[Collins] 30L-1 Electrolytics

[Dr. Gerald N. Johnson]

Good points. I've not compared the leakage of Atoms vs others. CD has 
been a reliable capacitor maker all my life like Sprague. And both have 
been around longer than me. There have been periods where Chinese makers 
of small electrolytics made explosives instead of capacitors. Package to 
look like and sold to computer board makers as capacitors. I suspect 
very small (farmstead living room) operations that didn't understand the 
details of assembly and forming. Or materials quality. Aluminum with 
foreign metals included doesn't make good capacitors or truck heater 
cores or plumbing and radiators for dehumidifiers. But those are way too 
common today.

The 30L-1 power switch is marginal anyway (especially on 120 volts) so 
increasing the turn on surge can't be a benefit. The transformer can 
probably stand it though it will make noise and the original diodes may 
short. The state of the rectifier art is far better that it was when the 
30L-1 was built. Diodes don't need shunt capacitors for equalizing 
transient reverse voltages and cheap diodes (1N4007) handle a lot more 
surge current and inverse voltage.

There are good reasons for the upgrade board for the 30L-1 power supply, 
modern parts are better.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association

On 1/19/2012 1:21 PM, Carl wrote:
> The key to long life is to completely read the cap specs. Most include
> expected life at rated temperature.
>
> Ive used CDE 381LX series for decades in amp repair work with zero
> failures.
>
> The Sprague ATOM's were leaky from new in comparison and are useful only
> in a "correct" restoration.
>
> I wouldnt deviate too much from the factory C since the surge current
> can annoy switches and marginal transformers unless a step start is
> added. Considering that the tolerance of those old caps and Atom's is
> mostly on the high side the 20uF or so total is sufficient at the low
> current involved in that amp.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- From: "Dr. Gerald N. Johnson"
> <geraldj at weather.net>
> To: <collins at mailman.qth.net>
> Sent: Thursday, January 19, 2012 12:48 PM
> Subject: Re: [Collins] 30L-1 Electrolytics
>
>
>> Look at Mouser catalog pages 823 to 826. One of the limits is ripple
>> current and the more compact the capacitor the less surface area it has
>> to dissipate heat from the ripple current. The higher capacitance part
>> will make the peak ripple currents larger (though the time shorter) and
>> I see in Cornell Dubilier that the 105 C rated caps have a lower ripple
>> current rating than the 85C even though some of the high temperature
>> caps are titled "high ripple current" their ripple current ratings are
>> lower.
>>
>> The Vishay/Sprague axial lead Atoms on page 865 I like for vintage
>> repairs because they have the surface area to dissipate heat like the
>> originals and Sprague was a favored vender half a century ago.
>>
>> Larger capacitors will improve the voltage regulation, at the cost of
>> higher peak currents the original rectifiers may not be able to handle,
>> at the cost of a greater capacitor temperature rise, and difficulty
>> fitting into the volume available.
>>
>> The upgrade boards have been created because the caps to upgrade the
>> original boards don't exist.
>>
>> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.
>>
>> On 1/19/2012 10:46 AM, Byron Tatum wrote:
>>> Hello-
>>> Can someone recommend to me a good replacement electrolytic for the
>>> 30L-1
>>> 100 uFD @ 450 VDC ones? I do not wish to replace the existing PC
>>> board with one
>>> of the upgrade boards at this time.
>>> I was looking at the axial lead capacitors (Mouser, Newark) and there
>>> are
>>> not many offered above 100 uFD. I am wanting to use higher capacity
>>> ones such as
>>> 220 ufd. Is it necessary to use radial lead units on the existing board?
>>>
>>> Any advice appreciated.
>>> Thanks, Byron WA5THJ
>>>
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>
>