Ahhhhh yes - memories of my USN training in electronics.
Here is a link to the other modules http://jacquesricher.com/NEETS/
The catch was a six year enlistment for two years of tech school.
Last edited:
book question
So I was looking into throwing Morgan's Valve Amplifiers onto my Christmas wish list and over on Amazon it is paired w/ two other books. One is Morgan's Building Valve Amplifiers and the other is Slone's Audiophile's Project Source book. Anyone familiar /w the Slone book? I know the Morgan's books are considered essential, at least the Valve Amplifier (non-build). I like the online learning but I really enjoy a book, easier to put down and come back to later.
Thanks
./e
So I was looking into throwing Morgan's Valve Amplifiers onto my Christmas wish list and over on Amazon it is paired w/ two other books. One is Morgan's Building Valve Amplifiers and the other is Slone's Audiophile's Project Source book. Anyone familiar /w the Slone book? I know the Morgan's books are considered essential, at least the Valve Amplifier (non-build). I like the online learning but I really enjoy a book, easier to put down and come back to later.
Thanks
./e
One thing to note is that Morgan's early chapters, minus the transistors, are really no different than the information you get from the RCA recieving tube manual--versions around the RC-30. It is presented differently, so just use the one that speaks to you best.
There is one weakness (or not depending on point of view) in the Morgan and RCA manuals. They don't really go into the details of PI filter design and important parameters. Morgan shows how to make a great regulated supply if that is what you want--I personally feel, based on my testing and listening, that the regulated supplies, which are of course feedback driven, do not give the full presense that a classic PI filter design, properly constructed, will. The key is 'properly constructed'. Improperly constructed leads to a whole host of problems.
Anyway, last month I spent the time to go through all the detail of classic power supply design and incorporated them into a spreadsheet which is available on my DIY web site for all to download: Tips&Ref. Download the "Standard Calculations" spreadsheet. The background for this is the "Electronic Designers Handbood", which is my favorite resource. I've codified all the needed calculations into a single spreadsheet and tables. In the past I've used Duncan's Power Supply tool, which is great, but not as accurate because you don't always know the load voltages and current relationships of your power transformer at your specific design specs. I now use the power supply tab on my spreadsheet for calculation transformer sizing, choke sizing, capacitor sizing, and so on, and then do a final check using these values with the Duncan tool to look at the first 500ms response. If you get the rectifier resistance correct, this tool is dead accurate.
There are also a bunch of other tools there that I found myself needing on a regular basis--so I included them in that spreadsheet.
Anyway, if anyone finds mistakes please notifiy me and I'll correct them and repost.
There is one weakness (or not depending on point of view) in the Morgan and RCA manuals. They don't really go into the details of PI filter design and important parameters. Morgan shows how to make a great regulated supply if that is what you want--I personally feel, based on my testing and listening, that the regulated supplies, which are of course feedback driven, do not give the full presense that a classic PI filter design, properly constructed, will. The key is 'properly constructed'. Improperly constructed leads to a whole host of problems.
Anyway, last month I spent the time to go through all the detail of classic power supply design and incorporated them into a spreadsheet which is available on my DIY web site for all to download: Tips&Ref. Download the "Standard Calculations" spreadsheet. The background for this is the "Electronic Designers Handbood", which is my favorite resource. I've codified all the needed calculations into a single spreadsheet and tables. In the past I've used Duncan's Power Supply tool, which is great, but not as accurate because you don't always know the load voltages and current relationships of your power transformer at your specific design specs. I now use the power supply tab on my spreadsheet for calculation transformer sizing, choke sizing, capacitor sizing, and so on, and then do a final check using these values with the Duncan tool to look at the first 500ms response. If you get the rectifier resistance correct, this tool is dead accurate.
There are also a bunch of other tools there that I found myself needing on a regular basis--so I included them in that spreadsheet.
Anyway, if anyone finds mistakes please notifiy me and I'll correct them and repost.
Looking for a little help, without starting a thread...
