[Ericus Rex]

I'm still waiting for Cheap Jack to show us how his wonderful phono stage is done.  And with only one tube!

[cheap-Jack]

Hi.

I'm still waiting for Cheap Jack to show us how his wonderful phono stage is done.  And with only one tube!

It is easy to tell it to someone who knows tube design/build AND also gets music audition experience. But do YOU?

c-J

[Ericus Rex]

Hi.
It is easy to tell it to someone who knows tube design/build AND also gets music audition experience. But do YOU?

c-J

I'm hoping you'll teach me, and Roger, a thing or two about tube design.

[guest78998]

Hi.
It is easy to tell it to someone who knows tube design/build AND also gets music audition experience. But do YOU?

c-J

All I see here is you avoiding the questions that are going to make you look stupid. Answer them and fail at it so we can all laugh at your stupidity. It's going to happen either way, so might as well get it over with now.

[Ericus Rex]

Getting back to the video...


Me being a tube-design noob, I've always been quite confused about cathode biasing.  Specifically, how the cathode resistor achieves a positive voltage on the cathode.  I do understand the concept of the voltage drop (voltage being 'consumed' by the resistor and dissipated as heat...right?).  But how does this voltage drop then put a positive voltage (of 2v in your example) onto the cathode?  If some of the voltage in the cathode circuit is being consumed by the resistor doesn't that just lower the voltage supplied to the cathode?  (Did I just answer my own question?)  Roger, is there any way you could describe this process to help out a helpless noob like myself?  Thanks!

[Roger A. Modjeski]

I'm hoping you'll teach me, and Roger, a thing or two about tube design.

I assure Jack that there are many here who can appreciate tube design and understand it. While we are waiting for him to share his design I would like to point out some of the problems with a single stage RIAA preamp design. We could do this simple analysis in dB but it's easier to understand in simple voltage gain.

1. The highest gain triode I know of is the 12AX7 which has a mu (voltage gain with an infinite load impedance) of 100 but in a practical circuit it is hard to get more than a gain of about 50 when driving a 100 K load. Since a RIAA stage has a loss of 10x at 1 KHz that leaves a gain of 5x. With a 5 mV cartridge that makes 25 mV available to the power amp which has a gain of 30 (typically) making the speaker receive a mere .75 V or 0.07 watts.  This would not be suitable for most listeners. If one had very efficient horn speakers, say 106 dB one could get 94 dB at one meter. I have chosen the most favorable conditions here by choosing a cartridge at the high end of output, a fairly high gain power amp and a very efficient speaker. Using a 86 dB/watt speaker we would only get 54 dB at one meter. A typical cartridge might be 6-12 dB lower and most amps have less than 30 dB gain.

2. Depending on where the EQ is placed there would be noise issues if it was done at the input of the tube and loading issues if it were at the output of the single tube if passive were used. If active EQ was used it would present an unconstant load to the cartridge. Modern listeners demand accurate RIAA EQ, low noise and freedom from loading issues.

Given the above I doubt there would be many takers for such a preamp. However, there is no doubt that some sound would be present but I would not call it Hi Fi.

[Roger A. Modjeski]

Getting back to the video...


Me being a tube-design noob, I've always been quite confused about cathode biasing.  Specifically, how the cathode resistor achieves a positive voltage on the cathode.  I do understand the concept of the voltage drop (voltage being 'consumed' by the resistor and dissipated as heat...right?).  But how does this voltage drop then put a positive voltage (of 2v in your example) onto the cathode?  If some of the voltage in the cathode circuit is being consumed by the resistor doesn't that just lower the voltage supplied to the cathode?  (Did I just answer my own question?)  Roger, is there any way you could describe this process to help out a helpless noob like myself?  Thanks!

It's a perfectly valid and good question. It also demonstrates why we like to go from plus to minus in our thinking.

