V4, a tube that has to do with FM tuning, just died. Dead. Off. No heat. I don't care about FM, but is it safe to run my receiver without that 6AU6?
I was careful in removing and cleaning them as suggested, using removal techniques I googled and a disposable antistatic cloth (no finger contact). V4 worked for a few minutes before I saw it cool down.
Anyways, most tubes are indeed original, several were replaced with Telefunken tubes and one tiny metal one I overlooked before is Sylvania. I found
this thread which names this as McIntosh's first receiver. I'm going to try what they specify there since I have pretty much all the same problems. I now realize that I'm missing 4 dummy plugs that should be on the phono inputs.
Tomorrow I'm going to get a better multimeter and test each and every resistor and capacitor that doesn't have to do with stuff I don't need (RIAA phono stage, FM). Now all I need to do is find where Q15-20 are hiding as they are in the direct signal path and I plan on replacing them. Those 6 transistors are quite elusive.
Edit: Just found this
http://www.audioasylum.com/scripts/d...ubeprimer.html
Quote:
One of the most common causes of problems in older amps (besides tubes)is the b+ filter capacitors. After 20 years or so, these things go BAD!It doesn't matter if the amp was never used since from the day it was built, since capacitors just deteriorate with the passage of time. Macintosh used very good quality caps in their amps, and there are many with original caps out there that are still running fine. |
Very reassuring. Less work (and cost) for me!
Also, scratch the transistor replacement. I doubt a 5 cent fairchild 2n3391a will sound better than what's already in there. If I figure out which are which (they aren't labeled) I'm going to shuffle them around a bit to see if a bad transistor is causing the background hum in the left channel. If not, they stay unless someone corrects my assumption.