When looking at valve data sheets, where do I look for current ratings?
Im looking for a power transformer for my 6DT5 SE amp... so looking at the data sheet.. so just the output valves for example..
Do I take the plate current plus the grid current? So, plate current - 44mA, plus grid current 1.5mA. So am I looking for a transformer with 90mA.
Is that remotely correct?
Charlie
When looking at valve data sheets, where do I look for current ratings?
Im looking for a power transformer for my 6DT5 SE amp... so looking at the data sheet.. so just the output valves for example..
Do I take the plate current plus the grid current? So, plate current - 44mA, plus grid current 1.5mA. So am I looking for a transformer with 90mA.
Is that remotely correct?
Charlie
That is a good rule, but not always possible when working with large currents. I remember that some of the Bottlehead kits used transformers (at least in the past--I don't know what they do these days) that were a under sized and ran very hot. This was on purpose and to save money.
Another problem is that ratings on transformers may be conservative or not, so there is always a final check required if you can't meet the 'double' current rule. My rule of thumb depends on the type of circuit. If you are running pure class A, then there will not be as much variation in current and you can run closer to the limit. So with class A amplifiers I try to stay within 80% of rated power, but I check the temperature after running at full rated current for several hours. Transformer can be warm, but should not be hot. If it remains cold, then I probably am over-designed.
As you move from class A to AB1, AB2, B, C, D, it is good to increase the percentage, but again, the circuit design and requirements will dictate the final needs. 200% may not be enough for a class B if you design to idle current specs and plan on running at max power continuously.
I'm no transformer expert and from time to time I run into trouble finding the correct transformer. I like to comment to some posts here...
All this writing about
1. x % oversizing
2. Check the temp after installation
Is this the way to find out what transformer is needed?
The first is probably costing to much and the second is expensive because you have to buy first and test later...
Many are so picky about the voltage/current settings of the tubes and write page after page how a mA in current can give such or so distortion etc...
But if asked how to calculate (excact!) a power transformer then there is silence in many cases.
OK, after your calculations of the needed voltage and current according to your schematic, you will take the next transformer (in power) from the list of a manufacturer.
If an excisting or used transformer with no voltage/current info is used; then the problem of getting data from it is a bit more problematic.
Different adjustable loads are needed to see if it can deliver the voltage and current needed for your application.
It would be handy if some one could design a small setup for it...
Cheers,
Tarzan
All this writing about
1. x % oversizing
2. Check the temp after installation
Is this the way to find out what transformer is needed?
The first is probably costing to much and the second is expensive because you have to buy first and test later...
Many are so picky about the voltage/current settings of the tubes and write page after page how a mA in current can give such or so distortion etc...
But if asked how to calculate (excact!) a power transformer then there is silence in many cases.
OK, after your calculations of the needed voltage and current according to your schematic, you will take the next transformer (in power) from the list of a manufacturer.
If an excisting or used transformer with no voltage/current info is used; then the problem of getting data from it is a bit more problematic.
Different adjustable loads are needed to see if it can deliver the voltage and current needed for your application.
It would be handy if some one could design a small setup for it...
Cheers,
Tarzan
Well there is another way--you can always cheat. I made my cheat sheet
Tips&Ref (download "Standard Calculations") and calculate the current and voltage drops on the Power Supply SpreadSheet. If your final calculated AC load voltage is within 3-4% of the no-load voltage you are great. If it is within 7% you are still OK. More than that and you better get a bigger transformer. Note that the AC load voltage is only related to current draw--not circuit design.
Job done. And I'm kind of joking about the 'cheating' part. I spent a couple weeks researching the power supply parameters used before the 1960's, and embodied all of that info into the spreadsheet. It works like a charm.
Online tube data sites - always useful
(snip)
This one is very good... I use it all the time:
NJ7P Tube Database Search
I was just looking back at some of my first posts. Other than being quite amusing I remember how much I struggled (still do) with abbreviations of terms and components.
