Outstanding teaching series. People generally spend a butt load of money and get way less learning. Thank you so very much for your efforts!!!

Im learning tube amps and im happy to come accross your channel!!!❤️❤️❤️

I'm with the rest of the folks enjoying this......making valve amplifier construction easy to understand and more importantly how they work!! Top stuff thanks mark

I just discovered your KZfaq lessons and I’m hooked. I’m a novice hobbyist. Your explanations and use of examples has benefited me greatly in this short time. Thank you so very much for sharing your knowledge!

Thank you, I used to think there was no need to try understanding tube amplifiers, as they were of the past Then I saw the topic for pt.1 and thought let me just watch a little. I am happy now that I did, somehow I now feel like I have learned more from the series than I grasped from solid state, videos and books on electronics, I truly appreciate it and will continue coming to classes here.

Thank you! The information on how the second half inverts the signal has cleared up some confusion from watching other videos. Many videos (that I have seen) don't stress this point. I know it's just me but that has cleared up a lot of confusion. I also found it helpful to know how different frequencies (high versus low) effect the power section and basically a key difference in sound between solid state and tube amps (if I'm interpreting that correctly)... anyhow.. Thanks!

Positive feedback: I started building tube amps because of your video's. Thanks a lot.

Great series. As an electrical engineering student with some experience with transistor amplifiers I can see a lot of similarities between tubes and transistors, mainly the plate signal inversion just like in a common emitter circuit. You can explain the theory with simply words but never skip the true principle of working. I can recognize that. Great job man. PS: I am a guitar player too and pedal maker, I was looking for some basic tutorials on tubes. Now I can read a marshall schematic and understand it completely. Thanks again

I am building a direct drive tube amplifier, you video's are excellent education resources

Awesome teacher! Thank you so much! Sharing the knowledge 👍👍Helping make the world go around.

We all love Uncle Doug and Bradthe Guitologist, you to did a fine job of explaining how tube amps work. Interstate transformer instead tube phase inverters I find interesting. Maybe a bit more on them. Thankz

Just found out today you existed. I always wanted to make my own tube preamp, then work on the power amp section later. I wish I came across this video earlier.

I just want to say ty so much I want to build my own guitar amp and am trying adsorb the wealth of info you have provided again very excited to continue watching this series and go hands on putting it into practice

That was absolutely superb. I understood everything! I think between your videos and Uncle Doug's videos, I've pretty much got the theory down. What I need to make progress on now is component value selection. I need to understand why a certain resistor or capacitor value is chosen. What is the theory at play. When (for example) a 1M resistor to ground is used as the volume control, *why* is it 1M, and not, say, 500K? What would be REALLY cool is, at some point, if you ever get the chance, build a push-pull amp on the bench with accompanying schematic and try different component values for bias etc, and see what the effects are on an oscilloscope. For example, I would assume if I wanted to build an exceptionally clean sounding amplifier, maybe for guitar, or maybe as a general purpose audio amplifier, I would keep the valves "cool" with respect to their bias. However, if I wanted (for example) a guitar amp with a bit of growl (think Marshall or Vox AC30) then I might select a "hotter" bias? If I wanted a "dirt"/distortion control, maybe I'd include a potentiometer that did little more than tune the bias within a fairly narrow band? Thank you so very much for taking the time to make these videos. *This* series in particular. There is a legion of valve amp fans around the world hanging on your every word, and I'm sure I speak for everyone when I say that we're very grateful indeed for the time you invest into making these videos in order to help folk like us de-mystify valve amps. With best wishes from Aberdeen, Scotland. Mark.

So cool. Everything you post is gold.

Mark thanks for another great video! I have really learned some things I did not understand about schematics and tube amps. I would love to see more in this series and also to understand biasing as well.

Excellent presentation. Extremely clear.

great content, greetings from Slovakia, sir.

awesome video series, i watched all 3 videos and i really enjoyed them all. helps me to understand more about vintage tube amp schematics. thanks so much and thumbs up!

Great series of videos, Thank you, and keep the good work comming.

The Dynaco and Fender were cathodyne, the one with the 12AX7 and EL84, is called a paraphase inverter.

Keep making these videos. Your doing GREAT.

Thank You so much !!!!! Please keep them coming, Learning a lot from you

You are the best teacher!

Great lessons. For some reason I am remembering the long tailed pair inverter having mismatched resistors in it… Maybe I’m thinking of blackface circuits? Thanks again for this presentation!

Way back in 1970, an instructor told me that if I ever encountered a push pull amp that was putting out about a third of the power, he pointed to one of the resistors that he said would cause that if it opened. Next time I was home, my brother's amp was putting out about a third. I looked at the schematic, went to a local TV shop and bought one resistor, went home and repaired the amp. Now, I'm trying to recall which of those resistors it was. Using that Fender amp is there a way to determine which resistor would cause that. My old training had become too foggy.

Excellent lesson, sir. Thank-you.

Thank You, please keep them coming. I'm new to the hobby and these are Great !

This series is really amazing. Thanks so much!!

