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Old 14th December 2010, 08:48 AM   #1
Klaatu is offline Klaatu  United Kingdom
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Default Universal Power Transformer

For me the hardest (most expensive) part about amp building is obtaining the right transformers.

I have found a friendly winding company who will 'do me a deal' if I order in quantity.

So that got me thinking. What would the ideal multi purpose power transformer look like. ?

How is this for start ?

400v - 0 - 400v @ 150mA
-100v @ 10mA
3.15v - 0 - 3.15v @ 2A
3.15v - 0 - 3.15v @ 2A
0 - 5v @ 3A

The idea is to be able to make as many different types and styles of amp using the same transformer.

I should add I love octal tubes and tend to use these for everything.

Comments welcome.
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Old 14th December 2010, 09:41 AM   #2
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If you will use some output tubes with +B about 180-200v, I think, that secondary coil must be 200+200 - 0 - 200+200v. /middle tap from every 400v/. I have box with PSU with different +B, GZ34 and 2 filtering CLCRC channels and 2 output transformers - 2.5, 5, 10 konm Ra. And I connect my tubes
EL11, EL12, 1625, GU50, 6CH8, 6LR8, 4P1L, 30P1S, 6S4S, EL84, 6E5P......ets, with preamplifiers, of course....

Last edited by azazello; 14th December 2010 at 09:52 AM.
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Old 14th December 2010, 10:24 AM   #3
Klaatu is offline Klaatu  United Kingdom
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Default You go me thinking...

After posting the original question and reading your reply, it seems that now what I really need is a separate PSU chassis which I could use to drive any amp I build.

I could create all my future projects with a plug at the back and simply hook up the power supply to which ever one I was listening to at the time.

So it seems what I need now is a supply which can provide

B+ 400v @ 200mA
B+ 200v @ 100mA
C- 100v @ 10mA
+6.3v @ 4A
+12.6v @ 2A

Using this I should be able to create a whole host of interesting a enjoyable amps and only build a single PSU ?

What do you think of this idea ? Do you think the above voltages are flexible enough ?
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Old 14th December 2010, 10:29 AM   #4
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I think, 400v - 100-150 ma
200v - 200 ma
......Low voltage output tube need more current.
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Old 14th December 2010, 10:39 AM   #5
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Or.....200+200 - 0 - 200+200 /150ma for 845 or GM70 with +B 1100v
and 12-0-12v/4A for some tubes and 845, GM70.
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Old 14th December 2010, 10:41 AM   #6
tinitus is offline tinitus  Europe
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well, Im not experieced with this, but found that supply trafos without heater windings tend to be cheaper
And I have seen a few cheaper standard trafos with possible heater voltage

I pulled the plug and ordered a heater trafo with 3.15-3.0-0-3.0-3.15, 5A
ofcourse its yet another trafo to handle

but I guess it also depends on whether its for DC or AC heater
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Old 14th December 2010, 11:11 AM   #7
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I have once built this kind power supply. It is based on Italian Inmadout-transformer, which is very reasonably priced (some 50 to 60). (see www.inmadout.com)

Click the image to open in full size.

Here the bias supply was done from 12-0-12 filament output by doubling the voltage. This output can also be used with tubes requiring 12,6 Vac for filaments.

Also both 450 Vdc and 225 Vdc is available.
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Old 14th December 2010, 06:39 PM   #8
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I'm use this transformer for my bench power supply:

Primary - 230 V
Secondaries:
2 x 189V / 400 mA
1 x 30V / 400 mA
1 x 70V / 100 mA (for BIAS)
3 x 6.3V / 10A
2 x 3.15V / 10A


This is toroid transformer is absolutely silent and went only slightly warm under heavy load.

It is connected to stabilized vacuum-tube based regulator, capable of 1A 360 - 460V.
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Old 14th December 2010, 07:01 PM   #9
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Klaatu, don't underestimate the need for big current on the heater supplies. For example, if you are going to feed an output stage with 4 EL34s, that is 5A @ 6.3v to start with.
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Old 14th December 2010, 07:05 PM   #10
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The transformers, power and output, required for a tube amp have keep me from building from scratch. My reasoning goes this way: I figure the most economical way to get transformers is to salvage them from an old amp. So I purchase an old beat up amp from some swap meet. Then I start looking at the chassis, and realize that the socket holes and sockets are already there, the layout is a proven design done by professional "tube" engineers, and there is no way I could possibly make a case that looks as good as what I already have in my hands. So I land up doing a restoration instead of a DIY.

Bobby Dipole
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