Consider investing in a looper pedal. This is an excellent experiment and touches on something I’ve thought about as well. Anyway, the looper will provide a consistent signal into to the amp as you change resistors. And by the way, that amp sounds great!
@YeatzeeGuitar
3 ай бұрын
Definitely needed if people like this stuff and want me to do more
@terrycaster4976
3 ай бұрын
You beat me to it
@jjshouseofjams522
3 ай бұрын
I thought you had a helix did you get rid of it. Helix has a great looper.
@YeatzeeGuitar
3 ай бұрын
@@jjshouseofjams522 long gone
@MikeM-Colorado
3 ай бұрын
Well done! I’ve been interested in doing that resistor experiment, but never got around to it. Since the cathode resistor is not in the signal path, I doubted that it would make an audible difference. But it does. To me, both modern resistors sounded hard and brittle compared to the CC. And, that is a nice tweed Princeton! I’ve not seen one that pristine.
@YeatzeeGuitar
3 ай бұрын
Thanks! Yeah it's the cleanest I've ever seen, I've owned it for a bit now too scared to do anything to it because it's so clean!
@theirritatedirishman5440
3 ай бұрын
It’s the same affect on tone as adjusting bias cold or hot. The real cathode tone change comes from the cathode capacitor. Just a small value change has an impact on bottom end and gain. If you go from 25mfd to even 35mfd you’ll head a change. And it’s a “Feel” thing too. There’s tone or sound and feel. Sag Vs Tight.
@rightlurker4674
3 ай бұрын
I think your experimental videos are great.
@YeatzeeGuitar
3 ай бұрын
🙏
@jjshouseofjams522
3 ай бұрын
A huge thanks to Yeatzee Guitar for getting my Princeton ready to rock. 🤘🤘
@YeatzeeGuitar
3 ай бұрын
It's killer!
@NINEWALKING
2 ай бұрын
Part 1 Tube amplifiers are very complex beasts. Especially guitar tube amplifiers have they own quirks that makes them different from home audio tube amplifiers. Hence one has to specialize into them to understand them good. Now let’s talk biassing of the preamp gain stages. It’s a necessary thing to have tube running some small current even when there is no signal present. With the signal you are modulating it’s current by applying voltage on the grid of a tube. So let’s establish grid are voltage controlled elements. So talking biassing only important state for us is no signal and pure DC state. Talking about your typical Fender amplifier we find 12xx7 family of dual triode tubes. Each gain stage uses one of those triodes mostly. Typical voltage coming from the nodal resistor to the plate resistors might be from middle and the high hundreds to middle and high two hundreds volt and even higher in some other amplifiers. I mentioned triodes so we can establish that plate current is for all practical applications the same as the cathode current because we have no screen element. I mentioned voltage because it’s most important thing there at that moment. So in no signal state plate resistor has only one function and that is to drop the nodal voltage to the acceptable plate voltage. Though this plate resistor has even more important function but that happens with the signal only and affects the tone for sure. So we have no signal state and plate voltage and cathode resistor and current is flowing. It’s constant current value and our tube is hot enough. Value will very more until the tube reaches its temperature and it will vary a little bit after it but not by much. So anyone will say resistance value determinate the current here and they would be partially right. Plate resistor is limiting current as well as the cathode resistor right? It does but at that logic you could set the biassing current by the plate resistor only. Plus your most used plate resistor value here is 100K and cathode resistor value is puny 1,5K. So major breaking of the current would be the plate resistor right? Wrong. What limits the actual current true the tube is voltage on the grid of the tube. Cathode bias resistor has certain voltage drop across it. This voltage drop references the cathode voltage at the more positive voltage level than ground of the amplifier. Hence ground is more negative point and that negative voltage drop is what is applying the brake and slowing down the tube. The very same principle is found on the output tubes of the cathode biased amplifiers but plate resistor is substituted by the winding of the output transformer. In the most cases that more negative than cathode ground level voltage finds its way to the grid true the grid leak resistor. Wait so small voltage of few volts to maybe 10V or bit more should find its way true high value grid leak resistor? That sound stupid right? But there is no grid current hence there is no voltage drop across the grid leak resistor and tat negative voltage passes it with no apparent voltage drop. Like I have said before. Complex things this amplifiers. Anyhow does changing type of the cathode bias resistor change the sound? Well it’s actual resistance value affects it a little bit but people often give it psychosomatic value. How much bias change is there in changing from 1650 Ohm (maximum tolerance) to 1700 Ohm value? Sure another one might be minus ten percent and there would be it more difference. But now remember everything saying that once tube is hot bias current value is almost stable but it still fluctuates a bit? Well your mains fluctuate as well. This translates in every voltage in the amplifier as well. And all this people advocating absolute precision of biasing should just answer what happens when you plug in your amp in the old venue and all the lights go on. Industrial fridges compressors go on and off. In house big PA amplifiers go on. Etc,etc. measure your mains. It ain’t your laboratory 120.00 V AC anymore and it will fluctuate. You lucky if you get 110V. All your perfect biassing is different now. Was it worth sweating about it? Did that voltage change has ruined your tone? Not that much right? Plus cathode bias principle has some tolerance built in. More plate voltage means more current flows. More current flows true the cathode resistor more voltage drop is across the cathode resistor. More. Voltage across the cathode resistor more negative ground gets compared to the cathode voltage. More negative ground is more grid will brake the tube bias current. So for the most cathode bias is autocorrecting bias. Inside of its range with the given tube it tries to automatically maintain the same bias current level. But it is not magical and at some point it reaches its limitations. For example voltage gets lower. Hence ground reference is less negative and tube starts drawing more current right? Yes. But more like draw further drops the voltage and at some point power supply might not be able to catch up. So voltage changes do affect cathode biasing. Look at the very old amplifiers with the cathode biased output tubes. Those were designed with 110V in mind. With current mains voltages even getting over 120 V lots of those amplifiers need cathode resistor changed to higher value to prevent those tubes from red plating. Look at the most original two EL84 amplifiers. Their cathode resistors were 100 to 130 Ohm most often. Now you need 150 minimum.
@YeatzeeGuitar
2 ай бұрын
Lot to digest here, but I appreciate you typing it out! Going to sit with this
@MrDiscomfortzone
3 ай бұрын
You can replace resistors, capacitors, and even tubes. As long as they are the same value and tube type as the design specifies, there will be little or no perceptible tone variations. Contrary to what guitarists may believe or expect, the circuitry as a whole, plus the speaker create the amps tone, not individual components.
@YeatzeeGuitar
3 ай бұрын
If the end result is the sum of it's parts, surely the parts have to have an individual effect at some level ya? I like testing that stuff got myself. Tubes are on the list, easy to test stuff now with the new camera / audio rig. Just need a looper I guess
@MrDiscomfortzone
3 ай бұрын
I should have clarified my thoughts a bit. Not all components in an amps circuitry affect tone. In fact, there are fewer components that affect tone than those that do not. Each stage within an amps signal path has a defined frequency response, as the engineer wanted. Frequency response is set by combinations of resistors and capacitors configured as low- and high-pass filters. Tone is mostly the combined effects of these RC filters. So no, the whole is not the sum of its parts; it's the sum of a few of the parts. But stay curious and keep asking "what if?"
@NINEWALKING
2 ай бұрын
Part 2 So biassing preamp triodes changes sound but not that much when the value changes by small margins. Things change a lot when you use 2,7K for example. That also changes calculation for the bypass cap as well. Higher the value of the cathode resistor smaller capacitance can do same effect. Now what does that bypass cap do and why people say one liners over them that only partially explain anything but keep people in dark about them? The do increase the gain of the given gain stage. How do they work and why? We’ll tubes aren’t perfect and their own stuff that make them work aren’t only doing nice stuff we use in amplifiers. There are unwanted effects happening that we try to fix. So bypass cap is not important for the biassing itself. Cathode resistor on its own does that. What bypass capacitor does is negates the inherent NFB loop that exists in the tube itself. Do not mix this with output topology of the amplifier this happens in every tube on its own. Though it functions little bit like NFB loop in that that it grounds unwanted NFB to the ground. Smaller value like 0.68 uF will affect only high frequencies and ground those unwanted frequencies to the ground. When they are grounded they do not disturb the original signal anymore and we hear it as the boost of the treble frequency range. Higher the capacity lower the frequencies get grounded and more wider the boost we hear. There are nice online bypass calculators where you can enter all the values and by changing capacitance or resistance you get nice graph of where do you boost and you get amount of the gain at those frequencies in dB. So no more mystery what bypass cap does. Back to the plate resistors. I have stated what it does with no signal. But it does ouch so much more and it does affects tone a lot. First let’s establish one thing that is sort of tubes thing. You can take “the output” from cathode or plate. Also you can inject the signal at different places but that part is not import for this part of the circuit. What matters in this part of the circuit is how the plate resistor is used to generate amplified signal we use to drive the grid of the next gain stage, why is it out of the phase with the original signal and why does it influence tone and gain so much. In this type of typical Fender gain stage we use the plate as “the output” of the gain stage. What we need is amplified music signal as higher voltage to drive the next gain stage. We feed that signal in the next tubes grid. As said above that grid has negative biassing voltage so we can’t have high positive plate voltage on the grid so we use the coupling capacitor to block off the plate DC voltage and let only signal component to the grid. Music signal is basically as AC and AC pass true the capacitor. So now signal is there. Let’s say perfect pitch A string and it’s 110 Hz. This signal voltage is small like 0.1 Volt. But it will affect the grid voltage. In positive part of the sinusoids of the signal it will be lowering the grid bias voltage and that will increase current flow true the tube between the pate and the cathode that is. Once we reach the time when signal silencers the negative amplitude it will bring negative voltage to the grid lowering the current true the tube. This in hand modulates current flow true the tube so it changes with the same 110 Hz as the input signal and has the same sinusoidal form as the original signal. Wait we can’t use current to feed the next grid right? Yes we can not. Here enters the plate resistor. That 110 Hz variable sinusoidal form current makes variable voltage drop over the pate resistor and that’s the “signal” we use to drive next tube grid. We know that higher the nodal voltage is more gain we can get out of the gain stage. But how come if we put 120K resistor we get more gain from the stage while that lowers the plate voltage? Simple more voltage drop is created with the same current true the bigger value plate resistor. More voltage drop more signal more gain. Why we say that we flip the signal phase using the plate as the output? Well when signal is in the positive amplitude our current grows and our voltage drop over the plate resistor grows. But that means that actual voltage on the plate is getting lower. And in the negative phase voltage drop is smaller hence plate voltage is more positive. So our signal is inverted and 180 degrees out of the phase. Now we know how plate resistor works and how important is it’s value. But why does the type influences the tone? Well every resistor type has his structure and that influences how it works. Cabin composition resistors are “least” refined. They are more noisy than carbon film resistors. But way they work makes them sound most vintage sounding. They are plastic tubes filed up with carbon substance with connections on the ends. While carbon film have resistive carbon film over the isolator. Carbon comp resistors are less stable and more sensitive. They last lest time and can’t take the heat. But they sound most true to the vintage amplifier. Just do not use them as nodal resistors. Tone difference there is not really there and metal oxide resistors last way longer and can take more heat. That carbon material inside of the carbon comp resistor is prone to cracking. Micro cracks will occur first and in the case of the plate resistors this will sound like arcing and high voltage discharge. When they get old. And when they were exposed in the heat as they do in the tube amplifier their outside tube will crack as well. They literally brake apart. Funny thing is that sometimes you do not see the crack until you desolder one leg and half of the resistor falls off. Still they sound the best and they have their place for sure. I do not think there is more to say about this part of the circuit. Plate resistor type maters to tone. Cathode resistor not that much.
@YeatzeeGuitar
2 ай бұрын
Appreciate you taking the time to write all this out, great to have as a reference point thank you for doing that!
