On Sat, 9 Aug 2008, Antonio Vernucci wrote:

I'd like to hear someone having tried to use a power transformer as output
transformer for the single-ended final stage of a tube communications
receiver (power 5W, maximum, frequency not higher than 4,500 Hz).

I haven't done it, but it was a pretty common trick to see in the
magazines in the old days.

At least one article pointed out that if you started with a 400Hz
transformer, which were common in surplus from aircraft, you'd likely
get better frequency response where you needed it.

Michael VE2BVW

The same problem with the DC flow in the
transformer exists when a power transformer
is used with a halfwave rectifier.
Typically the transformer rating is degraded by
60% when be using with halfwave rectication
due to the DC current flowing in the secondary.

Many folks have used filament transformers
as audio outputs replacements with good results.
The transformer rating is decreased by the
standing DC current, but it will
still handle a good amount of audio before
saturation on peaks occurs.

Peter

Tio Pedro wrote:
The same problem with the DC flow in the
transformer exists when a power transformer
is used with a halfwave rectifier.
Typically the transformer rating is degraded by
60% when be using with halfwave rectication
due to the DC current flowing in the secondary.

No, the DC currents sum to zero. That derating is only required when
the transformer secondary is poorly balanced.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Scott Dorsey" wrote in message
...
Tio Pedro wrote:
The same problem with the DC flow in the
transformer exists when a power transformer
is used with a halfwave rectifier.
Typically the transformer rating is degraded by
60% when be using with halfwave rectication
due to the DC current flowing in the secondary.

No, the DC currents sum to zero. That derating is only required when
the transformer secondary is poorly balanced.
--scott


How does that occur in a half-wave circuit?
It is a series circuit. The half-wave
rectifier produces a voltage across the load that is
a complex waveform with both a DC and an AC component.
Since it is a series circuit, the same situation exists in the
transformer secondary. DC sums would be zero with a full
wave rectifier or a full-wave voltage doubler.

Pete