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

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.
"Better to say nothing and keep them guessing than to speak and remove all doubt."
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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.
"Better to say nothing and keep them guessing than to speak and remove all doubt."
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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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