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Please don't laugh... first attempt at tracing out a schematic

Someone once told me that the dumbest question is the question not asked. Let’s test that idea…

Q: Do I have enough information here to determine which Hammond power transformer to use in a clone of this circuit? If not, what else do I need to do or know to figure that out?​

You can tell that I don’t have much understanding of the “why” behind what I’m doing here, but I’m damn curious about it! The only reason I’m tackling this project is that it looks like something I can handle. A good starting point, and I might learn something along the way!
 
Since you have a working amp to measure, it's really easy to spec the power transformer. Measure the AC voltage from pin 1 or 7 (on the EZ81) to ground, lets say that it's 260V. To measure the current, all you have to do is measure the voltage drop across the first resistor of the power supply and use ohm's law to find the current. I'll go with what Tom said above and say that it's 90 ma.

These measurements tell you that this amp uses a 260-0-260 transformer that can put out a minimum of 90ma. To be on the safe side up the current rating by 25-30% and use a 125ma unit.

Substitute your actual measurements for the 260V 90ma I used as an example.
 
Redboy said:
That's it?! I think even I can do that!

Thanks for the simple explanation, Scuzzer.
Click to expand...


Your welcome.

I think you picked an perfect project to educate yourself on tube amps. I'm no expert at this but 2 years ago I started playing around with a little EL34 mono push-pull amp and that was all it took. It's so cool to take a bunch of parts, put them together (correctly!) and then be able to listen to your favorite tunes.

If you're looking for power and output trannies check out the Edcor website http://www.edcorusa.com/products/class_x.html

If you're interested in how tubes work there are free book downloads (beginner to college level) here: http://www.pmillett.com/tecnical_books_online.htm

BTW, your schematic looks a heck of a lot better than the first one I did by hand.
 
Scuzzer said:
It's so cool to take a bunch of parts, put them together (correctly!) and then be able to listen to your favorite tunes.
Click to expand...
I think that about sums up the appeal of this hobby to me...
  • The mental exercise of learning all this new stuff.
  • The problem-solving aspect of turning a circuit into a schematic.
  • The hands-on nature of putting it together, and the satisfaction of "I did it!"
  • The esoteric nature of using tubes and "old" technology instead of transistors.
  • The gorgeous end-result of class A tube amplification through horns!
 
Redboy said:
I think that about sums up the appeal of this hobby to me...
  • The mental exercise of learning all this new stuff.
  • The problem-solving aspect of turning a circuit into a schematic.
  • The hands-on nature of putting it together, and the satisfaction of "I did it!"
  • The esoteric nature of using tubes and "old" technology instead of transistors.
  • The gorgeous end-result of class A tube amplification through horns!
Click to expand...

Yes! Exactly! Especially your 4th point. It still blows me away that 50 year old tube technology is competetive with most consumer gear made today. My friends and neighbors (heck even my wife) don't really understand why I'd be interested in such old technology but they'll all admit that it sounds amazing when I put an old 50's mono record on the turntable and turn it up.

My system is very mid-fi (not that I like that term) but instead of rushing out and buying expensive stuff to replace it, I think I'll just enjoy the journey, slowly tweaking and building stuff to upgrade specific parts of the system.
 
Yes! Exactly! Especially your 4th point. It still blows me away that 50 year old tube technology is competetive with most consumer gear made today.
Click to expand...

At the risk of sounding like a Luddite (which, as I age, I am in fact becoming), and at the risk of sounding political (see below): In 1969, we had the technology to "put a man on the moon". Interestingly, today, we don't.

In the moon-rocket case, the issue actually isn't political; the issue is more generally the investment in and maintenance of technology... the idea that newer is always better by definition just doesn't hold water any more IMO.
 
mhardy6647 said:
At the risk of sounding like a Luddite (which, as I age, I am in fact becoming), and at the risk of sounding political (see below): In 1969, we had the technology to "put a man on the moon". Interestingly, today, we don't.

In the moon-rocket case, the issue actually isn't political; the issue is more generally the investment in and maintenance of technology... the idea that newer is always better by definition just doesn't hold water any more IMO.
Click to expand...

I agree that newer isn't always better, a lot of technology advances today are more related to being cheaper to manufacture and sell. Most technology related products today do more, do it faster, and cheaper than anything that was available even 10 years ago. In most peoples minds that equates to better.

I think audio is a special case because the actual technology demands are very low. The technology of the 50's using just a diamond wiggling in a groove and very basic method of controlling electron flow was enough to get the job done, everything since then has just been refinement. I'd liken it to the evolution of the bicycle. You can spend $15,000 today on a bike but it's really only a lighter, slightly more refined version of what was available 40 years ago.
 
Scuzzer said:
Since you have a working amp to measure, it's really easy to spec the power transformer. Measure the AC voltage from pin 1 or 7 (on the EZ81) to ground, lets say that it's 260V. To measure the current, all you have to do is measure the voltage drop across the first resistor of the power supply and use ohm's law to find the current.
Click to expand...
All right, I finally got around to measuring this. Voltage on pin 7 measured 275V. The voltage on the transformer side of the first
resistor (390 ohms) was 320V and 285V on the other side. That's a 35V drop, which tells me I've got 90 mA current here...

New question: How much will my choice of output transformers determine which power transformer to use? I was thinking to use
the Hammond 125 SE series of OPT's because they look pretty versatile:

125BSE, 5 Audio Watts, 45mADC, 10K/5K/2.5K, 4/8/16/32 ohms
125CSE, 8 Audio Watts, 60mADC...
125DSE, 10 Audio Watts, 70mADC...

Of these, I was leaning toward the 125CSE. Does the 60mADC spec mean I need 60mA each to power these things? Do I need a
bigger power transformer now?
 
No, the 60mA spec means that at a max, you can feed 60mA through it. In other words, whatever current you plan on having at your plate, you need to find an OPT rated for it. I personally go with the 150% min rule (In other words, if you plan on running 50mA on your plates, get an OPT with at LEAST 75mA handling)

Regards,
Steve
 
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