开云体育

Ballast Resistors? Source?

Richard Oscoda Member Profile All Messages By This Member #31531 Edited Hello all, I am rebuilding a Hallicrafters SX-122. ?Two of the three ballast resisters are broken. ?Where do I find replacemets? ?
Dave Jordan All Messages By This Member #31532 Edited Amazon, eBay, Mouser toggle quoted message Show quoted text On Sat, Jan 18, 2025 at 1:28?PM Richard Oscoda via <upmeharties51=[email protected]> wrote: Hello all, I am rebuilding a Hallicrafters SX-122.? Two of the three ballast resisters are broken.? Where do I find replacemets? ?
thoyer All Messages By This Member #31533 Edited 开云体育 I buy most of my resistors and caps from Dave at ? Less expensive then Digikey and Mouser. ? Take some time and tidy up that soldering as well………. ? Tom W3TA toggle quoted message Show quoted text From: [email protected] <[email protected]> On Behalf Of Richard Oscoda via groups.io Sent: Saturday, January 18, 2025 1:28 PM To: [email protected] Subject: [HallicraftersRadios] Ballast Resistors? Source? ? Hello all, I am rebuilding a Hallicrafters SX-122. ?Two of the three ballast resisters are broken. ?Where do I find replacemets? ?
Richard Oscoda Member Profile All Messages By This Member #31534 Thanks for the supply lead. The soldering is messy because I was removing a huge yellow capacitor that is not on the schmatic. ? Showing my ignorance; can I create a 600ohm Axial Ceramic Cement Power by using two 300 Ohm in parallel? ?Also, the 10 percrent figure is more desireable than 5 percent?
Jim Whartenby All Messages By This Member #31535 Edited Checking the math and calculating resistor power ratings using the voltages found in the manual: Power (R43) = (265v - 150v)^2 / 6000 ohms = 2.2 watts, which at 5w is a X2 safety margin.? OK Power (R-69) = (265v - 205v)^2 / 1500 ohms = 2.5 watts, which at 5w is a X2 safety margin.? OK Power R-68) = (305v - 265v)^2 / 300 ohms = 5.3 watts, which is not good design work when using a 5w part.?? It seems that R69 should be at least a 10 watt part so that it too has a X2 safety margin! It also looks like the dreaded previous owner left C99 A, B & C in the circuit and poorly tacked soldered the replacement for C99B in parallel with the original filter capacitor.? To add to the problem, the location of the new replacement filter capacitor blocks the radiated heat form the three 5 watt power resistors.? So there is no wonder why R68 and perhaps R69 failed.? I assume that the only remaining good 5 watt resistor is R43 and it still measures close to 6k ohms? Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy On Saturday, January 18, 2025 at 12:52:22 PM CST, Dave Jordan via groups.io <wa3gin@...> wrote: Amazon, eBay, Mouser toggle quoted message Show quoted text On Sat, Jan 18, 2025 at 1:28?PM Richard Oscoda via <upmeharties51=[email protected]> wrote: Hello all, I am rebuilding a Hallicrafters SX-122.? Two of the three ballast resisters are broken.? Where do I find replacemets? ?
Jim Whartenby All Messages By This Member #31536 This is not a precision circuit so the extra money spent for a 5% part means little, 10% is good enough. I think that you mean to parallel two 600 ohm 5 watt resistors to make up a 300 ohm 10 watt resistor?? That is OK as long as you have enough room in that area.? I would place the two resistors side by side, not stacked.? If you plan to leave the original filter capacitor can in place, find a new location for the three replacement filter caps so that they do not block the radiated heat from the power resistors.? Heat is always the enemy of reliability. Regards. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy On Saturday, January 18, 2025 at 02:07:10 PM CST, Richard Oscoda via groups.io <upmeharties51@...> wrote: Thanks for the supply lead. The soldering is messy because I was removing a huge yellow capacitor that is not on the schmatic. ? Showing my ignorance; can I create a 600ohm Axial Ceramic Cement Power by using two 300 Ohm in parallel? ?Also, the 10 percrent figure is more desireable than 5 percent?
Richard Knoppow All Messages By This Member #31537 In SERIES, parallel will give you half the value. Maybe this was a typo. Generally speaking the closer the tolerance the better, i.e. 5% is better than 10% but the actual value is what is important. Resistors and capacitors are often closer to their nominal value than the tolerance limits. Using resistors or capacitors in either series or parallel will tend to average out their values, i.e. improve their accuracy. But, not always, a bunch from the same lot may all be high or low and using them in series or parallel won't improve the overall accuracy. For many applications in old radios the original resistors were only about 20% accuracy, more modern units are almost always 10% or better. If you are replacing low power carbon composition resistors use modern carbon or metal film ones, they are much better and will last forever. Modern plastic film caps are much better than the original paper caps and both are probably cheaper. toggle quoted message Show quoted text On 1/18/2025 12:07 PM, Richard Oscoda via groups.io wrote: Thanks for the supply lead. The soldering is messy because I was removing a huge yellow capacitor that is not on the schmatic. Showing my ignorance; can I create a 600ohm Axial Ceramic Cement Power by using two 300 Ohm in parallel? ?Also, the 10 percrent figure is more desireable than 5 percent? -- Richard Knoppow Los Angeles WB6KBL SKCC 19998
Richard Oscoda Member Profile All Messages By This Member #31538 Jim, thanks for setting me straight. I realize I would need to wire two 300 Ohm in series to get 600 Ohms. I can find 300 Ohm 5W 10 percent? Axial Ceramic Cement Power Resistors easily enough but have not found a 600 Ohm listed yet. I will replace the big silver can capacitor as I suspect that is where the failure occured.?
Richard Oscoda Member Profile All Messages By This Member #31539 Richard, thanks for getting me untangled. I am studying for tech, I was a novice back in 1980, so relearning things. I asked about the 300 Ohm pair in series because I can find 300 Ohm? Axial Ceramic Cement Power Resistor 5W easily but not 600 Ohm. ?Thanks for clearing up the 5 per cent vs 10 per cent tolerances. ?
don Root All Messages By This Member #31540 开云体育 If Jim is right about R-68 {I have not looked at the circuit}? we should be worried about R68 wattage.? As Jim says. A related thing;? when these were produced, what was the rated temperature rise and rated ambient temp used in the standards? And what is it now?? In general it seems that replacement resistors are now smaller in surface area, so they must run much hotter ?than originals, which also means that they will tend to over-heat neighboring components if allow to run hot . I am no expert on this, but if anyone has real data on these standards I would like to see it. ?Of course there might be various standards too. ? -- don??? va3drl
Richard Oscoda Member Profile All Messages By This Member #31541 I take the point about the wattage. I will go to a 10W resistor in the appropriate resistance.?

Previous Topic Next Topic