now we are starting to get in to the really cool stuff!!! thank you so much for not slacking on the math and continuing to show everything by equations and then visual representations. i believe this is where many electronics tutorials fall apart. now, what are the chances that you'd like to do one of these for an RF amplifier as opposed to an audio amplifier? getting into the equations behind the voodoo black magic that is RF electronics would be AMAZING!
What a fantastic video, Tony. Being new to understanding this stuff, I could easily follow along with the logic presented and understand the concept entirely. Well done!
A very useful episode in this series, as I’ve been trying to figure out how to test a suspect audio output transformer for one of my repair projects. Thank you, Tony.
I really like this series of vids! Nice that you do the math and back it up with visual measurements. Hope you do a series like this on AM/FM tuners along with alignment using basic equipment. The Sansui manuals always refer to some off the wall equipment. So today I learned size does matter, concerning transformers🙂.
Just found your channel and I'm subscribing because I'm learning a lot from you! I'm new to tubes and I'm about to build a hybrid tube amp consisting of 2 lm1875's and 2 jy6 (I think) tubes and I didn't realize the power supply was a 18v plus or minus AC power requirements which I have never heard of till now soooo I'm trying to figure all of this stuff out lol
Great taste in calculators. I have a DATS V3. It's much more robust and more versatile than previous versions. Like TubeDude mentioned, Parts Express has them and you can see all the specs there.
As always, nice video. Slow and very clearly explained like we all are complete id*&%$#s and never ever heard about output transformers. Thank you Tony for everything you're doing for the community. Those who need FFWD expert videos are free to go visiting other channels. I learn from your every single video some small bit and piece. Some here, some there. If only all teachers at school or at the Uni were like that. Slow, clear and with real world examples. Noone has been born into this world an expert. Thank you for taking your time and doing these.
With your oscilloscope that has a bode plot mode you can do a similar measurement(perhaps with less accuracy) by measuring the applied voltage to the transformer and the voltage over a shunt resistor(as output input), and if you set your current scaling according to your shunt value directly get the correct values on screen. This is useful for those of us that don't have an specific instrument to perform those measurements. You need to have a scope that allows you to use the difference between channels as a bode plot "channel" OR a differential probe(Micsig has some cheap ones) OR you can get creative and take advantage of the isolation of the transformer and the turns ratio if you dont have any of the previous options. Also you could use a current transformer(pretty cheap but only for AC) or a current probe, but until recently those were always really expensive.
After 3m13sec, there was some missing activation-sound !!.. Thanks for videos Tony :-) ..Always looking forward to them when you have time to make&share (..specially when schematics&talks is involved)
Xraytonyb, I learned something by watching your video, now I see another way to find impedance of an AF transformer. The way I was doing it was to use an AF Generator at 400 - 1000 Hz to feed through a series potentiometer into the primary, with the secondary loaded with a resistor of the rated secondary impedance. Read the generator voltage and adjust the potentiometer to read half the voltage at the primary. Then measure the resistance of the potentiometer and you have the impedance of the primary.
A pair of 6AQ5s or 6P1 will sound fine if it is 5K. I have done it before single ended as well as PP. Typically as you know 6AQ5s, 6V6s, EL84s are optimum between 6 and 8k depending on plate voltage. But I have a couple of SE output transformers that came from a Sony R2R which had 6AQ5 output tubes and the OT was 5K to 8ohms, So Sony designed this tape recorder with those tubes and an OT with that impedance. I used one with an amp and it sounds good with 6L6s and 6V6s. Also, I have a Kodak Projector amp which came with PP 6L6gb's and the amp also sounds great with 6V6s. As you know a 6AQ5 is a 7 pin 6V6. Tubes are very forgiving.
Howdy. May I be so bold trying to clarify things ? Firstly. The magnetic induction depends almost entirely on voltage, frequency and number of turns. Current has little effect on magnetization other than the 90 degrees shifted inductive magnetization. Second. The core does not convey or transport anything. The core only serves to keep the flux concentrated for tight induction. Third. What heats up the transformer is almost entirely ohmic losses in the windings. The oscillating flux generates some heat. Yes. But that is almost negligible. Fourth. The core size must be chosen large enough to accomodate wire gauges thick enough not to generate too much heat and to be able to dissipate the heat without causing the bobbin and wire varnish to melt and be a fire hazard. The core and winding outer surfaces do the heat dissipation into air. Fifth. There is a rule of thumb that says that the core cross section in cm2 should be about the square root of the power in watts. But this rule is empirical only. It is not derived from laws of physics. Sixth. How do we then understand the illusion of power conveying? Induction generates voltage over the secondary. This voltage starts driving current through the speaker. This current also fights the induction. The primary observes the induction going down and compensates by drawing more source current until the induction is restored. Regards.
A very good demonstration to determine the impedance of an audio output transformer . What software do you use to check linearity of the transformer's impedance. Thank you.
