So once again we're back to the infamous Tempo 2020. When we last visited this hybrid backwater I was adding a remote VFO . Many thanks to @N4PL Wald , @W7CPA Randy , bajapac , and Fantom the wonder dog... The molex plugs are common and available locally. Possibly because of not having to deal with the heat of the radio the external VFO has far less drift than the internal VFO. Now onto other irrational and unexplained behavior. Ever seen a switched RCA jack? Any of us with 2020's have. That wasn't it. The headphone jack wasn't it. The phone patch wasn't it. I quit looking and found receive audio at the card edge connector and called it a day. Now on to the unscheduled programming. RF derived ALC should not clamp a pair of 6146's down to 20 watts output. For testing purposes D362 on the PC-078 IF board has been lifted interrupting the ALC signal from Q1001 on the PA board. Full output results. With an annoying hum. I'm chasing the audio down looking for an audio or ground loop. Temporarily using my MC-50 for a High impedance mic . Most of the hum goes away but it is still visible (and audible) on a nearby web sdr. Several questions arise from the service manual and schematic. R388 on the PC-078 IF board appears to adjust the meter ALC, does R387 adjust the actual ALC ? I wonder if increasing the feedback resistor, increasing the gain of the audio chip has anything to do with the hum. PC-080 card, replace R551 with a 15k resistor instead of the 6.8K . Great gain improvement but ... So If any of this makes any sense I'd appreciate the input.
If you might be interested here is the link to my 73 Magazine review article on the Tempo 2020 Feb. 78 pg. 48. (pg 37 on the pdf) http://ia600708.us.archive.org/3/items/73-magazine-1978-02/02_February_1978.pdf
Thanks Dan but unfortunately the link breaks the browser on this machine :-/ I wouldn't be surprised at all if I've seen that link before. I have pretty much devoured everything I could find on the 2020. https://archive.org/stream/73-magazine-1978-02/02_February_1978#page/n35/mode/2up
