Steven P. Burrows wrote:
The B+ voltage delivered by the new transformer is about 50 volts higher
than Hallicrafters' original spec., which I was advised was not a big
problem.

That is correct, it is not a big problem, it is a *HUGE* problem.

Most of these older radios were designed for a 115V nominal power line
voltage. Today, people complain if the voltage is as low as 120V at the
outlet. It is more typically 123 to 125V. That means that even using the
original transformer, you will have nearly a 10% more B+ voltage than the
designers envisioned. So, your +225 will be +240V. You are running 50
more than spec, so your +225 will be +275, which will kill the caps and
shorten the lives of the tubes in your radio. (OBTW, the voltages I used
in the above description are just guesses. I am not certain what the
actual design voltage is for your radio.)


....

Next I removed the safety filter capacitors from the transformer primary
circuits. Fuse still blew. I traced out the primary circuit with a DVM
and found no short circuits in my wiring or from the transformer
windings to each other or to the transformer frame. With the transformer
completely taken out of the radio the fuse blowing stopped. I was
forced to conclude that the "new" transformer was a dud.

It was most likely damaged by the manufacturer. It is easy to nick a winding
through careless handling. The problem usually occurs where the inside end of
the primary (or secondary) crosses the windings to get to the outside where the
leads are attached. You can often cut the bobbin away, and find the short.


I don't have access right now to a variac, but I suspect that there
might be some sort of arcing in the transformer that doesn't show up
until higher voltages are applied. I still have this transformer, and I
might try looking at it again later this year when I can borrow a variac
from the university where I work.

Intermittent arcing is unlikely. Because of the relatively high currents,
and low voltages involved, it will usually burn off a wire, or weld it
permanently together.


I have replaced the suspect transformer and so far the radio is working
fine. My interest in using inrush current limiters is motivated by
trying to avoid a repeat of a damaged transformer, both in my father's
S-40B or my own.

Transformers are relatively immune to voltage spikes. For reasons of
manufacturing economy, the core is usually run right on the edge of where
it starts to become nonlinear (eg. saturation is beginning). If a spike
comes down the line, the spike will drive the core into saturation, and
that simple act will prevent the spike from being "transformed" to the
secondary. A lightning strike is a different matter. It will usually
cause an arc from the primary lead that is closest to the core to the core.
The lead will often be vaporized.


In spite of having a fancy microprocessor based Sony SW-77 to do my
SWLing on, I find using this old 'boatanchor' type radio irresistible.
After I finish up grad school (which I am starting rather late in life -
age 46) I plan to go for a ham license and possibly look into using
other BA gear.

They are a hoot! Welcome to the BA addiction/disease.

-Chuck