Larry,
The more components in a circuit, the odds of a failure grow expotentially.
Keep it as simple as possible is the way I was taught, and I think in these
days, we all sometimes over do what really needs to be done. It's the same as
the "build a better mouse trap" scenario. It's like do I use a simple zener
diode regulator circuit which has two components counting the resistor, or do I
use a voltage regulator IC circuit with many more parts in it? Especially when
the simple zener would do the same job just as good. I think that's getting to
be the case in some step start circuits too, when a simple diode, resistor, and
capacitor will control the time of a relay coil as good as using some
complicated circuit using an IC timer, etc.
Best,
Will
*********** REPLY SEPARATOR ***********
On 9/19/06 at 5:44 PM Larry Carman wrote:
>Bob, I must agree that overall simplicity is in most part a ham's best
>friend when it comes to amplifiers. Fewer components mean fewer problems.
>Many modern legal limit amplifiers allow no error for excess anything. The
>old engineering traits of doubling the power handling capabilities of each
>component have gone to the way-side. Many new amps have a mangle of
>circuitry, supposedly to depress any spikes, parasitic, etc, BUT, I hear
>too
>often of many new amps failing due to problems that these circuits should
>have managed before damage occurred. If tube grids had adequate power
>dissipation, some of the tube protection schemes would be unnecessary.
>Bob, your Henry is what I call a lifetime amp. We will all probably die
>before it does.
>Regards,
>Larry N5BIP
>
>-----Original Message-----
>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>Behalf Of Bob Maser
>Sent: Tuesday, September 19, 2006 3:02 PM
>To: Ian White GM3SEK; amps@contesting.com
>Subject: Re: [Amps] Step Start on a 3KA Amp
>
>Please remember that this thread started by me asking about a step start
>in
>a 30+ year old amplifier from Henry, the 3KA. There are a lot of things
>that could have been done differently in this amp but it is a rock solid
>amp
>
>that will put out the legal limit and then some all day long. Try that
>with
>
>some of the modern day Kleenex amps.
>
>Bob W6TR
>----- Original Message -----
>From: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
>To: <amps@contesting.com>
>Sent: Tuesday, September 19, 2006 2:48 PM
>Subject: Re: [Amps] Step Start on a 3KA Amp
>
>
>> Phil Clements wrote:
>>>
>>>
>> Will had written:
>>>> The first 1 to 5 cycles is the worst part of the surge, but from tests
>>>> that was run by a ham on this mailer, the transformer didn't settle
>down
>>>> until 30 to 40 cycles. This was captured on a storage scope and I have
>>>> the
>>>> results here somewhere saved as a jpeg photo. Anyhow, a 1/2 second
>delay
>>>> is about all that's needed on the step start. I'd say they used this
>>>> heater cone over its greater power rating than would be a 25 watt or so
>>>> resistor.
>>>
>>>The reason for the cone heater instead of a 25-50 watt resistor is that
>>>this
>>>is a "manual" step-start circuit on the Henrys. It only has three parts;
>a
>>>cone heater, a switch, and the operator's hand. As the switch is rotated
>>>from off to on, it allows the mains current to flow through the cone
>>>heater,
>>>step-starting the power supply. Since it is possible for the operator to
>>>screw up and leave the switch in a position that the cone heater is
>still
>>>in
>>>the circuit, it required a robust resistance in order to stand the
>>>continuous duty in a situation like this. Some folks who don't read the
>>>Henry manual think this is a "hi-lo" or "SSB-CW" power switch instead of
>a
>>>step-start, and try to operate the amp in the intermediate switch
>>>position.
>>>Even the robust cone heater has its limitations (300 watts-1000 watts,
>>>depending on the model) and will fail open after this abuse goes on for a
>>>period of time. A savvy operator, when turning on the amp, will pause in
>>>the
>>>intermediate switch position until the HV meter gets up to 3/4 of its
>>>final
>>>normal value. This will usually take less than one second. At any rate,
>>>when
>>>the HV meter has come to a stop during turn-on, the "step-start"
>function
>>>is
>>>complete, and the switch should be moved to the "on" position
>immediately
>>>to
>>>prevent over-heating of the coil on the cone heater.
>>>
>>
>> Sounds a bit primitive - no wonder it needs that big resistor! With so
>> many well-known ways to make a completely automatic step-start, it seems
>> a really strange decision to use a manual switch and leave the whole
>> thing wide open to operator error.
>>
>> Replying to Will's comment also, a step-start is really only about the
>> first few big cycles of inrush current. There is no point in waiting
>> until the current has "settled down" to the last few percent before
>> switching the surge resistor out. All it does is heat up the resistor,
>> with no real benefit to the power supply components.
>>
>>
>>
>> --
>> 73 from Ian GM3SEK
>>
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