<html><head><style> body {height: 100%; color:#000000; font-size:12pt; font-family:tahoma,new york,times,serif;}</style></head><body><br>I expect the worst spikes occur when the PS is switched off and the primary happens to be at max voltage.<br>Don't skimp. A shorted cap will ruin the xfmr, if there isn't a good fuse.<br>WL<br><br>----- G3OOU--- via Heath <heath@puck.nether.net> wrote:<br>> <br>><br>> <br>><br>><span id="role_document" color="#000000" style="font-family: Arial" size="2;"><br><br>><div>Hi Doug<br>><div> <br>><div>I think that you are referring to C59 across the high voltage secondary of <br>> mains transformer T-1. This capacitor must have a voltage rating in excess of <br>> 1.414 times the rms voltage across it plus an allowance for the mains supply to <br>> rise to its maximum tolerance and then some additional contingency. The <br>> 1600v rating seems very reasonable to me.<br>><div> <br>><div>You can get high voltage ceramic capacitors and use two or three in <br>> parallel to make the total capacitance required.<br>><div> <br>><div>I assume that the original capacitor was intended to reduce spikes from the <br>> mains as it is a large value and probably the wrong type of construction for <br>> high frequency RF decoupling.<br>><div> <br>><div><font lang="0" face="Arial" size="2">73<br></span><span color="#0000ff" lang="0" style="font-family: Arial" size="4;"><em><br>Bob</em></span><em><span color="#000000" lang="0" style="font-family: Arial" size="2;"></span></em><span color="#000000" lang="0" style="font-family: Arial" size="2;"><br>Bob F Burns G3OOU, <br>> G-QRP 6907, @BobFBurns<br>Crystal Palace Radio & Electronics Club: <a href="http://www.g3oou.co.uk/" target="_blank">www.g3oou.co.uk</a><br>Technical web site: <a href="http://www.qsl.net/g3oou" target="_blank">www.qsl.net/g3oou <br>><div> <br>><div><br>><div>In a message dated 25/10/2017 01:30:10 GMT Standard Time, <br>> dkdavies3@gmail.com writes:<br>><blockquote style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><font color="#000000" face="Arial" size="2" style="BACKGROUND-COLOR: transparent"><br>><div dir="ltr">I need to replace a buffer capacitor in the power supply <br>> rectifier circuit in an old HW-10 Shawnee I'm trying to restore. It is a <br>> paper cap, oil filled and the value is 0.047uf @1600 volts. I can find a <br>> 0.047uf one but nothing rated at 1600 volts. Is this a critical value or <br>> can I replace it with a polypropylene one rated at 650 volts? <br>><div><br><br>><div>Doug<br>><div>VE7DRF<br><br>_______________________________________________<br>Heath <br>> mailing <br>> list<br>Heath@puck.nether.net<br>https://puck.nether.net/mailman/listinfo/heath<br></span></blockquote></a></font></font></body></html>