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1964 Zenith Console tube preamp SS amp left channel went out!

B

Brownie Mix

New Member
Hello everyone!
I have a 1964 zenith console stereo with a tube preamp and solid-state amp. I’m redoing it for a buddy of mine. When he brought it to me I opened it up cleaned and lubed all pots and switches. Replaced all the burnout lamps with warm white LEDs and installed a DAC to the tape-in terminal. looked over everything really well. The caps and solder joints look to be in good shape. EVERYTHING looked fine. put it all back together was working great. Took it to him And he listened to it for a couple days, and the lights went out. So I went and pulled the amp and preamp out brought it home. Figured it was a fuse or something, but it worked fine when I plugged it all up at my house. So I took it back to him. He listened to it for a couple hours and went to adjust the presence knob and he said he heard a little bit of a pop and then the left speaker channel is not working now. I went and grab it again was originally thinking the output transistors, but I swapped those back-and-forth and it didn’t seem to matter. So any ideas if it would be in the preamp? I can’t find a schematic on this thing so it’s a little bit of a head scratcher plus I’m a little new to the whole tube thing as far as working on them. I threw in some pics. Thanks in advance. Oh I should add that. He told me when the lamps all went out stereo was still working, so not really sure what happened there.
 

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Brownie Mix said:
Hello everyone!
I have a 1964 zenith console stereo with a tube preamp and solid-state amp. I’m redoing it for a buddy of mine. When he brought it to me I opened it up cleaned and lubed all pots and switches. Replaced all the burnout lamps with warm white LEDs and installed a DAC to the tape-in terminal. looked over everything really well. The caps and solder joints look to be in good shape. EVERYTHING looked fine. put it all back together was working great. Took it to him And he listened to it for a couple days, and the lights went out. So I went and pulled the amp and preamp out brought it home. Figured it was a fuse or something, but it worked fine when I plugged it all up at my house. So I took it back to him. He listened to it for a couple hours and went to adjust the presence knob and he said he heard a little bit of a pop and then the left speaker channel is not working now. I went and grab it again was originally thinking the output transistors, but I swapped those back-and-forth and it didn’t seem to matter. So any ideas if it would be in the preamp? I can’t find a schematic on this thing so it’s a little bit of a head scratcher plus I’m a little new to the whole tube thing as far as working on them. I threw in some pics. Thanks in advance. Oh I should add that. He told me when the lamps all went out stereo was still working, so not really sure what happened there.
Click to expand...
Forgot to mention chassis # 10M9T25Z-8MT25
 
Search Samswebsite.com for a schematic. Might be in 766-12.
Looks like Lots of old caps and other parts that could be the problem.
There are some threads here on old Zeniths that may be of use too.
 
Bradbrews said:
Search Samswebsite.com for a schematic. Might be in 766-12.
Looks like Lots of old caps and other parts that could be the problem.
There are some threads here on old Zeniths that may be of use too.
Click to expand...
Brad Thank you. I think I have ruled out the amp being the problem. I might try to hook another preamp but I will need to rig some wires for the funky plugs. I’ll check the SAMS site as well. Thanks
 
Being that you have a hybrid unit with tube tuner and a transition to solid state somewhere in between a schematic would sure be easier!
Do any inputs work now? Are any different than others?
Many times consoles have pictures of the tube layout and other valuable information. If you are lucky enough they even have a schematic tucked away inside.
Have you looked?
 
Bradbrews said:
Being that you have a hybrid unit with tube tuner and a transition to solid state somewhere in between a schematic would sure be easier!
Do any inputs work now? Are any different than others?
Many times consoles have pictures of the tube layout and other valuable information. If you are lucky enough they even have a schematic tucked away inside.
Have you looked?
Click to expand...
There is a schematic on the back of it, but it just shows what type of tubes doesn’t say what tube drives what. Like I said the right speaker works fine. The left speaker no longer works, but it did before. I’ve powered off and unplugged a tube, powered it back on And it still works on the channel so doesn’t seem like any of the tubes are affecting the signal and I swapped all of them back-and-forth and it did not help the left channel. I did download schematic from Sam website.com so I’m starting to tackle it now. Looking at the schematic, I think I can hook up another preamp to the correct leads and see what happens .
 
You might try exercising or cleaning the internal speaker selector switch, they cause a lot of problems on these models, also press all of the function buttons,
Especially the stereo and mono buttons.
As someone above pointed out, there are a number of old electrolytics that should be changed.
I don't think a different preamp will work because the Amp gets its negative feedback from the preamp section.
 
One other thing, the tubes are for the tuner, the preamp has transistors, those small silver button looking things near the center, they are in sockets, wiggle them or remove them and put them back one at a time.
 
orthophonic said:
One other thing, the tubes are for the tuner, the preamp has transistors, those small silver button looking things near the center, they are in sockets, wiggle them or remove them and put them back one at a time.
Click to expand...
Thanks. Yes I found out the tubes are for tuner only. I did swap the little transistors for left and right channel and the left channels worked fine in the right so they are fine. Like I mentioned in the first post he said it was working fine and he adjusted the presence knob and he heard a pop and the left speaker stopped working. so I’m thinking it’s a capacitor but they all look fine and as you know there’s hundreds of them. I don’t believe there is a speaker selector switch. I’m about to give up. I’ve stared at this and tested on it for 2 1/2 days now. I just hate it when I can’t fix something lol
 
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