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

[Will Matney]

Ott,

Your totally welcome, any time.

Will

r391 wrote:

> Hi Will...
>
> I think what is going on here is that as connected, 100 volts instead 
> of 120 volts is being supplied to the filament transformer by the HV 
> transformer primary in some sort of buck/boost connection.  After 
> reading your two posts and thinking about it a bit its probably a bad 
> idea to do anyway in that I would think you would have to add the 
> filament transformers current load to the HV transformers primary 
> current load... which would overload the HV iron primary...
>
> Guess this was an accidental rather than intentional connection... 
> I'll redo it per schematic tomorrow...
>
> Thanks again for your guidance.
>
> Ott
>
> At 12:45 AM 11/20/2004, you wrote:
>
>> 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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