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Old 20th September 2008, 04:06 PM   #1
abacus is offline abacus  Croatia
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Default TubelabSE 300B power transformer ?

Recomendations for power transformer ?
THNX
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Old 20th September 2008, 10:45 PM   #2
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Hammond 272JX. Link
That's what I use and it works well for my Tubelab SE with 300B tubes.
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Old 21st September 2008, 09:13 PM   #3
abacus is offline abacus  Croatia
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I have in mind something like this for power transformer 320-0-320, 5.0V@4A - 6,3@8A (custom made) any suggestions or is this one allright?
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Old 21st September 2008, 11:03 PM   #4
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This page from Tubelab website shows the requirements for PT. Scroll down about half way. As long as your PT meets the voltage, amperage and center taps required it should be fine.
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Old 21st September 2008, 11:07 PM   #5
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I have also used the Hammond 272JX in a 300B amp. It is only rated for 300-0-300 volts, but actually delivers 330-0-330 volts here. This is not uncommon for a Hammond transformer. A 372JX would be required in 230 volt countries.

A custom transformer would certainly work. You need a high voltage winding that delivers 330-0-330 volts at at least 175 mA. 320-0-320 volts would be OK. The 5 volt winding should be rated for 3 amps and the 6.3 volt winding should be capable of at least 4 amps.

It is permissible to slightly overspecify the current ratings but specifying too much current can be dangerous if the transformer delivers too much voltage with the actual load current. Using a 4 amp rating for the 5 volt winding could result in more than 5 volts to the 5AR4 which only draws 1.9 amps. The 6.3 volt winding is not as critical since the 300B filament supply is regulated. Too much voltage can cause the regulator to overheat. The high voltage should be close to 330-0-330 volts under load.
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Old 22nd September 2008, 08:43 AM   #6
abacus is offline abacus  Croatia
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320-0-320, 250mA, 5V@3A, 6.3V@5A something like this ?
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Old 22nd September 2008, 11:49 PM   #7
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That should work.
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Old 23rd September 2008, 11:05 PM   #8
abacus is offline abacus  Croatia
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I think this will be final: PT 330-0-330, 250mA, 5V@3A, 6.3V@5A
OPT 3.4K, 4-8 ohm and Choke DC 200 mA - 6 H - 150 ohm.
All transformers will be custom made, so i want to be sure before ordering. Any suggestions or is this OK?

THNX
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Old 24th September 2008, 12:28 AM   #9
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Quote:
Originally posted by abacus
I think this will be final: PT 330-0-330, 250mA, 5V@3A, 6.3V@5A
OPT 3.4K, 4-8 ohm and Choke DC 200 mA - 6 H - 150 ohm.
All transformers will be custom made, so i want to be sure before ordering. Any suggestions or is this OK?
Those numbers look fine.

What brand is OPT? I use Electra-print's 3K Ohm primary, 100mA current, 15w max power, 8 ohm secondary and I'm happy with it.
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Old 24th September 2008, 02:33 AM   #10
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Quote:
Any suggestions or is this OK?....... I use Electra-print's 3K Ohm primary, 100mA current, 15w max power
Your numbers look good. If you are having the OPT's custom wound, make sure that your winder understands the standing DC current requirement for SE OPT's. They should be gapped for about 75 mA of current and rated for at least 10 watts. A SE OPT that would do a 300B justice should weigh at least 3 KG.

If yours was the recent PC board order from Croatia, it was shipped this morning. Europe usually takes 10 days to 2 weeks depending on customs.
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