: Zenith Y960 hum  ( 1099 )

BRETTZKY99

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Zenith Y960 hum
« : October 08, 2020, 12:16:23 PM »
i've got a Y960 with a bad 60hz hum on all audio inputs.   turning up the volume drowns it out but the hum is still there between tracks or at lower volume

i have re-cappped the amp and the tuner, still hums.

the only way to decrease the hum has been to add a ground wire between the amp and the center of the tuner.  even then, the hum is still there but it's much more quiet

it's been a frustrating process.   Does anyone have any thoughts or advice on this matter?

electra225

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Re: Zenith Y960 hum
« #1 : October 08, 2020, 12:28:50 PM »
Did it hum before your re-capped it?  Could you possibly have a floating ground somewhere, like at a filter cap, perhaps?
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BRETTZKY99

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Re: Zenith Y960 hum
« #2 : October 08, 2020, 12:36:54 PM »
Did it hum before your re-capped it?  Could you possibly have a floating ground somewhere, like at a filter cap, perhaps?

yes, i was hoping the re-cap would cure the hum but it's still there.

TJ

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Re: Zenith Y960 hum
« #3 : October 08, 2020, 12:47:39 PM »
Almost sounds like an electrolytic capacitor got wired in backwards and is therefore not doing any filtering.
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BRETTZKY99

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Re: Zenith Y960 hum
« #4 : October 08, 2020, 12:58:33 PM »
Almost sounds like an electrolytic capacitor got wired in backwards and is therefore not doing any filtering.

thanks

to be clear, you're suggesting it was a miswire at the factory and hummed for ~50 years before I found it?

or you're saying it was miswired during the re-cap by following the original factory wiring?

TJ

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Re: Zenith Y960 hum
« #5 : October 08, 2020, 01:14:32 PM »
From the sheet that you attached, it looks like there was a bad filter cap, which was replaced during the recap, and That would have caused the initial hum that you described pre-recap.  The hum after the recap could be that an electrolytic was wired in backwards, could have became disconnected inside the can that was re-stuffed, or one of them could have simply gone bad prematurely, it does happen.

I don't like re-stuffing cans for this very reason, it makes it harder to diagnose if there is an issue post recap.  I like leave the cans in place for aesthetics, and put the new caps on the underside of the chassis incase they were to need diagnosed or replaced for whatever reason in the future
My Consoles:
1962 Motorola SK112CW-FM, All original tubes
1958 Magnavox Continental - DIY Concert Grand!
1957 Magnavox Brittany - Amp 148 Magic!

BRETTZKY99

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Re: Zenith Y960 hum
« #6 : October 08, 2020, 01:22:17 PM »
The hum after the recap could be that an electrolytic was wired in backwards, could have became disconnected inside the can that was re-stuffed, or one of them could have simply gone bad prematurely, it does happen.

I don't like re-stuffing cans for this very reason, it makes it harder to diagnose if there is an issue post recap.  I like leave the cans in place for aesthetics, and put the new caps on the underside of the chassis incase they were to need diagnosed or replaced for whatever reason in the future

thanks, did you have a chance to see both photos i attached?  new caps were added under the chassis, the original cans were not restuffed.

TJ

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Re: Zenith Y960 hum
« #7 : October 08, 2020, 02:13:33 PM »
The top of your sheet of work done clearly says that 3 cans were rebuilt.  That's what I was going off of.
My Consoles:
1962 Motorola SK112CW-FM, All original tubes
1958 Magnavox Continental - DIY Concert Grand!
1957 Magnavox Brittany - Amp 148 Magic!

BRETTZKY99

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Re: Zenith Y960 hum
« #8 : October 08, 2020, 02:31:59 PM »
The top of your sheet of work done clearly says that 3 cans were rebuilt.  That's what I was going off of.

understood, thank you!

electra225

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Re: Zenith Y960 hum
« #9 : October 08, 2020, 03:32:14 PM »
I can't clearly see the markings on the new caps you installed so......


Assuming you have them wired right (they look right from what I can see) may I suggest you bridge the filters with other electrolytic caps of slightly higher capacity and higher voltage.  Perhaps you have an under-capacity filter cap.  I've had that happen in the past.  One gets mismarked, or is defective right out of the box.  It's worth a try, costs nothing and will lay to rest any question of defective/miswired/under capacity filter caps.



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electra225

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Re: Zenith Y960 hum
« #10 : October 14, 2020, 07:41:51 PM »
Has there been any progress on locating the hum?  Inquiring minds want to know......... ;)
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turbineoil

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Re: Zenith Y960 hum
« #11 : April 26, 2021, 02:41:48 PM »
Has there been any progress on locating the hum?  Inquiring minds want to know......... ;)

I have a Y960 with the same issue.  Hummed before the recap.  Hummed after the recap. 

Was chatting with Senior Steve last year. I set aside the project for awhile.  Going to install new rectifier diodes and capacitor that goes across them. 

Hum is on all inputs regarding of volume.

Hiss is present but changes characteristic in relation to the volume control.

TC Chris

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Zenith Y960 hum
« #12 : April 26, 2021, 04:29:54 PM »
Hum on all inputs?

Chris Campbell

turbineoil

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Zenith Y960 hum
« #13 : April 26, 2021, 09:04:11 PM »
Hum on all inputs?

Chris Campbell

Hi TC Chris,

Yes - hum on all inputs.  Appears to be 60Hz.  100% of the electrolytic capacitors in both the tuner/preamp and amp were replaced. 

It hummed before the recap and after the recap.  It does sound better after the recap though. Two capacitors were completely dead on the tuner preamp chassis.

The transistors on the tuner / preamp chassis are silicon.   But the transistors on the amp chassis are germanium.  Swapped transistors from right to left and didn't notice a difference.

Here are the germanium transistor readings:

Output transistor #1

Current gain hFE = 10
Test current. iC=2.5mA
Based -Emitter V. Vbe = 0.183V
Test current Ib=4.756mA
Leakage current Ic= 0.178mA

Output transistor #2

Current gain hFE = 13
Test current Ic= 2.5 mA
Based -Emitter V. Vbe = 0.180V
Test current. Ib = 4.759 mA
Leakage current = Ic = 0.299mA

Output transistor #3

Current gain hFE=11
Test current IC=2.5 mA
Based -Emitter V Vbe = 0.179V
Test current IB = 4.73mA
Leakage current Ic= 0.255mA

Output transistor #4

Current gain hFE = 13
Test current. Ic= 2.5mA
Based -Emitter V. Vbe = 0.180V
Test current. Ib= 4.759mA
Leakage current = Ic = 0.299mA

Driver 1

Current gain hFE = 62
Test current. Ic= 2.5mA
Based -Emitter V. Vbe = 0.207V
Test current. Ib= 4.734mA
Leakage current = Ic = 1.081mA

Driver 2

Current gain hFE = 46
Test current. Ic= 2.5mA
Based -Emitter V. Vbe = 0.178V
Test current. Ib= 4.763mA
Leakage current = Ic = 0.905mA
[/quote]

TC Chris

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Zenith Y960 hum
« #14 : April 28, 2021, 09:05:30 PM »
On early transistor radios and TOs, Zenith kindly used transistor sockets.  If your amp has them you can pull transistors until the hm stops to identify which stage it's coming from. But you said "regardless of volume," so it's likely after the volume control.  If no sockets, start lifting wires to see when the hum stops. Or use a signal tracer?  My first signal tracer was a high-impedance headphone with a .05 mfd cap in series.

Chris Campbell