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Old 12th January 2012, 10:22 PM   #1
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Default Paralleling filament transformers

Hi
For reasons of having modified my amp , one of the filament transformers is having a bit of trouble driving the heaters. It is rated 2A @ 6.3 V. I have another tranny which is a different brand rated @1A.A bigger tranny wont fit in the space available (so swapping out the 2 A one isnt an option) but I can shoehorn in the 1A one. I can of course mount a bigger one externally but am loathe to do that for aesthetic reasons.
So can I parallel the 2A and 1A provided I get the phase correct of course.
Thanks
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Old 12th January 2012, 10:25 PM   #2
DF96 is offline DF96  England
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You may need balancing resistors as it is unlikely that the voltages will be equal. Better to drive some valves from one and some from the other?
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Old 12th January 2012, 11:44 PM   #3
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Paralleling transformers that are not identical is just asking for trouble.
How about using the bigger transformer for the output tubes and thje smaller for the rest of the tubes?
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Old 13th January 2012, 07:19 PM   #4
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Hi there.
I have tracked down the inability of my filament setup (regulated as per pete Milletts regulators for his complex 300b amp)to maintian steady voltage to a wiring issue. Now i get a stable voltage.
Initially,I would measure the voltage to the 2 6sn7's and it would vary by .1 of a volt (it would hunt) then after 20 minutes it would drop .2 to .25 of a volt and the tranny would get hot (filament tranny that is). I isolated the issue by wiring each sn7 socket independent of the other and no shenanagens at all. I can only conclude it was my soldering when i had the 2 sockets connected in parallel for heater feed. I seem to have fixed it for now. I thought the transformer was not up to the job (custom wound 2 Amp 6.3V) and so i hooked up the other one I had which supplied 3A and found it was doing the same hunting. Given 2 sn7's would consume 1.2 A max, I couldnt understand why the regulator was not rock solid like the other regulators on board. I swapped regulator boards to eliminate it as a variable and found that all regulated supplies and even the 3A transformer would hunt. I swapped out sn7's etc so in the end i narrowed it down to tube socket or wiring
I , after much reading, have surmised that paralleling transformers is not desireable at all and best avoided.
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Old 13th January 2012, 10:00 PM   #5
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Run some heaters off one transformer the others on the second one.
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