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 Post subject: Germanium output transistors -- can these cause 60Hz hum?
PostPosted: Feb Tue 04, 2020 10:08 pm 
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Can failing germanium output transistors cause 60Hz hum in a 1960s era Zenith solid state console? Or is 60Hz hum more likely to be a grounding issue?


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 Post subject: Re: Germanium output transistors -- can these cause 60Hz hum
PostPosted: Feb Tue 04, 2020 10:28 pm 
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Joined: Jan Thu 16, 2020 12:29 am
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zenithconsole wrote:
Can failing germanium output transistors cause 60Hz hum in a 1960s era Zenith solid state console? Or is 60Hz hum more likely to be a grounding issue?


Technically possible if there was a failed one in a power supply regulator, but not likely in the amplifier itself.

Grounding issues can cause hum.

But in the context of the most likely thing to do it, is failing electrolytic capacitors. But I'm guessing you asked the question because they were already replaced ?

Output transistors cannot cause hum themselves, though if there was excessive output stage current it could overload the power supply perhaps, but that would be obvious from voltage tests and the transistor's temperature.


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 Post subject: Re: Germanium output transistors -- can these cause 60Hz hum
PostPosted: Feb Tue 04, 2020 10:38 pm 
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Location: Annapolis, MD
Hum....AKA the 60 or 120 Hz AC component of a node voltage is too high.
Causes:
(filter) capacitance too low.
Current load too high (this includes the filter cap leaking)
Common mode resistance too high...eg a bad ground.

Everyone's favorite place to start is filter capacitors.

_________________
-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Germanium output transistors -- can these cause 60Hz hum
PostPosted: Feb Tue 04, 2020 10:54 pm 
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Joined: Apr Sun 16, 2017 7:57 pm
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I recapped the amp (including 3 new surface mount filter caps) but not the tuner preamp.

Hum existed prior to recap and remains after recap.

Photos of recap here: viewtopic.php?f=6&t=370826&start=20

If I listen to the TAPE OUT (line out) from the tuner/preamp, the hum is not present, suggesting the hum is occurring after that point.

Any trouble-shooting ideas are welcome.


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 Post subject: Re: Germanium output transistors -- can these cause 60Hz hum
PostPosted: Feb Tue 04, 2020 11:26 pm 
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Can you post a link to the schematic?

"Surface-mount" electrolytics??--- never seen THAT before....

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-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Germanium output transistors -- can these cause 60Hz hum
PostPosted: Feb Tue 04, 2020 11:34 pm 
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Joined: Apr Sun 16, 2017 7:57 pm
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pixellany wrote:
Can you post a link to the schematic?

"Surface-mount" electrolytics??--- never seen THAT before....


Hi Mark

Please see link to schematic in the first post of this thread: viewtopic.php?f=6&t=370826

By surface mount, I mean can caps. EIA codes indicated they were manufactured by Mallory and GE. I replaced two of these with Nichicon snap ins and the multi section can with a Hayseed can stuffed with Nichicon radials.


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 Post subject: Re: Germanium output transistors -- can these cause 60Hz hum
PostPosted: Feb Tue 04, 2020 11:46 pm 
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Joined: Jan Thu 16, 2020 12:29 am
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The usually protocol for fixing a problem like this is to simply sit down with it, with a scope, and go through the signal pathways and check the power supply. For checking the power supply for ripple the scope is simply used with a x10 probe and its input attenuator set for AC coupling initially and winding up the scope gain to measure the ripple. You would soon find where the hum signal is originating.

Without a scope you have to use "indirect methods" like using a capacitor to shunt AC signals to ground to attempt to find where the issue is arising. You appear to have done a very competent job of re-capping it, so the next step, if you work on amplifiers a lot, is to get 1) signal generator, 2) scope & 3) dummy speaker load and the world will be your oyster.


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 Post subject: Re: Germanium output transistors -- can these cause 60Hz hum
PostPosted: Feb Wed 05, 2020 10:06 am 
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Joined: Apr Sun 16, 2017 7:57 pm
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How common is it for solid state rectifiers to fail? If one of the two was going bad, could it cause 60Hz hum?


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 Post subject: Re: Germanium output transistors -- can these cause 60Hz hum
PostPosted: Feb Wed 05, 2020 2:07 pm 
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Location: Utica, NY 13502 (USA)
Please post all questions and comment about this radio in the original thread.

https://antiqueradios.com/forums/viewto ... 6&t=370826

Multiple topics about the same radio are not allowed in order to keep the discussion in one place.

Dave


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