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Old 11th November 2010, 11:59 AM   #141
49 - for the 18th time
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Quote:
Originally Posted by escopunk View Post
Here is a great resource for new people, I have the real copy.

Enjoy

http://jricher.com/NEETS/14178.pdf
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.
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Old 11th November 2010, 04:45 PM   #142
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[QUOTE=DF96;2361432 Simple circuits may work better with valves. Horses for courses.[/QUOTE]

Absolutely agree.
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Old 28th November 2010, 03:51 PM   #143
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Default 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
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Old 28th November 2010, 10:18 PM   #144
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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.
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Old 2nd December 2010, 11:43 AM   #145
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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
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Old 2nd December 2010, 11:55 AM   #146
SY is offline SY  United States
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Remotely, yes. Plate plus grid currents, and you'll want a bleeder as well. Safe rule of thumb is to at least double the estimated current when sizing the power transformer- that way, it will run silent and run deep.
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Old 2nd December 2010, 02:04 PM   #147
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Thanks SY, may take a while but ill get there in the end
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Old 2nd December 2010, 03:37 PM   #148
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Remotely, yes. Plate plus grid currents, and you'll want a bleeder as well. Safe rule of thumb is to at least double the estimated current when sizing the power transformer- that way, it will run silent and run deep.
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.
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Old 3rd December 2010, 04:29 AM   #149
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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
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Old 3rd December 2010, 06:50 AM   #150
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Quote:
Originally Posted by Tarzan View Post
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
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.
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