So I was using said unit and it randomly quit transmitting after about an hour of use. The lights on the unit were still on despite it not transmitting. the next day I plugged it in, it worked for an hour and did the same thing.

I have two of these AM60-450 units, one that I re-capped/put new regulators in the power supply and one I haven't yet. So I swapped the PSU from the intermittent unit to the "unrestored" unit. It's been working great for several hours......

Anybody here have their BT modulator quit randomly?

Did you cut a half wave dipole to the transmit frequency? If you didn't and the current antenna is reflecting most of the power back into the BT you could be tripping a protect circuit... especially if the output is cranked.

Been a while since I opened one of mine but if any heatsinked semiconductors exist the thermal paste could have expired.

Also there's lytics in the TX section too... those are not above failure.

Hmmm I didn't think of thermal protection circuits. My antenna is a set of small DTV rabbit ears. I tried a tuned dipole but it didn't perform well. I might try building another one.

Would it be a good idea to use a 75 to 300 ohm balun or just terminate straight to coax?

I followed this video with the exception of using that fancy meter http://www.youtube.com/watch?v=z4dhRt7tmd4
I can send a block radius with this setup. The percentage length he removed to tune it should apply to and channel.