[[email protected]]

I have a transformer with 5V 4A winding, does it adequate for 2 x 5R4 since each 5R4 is 5V 2A?

thanks!

[Eike Lantzsch, ZP6CGE]

wrote:
I have a transformer with 5V 4A winding, does it adequate for
2 x 5R4 since each 5R4 is 5V 2A?

thanks!

The question is not so much if the amperage is OK but if the
transformer's isolation is good enough to stand the high voltage of the
B+ present on the rectifier's filament (direct heating). Ordinary
transformers for low voltage are not designed for this application. If,
however your transformer was meant to supply the heaters of rectifier
tubes, than you can assume that 300-400V are OK. Well - "assume" does
not mean that you can be sure.

Kind regards, Eike
--
"Discipline may only mean a hundred men making the same mistake
at the same minute" - G. K. Chesterton (1908)

[Robert Kowalczyk]

"Eike Lantzsch, ZP6CGE" wrote in message
...
wrote:
I have a transformer with 5V 4A winding, does it adequate for
2 x 5R4 since each 5R4 is 5V 2A?

thanks!

The question is not so much if the amperage is OK but if the
transformer's isolation is good enough to stand the high voltage of the
B+ present on the rectifier's filament (direct heating). Ordinary
transformers for low voltage are not designed for this application. If,
however your transformer was meant to supply the heaters of rectifier
tubes, than you can assume that 300-400V are OK. Well - "assume" does
not mean that you can be sure.

Kind regards, Eike
--
"Discipline may only mean a hundred men making the same mistake
at the same minute" - G. K. Chesterton (1908)

Where do you get this information from? Manufacturers data?
And what is the safe limit to use such transformers for directly heated
rectifiers?

Regards. Robert.



--- Posted via news://freenews.netfront.net/ - Complaints to ---

[Phil Allison[_3_]]

"Robert Kowalczyk"
"Eike Lantzsch, ZP6CGE"
I have a transformer with 5V 4A winding, does it adequate for
2 x 5R4 since each 5R4 is 5V 2A?

The question is not so much if the amperage is OK but if the
transformer's isolation is good enough to stand the high voltage of the
B+ present on the rectifier's filament (direct heating). Ordinary
transformers for low voltage are not designed for this application. If,
however your transformer was meant to supply the heaters of rectifier
tubes, than you can assume that 300-400V are OK. Well - "assume" does
not mean that you can be sure.


Where do you get this information from? Manufacturers data?


** Transformers for use in tube amplifiers need a higher standard of
insulation to cope with the DC and AC voltages involved. Unless a maker
states that a transformer is INTENDED for such use it is unwise to assume
it is OK.


And what is the safe limit to use such transformers for directly heated
rectifiers?

** Depends on the particular transformer, how it is constructed and what the
maker says.

Eg if the tranny is of " split bobbin" construction with the primary and
secondary wound on separate halves, then it may well be is capable of
withstanding 500 volts DC or more between those windings.


..... Phil

[[email protected]]

Generally most modern transformers are hypotted for 2 to 5 kV and as a
practical matter it will work. However in a commercial product you
want a design rating for type approval. If it's a very old transformer
all bets are off, unless it was specifically made for the purpose.

But you should always shoot for a safety margin on the amperage. If
it's rated for 4 A, i wouldn't use it in continuous service at that
limit rating. Homebuilders have the big advantage of being able to
derate stuff by a margin the MBAs would not tolerate.

[NT]

On Apr 2, 1:51*am, wrote:
Generally most modern transformers are hypotted for 2 to 5 kV and as a

I tested a pile of brand new mains TFs several years ago at either 1kV
or 1.5kV, over 50% failed. They all passed 500v testing.


practical matter it will work. However in a commercial product you
want a design rating for type approval. If it's a very old transformer
all bets are off, unless it was specifically made for the purpose.

Unfortunately there are also a minority of new transformers with
barely functional insulation too. Easy to spot though, no bobbin or
other visible insulation.

*But you should always shoot for a safety margin on the amperage. If
it's rated for 4 A, i wouldn't use it in continuous service at that
limit rating.

The makers specify it as being good for it. In practice tolerances
mean you might end up with it overrunning a tiny bit, which isnt
important with a transformer.

Homebuilders have the big advantage of being able to
derate stuff by a margin the MBAs would not tolerate.

.... or do the exact opposite, and overrun it. Heatsink a tranformer
well enough and it can be massively overrun. Transformer life
expectancy depends on temperature, and they run at well below any hard
cutoff point.


NT

[Phil Allison[_3_]]

"Nutcase Troll"

I tested a pile of brand new mains TFs several years ago at either 1kV
or 1.5kV, over 50% failed. They all passed 500v testing.


** None of them would pass the 1 minute flash test standard of 4kV AC.

Unfortunately there are also a minority of new transformers with
barely functional insulation too. Easy to spot though, no bobbin or
other visible insulation.

** Really ???

Transformer life expectancy depends on temperature,

**There is a point where the enamel on the wire softens, but otherwise life
span depends on good construction techniques, good enamel on the wire and
operation in a dry environment.

BTW:

I have seen a batch of 400VA trannys fail after some years due to self
adhesive insulation tape - the yellow stuff you see all used the time

The tape had been ( mistakenly ? ) laid in direct contact with the windings
allowing the adhesive to eat through the enamel and cause shorted turns.


.... Phil