Great series! Thank you. I'm learning a lot.

Outstanding series!

Wow, thank you. I have learned many interesting notions.

Best class anywhere......

Fantastic explanation. Thanks for doing this.

Great stuff! Just one comment: the ECC83/EL84 example beginning at 12:55 is not a Long Tail Pair phase inverter but a Floating Paraphase PI...

It looks to me that the pentode in that ST-70 (7199) is strapped to a triode. I have no idea how the gain would look but it should be reduced by quite a bit. Great series, by the way. Thank you.

Another excellent video Mark!

For cathode biased power tubes, the best way to go is to use a separate resistor for each tube. This eliminates hum before it goes to the output transformer. Because tubes are never perfectly the same when you buy them. They can be matched, but not as well at it should be.

The first illustration with transistors needs a negative voltage supply with a speaker attached to a ground wire or to a virtual ground made with big capacitors in case an uni polar power source is used. A phase is important even in case of a single ended amplifier. Because as a reaction on a sharp impulse a speaker membrane must move in a desired direction. Otherwise, no good bass is available. A long tail pair inverter is not an ideal because a noise from a power source appears on two legs differently. It negates only on the second tube that is connected with a common gate. Also, two legs have a different Miller's effect value.

In the EL84 push pull R4 should be compensating for the double amplification that the plate will be outputting due to A triode sending the signal back into B triode so I think R2 and R4 should be not equal, I was educated by uncle Doug and his wild animals, this is also shown in fender schematics as such which would imply there maybe some amplification via the K.

Note that contrary to what you said initial dual triode stage IS OBVIOUSLY NOT a long tail pair and no audio signal shows on joined cathodes because of large capacitor C3 shorting them to the ground. Instead the two are two normal amplification stages with the second (right) one receiving its input through C4.

Another great video - thanks

Maybe a better way to say it is that every Triode is both a ‘PNP’ and ‘NPN’ But when using it as both you don’t have amplification, but it’s good that the most common tube 12ax7 is a dual triode, so perhaps that is a compensation.

This diagram shows each transistor handling only half of the load. In push pull, both amp modules act on the ENTIRE signal. One is pushing while the other one pulls and vice versa. The diagram looks more like a regulator with one transistor wired backward. XD

10:36 Figure 2 and 3, I like differential phase inverter driver type that gives symmetry waveform and impedance.

Priceless, many many thanks.

Better analogy is your pedal down and controlling speed with your brake. That shows the waste. (I guess)

Circuit example #6 looks like a paraphrase inverter circuit.

For the transistor push-pull circit, shouldn’t there be a capacitor connected in series with speaker? Without it, the lower half cycle won’t work.

thanks man that is helpful but I still have the problem with a peacemaker 60

So theres no gain where the signal comes off the cathode of the the 2nd half of tube 1. But why does that also apply to the signal coming off the anode? I'm trying to learn. 👍

More, please.

Thankyou ,this is great help.

The 15.6 Ohm resistor in the ST70 is not really a cathode resistor; it's just a current-sensing resistor. The ST70 is a fixed-bias amp with a negative bias supply, so you're kind of misleading people by discussing that as a cathode resistor. Dynaco chose the 15.6 Ohm value so the bias reading would be 1.56V, the same as a fresh battery since it was made in the old days when analog voltmeters were harder to read accurately. You could compare the ST70 to an EICO HF-35, which is a cathode-biased power amp.

Awesome Content!

18:17 - when the signal is fed into the grid of the el-34's doesn't that invert the signal again? so the top el-34 amplify's the bottom half (not top) and bottom el-34 amplify's the top half (not bottom). I may be incorrect, just asking... love the vids, thanks.

Thanks for the video. In circuit 6 don't we also feed second grid of that ecc83 from first plate of the same tube which results in inverted signal on the second plate?

I`m an older man from Norway and l found your video very explainable and good in all regards. I have a main transformer 175-0-175 Volt incl 6.3 and 5 Volt . Suppose this woul be fin for 2xEL84.What is the minimum high voltage on the main transformer if l`l use EL34 or 6V6 ?

Very informative series so far. One thing I've had issues with from schematics with no parts list are what type of capacitors to use where. I know that different types can affect the sound if they are in the signal path, but where would you use a ceramic, mylar or whatever in the other parts of a circuit. Electrolytics are obvious but the others can be confusing.

This is one of my desired video. I´m reading the book "solidstate_guitar_amplifiers_teemu_kyttala_v1.0" (which I recomend for those who want to go deeper in amplifier design, google for it) and I didn´t understand long tail meaning and how it could separate both cycles for individual amplification. In solid state amplifiers I understand because it works with a pair of PNP_NPN transistor, like you explain in the beginning of the video.I´m going to print Fender and st-70 schematics and write down all information. I am learning a lot with your videos, thanks for your time.I am pretty sure that those Bias videos would be superb

Well done and thx so much, but one question : in the pnp/npn picture, the lower half can‘t work , I think the speaker should be connected to 1/2 of the power rail to make the lower transistor work. Am I wrong ?

