"Gene McCalmont" <[EMAIL PROTECTED]> made an utterence to the drakelist gang ---------------------------------------------------------------------- Good Morning Jason; R12 is a "protection" resistor that is the last line of defense between the L-4PS HV section and the L-4B RF deck. The resistor was meant to "blow" if there are problems at the RF deck level to protect the power supply from damage. Since R12 did let go, suspect problems "down stream" from the HV section of the L-4PS rather than the power supply itself. I've seen these go under the following conditions:
1. Overdriving the amp wherein one or both tubes pull too much current causing the resistor to let go. 2. Arching either in the tube(s) or tank circuit caused by either a defective 3-500z or improper tuning and loading of the amp. The arc momentarily draws excessive power through the HV section. 3. Arching at the antenna changeover relay caused by "hot switching". That is, a momentary "stutter" in the keying circuit causing the relay contacts to "bounce". I did this once when mindlessly letting up pressure on a Shure 444 PTT switch while speaking into the microphone. I lost both finals in the T-4Xc and R12. 4. One or more components in the RF deck have shorted to ground causing excessive HV current. Frankly, from your description, I would suspect that this is the most probable problem. I would first unplug everything, remove the bottom cover of the RF deck and do a visual inspection to see if something obvious jumps out. Checking things like bypass capacitors and looking for burnt or cracked resistors are obvious. Also check the antenna changeover relay and other components in the tank circuit for obvious damage. You might just get lucky. Let me know how you do and best regards; Gene W5DDW Gene McCalmont 270 Oak Ridge Ln. Argyle Texas 76226 "Jason Buchanan" <[EMAIL PROTECTED]> made an utterence to the drakelist gang ---------------------------------------------------------------------- hi all, R12 in my L4-PS burned to a crisp. Any ideas why and what I should look for as to why this happened? Amp was working fine when this happened - I powered it off as soon as I noticed the smell. 73 Jason N1SU ---------------------------------------------------------------------- On Behalf of "Gene McCalmont" <[EMAIL PROTECTED]> Submissions: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: http://www.zerobeat.net Brought to you courtesy of TLCHost.net http://www.tlchost.net/ ----------------------------------------------------------------------
