You do a really good job of explaining these things in laymen's terms to us newbies Brad. Much appreciated for the work that you do and how you teach us all.
Love watching you do this stuff. When you were soldering in the choke around the 19:00 mark I had a flashback to my Army electronics school days and the sergeant yelling "NO WATCHES, RINGS OR DOG TAGS!" at us constantly and I had a bit of a cringe when I saw your rings on LOL
Your Sergeant has explained to me why when my wedding ring hit the power supply output on my 100 watt Acoustic 4-10s amp, I saw a flash that looked like a nuclear bomb going off and ended up missing 100 bucks worth of gold off the ring.
EXCELLENT post, Brad. LOVE this stuff. I know that you're enduring or at least HAVE endured past personal issues but THIS video is the reason that I am a follower of yours.
As with all things guitar, gear forums will worship at the altar of the choke as some magical tone shaping mod when in reality it just lowers noise/hum/hiss
In this case, I don't think the hum was lowered. I think that was already about as low as we were able to get it, but a choke will lessen wear on other components in the power section.
It's also a bit of a conditioner is the way I look at them, lowering the noise floor is a benefit. I'm going to listen to what brads points are just to see what he has to say I don't know everything yet🤣
@@TheGuitologist You're wicked smart Brad ! Thanks for the layman breakdown. I get the gist but the serious technicalities is what I lack. I just haven't learned to read schematics yet. The experiential knowledge you have is invaluable. Really appreciate it. 👍✌
HOLY SHIT MAN! Brad your blowing my mind with this stuff. I give you all the props when it comes to this science behind this stuff. Your the amp science guru! All the credit to you! Wonderful video!
I literally just added a choke on my latest amp build last week! Excellent video Brad 😊 choke makes such an awesome difference. Cleans up the power supply and I found hat in my amp it tightened up the response and added clarity. Oh, made the amp quiet as well! Have an awesome day dude!
@@TheGuitologist Ah thanks man! Very kind of you 🙏 Yep - on my way for sure! I have another two builds planned already! Its addictive! 😃 Have an awesome day!
Enjoyed the white board explanation man! I hope you’ll continue with that kind of break down in future videos. I get kinda cross eyed with schematics some times but watching someone draw things out like that while explaining in simple terms is great!
The whiteboard explanation of a choke/inductor and capacitor is a better explanation of either than I ever got going to school for electrical engineering. I wish I had this video 10 years ago!
You are a lot more knowledgeable about this than I am, when you installed the Choke, I see that both the power transformer and output transformer are both facing the same direction, I always heard one much place the in opposite facing direction, might that have been one of the sources to the hum?
U will never get rid of the noise whith the transformer placement. This is why placement and orientation matters . Great job on explaining chokes . Really enjoy your videos
I'd just like to point out something, courtesy of Mr. Blencowe: The Valve Wizard "Many Fender-derived amps use a choke-capacitor (LC) filter to supply the power valve screen grids. An LC filter is a second-order filter, so it provides steeper attenuation of ripple than an RC (first order) filter, and a choke has only a little DC resistance so it doesn't drop much DC voltage. Fender was interested in maximising voltage in order to maximise clean output power. These days people like to overdrive their amps, so there is no need to squeeze out every last watt of clean power, so many amps use RC filtering for the screen grids, which is much cheaper than using a choke. The exact value of choke is not critical, but it muct be remembered that an LC filter also resonantes at its corner frequency, which is given by: f = 1 / (2 pi sqrt[LC] ) If this is not well damped then it can cause the supply voltage to 'ring' when triggered by certain notes or rhythms, so it is usually best to keep the resonant frequency below 10Hz, out of the audio range. This will require a capacitor larger than: C = 1 / ( L × [2 pi f]^2 ) Since smoothing capacitors are most readily avalable in the range of 10uF to 100uF, you usually see chokes in the range of 20 to 2 henrys."
Man, of all the books I have, “designing tube preamps for guitar and bass” is my absolute favourite. I’ve bought a number of tube amp books over the years, but anytime I’m having to solve a problem, I always revert to that book because any answer I need is in there, and is usually listed in the table of contests too, so it’s easy to find. I actually have the book on my bedside table at the moment, I’m about to do a big makeover of a little amp and I’m going through the book working out what mods I’m going to do, what value resistors and caps, etc. etc. such a great resource.
