Tube747 wrote:
Hello RATS!
I am looking for a low DCR power transformer for filament supply of rectifier
tube because some one told me that the low DCR power transformer the better
regulation it is.
I want to use the 6D22S rectifier tube (2 for full wave rectification).
Therefore, the power transformer for the filament of this tube is going to be
6.3V 4A, will it be ok?
Each 6D22S with the heater spec. 6.3V 0.9A.
Also, if I order a power transformer which has a lowest possible DCR on the
secondary winding with centre tap and lowest possible ACR on the primary
winding, will it be damage the tube (6D22S)?
I saw a transformer like that from my friend's place for the 6D22S which look
like a 300VA transformer and quite heavy as a filament transformer for only
6.3V @ 4A. Any problem if using such as transformer with the rectifier tube
like 6D22S?
Thanks!
The DC resistance of a filament winding has very little to do with
anything, at least directly. Since the load is essentially constant,
there's no real concern about "regulation" of a filament transformer.
By choosing a transformer that has the correct voltage at the rated
current, you will automatically take into account DC resistance and
other transformer losses. If you choose a transformer with a far higher
rated current than what you actually need, your voltage will tend to be
higher. For 6.3 volts at 1.8 amperes a 4A transformer would be more than
adequate, the voltage might be a bit higher than ideal, but if you get
one from a reputable manufacturer it shouldn't exceed the tubes' rating.
On the other hand, the DC resistance of the plate winding (HT winding)
can play an important part in determining final output voltage,
regulation, and even the maximum safe input capacitance of the filter
network. The effects of this are easy to simulate using a program like
Duncan Munro's "PSU Designer II".
Cheers,
Fred
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