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Title: Who in there right Mind? Post by: N8ETQ on September 18, 2013, 12:40:41 PM Found this on the primary side of power xfmr in an AL-80A.. Amazing! The guy even strapped another 10 ohm 10 w across it after this one melted! One Dam tough "R"... I found a bunch of bad diodes.. Never saw one melt like that. /Dan Title: Re: Who in there right Mind? Post by: KL7OF on September 18, 2013, 01:13:17 PM Looks like it melted because of RF......not current overload..???
Title: Re: Who in there right Mind? Post by: N8ETQ on September 18, 2013, 03:42:26 PM after a little more "pokin'" around it looks like part of a Harbach Soft Start install gone Wild... I think you need to get a diff. R for 110VAC on those. Nice clean little amp. Hope the guy didn't ruin it. God never intended for a medium power amp to run off 110 VAC. Can I get an "Harrumph"? /Dan Title: Re: Who in there right Mind? Post by: KA9EGW on September 18, 2013, 04:23:37 PM Harrumph!
Title: Re: Who in there right Mind? Post by: WQ9E on September 18, 2013, 04:55:08 PM When anyone installs one of these mods there needs to be a fuse that will open if the relay fails to short across the resistor after the "soft start" period. I have seen a couple of cases where damage was done from resistor shrapnel with this style of modification.
Title: Re: Who in there right Mind? Post by: N8ETQ on September 18, 2013, 10:10:03 PM Good Idea Rodger, An appropriate SLO-BLOW in series with the "R" that also gets jumped out by the relay should do it easily. This could be the first time I've used my Tektronics current probe! Thanks, /Dan When anyone installs one of these mods there needs to be a fuse that will open if the relay fails to short across the resistor after the "soft start" period. I have seen a couple of cases where damage was done from resistor shrapnel with this style of modification. Title: Re: Who in there right Mind? Post by: WQ9E on September 19, 2013, 11:59:41 AM Dan, AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
You are welcome. If you are rebuilding the circuit you might also consider using a relay with an extra set of contacts for the step start circuit and use one set of contacts in series with the T/R line so that the amp cannot go into transmit mode until the step start relay closes. I set up my homebrew amplifiers this way. |