this will be a filter input not choke input amplifier. the capacitors will be 50uf @ 500v the first 2 at the power supply wired in series parallel followed by 2 at the screens of the kt88 also wired in series parallel and 4 more cap in the preamp section all 50uf @ 500v. I'm having a power transformer made that will be 500 0 500 at the H.T how many hennery do i need ? I've gotten different answers like from 4-8 hennery but o more than 10 also would you know how many ohms it would be thanks Jack
Just to be clear are not these voltage waveforms you reference only valid when there is a load resistor present on the output side of the power supply? It looks like the output is open circuit.
Best capacitors are oil in paper u can use motor run capacitors for hvac systems u can use ac capacitors there voltage ratings are 1.4 x of what they are rated at at ac voltage and they are cheap and long lasting
