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 Zenith 5-S-126 Electrical question

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pred



Posts : 18
Join date : 2010-10-14

PostSubject: Zenith 5-S-126 Electrical question   Thu Oct 14, 2010 2:13 pm

I have been tinkering with a Zenith 5-S-126 Cube lately, I have run the set for a couple hours and plays real strong, BUT here is what's bugging me.
Notice in the diagram the 240 Volts off the rectifier tube @ 112 Volts seems a bit odd.
I ran the variac down to 91 Volts to achieve that low number, But then the heaters were at 4+ or so volts.
I am now running the set at 109 Volts and the heaters are at 5.8 VAC and 267 VAC on the B+ and 287 VDC.
Now dont go and quote me, I ran these numbers a few days ago and cant remember them exactly, But these #s are close enough.
Here's the diagram.
http://www.nostalgiaair.org/resources/887/M0024887.htm
I have another of the exact same set, But dont really feel like fighting the rubber mounting washers again in the cube radio.
Does something seem fishy here to you?
Like the Nostalgia Air diagram is wonky?
I was going through withdrawal with ARF down.
Glad this is here for the time being.
Now, Tell me what's going on.
OH, Set completely recapped and new resistors where needed.
Peter
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tubes4life



Posts : 33
Join date : 2010-10-12
Location : northern Florida

PostSubject: Re: Zenith 5-S-126 Electrical question   Thu Oct 14, 2010 2:50 pm

If I'm not mistaken, the standard back then was 117 volts...so 112 does seem like it would be a typo.

But you've still got voltage discrepancies. Did you measure the secondaries on the power trans to see what it's putting out?
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Johnny



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PostSubject: Re: Zenith 5-S-126 Electrical question   Thu Oct 14, 2010 11:33 pm

I just completed a restoration on a 5-S-126 cube. It's completely done and works great. In fact it's still sitting on one of my benches. Been listening to it every day. It was a complete resto with everything replaced, cleaned etc. etc.

So what you're asking is that with the paperwork showing a line voltage of 112 volts that the 240 volts at the rectifier is not correct?

I definitely agree with Peter. Check that power transformer. All of my voltages were well within tolerance of the paperwork. All a bit high but very normal with todays higher line voltages. If I can be of more help just ask. Like I said it's still on the bench but it is all assembled and in the cabinet.

Johnny
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pred



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PostSubject: Re: Zenith 5-S-126 Electrical question   Fri Oct 15, 2010 5:01 am

OK I will try and get a peak tonight,
But with rectifier tube pulled, What do you get at B+ Pins to chassis?
Peter
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Dave McClellan



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Join date : 2010-10-13

PostSubject: Re: Zenith 5-S-126 Electrical question   Fri Oct 15, 2010 5:55 am

I have raised this issue of high B+ values on the forum before. I just finished restoring a Zenith 6S223. The rated line voltage is 117 volts. At 115 volts in (through a variac):
B+ at Rectifier: 331 (spec is 322)
B+ at 6F6 screen: 267 (spec is 247)
B+ at 6F6 plate: 252 (spec is 231)
B+ at 6A8 plate: 267 (spec is 245)
B+ at 6A8 osc plate: 237 (spec is 200)

So I would not DARE run this radio at our NORMAL line voltage of 123 volts!

The original input filter capacitor was 16mfd - I used 22mfd (measured at 22.5). Output filter was 20mfd (again, I used 22mfd). This may account for some difference.

It seems that ALL Zeniths I have restored have much higher than rated B+ voltages. I don't think the specified 1000 ohms/volt meter vs a modern DVM would account for the difference when measuring power supply voltages. Since my line voltage is 123 volts, I always use a bucking transformer when playing my radios - 115 volts input.
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smeezekitty

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Location : Washington/USA

PostSubject: Re: Zenith 5-S-126 Electrical question   Fri Oct 15, 2010 11:00 am

Dave McClellan wrote:
I have raised this issue of high B+ values on the forum before. I just finished restoring a Zenith 6S223. The rated line voltage is 117 volts. At 115 volts in (through a variac):
B+ at Rectifier: 331 (spec is 322)
B+ at 6F6 screen: 267 (spec is 247)
B+ at 6F6 plate: 252 (spec is 231)
B+ at 6A8 plate: 267 (spec is 245)
B+ at 6A8 osc plate: 237 (spec is 200)

So I would not DARE run this radio at our NORMAL line voltage of 123 volts!

The original input filter capacitor was 16mfd - I used 22mfd (measured at 22.5). Output filter was 20mfd (again, I used 22mfd). This may account for some difference.

It seems that ALL Zeniths I have restored have much higher than rated B+ voltages. I don't think the specified 1000 ohms/volt meter vs a modern DVM would account for the difference when measuring power supply voltages. Since my line voltage is 123 volts, I always use a bucking transformer when playing my radios - 115 volts input.
How is it at 110?
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tubes4life



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Location : northern Florida

PostSubject: Re: Zenith 5-S-126 Electrical question   Fri Oct 15, 2010 8:23 pm

pred wrote:
OK I will try and get a peak tonight,
But with rectifier tube pulled, What do you get at B+ Pins to chassis?
Peter

I would think that with the rectifier pulled, you would have 0 volts B+.
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Wcirco

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Location : naptown

PostSubject: Re: Zenith 5-S-126 Electrical question   Fri Oct 15, 2010 8:28 pm

tubes4life wrote:
pred wrote:
OK I will try and get a peak tonight,
But with rectifier tube pulled, What do you get at B+ Pins to chassis?
Peter

I would think that with the rectifier pulled, you would have 0 volts B+.

I think he means at the rectifier plates. should be around 300VAC at the plates of the rectifier to ground.
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