Dude, great timing... I’ve built and modded a number of amps (since I started watching you many years ago), and I’m about to embark on a huge build which will have a choke, and I’m learning what I can about the subject before I order the parts...
The 10 henry choke in the tube manual is for a choke input filter. As you correctly stated earlier, that kind of filtering is not used in guitar amps (because of the larger choke). The filters we are used to are capacitor input.
Very nice and visual explained! I calculated my self nearly to death in my studies about filters on university, and your video explains it all clearly without using eny Formula. Well done sir!
I feel like if concepts are understood roughly first, the equations make way more sense. Inductors is some tough math though. Everything has a time component. Best understood with graphs.
I just loved the videos you made for this amp. I never get the chance to work on tube based circuits so to me anyways, this type of stuff is just great. I do have some schooling on tube circuits because back in the 70s they were still teaching both types of circuits in high school (3 yrs) but tubes were definitely on their way out. Except for guitar amps and some other exceptions. I don't want to sound like a frickin' 62 yr old fan boi, but I do dig your show. Great Job!
awesome video! Even an amateur tinkerer like me can understand. The before-after noise comparison didn't sound all that different but when you factor in the increase in wattage it actually is a lot quieter! and now I know a choke kind of does what I thought it would do, there's no secondary winding to grab the magnetic field so the primary winding grabs some back? or something? so it has an electrical cushioning effect. well, the important part is it makes the amp louder and less noisy and increases your rectifier tube lifespan.
That was one of the most informative vids you've ever produced Brad! My one question for you is: what do you use to test inductance? I've been needing to get an inductance tester primarily for car audio inductor testing, but I've been hesitant to purchase one of the cheap ones which are all made and sold in China. It seems they're all I can find or perhaps those are all that's available.
Early on when tube amps had electrodynamic speakers they did not use a choke... well, they did, but it was the magnet coil of the electrodynamic speaker that acted like the choke. Once permanent magnet speakers became available the need for a choke arose.
There's something to be said for keeping the originality, but I'll take function over form any day. Changing the caps and adding the choke sure blows originality out of the water. For all the times you've pulled the chassis you should have added a 1/4" jack and plug for the speaker connection. That's not original but it beats the hell out of de-soldering it.
Spot on treatise of the choke function! Given the added advantage we now have of extended component capacitance (and voltage ratings), the choke, these days, adds little but weight. Folks did use that Amp as was, after all. ;-) That experiment DID show useful, IMHO.
I most often use 2 chokes, one right off the rectifiers, and another one between the first 2 caps. Doing this you can use a smaller value of inductance on the first choke, as long as the current rating is sufficient.
Great information having a problem with mine on my old house tube amps need replacing (heat) finding parts not easy to get matching part numbers thanks for this info
First time I saw a configuration similar to Fig. 30.1G was in the schematic for a Hammond spinet organ similar to the one from which a Rola field coil speaker had been pulled; the field coil was between circuit ground and the transformer's center tap. If the power transformer is designed to provide, say, 90V more than what you want at your output tubes' plates, and you must use a field coil speaker, this is an elegant way to simultaneously power the field coil and filter mains hum.
Excellent discussion, Thanks. You have a great teaching style that takes a complex subject and makes it very easy to understand. Just like my other amp guru Uncle Doug. Oh, and I'll soon be building the Bias probe, probably two of them for push/pull amps.
Funny i just acquired a bunch of tvs with plenty of chokes... great timing as per usual brad.. yoy and Uncle Doug just have a knack for answering whats on my mind lol
Hammond makes some good parts and are really sought after in amps, especially Hammond transformers from the 70s. I have a traynor that has huge Hammond transformers
in this case, hum wasn't affected. The choke was still a good upgrade though because the rectifier and everything else in the power supply will be less stressed because of the choke. In other cases, the affect on hum may be more pronounced.
@@TheGuitologist Oh i see, thanks for your kind answer. I have a 5F1 clone and was considering adding a choke to reduce 50hz hum but i probably will learn to live with it as it is not as bad. Cheers!
