[ARC5] power supply hum

[Tim]

Yep - That should do it !!!
Tim

On Thu, Jan 22, 2015 at 7:21 PM, Scott Robinson <spr at earthlink.net> wrote:

> ...and another way to get rid of whiskers is this:
>
> DISCONNECT ALL CIRCUITRY FROM THE CAP FIRST, except the frame ground!!!
>
> Take a 300V power supply, put a 10K resistor in series with it, and apply
> that from stator to ground. Now rotate the shaft back and forth and watch
> the nice light show. When the light show stops, the whiskers are really
> gone. Watch where you put your fingers...
>
> So long as you disconnect ALL wiring to the capacitor except the frame
> ground, this will do no harm. I learned it from a 92 year sold radio
> repairman here in San Francisco and have used it to good effect.
>
> /scott
>
> On 1/22/15 5:47 PM, Tim wrote:
>
>> Also, beware of the possible presence of "tin whiskers" growing on the
>> variable capacitor plates.  Those drove me nuts on a GRC-9 receiver until
>> I
>> figured it out - one whisker shorted out the local oscillator section at
>> some tuning positions. The cap plates were apparently tin plated...
>> Practically invisible, a few microns in diameter, and were pretty
>> resistant
>> to removal with an air duster can...  Some interesting physics going on
>> with those little linear crystals.
>>
>> Tim
>> N6CC
>>
>> On Thu, Jan 22, 2015 at 5:30 PM, Kenneth G. Gordon <
>> kgordon2006 at frontier.com
>>
>>> wrote:
>>>
>>
>>  On 23 Jan 2015 at 8:12, Leslie Smith wrote:
>>>
>>>     DS suggested I look at the tuning gang, and I intend to return to
>>>> this
>>>>    area.
>>>>
>>>
>>> It could be that the plates are not centered, or there is a bent plate,
>>> that is
>>> shorting the cap when it reaches a certain point.
>>>
>>>     The LO works when the tuning is set to around 200kHz.
>>>>    The LO stops working when I tune the set above 270 .. 280 kHz.
>>>>    I put the CRO on the oscillator plate lead.  ( see 15 to 20 volts
>>>> RMS)
>>>>
>>>> I put the CRO on the oscillator grid (triode section, pin #5).
>>>> I see nothing.
>>>>
>>>
>>> That would not surprise me. Unless you are using a very high-impedance
>>> probe, or an RF probe, you will be shorting out anything that "is" on the
>>> grid.
>>>
>>> Ken W7EKB
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