Re: Halicrafters SX17 transformer
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John There are various catalogs from replacement transformer manufacturers, I looked at STANCOR and THORDARSON, for example.? There are others.? I have not looked at my junque box so there are still other possibilities. ? STANCOR? model PC8420 / PM8420 (same transformer, different mounting) has the following specs: 2 1/2 inch by 2 9/16 mounting hole spacing 325 - 0 - 325 volts @ 150mA 5 volts @ 3 amps 6.3 volts @ 5 amps
THORDARSON? model 22R05 2 1/2 inch by 3 1/8 inch mounting hole spacing 300 - 0 - 300 volts @ 120 mA 5 volts @ 3 amps 6,3 volts @ 5 amps
Another transformer of interest is the one found in the Hewlett-Packard 200CD audio oscillator.? This might be available either locally to you or on eBay?? It has 115 - 230 volt split primary windings which is a plus. PAECO model 910-94 2,5 inch by 2.34 inch mounting hole spacing 315 - 0 - 315 volts @ 125 mA 5 volts @ 2 amps 6.3 volts @ 3.55 amps.? It should do 4 amps with no trouble. This is an over designed power transformer with very conservative ratings so it should fit the bill but it's mounting is upright not horizontal like that in the SX-17.? It also contains a 8H @ 125 mA filter choke.? The manual is available on-line, with photos.? I have a history with this transformer.
Regards, Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Thursday, May 30, 2024 at 05:28:29 AM CDT, John via groups.io <siloam@...> wrote:
I completely forgot about noting the current on the low voltage windings! I added up the heater currents and arrived at the same 3.9A that you did. In addition to this, according to the data-sheet, the heater for the rectifier on the 5V winding takes 3A.
For the exercise, I also tried calculating the valve currents according to the cathode voltage and the cathode resistor. I did struggle to understand how to apply that for the 6R7 and the 6J5, but was able to do calculations for some of the other valves. The meter amplifier valve also puzzled me since the 95ohm resistor and 10V cathode voltage would suggest 100mA or thereabouts, but the data-sheet states that the maximum running current for the 6J7G is 2mA, so that didn¡¯t make sense. For those that I was unsure of, I just used the value from data-sheet and arrived at somewhere around 150mA which is in a similar ball-park, although in all probability there are errors in my calculations. The values for first two 6K7¡¯s were also curious as they come to approximately 12mA (8/700) which is more than the 10mA shown on the data-sheet. There is, of course, R1, the RF gain control in series, but one would presumably have to assume the highest case at minimum setting? It would seem that the valves can be pushed pretty hard at that setting.
I struggled a bit with the transformer screw positions but they seem to be placed 100mm (4 inches) apart on the long side and 77mm (3 inches) apart on the short side. Removing the transformer would allow me to make more precise measurements, but that will have to wait for another day or two until I am feeling well enough. I came down with some kind of bug a coulple of days ago.
Anyway, thank you for your help and for taking the time and trouble to confirm the calculations.
As a matter of curiosity, what catalog are you looking at please?
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Jim Whartenby