In fact, for a while I thought "What iron did you use?" meant "What soldering iron did you use?".... as you can imagine, was a little confusing. Other than that, just the general SE PP kind of stuff, that I remember confusing me, until the brain cells worked a bit harder.
I think it would be good if there was a small sticky on this. Also, there seems to be lots of questions about beginner amps and types of valves. Like, the ECC88 could have a list of all corresponding names. And there could be a list of beginner projects etc.
You could have all this in one sticky, sort of like an index, maybe even wiki page or blog, so if you're not sure about something (as I am 95% of the time I'm on this site) you could check there first.
'The Newbies Index' maybe....
In fact, for a while I thought "What iron did you use?" meant "What soldering iron did you use?".... as you can imagine, was a little confusing. Other than that, just the general SE PP kind of stuff, that I remember confusing me, until the brain cells worked a bit harder.
I think it would be good if there was a small sticky on this. Also, there seems to be lots of questions about beginner amps and types of valves. Like, the ECC88 could have a list of all corresponding names. And there could be a list of beginner projects etc.
You could have all this in one sticky, sort of like an index, maybe even wiki page or blog, so if you're not sure about something (as I am 95% of the time I'm on this site) you could check there first.
'The Newbies Index' maybe....
Hi ! im trying to understand the topo logic from this line pre amp. How do you choose the Rp resistor ?
An externally hosted image should be here but it was not working when we last tested it.
How to select anode load resistor
This seems like a simple question. One could apply the rule of thumb and answer that the load resistance should be between 2 and 3 times the plate resistance. Alas, it is not always that simple. This rule will work, fairly well, but a number of things should be considered:
1. Circuit requirements--i.e. how much gain is required at standard and loud listening. This will help direct you to the right tube. Normally, 12dB of gain is sufficient for a pre-amp, but depending on your power amp and input circuit you may need more or less. There is a tendency to build power amps with higher and higher input sensitivity (a very bad idea IMHO) so that a pre-amp is not always needed. Power amps from before world war II often required 7 volts peak to peak to drive them to full power. Now you see that only .35V is often needed. This moves the gain section from the pre-amp to the power amp and increases complexity and/or stages in the wrong place. (IMHO--again). 12dB of gain can be had with a 12B4A tube, or a medium mu tube with a lower ratio of R / r. Always use a tube with the lowest mu (gain) possible to reduce noise. Don't forget to consider maximum and input voltage requirments and analyze your circuit at these points as well.
2. Tube type. Some tubes run best really hot--like the 5687. Some tubes run well with current way below normal recommendations--like the 6DJ8. What you want to do is look at the tube curves and pick a linear operating region.
3. Resistance size. Resistance noise is proportional to resistance and heat. A larger resistor (wattage) and smaller resistance is desirable for a super quiet stage. This must be balanced against points #1, and #2.
4. Topology of the rest of the circuit. What voltages are available? What about heater requirements? Will you be adding or modifying in the future. These must be balanced against 1,2, and 3.
5. Cost of ownership. 6DJ8's for example improve dramatically as the price of the tube goes up--and it can exceed $1000 a pair for the best of the absolute best. 12B4A's will never cost more than $20 for the best, and everything else falls inbetween. The 6CG7 (or 6SN7 which is the Octal equivalent) is probably my favorite go-to tube for medium gain stages, and the 5687 or 12B4 is best if high output voltages are required. Intermediate signal stages are best handled with 6DJ8's for most applications, should you need an extra gain stage.
There are more points that could be added (like circuit layout, etc.), but these 5 points are the key ones to consider.
Or you can follow the rule of thumb and get a reasonably good solution, but if you take the time to examine all the variables you can get a really good solution.