@NINEWALKING
2 ай бұрын
@YeatzeeGuitar you are welcome. The idea was to give complete information about what happens in just one smallest and most basic element of the tube amplifier, the basic triode gain stage. That information should just show how complex things are and how even by the simple parts people tend to misunderstand and look at only one side of the things while even simple part as the plate resistor has more functions. Things just get wilder after that, like usage of, for example, cathode follower and then how and what happens in all possible versions of the phase inverters. Even simpler things like working of the output transformer in push pull amplifier gets misunderstood way too often. People, especially techs that are coming from solid state home and PA amplifiers, have need/urge to draw the signal path as in the current serial flow. Wel in tube amplifiers, things happen on stages and actually in parallel groups where each part has its own current circle, but the next stage doesn't conduct that current but uses the voltage drop created by it. Even people draw how signal comes into the output transformer and then "goes" true the transformer and into the speaker. The output transformer is very much the isolator and prevents the high DC voltage from reaching the speaker. It is not a problem when someone uses their understanding of things to do what they do. My problem is when people try to spread their misunderstood things as real knowledge and truth without knowing it deeply. There is a huge responsibility that people do not even see. It is, most of the time, not malicious action, but just honest misunderstanding. Things like one-liners just make things worse. Sure, they might solve the issue at hand, but do not explain anything and promote dangerous half knowledge representing it as expert information. People are not even aware of how much they actually do not know. Plus, the existence of trolls makes it almost impossible to get the proper information over. The ego of the people and the need to handle trolls and haters closes them from learning stuff. Closes them from recognizing people who do know stuff in depth. Me saying I have designed many guitar amplifier schematics that are unique and working and lived by people just sounds like fake boasting and internet keyboard warrior. Plus, we live in a politically correct world where the way of saying things is more important than what is the message or is it the truth. People can't take even a hint of criticism, even one that is of a constructive kind. I often feel like I am stuck in the movie Idiocracy. I do not need internet recognition of what I know. I have it in real life. I have had my work tried by a few important people in the industry and got their appraisal. That is more than enough to satisfy my ego forever.
@lightaces
3 ай бұрын
The biggest difference seemed to be the value, not surprisingly. But even there, I only really heard a difference on one clip, and it was probably just your pick attack.
@cgavin1
3 ай бұрын
I may be wrong but I'm fairly sure cathode resistors only have a few volts across them and are decoupled by the bypass capacitor .. so aren't a good place to use carbon comps if that lovely distortion is the goal. Plate resistors and grid resistors though .. But even then in the Fender style LTP phase inverter, where you'd think there'd be loads of voltage swing, its enclosed in a negative feedback loop .. Grid resistors in all but output stages also do no good, because the signal level is typically too low. There's not really too many places to place carbon comps in an AB*** style circuit where they won't just be wasted and even introduce unnecessary noise.
@MichaelSmith-rn1qw
3 ай бұрын
I didn't really notice any difference when you jumpered in the various resistors. The original out of tolerance resistor sounded just fine to me.
@fiddlix
3 ай бұрын
I think the Vishay metal film sounded best. Fuller and warmer imho.
@RonnieRedd
3 ай бұрын
Like the new setup 😊
@YeatzeeGuitar
3 ай бұрын
Thanks!
@ruffryder13
3 ай бұрын
I think ive heard people say that resistor makes tubes tin hotter or cooler? Could be interesting to see what difference the resistor makes in that respect too.
@YeatzeeGuitar
3 ай бұрын
Yeah cathode resistor is changing the bias of tube
@IAmChrisR
3 ай бұрын
Yeatzee, I apologize in advance for this, trust me, I'm no math whiz, but 20% of 1,500 (1.5k) is 300 right? Wouldn't that mean up to 1.8k would be within a 20% tolerance and as low as 1.2k. By my math, 1.7k would be just a hair over 13% from 1.5k. But I'm interested anyway!
@YeatzeeGuitar
3 ай бұрын
Haha look again above the amp at 0:23 😉 I misspoke, they're 10% tolerance resistors not 20%
@matthewf1979
3 ай бұрын
Did you ever figure out what was going on with your Princeton?
@YeatzeeGuitar
3 ай бұрын
It's completely fine! Dirty speaker contact or something 🤷♂️
@rightlurker4674
3 ай бұрын
It looks like you are connection the resistors in parallel - the existing resistor is still in the circuit. Does that make a difference? Would you have to compute the equivalent resistance of the two parallel resistors?
@YeatzeeGuitar
3 ай бұрын
The other resistor is only connected at the ground side, so it's not in circuit. Hard to tell from the camera angle but yeah
@rightlurker4674
3 ай бұрын
@@YeatzeeGuitar Ah. I get it. Thanks!
@sgt.grinch3299
3 ай бұрын
My poor hearing doesn’t allow me to hear a big difference.
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