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Old 20th August 2004, 04:25 PM   #1
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Question help with Optomal placement of output transformers.

Hello all, i am building a 150W EL519 tube amplifier. It is a PP el509 anp tith 12ax7 preamp 12au7 phase splitter and 6bm8 screen regulators The amplifier and screen regulator sections will be housed seperately from the power supply components to minimise hum. I am building the input/phase splitter section on a PCB of my own design. It is star grounded on the pcb, and single sided so there arent overlapping traces, and i kept the traces as short as i could.

I am trying to fit everything on a 13X13 piece of aluminum. It is a tight fit. The output transformers are hammond 1650T's. They have a footprint rectangle of 4.5 x 3.75.
What i would like to know is exactily how close can i put these transformers to the el519's without risking the heat of the tubes cooking the transformers?
How close can i put the transformers to each other without risking them picking up signals from eachother?

And is it better to put the transformers like this:


windings
..~~~~~~.................. ~~~~~
..~~~~~~................... ~~~~~
=========.................========
========= laminate.....========
=========.................========
..~~~~~~....................~~~~~
..~~~~~~.................... ~~~~~


or

.....|||..........|||
..$$|||$$....$$|||$$
..$$|||$$....$$|||$$
..$$|||$$....$$|||$$
.....|||..........|||


Ignor the "...." they are just to keep everything lined up


^-------- ~2 inches

If i configure this way i can fit everything on the 13x13 board with about 2 inches between the transformers and a good amount of room between tubes and transformers.


Depending on how close i can put the transformers to the tubes i may be able to fit it all on the first way and the transformers can be a little further apart.


Thanks alot
Tom
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Old 20th August 2004, 07:57 PM   #2
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It's better to have the transformers' laminations at right angles to one another. It's doubtful that the tubes' heat will cook the trannies, but I would worry about how placing the tubes too near the trannies might affect tube life. You'd do well to make sure that there's LOTS of air circulation room aound those tubes, especially if you're running them at high power.
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Old 20th August 2004, 08:11 PM   #3
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Don't know about EL519s, but I found that my 300BSE amp was degraded if the trafos were less than 8 or 10 inches from the output valves.

I prefer to mount the trafos on the loudspeaker stands and run 2 foot high voltage/low current speaker cables from each monobloc. Harder to do in a stereo amp, I know.

If you're tempted to do this, be sure the cable insulation is sufficient to resist the usual domestic threats; 500V up the vacuum cleaner pipe could get hair raising.
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Old 20th August 2004, 09:30 PM   #4
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Quote:
Originally posted by SY
It's better to have the transformers' laminations at right angles to one another. It's doubtful that the tubes' heat will cook the trannies, but I would worry about how placing the tubes too near the trannies might affect tube life. You'd do well to make sure that there's LOTS of air circulation room aound those tubes, especially if you're running them at high power.

Quote:
Originally posted by Rod Coleman
[B]Don't know about EL519s, but I found that my 300BSE amp was degraded if the trafos were less than 8 or 10 inches from the output valves.


How does placing the tranny near the tube affect its life
or degrade the sound?

What if i place steel boxes around them to magneticaly shield them?
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Old 20th August 2004, 11:00 PM   #5
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Quote:
How does placing the tranny near the tube affect its life
or degrade the sound?
I found that moving the trafo away from the O/P valve reduced hum - then I found the hum was still there when only the filament power was applied (no B+). This effect varies with the angle of the lams relative to the valve (best with them at right angles) but seems like there is field coupling you could do without. I suppose there is similar coupling of the anode current too. Steel shields may reduce this effect but may act as unintentional core material between other components. I figured the safest route was to keep the two apart - maybe there are ways to minimize the problems of proximity mounting, but I did no experiments in that direction.

Rod
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Old 20th August 2004, 11:55 PM   #6
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A steel box won't do much good. And you have intrinsically less of a problem with radiated field and hum than guys going the single-ended route. Just keep the tubes far enough away for good ventilation and you'll be fine.
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