In article ,
Carter-k8vt wrote:

Let me toss you a minor curve ball: If you were repairing this
radio in its era, you would indeed be looking for a replacement
transformer with approximately a 270-0-270 high voltage secondary
winding; this is because it was designed for 110 volts AC coming
out of the socket on your wall.

John Byrns wrote:

How can we be sure it was designed for 110 volts AC coming out of the
socket on the wall?

Well, I can't "be sure". See below.

But that is really irrelevant because the schematic says the voltages
were measured with 117 volts AC coming out of the socket on the wall,
not 110 volts AC.

I would humbly offer in my defense that I do NOT have the schematic for
this radio, nor did I try and find it on line. I just went by the
partial schematic sent by the original poster which
made NO mention of 117 volts.

Today, that voltage is 115 to 120 volts or even a bit higher and
using -today's- line voltage with a 270-0-270 winding would give
you a bit more than the 265 volts DC B+ that you are looking for.
So, what I am saying is that you could (should?) look for a
transformer with a 220-0-220 or 250-0-250 high voltage winding;
i.e. less (than 270-0-270) is better.

The specifications listed with the schematic say the radio is
designed to operate with voltages coming out of the socket on the
wall of 105-120 volts AC, which would seem to cover "today's" voltage
of 120 volts.

Again, I do not have the schematic so I cannot read what you are
quoting. However, I would respectfully suggest that the 117 volt figure
they quote is a NOMINAL number. Although I was probably either not yet
born (or was very young) when this radio was new, it is my best
understanding that, GENERALLY SPEAKING, line voltages were
(significantly?) lower back then and higher today, no matter what was
printed on the schematic. Also, please note that I stated "could
(should?) look for a transformer with a 220-0-220 or 250-0-250 high
voltage winding". So I -did- try and leave a little "wiggle room". :-)


Unless the OP has a voltage greater than 120 volts AC coming out of
the socket on his wall I would think he should go for a transformer
to the original spec. Also if his line voltage is high, going for a
transformer with a lower voltage high voltage winding is going to do
nothing to bring down the heater voltage to normal.

But isn't "half a loaf better than none"? Instead of having the B+ AND
filament voltage be high, you would at least be making the B+ lower.

Going from 110 volts primary to 120 volts will raise the B+ from 265 to
290 volts, while raising the filament voltage from 6.3 to 6.8+ volts.
Neither is a desirable situation, but I personally would rather have the
lower B+. Your mileage may vary.

If this is really an an important issue, what he should do is look
for a transformer with a tapped primary, unfortunately these don't
seem to be as common as they once were when the transformers in some
equipment had taps for low and high line voltage as well as the
nominal line voltage.

Agreed! Theoretically, a tapped primary would be the perfect solution;
-realistically-, that ain't gonna happen. Realistically, the choice is
between both high B+ AND high filament voltage versus just high filament
voltage. You pays yer money and you takes yer pick...

Regards and Happy New Year,
Carter K8VT