One little trick that a high school classmate pulled on us when we were in grammar school was to bring an output transformer and a D cell battery to class. He would put the battery on the speaker side of the transformer and have one of us hold the input leads. The second he touched that battery we got a big jolt! It wasn't until years later that I finally understood how a dc voltage could shock you using an ac device. Had he touched the wires to the transformer BEFORE we touched it, nothing would have happened but by doing it the way he did he momentarily created a current flow in the coils and we got zapped! Since he was on the "low" side it meant that he was amplifying the voltage that we got. Modern transformers are too small and don't have the potential that those old tube type transformers did so it wouldn't work otherwise. Some have argued with me about it until I did the same thing and it made believers out of them. The current flow is of very short duration so if you hold on to the leads after the initial jolt, nothing else will happen.
Richard, What gave you the jolt was the high voltage pulse created by the turns ratio and the magnet field rabbly changing as the battery was hooked up and disconnected. The strongest jolt happened when the battery was disconnected causing the sudden collapsing of the magnetic field creating a high voltage impulse. In other words it was really acting as a spark plug ignition coil.
You didn't try to dazzle us by drawing load lines on the tube data sheets so I don't think there was too much maths in this tutorial ;). An interesting tid bit is that the primary transformer impedance connected to the pentode is not selected for maximum power transfer but for minimum distortion (pentodes are awfully non-linear).
I'm get readings of between 4 and 9 megaohms when I connect between the primary and secondary windings on a suspect output transformer. So I assume thats the problem with my amp? Massive amounts of humming and no sound from speaker?
I'm not sure what you are referring to, but this amp is push-pull. It uses 6P1P outputs, which are similar top the 6AQ5 or 6V6, but with different pinout. The 6BQ5 has higher gain and a few other differences, so some of the component values would be different, but it would still be the same circuit. If you watch and learn from this series, you should be able to understand how it works. Thanks for the comment!
@@xraytonyb Yes, I realize it's push pull, stating that I wish it was El84/6BQ5 and it seems so close to having the component values to be of such. I'm assuming they knew about the EL84, but wanted to design it using the less desirable, cheaper tubes to sell a complete package at an affordable price. I should've left the "push pull" part of my comment out, which was irrelevant to my point. I've been watching this series and I'm learning a LOT. Many terms and concepts had me lost until I started watching your channel a year ago. I love this hobby, because it's challenging and seems to be endless in depth. Thank you Tony for sharing!
Howdy. Nice. About getting laminations for OPT:s. Check eBay for Line Transformer or Audio Line Transformer. One will get several hits. I settled for Parts Express. They have 100 W 70 V items for about 30 dollars a piece. I ordered two and rewound them. The laminations are good audio grade steels. Regards.
I've seen this impedance ratio video over and over on different channels. Why not just put an LCR meter on the primary, measure the inductance and use the formula Inductive Reactance (impedance) = 2 * Pie (3.14) * F * L? I believe the standard frequency (F) used is 1 Khz. Would that not save a little effort? Thanks!
You can buy step-up / step-down transformers for this purpose. The only thing you need to watch is the frequency (50 vs 60 Hz). Most receivers don't care, as they rectify the power to DC, but some things like turntables and tape decks can be affected.
Hi Tony, first of all..great videos! Very well explained stuff! My question: many times you hear people say that a tube amplifier produces a more warm sound than a solid state...is that because of the behaviour of the output transformers and if so, what causes that difference?
Yes. Measure one side, then measure the other side. For example, turn the variac up until you see 1V on the secondary, then take the meter off and measure the voltage on the primary.
Yes, but this amp uses cathode bias, so the cathode resistor has some of the voltage dropped across it. As a result, they are only being slightly naughty with the anode voltage ;)
Hi Tony. Something doesn’t make sense here: Why would a higher-power amp (which, presumably, would need a higher B+ voltage) need a lower impedance of the primary? That seems like it would be equivalent to saying that “if I can safely put a 10k resistor across the 120 volt mains, then I should be able to put a 5k resistor across 240 volt mains).” But, of course, you’ll just end up with a burnt 5k resistor if you do that. 🤣😂
Tony is right. Most of the guitar amps that I work on that have push-pull 6L6 tubes running at 400-500V on the plates, are connected to output transformers with 2000 ohm primaries. Your example doesn't take into consideration the wattage rating of the resistor a 5k resistor across a 240V mains will be just fine if it is rated above 12W conversely, a 10k 1W resistor across a 120V line wouldn't last too long. In transformers, the larger diameter the winding, the more current they can handle, this increase in diameter also makes their resistance less.
you are wrong. it is a 5k transformer meant for Class A Amplifier. and we know Class A modifies impedance downward. more precisely Push-Pull Class A. you do not measure that "5k" or "8k" at the output, you measure it at a single section of the primary, when it delivers nominal power signal, not music, but tone, full power. how you do that?
