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Re: [Amps] Trio TL-922 Filament Transformer...

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Subject: Re: [Amps] Trio TL-922 Filament Transformer...
From: Will Matney <>
Date: Sat, 20 Nov 2004 00:25:00 -0500
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It's not good to do this as the unbalance will cause the transformer to heat up as it's doing. Remember when there's a voltage drop, there's a current rise. Any increase in the electrical current of the coil directly causes an increase in the magnetic current and thus more heat. The current increase is caused where the load resistance will be lower due to the tubes heater not getting hot enough. The tubes spec sheet will give the recommended voltage and what current it will run at. This is where it should be ran and the transformer will not run as hot. The spec sheet will give a minimum, recommended, and maximum heater voltage. If you would want to run it at a slightly lower voltage, the transformer needs to be sized for this current increase. Hope this helps.

Will Matney

r391 wrote:

Tonight I decided to pull some PM on my Japanese Trio TL-922...

Filament voltage 4.8 volts... at the tube pins... thought hmmm... better a little low than a little high?

Felt the filament transformer and it felt quite warm after only 5 minutes or so of operation... this is the first time I've done this so I don't know how warm the transformer should feel after 5 minutes so...

Out of curiosity I decided to check mains input voltage to the filament transformer and it was 122 volts on one leg and... 102 volts on the other so that the two primaries input voltages are unbalanced to each other by 20 volts...

Thinking "that can't be right" as the schematic shows "0" to "0" and "120" to "120" between the two transformers so that their both shown to be phased the same way and that my 122 volt line voltage should appear on all of the primary windings equally... I decided to trace the wiring.

Found the installed wiring different from the schematic... this difference is either from the factory or by previous owner design but is such that one of the 120 volt lines from the filament transformer is connected to the 100 volt connection on the HV transformer thus feeding one of the filament transformer primaries 100 volts instead of 120 volts while the other primary was connected to the 120 volt connection on the HV transformer and receiving 122 volts...

Was wondering if this is a factory wiring error or a deliberate attempt by the factory or a previous owner to adjust the filament voltage... anyone seen this before?

tnx, Ott

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