[Amps] Fwd: Rectifier equilization?

[Paul Christensen]

Last year, while standing in the boarding line for a flight to Tampa, the 
guy behind me was wearing a Semtech Polo shirt.  He was an applications 
engineer working on an MRI power supply project.  We had a great 
conversation aboard the flight that began with me telling him about my small 
collection of SCH series spare parts and that drifted into a discussion 
about Semtech's current diode array product line.   Their diode 
manufacturing technology has significantly progressed since the 1960s when 
they were producing the SCH series arrays for ETO's Alpha Seventy 
amplifiers.

Although I have enough of the Semtech diode blocks to last the life of my 
two older Alpha amps, I'm sure a quad set of five 1N4007 diodes mounted in 
series on a small PCB would perform just fine as the continuous current 
rating would be double that of the SCH5000.

Paul, W9AC


----- Original Message ----- 
From: "Alex Eban" <alexeban at gmail.com>
To: "'Paul Christensen'" <w9ac at arrl.net>; "'Amps'" <amps at contesting.com>
Sent: Monday, September 16, 2013 6:24 AM
Subject: RE: [Amps] Fwd: Rectifier equilization?


> Semtech were known to be crazy about their diodes.
> I remember Magnavox was using them in the GRC-106 SSB radio at 2400 volts.
> The nly one ever gone was one cracked by over tightening the mounting
> screws. I think that the diode chips inside the pack were way overkill but
> it paid off.
> Alex 4Z5KS
>
> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Paul
> Christensen
> Sent: Sunday, September 15, 2013 6:16 PM
> To: Amps
> Subject: [Amps] Fwd: Rectifier equilization?
>
>
>> As a data point, ETO used a quad set of Semtech SCH5000 "SlimPac" diodes
> in the Alpha 70 and 77 series.  These are rated at 5KV but only 500mA of
> continuous current.
>>
>> It may have been a marginal design, but I don't believe there's been a
> really poor history of diode failure in these amps over the years.
>>
>> Paul, W9AC
>>
>> Sent from my iPhone5
>>
>> On Sep 14, 2013, at 9:44 PM, Jim W7RY <w7ry at centurytel.net> wrote:
>>
>>> I completely agree that 6A10s are real overkill.
>>>
>>> 73
>>> Jim W7RY
>>>
>>>
>>> On 9/14/2013 12:14 PM, Manfred Mornhinweg wrote:
>>>> Bill,
>>>>
>>>>> FYI for next time, 6A10 diodes have become preferred by many for
>>>>> high power use because of their 6 amp continuous and 400 amp surge
>>>>> ratings and moderate cost.
>>>>
>>>> I don't mean to say anything against 6A10 diodes, they sure work fine.
> But they are HUGE overkill. Even if the filter capacitors had zero
> equivalent series resistance, and the power outlet where the amp is
> connected had zero impedance, and there were absolutely no inrush limiting
> system used, and the power were switched on in just the worst possible
> moment (peak of waveform), just the resistance of the HV transformer will
> limit the current to roughly 20 to 30A, or maybe 40A if the transformer is
> really beefy. And such a condition of course doesn't happen in real life -
> specially the line from which the amplifier is powered does have some
> resistance and also some inductance. In practical use, in a normal home, 
> it
> would be really rare to see more than 15A inrush current.
>>>>
>>>> 1N5408 diode has a 200A surge rating, which is still big overkill. The
> humble 1N4007 with its 30A surge rating would be about the right part to
> choose for a cost-conscious builder! It's also comfortable with the 
> average
> current. Rated at 1 ampere average, a bridge rectifier using strings of
> 1N4007 diodes is good for 2 amperes. That gives enough headroom for a 
> legal
> limit amp.
>>>>
>>>> Feel free, of course, to use big diodes, if it gives you peace of mind.
> But it shouldn't be technically necessary.
>>>>
>>>>
>>>> Jim,
>>>>
>>>>> ##  Both my 1N5408 and 6A10  diodes have identical lead diameters.
>>>>
>>>> So do mine.
>>>>
>>>>> Both are I think,   .050
>>>>
>>>> Yes.
>>>>
>>>> Manfred
>>>>
>>>> ========================
>>>> Visit my hobby homepage!
>>>> http://ludens.cl
>>>> ========================
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