This seems like a simple question. One could apply the rule of thumb and answer that the load resistance should be between 2 and 3 times the plate resistance. Alas, it is not always that simple. This rule will work, fairly well, but a number of things should be considered:
1. Circuit requirements--i.e. how much gain is required at standard and loud listening. This will help direct you to the right tube. Normally, 12dB of gain is sufficient for a pre-amp, but depending on your power amp and input circuit you may need more or less. There is a tendency to build power amps with higher and higher input sensitivity (a very bad idea IMHO) so that a pre-amp is not always needed. Power amps from before world war II often required 7 volts peak to peak to drive them to full power. Now you see that only .35V is often needed. This moves the gain section from the pre-amp to the power amp and increases complexity and/or stages in the wrong place. (IMHO--again). 12dB of gain can be had with a 12B4A tube, or a medium mu tube with a lower ratio of R / r. Always use a tube with the lowest mu (gain) possible to reduce noise. Don't forget to consider maximum and input voltage requirments and analyze your circuit at these points as well.
2. Tube type. Some tubes run best really hot--like the 5687. Some tubes run well with current way below normal recommendations--like the 6DJ8. What you want to do is look at the tube curves and pick a linear operating region.
3. Resistance size. Resistance noise is proportional to resistance and heat. A larger resistor (wattage) and smaller resistance is desirable for a super quiet stage. This must be balanced against points #1, and #2.
4. Topology of the rest of the circuit. What voltages are available? What about heater requirements? Will you be adding or modifying in the future. These must be balanced against 1,2, and 3.
5. Cost of ownership. 6DJ8's for example improve dramatically as the price of the tube goes up--and it can exceed $1000 a pair for the best of the absolute best. 12B4A's will never cost more than $20 for the best, and everything else falls inbetween. The 6CG7 (or 6SN7 which is the Octal equivalent) is probably my favorite go-to tube for medium gain stages, and the 5687 or 12B4 is best if high output voltages are required. Intermediate signal stages are best handled with 6DJ8's for most applications, should you need an extra gain stage.
There are more points that could be added (like circuit layout, etc.), but these 5 points are the key ones to consider.
Or you can follow the rule of thumb and get a reasonably good solution, but if you take the time to examine all the variables you can get a really good solution.
PS: My last reply was general and may not have answered the specific question asked.
This looks like an instrument amplifier input. What is the purpose of this pre-amp?
For the output gain control to work properly it must go to a high impedance input--read tube amplifier. A standard 1-10K input impedance for transistor amps would be incorrect for this amplifier, but the high value output capacitor in series with a 20K resistor suggests that such is the target. In addition the huge bypass capacitor suggests a very low Rk which is not consistant with the output design. A 100 ohm Rk gives a high pass at .7Hz--very unusual and potentially unstable with a choke input power supply. A Rk of10 ohms would not be a medium mu tube design. It would be more in line with a power tube like the 6AS7.
Input low pass could be around 50KHz at low volume, depending on the tube--again, somewhat lacking for an audio amplifier today.
This looks like an instrument amplifier input. What is the purpose of this pre-amp?
For the output gain control to work properly it must go to a high impedance input--read tube amplifier. A standard 1-10K input impedance for transistor amps would be incorrect for this amplifier, but the high value output capacitor in series with a 20K resistor suggests that such is the target. In addition the huge bypass capacitor suggests a very low Rk which is not consistant with the output design. A 100 ohm Rk gives a high pass at .7Hz--very unusual and potentially unstable with a choke input power supply. A Rk of10 ohms would not be a medium mu tube design. It would be more in line with a power tube like the 6AS7.
Input low pass could be around 50KHz at low volume, depending on the tube--again, somewhat lacking for an audio amplifier today.
Hi Guys,
just want your opinion on this..
a 12ax7 tube from National(made in Yugoslavia) printed in red
if this IS normal for tubes (Some) to have that kind of "GLOW"
OR are these factory REJECTS?
thanks
YouTube - 12ax7a from National
just want your opinion on this..
a 12ax7 tube from National(made in Yugoslavia) printed in red
if this IS normal for tubes (Some) to have that kind of "GLOW"
OR are these factory REJECTS?
thanks
YouTube - 12ax7a from National
Last edited: