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Old 20th February 2011, 11:24 AM   #1
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Default Transformer question

Hello everyone,
I am looking for a ~30-31v transformer to power some filaments. They seem to be few and far in between, so my next thought is a 480v-->120v transformer. With 120v on the primary I should get my ~30-31v on the secondary. I found a fairly cheap, new one on "the bay" that is rated for
100va. So, if my math is correct, if it is used as designed, the secondary will only do ~830ma. So, am I correct in saying if I need 30v @ 2a this transformer is not it?

Thanks
Ray

Last edited by rsumperl; 20th February 2011 at 11:32 AM.
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Old 20th February 2011, 12:16 PM   #2
Doz is offline Doz  United Kingdom
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Can you not get a 15 - 0 - 15 out there?
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Old 20th February 2011, 12:45 PM   #3
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I've looked and haven't seen any. Any suggestions besides eBay?
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Old 20th February 2011, 01:38 PM   #4
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Why 30V for filaments?
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Old 20th February 2011, 03:36 PM   #5
RTF671 is offline RTF671  United States
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Quote:
Originally Posted by thelenster View Post
Why 30V for filaments?
Series heaters. They add the overall voltages up and the current more or less stays the same. For example a 12AU7 can run 6.3v or 12.6v. You can take it further and run 4 12AU7s at 50.2v @ 150mA.

Antek is a company that puts out a variety of torodial transfomers. They have a bunch at 30 or 32v starting from 10 VA.

AnTek Transformers product index
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Old 20th February 2011, 04:29 PM   #6
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That's what I suspected. Why not run them in parallel @ 6V? Much more standard, easier to procure a Xfmr at desired current. Also easier to see which tube is dead if the heater burns out(rare condition). Toriod transformers are superior for coupling, but costly. Plitron, in Canada is an excellent house dealing in toriods, but there are lots of other sources.
Just went to the AnTek link. Seems interesting but just wondering if they're marketing Chinese made stuff, or a true design house.
Regards
You don't need tight coupling, or regulation for heaters
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Old 20th February 2011, 04:55 PM   #7
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Actually the tubes are 31LQ6's.
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Old 20th February 2011, 05:16 PM   #8
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try contacting them with the specs you need. Transformers and Power Converters From Avel Lindberg, Inc.
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Old 20th February 2011, 05:38 PM   #9
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Maybe one of these:
RT-202 - TAPPED OUTPUTS: 11VDC@4A THR

or two of these:
TR-36009 - 16vac ct 2.5a, 36vac ct 300ma, prim 110v or 220v,
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Old 20th February 2011, 09:28 PM   #10
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Quote:
Originally Posted by thelenster View Post
Toriod transformers are superior for coupling
Yes, and that is a major drawback of the toroidal power supply transformer.
For a power supply transformer we need pure inductive coupling of the 50 - 60 Hz line voltage to the secondary voltage(s) of the transformer. Coupling of higher frequencies (line pollution) is what we do not want. Electrostatic shields between primary and secondary sections can prevent high frequency coupling but in a standard toroid this is uncommon.
Besides toroids are very sensitive to low frequency line pollution (DC like) because the highly efficient (closed loop) core of the toroid is easily saturated, especially in standard transformers already approaching max T in normal circumstances. Where toroids excel is in low stray fields, but in well designed EI or (preferably) c-core transformers this can also be achieved.
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