Looking at the schematic in the video you can see that the plate resistor, the tube and the cathode resistor are all in series and the current flows from top to bottom. I don't even want to think about electrons at this point, its not necessary. If a current of one milliamp is flowing down this chain it has no where to go but to ground. It flows through the plate resistor causing a voltage drop of 100 volts for a 100 K plate resistor and a drop of 2 volts for the cathode resistor of 2 K ohms (typical values). The rest of the voltage is dropped across the tube. With a 250 volt supply that leaves 148 volts across the tube. I wouldn't bother to think of the consumption of voltage and current unless I am designing a power amp. What we want is gain here because this is a voltage amp not a power amp. We just want to increase the voltage of the signal. These single stages cannot drive a load, not even a headphone because that takes some current and one milliamp is nothing for even a headphone.

We use cathode bias because it is simple, convenient and is more stable than putting a 2 volt battery on the grid or in series with the cathode. Early radios up to the late 1920's used a "C" battery to provide this voltage but this was quickly abandoned in AC sets.

Now here's the cool part, how does this make an amplifier? It turns out that the current in a tube be it triode or pentode will vary greatly with the signal on the grid. This is called the transconductance or gm of the tube. The 12AX7 is rather low at 1600 micromhos (1.6 Ma/Volt) and the 6922 is at the high end at 12 mA/volt. These concepts are explained in depth in a paper I had published in Glass Audio some 25 years ago. You can read it here:  http://tubeaudiostore.com/suitof6dfora.html along with some other papers that are available here:  http://tubeaudiostore.com/tubin1.html

In short, the voltage signal on the grid (input) causes a change or swing in plate current that causes a change in plate voltage which is developed across the plate resistor (output). The upcoming video on 2 stage amps will get more into this. Right now I just want people to get a clear picture of how we set up or bias a single tube gain stage. The resistors are there to set up the operating parameters of the tube and these parameters vary for different tubes and different applications but not over a terribly large range.

What the cathode resistor does is to raise the cathode 2 volts above ground. Since the grid is at ground potential either by a resistor to ground or the source driving it, the relative voltage between it and the cathode is negative 2. A very convenient way to get a negative voltage in a circuit where there is only a positive supply. This cathode resistor will lower the gain of the tube unless we put a capacitor around it to bypass all the AC signal back to ground. This capacitor is called a cathode bypass. In some cases the cathode bypass capacitor is not used having the advantage of lowering distortion (by the same amount as it lowers gain) and making the gain of the stage less dependent on tube gain. This is called local  feedback or cathode degeneration.

I encourage readers to learn these simple terms as they are universal and make discussions possible where pictures may not be available. So far just remember: plate resistor, cathode resistor, cathode bypass and output coupling capacitor... and of course TUBE. Add a power supply and you have a voltage amplifier.

[cheap-Jack]

Hi.

I'm hoping you'll teach me, and Roger, a thing or two about tube design.

if you really want to learn audio electronics, particularly on tubes, may I suggest to read up
"Radiotron Designer's Handbook, 4th edition" to learn it.

Get the basic knowledge & then you'll understand what I am talking about tubes.

c-J

[cheap-Jack]

Hi.

All I see here is you avoiding the questions that are going to make you look stupid. Answer them and fail at it so we can all laugh at your stupidity. It's going to happen either way, so might as well get it over with now.

More you talk more you sound like an empty vessel.

Sorry emply vessels would not qualify for my teaching.
Learn more audio electronics before you DARE challenge me!

c-J

[srb]

That said, I still make some casual bucks acting as a free-lance sound consultant.
I build & sell to order, 4N pure silver interconnects & power cords for a premium price.

I don't know how much you might know or not know about tube circuits, but what's actually more interesting is how is this possible?  Seriously, wouldn't either of these endeavors require at the very least some small degree of social interaction skills with other human beings?
 
Steve

[Ericus Rex]

Hi.
if you really want to learn audio electronics, particularly on tubes, may I suggest to read up
"Radiotron Designer's Handbook, 4th edition" to learn it.

Get the basic knowledge & then you'll understand what I am talking about tubes.

c-J

I'll check out that book.  Thanks.