4:47 - The filter in the middle is a three pole filter - so the out-of-band roll-off will be steeper compared to the two pole below. You'll get something like 20dB of attenuation per decade (freq) for each L or C. Therefore the pi filter in the middle should get you (at least) 60dB of attenuation out somewhere around 60Hz (assuming the passband ends at 6Hz) whereas the two element filter at the bottom would be in the ballpark of 40dB a decade out. So, the pi filter in the middle is not only cheaper and lighter - it's fundamentally better at rejecting those pulses coming off of the rectifier tubes. "Handbook of Filter Synthesis" - A. Zverev "Microwave Filters, Impedance Matching and Coupling Structures" - Matthaei, Jones, & Young (I'm an engineer in real life - 24 years in Silicon Valley)
Howdy. Nice. Using Solid State rectification the choke may be replaced with large capacitors. Yes. But the transformer current becomes spiky. Spiky current produces lots of reactive power. It may happen that the transformer VA rating is too low. Could explain why burnt out power transformers are sometimes experienced. Tube rectifiers don't tolerate spiky current. The spec.s will tell the largest allowable input capacitor. More DC filtering is needed and this is why chokes are mandatory. High Regards.
Great video, Brad. A choke is a must in a tube rectifier circuit. Any decent amp would have a Pi filter on the B+. I don't know why an engineer would choose an LC over a Pi, other than cost reduction. The amount of ripple and IMD reduction provided by that second cap is certainly audible.
Not sure if it has been mentioned, but you are at almost 30mA on one channel so that is 60mA for both. The choke is rated at 50mA, did you reach inside and feel if the choke is getting hot?
I just thought this guy was making a joke right? If not he should meet the guy that tunes the pianos at our studio. He talks about theories that make the internet seem reasonable but no one makes the pianos sound like he can. We love when he comes and tells us all his wild stories wether we believe it or not, it's always a day we talk about for weeks after he leaves.
Great video, Brad. I like the idea of the cathode hookup on the bias probe. Would you know the benefits of using the 30.1F vs 30.1G wiring or vice versa?
Hey there can i suggest to you that you ignore these critics if they know so much why are they watching you ???? really i think you are good at what you do and very good at explaining the works !!!!☮👏🏴☠️
Trying many amps hasn't quenched my dream of experiencing Univox and Teisco. They're nearly impossible to find in France or Europe. I recently had a lot of fun with a Univox PHZ-1 phase shifter (relabelled BST LM-200 in France). If you'd like to give it a shot, my experimentations are on my channel.
I don't know if it's just the compression in the video but in the comparison section I heard only a VERY slight reduction in hum that was accompanied by a VERY slight increase in hiss, didn't seem to be very effective at all and the overall noise level seemed to be the same. What's up with that?
I think you are correct. I believe in this particular amp, the noise had already been reduced about as much as it possibly could be reduced using other means of virtual center taps and lead dress, ground buss, etc. I did a TON of work to get the amp this quiet. Even with the lack of improvement on hum, which was already pretty damn low, I still think a choke is good for the amp. All the power section components will not wear as fast or be as taxed by inrush currents.
Many years ago I sent one of my amps to be worked on at a then well known facility who used to sell mod kits. When I got it back it was working but they removed the original choke and substituted them for some resistors; if I remember correctly. I heard it would do the same thing but makes me wonder if the outfit wasn’t that honest and they just confiscated my amp’s choke for their use/gain. Later on I had to buy another choke and get it installed by another tech.
@@highpath4776 I had a guitar shop charge me extra on my guitar after having pick ups swapped. Because he took It on himself to replace my pots. Why? What's wrong with my pots? They were bad. Can I have em back? No. Why would you want them? I'm out of this place. Started trying to do stuff myself after that.
Say you did build a guitar amp with a choke input filter, where would you wire in a bleeder resistors say the choke does not arc when you turn the amp off? What value and wattage resistor might you use? I actually did build one with a choke input and it’s awesome, but I do have the arc issue.
sorry brad but it seems in flat out mode you're on the threshold of motorboating . it sounds like some tube needs more dc isolation . i put a choke on a marshall class 5 ( single 6bq-5 power tube) with great result now there's no hum but we can only hear noise from the preamp tube.
I usually add a solid state rectifier if I'm trying to up the B+. I'm of the opinion that the "sag" that you get from tube rectifiers is overrated. I believe what people hear when they swap out the tube rectifier for solid state has more to do with the B+ change than actual "sag" at any rate. Eddie Van Halen used a variac to lower the B+ and get that same squishy sound. Chokes are a nice way to get some extra volts as well.
