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

[Will Matney]

One other note of importance I left out. Placing 120 volts on the 100 
volt tap will cause more current to be drawn by itself. This is because 
the turns per volt will be different and cause the transformers primary 
to not have enough inductance for 120 volts. This is also known as the 
"ampere turns" in a transformer. A 20 volt difference is 20% of the 
total voltage and is a good amount. The current should raise 20% just by 
this, not counting what the load will draw extra. For 5 volts and 10 
amperes as standard, it would raise the current to 12 amperes. That's a 
good amount when figuring the circular mils of a conductor for heat 
dissipation and the amount of iron in the core stack in a low voltage 
transformer.

Will Matney


Will Matney wrote:

> Ott,
>
> 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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