sb101,102,hw101.

[Keith Rowland]

People, I am not sure there is really a problem with this line voltage.  Most
of the older stuff was designed to operate from 105-125 VAC.  What's the
problem?

Keith

"Gerald C. Lemay" wrote:

> Let me see if I understand this. Assuming a transformer was designed for
> 110VAC input to get 12.6VAC means a ratio of 12.6/110=0.1145. So with
> 125VAC line you would get 0.1145 X 125=14.32V. So if you want to drop the
> heater voltage down to 12.6V, let's assume a heater current of about 5A.
> To drop 1.72V at 5A, R=1.72/5=0.34 Ohm. The figures are not in agreement
> with what I read but the approach is a sound one. If your line voltage
> runs high (whatever that means) the proper way to adjust it is by
> measuring the heater winding voltage. That really doesn't apply to me
> because I very seldom go above 122VAC. Line voltage at my place is pretty
> steady at 120VAC plus or minus a couple of volts. I've been trying to find
> out if this business of higher line voltage being used with transformers
> designed for lower input is factual or mythical. The transformer
> manufacturers are not helpful. Even today you see transformer
> specifications with primary line voltage at 115VAC! I'm not sure it was
> ever intended to be a tightly controlled spec. Even tube heater
> characteristics varied from tube to tube and it was not uncommeon to find
> the actual voltage required to draw the speicifed heater current to vary
> by several percent. Back in high school shop class (1967)the lab books
> always specified 117VAC as being typical line voltage.
>
> > In a message dated 2/5/03 3:17:21 PM Eastern Standard Time,
> > w2jjm at MSN.COM writes:
> >
> >
> >> This line of equipment was designed when AC line voltages were much
> >> lower than they are today. If you want a cooler running rig with no
> >> loss of 6ea8 and
> >> 6au6 tubes due to leaks and shorts the solution is easy. In your HP-23
> >> power
> >> supply install four (4) RS-271-131 one (1) ohm 10 watt resistors all
> >> in parallel
> >> in the 12.6 volt feed lead. This 0.25 ohms will bring your two
> >> filament strings
> >> down to mfgs specs of 6.3 vac. If there is any small imbalance left
> >> you may wish to hand pick your pilot lites. Good luck.
> >>
> >
> > James,
> >
> > You are kidding, right?  Is it April fools yet?  12.6V/.25 ohms = 50.4
> > amps, or 635W.  Did you mean 10 ohms? (63.5W, nah)  Did you mean 100 ohm
> > resistors? (6.35W, maybe).  Whatever the value or power drawn, lets not
> > forget to make sure that the transformer can supply this additional load
> > without exceeding its rating, making it run hot, etc...
> >
> > On a hunch I looked at the Shadio Rack site, and yep, you mean 1 ohm.
> > What gives?  Maybe you mean .25 ohm in series?
> >
> > Bob, WB2UJD
> >
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