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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