Cobra 139XLR TR36 Relocate

Cobra's Technical Bulletin 1218 describes how to relocate TR36 using a modification kit. We all know that kit isn't available anymore. The interesting part is that the boys at Cobra went gonzo over moving the transistor when they really didn't need to. TR36 is a power source for the led display. As the transitor heats up, the heat can make the adjacent crystals shift in frequency. The easiest thing to do is move TR36 off the little sheild plate and onto the actual frame of the radio. The frame is steel and much thicker. The area under the channel selector is perfect as a new location.

		The move is simple. Find the legs of TR36, unsolder them and remove the hardware that attaches it to the sheild plate. The collector circuit has a 56 ohm 2 watt resistor in series with the +12 volt supply. It's wrapped in an insulating material asn sits just behind the transistor which is WAY TOO CLOSE to the adjacent crystals. My suggestion is to also remove the resistor because it will generate heat too. Bending the legs on the resistor allow it to be soldered to the center (Collector) of the remounted TR36. I like to use silicon pads instead of mica and compound. The pads never dry out like the compounds do. The original bolt, insulating washer, nut and lock washer can be reused in the new location. The base of TR36 connects to a wire that runs back through the old location hole and is soldered to a 10k resistor R152. You can see the resistor in the super sized picture. It's just behind the 2SA719 transistor. The emitter is connected to a wire that runs to a un-used hole (R151) that is on the same pad as two existing wires. The open side of the 56ohm resistor connects to a wire that is run back to the original PC board hole that the resistor came from (+12vdc).
This is the original location.	Here's TR36 relocated

KB2UMJ at Y a h o o dot com

9/2/2014

Another shot of the relocation

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