Author	[Modern View]
David Bean 08-19-2012 13:18:38 24.126.223.218 Report to Moderator	Years ago we used to use a variable resister or rheostat to slowly bring an old short wave or ham radio to life by starting with low voltage and increasing it over a period of time. Don't know if that is still something that is done to old equipment. Friend found an old Halicrafter short-wave radio, tube type, and wants to see if it will work. I have a rheostat, it's actually a gang of three, each about the size of a softball. Seems I remember using it for this before. Not sure about the wiring to get lower voltage. Picture of the rheostat wiring schematic and wiring terminals below. To get lower voltage (this would be 110v ac) wouldn't I connect the source 110v to terminals 1 and 4 and the load to terminal 3 and 1 (or 3 and 4)? Looks like terminals 5 and 2 provide a fixed step down voltage??? Forgive my memory. Used to know all this stuff but it's been 30+ years since I messed with it. [Reply]   [No Email]
David Bean 08-19-2012 14:46:54 24.126.223.218 Report to Moderator	Re: OT - Rheostat wiring in reply to Colin King, 08-19-2012 13:18:38   That's sounds familiar. Thanks for the quick responses JMOR.   [Reply]  [No Email]
JMOR 08-19-2012 14:27:51 72.181.173.171 Report to Moderator	Re: OT - Rheostat wiring in reply to Plane Bart, 08-19-2012 13:18:38   I think that is a fair assessment. Usually rheostat is a 2 terminal variable resistor, generally for higher current levels than potentiometers (3 terminals). Yours is neither, however, as it is more of a transformer with taps at every winding, selected by rotating the knob to position a sliding brush over the windings. Variac must be used on AC only, whereas a rheostat or potentiometer doesn't care, AC or DC.   [Reply]  [No Email]
David Bean 08-19-2012 14:00:55 24.126.223.218 Report to Moderator	Re: OT - Rheostat wiring in reply to David Bean, 08-19-2012 13:18:38   If #4 did not exist, for example?   [Reply]  [No Email]
JMOR 08-19-2012 13:54:45 72.181.173.171 Report to Moderator	Re: OT - Rheostat wiring in reply to JMOR, 08-19-2012 13:18:38   " If there was only one tap on the resistive side it would be a rheostat, right?" Sorry, I don't follow what you mean here?   [Reply]  [No Email]
David Bean 08-19-2012 13:47:01 24.126.223.218 Report to Moderator	Re: OT - Rheostat wiring in reply to david G, 08-19-2012 13:18:38   Thanks JMOR! OK...that sounds right to me. If there was only one tap on the resistive side it would be a rheostat, right? I think that stuff is still in my head, if I could just get to it!   [Reply]  [No Email]
JMOR 08-19-2012 13:36:00 72.181.173.171 Report to Moderator	Re: OT - Rheostat wiring in reply to Spade - IN, 08-19-2012 13:18:38   David Bean said: (quoted from post at 16:18:38 08/19/12) Years ago we used to use a variable resister or rheostat to slowly bring an old short wave or ham radio to life by starting with low voltage and increasing it over a period of time. Don't know if that is still something that is done to old equipment. Friend found an old Halicrafter short-wave radio, tube type, and wants to see if it will work. I have a rheostat, it's actually a gang of three, each about the size of a softball. Seems I remember using it for this before. Not sure about the wiring to get lower voltage. Picture of the rheostat wiring schematic and wiring terminals below. To get lower voltage (this would be 110v ac) wouldn't I connect the source 110v to terminals 1 and 4 and the load to terminal 3 and 1 (or 3 and 4)? Looks like terminals 5 and 2 provide a fixed step down voltage??? Forgive my memory. Used to know all this stuff but it's been 30+ years since I messed with it. Not that it matter a lot but that is a Variac or variable transformer, whereas a rheostat is a variable resistor. 1,4,3 are what you want, since if you involve 2/5 you would be able to adjust to something higher than line voltage input, which would likely be very bad for your radio. This post was edited by JMOR at 13:37:59 08/19/12 2 times.   [Reply]  [No Email]