sb101,102,hw101.

[Gerald C. Lemay]

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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