Zenith Console combo

[JB5pro]

Originally Posted by DaveWM

Picked this up yesterday, dont know when I will get to it, but at least I will have it when ready.

That is the one I mentioned that was from Boca Raton. Glad it got saved!

[DaveWM]

while playing with the tuner I checked the phone input, seems like a lack of separation going on, seems like there is some signal leakage.

I am thinking decoupling or some other power supply problem. I will put a scope on the B+ supplies and see how much signal modulation is there if any.

[ctc17]

my ctc17 combo lost stereo separation too. I use the tape input for the cable box.

I figured it was a burnt or failed ground somewhere but you bring up a good point.

O, btw... on both my zenith combos with the same tuner, the bass is mono and the high end is stereo.
I never questioned it because thats the way systems with subwoofers are setup. There should be little to no stereo information in the bass and it makes sense to have it monoed out.

[DaveWM]

its goofy. I put in a signal 400hz into the left channel thru the phono, then I scope the base of the left transistor and compare to the base of the right. WTF the signal is about 1/3 the Left.

there is a network of resistor that connect the two bases togehter on mine its a 56k/22k/56k. I removed the transistors from the sockets and check the resistance, total was about 160k which would make since after accounting for drift there was nothing else in the circuit but for the disc coupling caps.

I dont know why this would be the case, but I can clearly see the 400hz on the base and of course the collector of the right channel.

I wonder if there would have been any reason to tie the two channes together?

[DaveWM]

I will check the replacement tuner if it does the same thing then between us thats 3 that lack decent separation, and maybe its just the design.

If so I may be inclined to see what I can do to break that connection and see what happens. Worst case is I muck up a few transistors, but since they are in sockets, big deal....

what bugs me is to go thru all the effort in the mpx to separate the channels just to throw them back together in the amp.