[guest78998]

Hi.
More you talk more you sound like an empty vessel.

Sorry emply vessels would not qualify for my teaching.
Learn more audio electronics before you DARE challenge me!

c-J

Or what is going to happen? Your going to fight me over the internet... You may know more about electronics then me, but that doesn't change that fact that you are an asshole, and assholes are the true ignorant people. You can know everything about electronics, but if you are perceived as an asshole, no one cares how much you know and no one will want to learn from you.

[guest78998]

I don't know how much you might know or not know about tube circuits, but what's actually more interesting is how is this possible?  Seriously, wouldn't either of these endeavors require at the very least some small degree of social interaction skills with other human beings?
 
Steve

touché

[G Georgopoulos]

This is the first in a series of videos that intend to cover the entirety of tube preamp design. Starting with a single stage we will build on basic concepts to multistage amplifiers and their power supplies. Here is the link to the video: http://youtu.be/mrMGGHp8yLk and please follow our channel. We will post on AudioCircle when we put up new videos.

Hi Roger, it's a nice video,but it doesn't say much... 

[stevenkelby]

Roger I think the video is a great introduction for those that are new to tubes, looking forward to the next one(s)!

Steve.

[cheap-Jack]

Hi.

(1) I don't know how much you might know or not know about tube circuits, but what's actually more interesting is how is this possible?

(2)  Seriously, wouldn't either of these endeavors require at the very least some small degree of social interaction skills with other human beings?
  Steve

(1) But you now know that I know maybe a bit more than you, & many many many others on tubes. I've already been enjoying my LP music, mainly classicals using my DIYed 1-tube stereo RIAA phonostage for a few years now.

     That said, it is NOT my job to babysit whoever wants to know about tubes withOUT making an effort to learn it by reading relevant textbooks first like what I had done. Sorry,  I don't get paid here for babysitting here, my friend.
 
(2) Your such comment should be addressed to someone who started challanging me with foul language.
      Every mother's son can swear, & I can swear back at that character, using the F... 4-letter words.
      BUT I've chosen NOT to as I have at least some "degree of social interaction skills with other human beings".

If any AC readers want to learn how I have done it, then show some genuine respect to make a request to
me like Ericus Rex & Roger M just did.

 If I consider one gets enough tube knowledge & passion for quality music, I surely teach him. Otherwise please don't bother to ask. This is MY call, like it or not.

See how I answered Ericus Rex & how he replied me with a big "Thanks". That is what I called mutual respect.

Unfortunately not many people can be so civil. We have just seen one here, being totally ignorant yet arrogant & BAD mouthed.

c-J

[rbwalt]

hey guys lets keep the language used here on the civil side shall we. engineers are what they are. i know because i have a number of good friends that are Me"s and EE's. they just plain drive you nuts if you  try to convince them to  think or explore out of the box. it is how they are taught and how they must operate at their work.

[cheap-Jack]

Hi.

hey guys lets keep the language used here on the civil side shall we. engineers are what they are. i know because i have a number of good friends that are Me"s and EE's. they just plain drive you nuts if you  try to convince them to  think or explore out of the box. it is how they are taught and how they must operate at their work.

Yes, no foul langugage here, please. MEs, EEs & ordinary Joe Blows.

I am an EE but I don't go by the conventional wisdom laid down by the textbooks as I always think "out of the box". Like the 1-tube stereo phonostage I DIYed built & now enjoying quality music thru it, from
Pavarotti, Domingo, Mario del Monaco, Joe Sutherland, to Victoria de los Angeles ..........

c-J

PS: if you don't know those master singers, sorry I can't help you as it is a culture.

[Ericus Rex]

hey guys lets keep the language used here on the civil side shall we.

+1

Havik, those kinds of attacks are unfortunately the norm on many other sites but we try to be more civil here on AC, whether the other side has earned that civility or not.

[cheap-Jack]

+1

Havik, those kinds of attacks are unfortunately the norm on many other sites but we try to be more civil here on AC, whether the other side has earned that civility or not.

BINGO !!!

c-J