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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