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Line Output Transformer needs schema

Hi all,

I'm currently using a kit preamp using a E88CC. Now I'm looking for a new project - no kit anymore - and need some advise from you.

I like a better suitable (for audio) tube than the E88CC, for example I heard good stories about the 5687. And I like to use these output transformers: 5k:600, 50 mA max.

Gain can be very low, because I'm using a sensitive amp and only a 2V cdplayer.

I've come across this schema http://www.arduman.com/aa/Sayfalar/fluschem.htm but I don't like the PSU design.

What do you think about this, and about the 5687, and what other schemas would you recomend for use with my transformers?

Thanks very much, Ralph
 
Hi Ralph,

what is it that you dislike about that PS ? It's a nice
tube rectified supply with a choke input filter. That's
about the best you can do. I'd recommend to use
it with Oil Caps. Would be the perfect fit for a transformer
coupled preamp.

What's unnecessary is the DC heater supply. This adds
a silicon rectifier bridge which bears the danger to
introduce switching noise. Use AC and elevate it may be
to +20V. Should be very hum free.

A nice twist to the schematic you linked is the ultrapath
topology. Check out: http://www.execpc.com/~n9zes/schem1.htm

This will give improved resolution due to a shorter
signal path.

Thomas
 
Hi Thomas,

Thanks for your response. The Ultrapath also looks good! Do you think I can use the 5k:600 output transformer in this design, or better 15k:600? What tube do you recommend in this design, when I need little gain?

Here's another version of the Ultrapath http://www.execpc.com/~n9zes/ralph.html using a 5687. But ... isn't 85v 8 mA WAY too low??

I read somewhere on this forum that you don't like the Euridice project. http://www.fortunecity.com/rivendell/xentar/1179/projects/euridice/Euridice.html

Anyway, there's so much to choose from, it's very hard for a beginner to find a 'definitive' schema to start with ...

Ralph
 
Ralph,

the 5687 would work fine with that transformer. And
yes I'd also prefer to run it at a higher voltage and current.
The reson why I dislike the use of the 417 or 5842 is that
it runs at too low bias voltages which bear the danger
of overload or operation in non linear regions.

The 5687 is much better in line level applications,
especially when little gain is needed, as in your case.
You will end up with a gain of a litle over 3x

Run it at high voltages and current and you will have
a nice headroom.

Thomas
 
Ralph,

When you wrote that you disliked the fluence PSU, I had
the impression that you already have very specific ideas
how a PSU should look like.

Such a power supply is fairly simple to design. If you are
lacking some basic knowledge about PSU design, I
suggest to read some literature first. Most old tube books
have chapters on PSUs. Also the introduction sections
of tube manuals.

If you have come up with a PS design, I'd be glad to
review and comment it.

The elevating of heater supplies is very simple. You need
a voltage divider from B+ and hook one side of the
heater supply to the tap and decouple it with a cap
to ground.

Thomas
 
Ralph,

some comments about the schematic:

The transformer voltage is way to high for 180VDC.
Typically you will get a little over 1.1 times the secondary
voltage on one leg. Beware, this is a soft number and
depends on many factors: DC resistance of transformer
secondary, core material and size of transformer,
size of first cap, rectifier tube, DC resistance of chokes, etc.
Some experimantation is always necessary. In a cap input
filter the DC voltage can be influenced by the size of the
first cap (smaller cap, less voltage, down to 0.9 times
trafo voltage for no cap).

In your case 200-0-200V would be about right.

To get a better feeling about PSUs, play around with this
nice tool: http://www.duncanamps.com/psud2/
It's easy to use.

So you decided to use DC on the heaters ? Why not
just hook th heaters to a 6.3V AC winding and elevate
it to 20VDC ?

Thomas