I will add one other thing about heat. Heat by itself is bad enough but the worst part is the almost microwave heating effect that a PA has when it's turned on and off. It super heats when turned on and cools very fast when turned off. This has a tendency to rip the guts out of most transistors and PC boards due to the expansion and contraction.
Quintron found this out and was one of the few that made their 900 MHz PA decks dependable. Paul -----Original Message----- From: skipp025 [mailto:[EMAIL PROTECTED] Sent: Tuesday, January 04, 2005 10:45 AM To: [email protected] Subject: [Repeater-Builder] PA heat issues > "Gary" <[EMAIL PROTECTED]> wrote: > My MSR has the TLD2532A 110 watt intermittent PA. NCD > is more my terminology (non continuous duty) than > anything else. I got into the habit of refering to > an intermittent PA as non continuous duty (NCD) > by hanging around another tech that used it. > He was also the one that filled me in on MSRs' PA > history. (however right or wrong the info was) No problem Gary... Heat is a killer of electronics... your pa is continuous duty, just at reduced power levels. People don't realize any reflected and high foward power results in fast heat build up. The low duty cycle pa has a problem with heat build up in lock to talk (repeater operation). > I was running my first PA at 60 watts when it failed. Were the power control board V-limit and I-limit pots properly set? It should have shut itself down when trouble started. > The only thing different that I'm doing now than > before, is I am using fans to blow air out of the > cabinet top side vents, plus a fan blowing across > the PA heat sink fins. Before, I was just blowing > accross the heat sink fins only. I'm not sure how > efficient the PA heat sink fan is, because I had > to do some creative engineering to get a fan mounted > to blow up the fins from the bottom. Sucking air up and out of the MSR Cabinets, through the top side air vents is the best option. You can remove the cabinet lid and covers without a lot of grief. It takes the proper size torex bit and ratchet. I use small metal bar stock to mount small ~4 or 5 inch dc fans across the vertical rails at the vent level. The cover slips right over the fans, which are triggered by extended cos logic and a timer. > My site owner requires repeaters to be in cabinets > with covers on, and you would know how little room > there is to get a fan mounted to blow on the MSR > PA with the front cover on the cabinet and still > do some serious air movement. Your site owner is smart... yes, I know about the limited cabinet room. Hence the above fan mounting information. > It does work and looks somewhat professional. > This repeater was getting heavy use at the first > PA failure, but now not as much use. This may > have something to do with its'longevity now. > Gary KB7TRP 73's Gary, skipp Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
