Laryn Lohman wrote: > A Z matcher's purpose is basically to maximize the efficiency of the > amplifier. So with our repeater transmitter (VHF), which is two amps > rated at 225 watts when combined, I adjusted them for minimum current > draw at max power out. As you adjust, you'll soon find combinations > that substantially reduce the current draw with no loss in power out.
I like this idea. Might as well try it. :-) > I've also added fans to the heatsinks and to the component side of all > (3) amps in this transmitter. Power out is set to 180 watts and so > far, zero trouble in 7 years. I admit that my experience with these > amps is much more limited than yours, Nate, so my <luck> may catch up > some day. I want to add fans too. I know the things are EIA rated for 100% continuous-duty, but the number one killer of RF power transistors is internal metal migration due to heat... so shedding heat in any way possible seems like a good idea. Interestingly, most PA's are also only rated for continuous-duty at full power output up to 10,000' MSL. With one site here at 9,000' MSL and the other at 11,440' MSL and two others around 8500' MSL, I figure they're all running in the "harder to cool" end of the specification band. All above 85% of the rated altitude numbers. So cooling has been a worry for a while, but I haven't fashioned something I "like" for mounting fans on them. I've seen a number of used MASTR II PA's with fans tie-wrapped to the front cover... that would certainly help too, I suppose. Even Crescend only specs up to 10,000' MSL, and their commercial stuff (while pricey) is well-respected here in the list and off. Then add our insidious lightning, and I'm sure they're being abused... to some extent. But frankly, even if I have more "experience" than you do, all I've been accomplishing is blowing them up -- ha! -- so I might as well try other ideas! (To be honest, out of frustration a couple of our techs pointed out that one of our systems ran for close to ten years on a Henry PA, and that the PA was still in the club's storage -- otherwise known as my basement. I called Henry and they offered to modify it for a 1/4W input and re-tune it to the problematic site's frequency critically on their bench for less than $100... so off it went. It's back from Henry and sitting here tempting me to go put it in and see what it can do. The physical mounting is a problem at that site, so I don't know if it's worth trying or not. Out of curiosity, anyone reading along running any Henry PA's on their systems, or have any thoughts on the idea?) Nate WY0X