Hi Mark. Great video on Push Pull. One question: Where and how would you add a tone control pot in the EL84 Push-Pull amp?

So it looks like most of these examples were for integrated amplifiers, so the schematic for a dedicated preamplifier with "balanced" XLR outputs would end with the dotted line box (about 19:00)? And would then go through amplification and summation in a power amp or monoblock amp later?

Hello, and thank you for this enlightening explanation! I'm just a neophyte but I think there is a slight problem in the diagram (see 18:15). The little blue sinusoid representing the signal should only show half a sinusoid (the top half) at the output of each EL-37, am I right?

Thank you so much! I can't wait for the Bias Vids. So in the Fender amp I think I get the inputs. 1 Master gain control and 2 Channel gain controls yes? All they are doing is shunting to ground in a variable way but why is the Master's element tied to one channel and not both? Also, the elements of the Channel pots are tied to the wiper of the Master yes? Also also, is it as simple as adding a variable pot to each cathode of the output tubes in a fixed bias amp to convert it to variable bias using unmatched tubes?

Question.. I am working on a Philco 90 tube radio with push pull 45 tubes and I am looking for information on the first audio transformer that is feeding the grids of the 45 tubes. Could you help me or direct me to a proper video for this? Mine is completely open and after opening the top it is fried so I cant repair it. On top of that, I just want to understand how it works. It will help me in my search for the right replacement. Thanks in advance.

Hello Mark, I recently completed building a Dynakit ST-70, and it is fantastic, but I have an existing condition of AM radio interference. As a quick fix I installed RF ferrite chokes on the power cord, and the line input. This works, but I would like to install RF chokes inside the amp as a permanent fix. The offending AM radio station is 1500 kHz. The transmitting antennas are only a few blocks from my house, and this interference affects, other audio equipment too. Can you feature on your channel RF choke solutions for tube radios, and guitar amps? What components are best and how to install them into existing circuits? Richard Trask - San Jose CA

Can I ask you a dumb question, on the AB transistor schematic if we trace the ‘electrons’ in both the ‘push’ and ‘pull’ stage one seems more conventional than the other, so my question is for the seemingly less conventional stage the ‘pull’ In the pull stage, obviously the input signal has the NPN ‘off’ and the PNP ‘on’ so do the ‘electrons’ flow from the ‘negative’ terminal up through the PNP and then through the inductor or speaker inductor...back to themselves? Or do the ‘electrons’ flow from the ‘negative’ up through the inductor then through the PNP and back to themselves?..... This mode seems to be the most unconventional.

Great videos, I've been watching your electronic videos and others for a few years now. I enjoy the videos more than reading books lol. I'm going to school for electrical engineering and am hope to work in audio in the future. I've built a few amps and recently built a single ended el84 stereo based on the Magnavox 8601. I went off of the schematic that removed the tone section for a flatter frequency response but find it lacking a little in the mids and bass. I tried a cathode bypass cap on the 6eu7 cathode and got more gain but tone was worse. I'm confused on what they did on the original Magnavox circuit as far as what type of filter they have setup around the 6eu7, not sure if it is a low pass, high pass or band pass. Would be awesome if you could give me an idea of how to tweek that circuit or even make a simple tone control based around that circuit would be appreciated. Ps very nice tube pickups at that ham fest, wish I could find those kind of deals.

Hi Mark, I was just looking at the schematic for the VTA ST-70 and noticed they use the grid for the bias or at least it is marked bias. The Cathodes are using a fixed 10 ohm resistor 1 for each tied to ground. Just wondering why they do it that way?

30:30 - What is the purpose of the 'extra' resistors in the cathodyne circuit (1500, 1 MEG)?

Great lesson Mark. The part about the Cathodyne PI that I dont understand is the voltage differences from both the plate and cathode. The Fender AA964 Princeton Reverb is a good example. ~230VDC from the PI plate and only~65 VDC from the PI cathode yet it works out fine in the end. How can this be? Thanks very much!

Question about the ST70: why does the plate from the pentode half of the 7199 connect directly to the grid of the triode half with no coupling capacitor? You'll have...whatever the B+ is on that plate. Is that right? If so, why? I thought control grids usually had minimal DC?

If you have a 12ax7 dual type tube, if you have a problem with a lower quality of amplification on one side, what stops the other side from picking of the signal from the weaker? In other words, what keeps the signal staying on it's own side?

I have a Gibson amp that uses a transformer pi, would i gain anything by switching to a split load pi?

What about High Voltage feedback from the output tubes to the input tubes not covered anything about feedback

Hi Mark, I noticed many types of hi-fi amps use the 7199 tube, and they aren't cheap. Is there a reason a 6EA8 tube couldn't be used for the same application? The triode section has even more gain than the 7199. Maybe reasons beyond my understanding. I know the sections are swapped and the socket would need to be rewired.. But is there another reason it cannot be used or undesirable? Thanks, Tom

AB does not really seem worth it today. Increased weight, complexity, risk, bigger power supply, not to mention potential mistakes in matched tubes.