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 Post subject: Zenith 7S232, getting ready
PostPosted: Nov Mon 18, 2019 4:03 am 
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Joined: Nov Sun 17, 2019 8:32 pm
Posts: 4
Location: Lafayette, IN
Hello, everyone. This is my first post so, up front, let me say that I’ve found that this site is a great resource for the “crash course” I’ve been taking to prep electrically a Zenith I’ll be talking about. I’ve noticed the willingness of this group to share their knowledge with anyone who hopes to keep these beauties performing.

I’d like to share some thoughts about getting this very nice Zenith 7S232 up and running. Except for the capacitor on top of the chassis and power cord, I think it’s quite original.

I haven’t powered it up yet. I have no idea of its state when last powered down.

Rather than having this radio sitting around looking pretty, I’d like to see it working. For this radio, I realize that all of the capacitors will need replacing and the resistors will need to be checked. I’ve purchased both, referencing the schematic.
I understand that if the tubes are pulled, the transformer can be powered up incrementally to check for overheating. When the radio is ready, it will be powered up the same way.
I have a variable transformer that has a digital meter to monitor volts and amps and it’s accurate.

Further, I’d like to keep this radio as original as possible so I won’t change anything on the topside of the chassis. I hope only replacing the capacitors will be enough but we’ll see.

The chassis is out of the cabinet. I’ve gone through the shutter dial, freed up the “clock” gearing, cleaned the tubes, and replaced the grommets on the variable condenser. I think I’m at the capacitor replacement stage.

If anyone is wondering, it has the 6U5 tube. It needs two small knobs. A few photos will follow.

David
Lafayette, IN

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 Post subject: Re: Zenith 7S232, getting ready
PostPosted: Nov Mon 18, 2019 5:02 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 26159
Location: Detroit, MI USA
With a little searching, you can probably find an original electrolytic (bad of course) to mount on top of the chassis strictly for appearance, and install the new ones underneath the chassis.

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Dennis

Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Zenith 7S232, getting ready
PostPosted: Dec Sun 08, 2019 6:18 am 
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Joined: Nov Sun 17, 2019 8:32 pm
Posts: 4
Location: Lafayette, IN
Hello, folks. Would someone be so kind to offer me some direction in regard for soldering the wires on the C17, C18, and C19 caps I’m replacing? I have replacement capacitors that are polarized and I’m unsure how they should be oriented, considering the flow of things. There’s nothing on the schematic that I understand that directly depicts caps being polarized. I realize that it’s possible I should install non-polarized caps instead.

The C17 capacitor I’m replacing wasn’t original. Its negative lead, which was also connected to the capacitor body itself, was soldered to the candohm as in the schematic.

C18 (to the left of the candohm in schematic) and C19 were in the can on top of the chassis. But still, I’m not positive about where the negative and positive wires should be soldered.

Also, is the center tap here going to the candohm considered to be HV and labeled B+? I have yet to apply power to the transformer.

Any insight is very much appreciated!
David

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 Post subject: Re: Zenith 7S232, getting ready
PostPosted: Dec Sun 08, 2019 2:59 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 26159
Location: Detroit, MI USA
The center tap of the HV secondary on the power transformer is always the most negative point in the circuit. In this case that is also the left end of the candohm's 300Ω section. The remaining taps on the candohm are all still negative, but less negative than the CT of the HV winding.

The filament of the rectifier tube in this set is the most positive point. B+ is the circuitry connected to the speaker field.

Therefore, as drawn on the schematic, C 17, 18, and 19 all have their negative ends at the top of the symbol, and their positive leads are at the bottom of the symbol.

Also, make sure that you have the speaker plugged in any time you apply power to the set. Bad things can happen if it isn't.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Zenith 7S232, getting ready
PostPosted: Dec Sun 08, 2019 4:57 pm 
New Member

Joined: Nov Sun 17, 2019 8:32 pm
Posts: 4
Location: Lafayette, IN
Thank you, Mr Detrola, for your reply explaining the theory for me along with the answer I was looking for. It's very much appreciated. I was very much leaning toward the negatives being "up" but something made me unsure. I've gathered lots of tidbits on this site and gained another with your mention of needing the speaker to be plugged in at power up.

Here's where we are today. Replaced the resistors and capacitors up until the confirmation of the 3 electrolytics, (one is in). The untouched original brown plastic caps/resistors here, I understand, are mica so I left them alone. If someone says I'm wrong, I'll change them. I trust the group here. There are two resistors buried under the band selector switch that would be unreachable unless a lot of unsoldering is done. (2nd photo, one is to ground). And, I'm going to replace the candohm with ceramic resistors after reading the opinions here.

David
Lafayette, IN

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 Post subject: Re: Zenith 7S232, getting ready
PostPosted: Dec Sun 15, 2019 6:11 pm 
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Joined: Nov Sun 17, 2019 8:32 pm
Posts: 4
Location: Lafayette, IN
Hello! Finished with replacing the aged components under the chassis including the candohm section. So, with the chassis on its side and all of the tubes removed and speaker plugged in, I gradually increased power to the transformer to see if it would overheat. It seemed fine, so for the real test I installed the tubes and applied power in stages going up to 117v. All the tubes were lit but not a peep from anything. Socket voltages were good in some places but off the scale in others. Not knowing what to do next, I took my time and went through them again. No change of course but while pondering what the next step should be, I was startled when out of the blue, the speaker came to life! With a short wire for an antenna, it received a station! I’m happy about that!

I immediately began to wonder what triggered the radio to work: was something loose or shorting but became resolved, even if temporary? Did the transformer warm up and change its state for the good? After an overnight cool down, the radio fires up fine. Anyway, there’s more to be done. The indicator tube isn’t glowing green at all and, at this point, I don’t know about what to expect for receiving signals other than by doing through the alignment.

David


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