>
>Hello: It is bad engineering to accept bad efficency and compensate with
>cooling. Regarding the SB 220 switches, HEATH may have changed later from
>the original yaxley receiving type ones - I do not know.
The bandswitch used in the SB-220 was never a receiving type. The
switch mfg.'s current rating was 15A @50/60Hz. The insulation was always
ceramic. The withstanding potential was c. 5000v.
> I am worried about
>the current capability of those tiny paralellt receiving type switch
>contacts. Definitely no more than a few amperes I am sure.
>
Definitely not a good bet.
later, Hans
>----------
>>Från: measures <2@vc.net>
>>Till: "Phil Clements" <philk5pc@tyler.net>, "AMPS" <amps@contesting.com>,
>"Larry Molitor" <w7iuv@nis4u.com>
>>Ämne: Re: [AMPS] Coil heating
>>Datum: sön 25 jun 2000 21.21
>>
>
>>
>>>
>>>> The curious part of this whole business was the location of the heating.
>>>> With turns on BOTH sides of the tap involved, I have to wonder what,
>>>> exactly, was going on there. In the past, when I've melted down tank
coils,
>>>> the heating (and deformation) was confined to the center of the active
area
>>>> of the coil. Has anyone else seen this effect?
>>>>
>>>IMO, the heating was at the tap point, spreading out each way. Chances are
>>>the "black" area would have spread with time.
>>>
>>>There has been mention on the reflector of directing cooling air on a coil
>>>to prevent "melt down." This does nothing about the losses due to under-
>>>engineering. RF is being converted into heat and does not reach the antenna.
>>>Heat can be eliminated by selecting the proper components for the job to
>>>be done.
>>
>>Copper has a positive temp. coefficient. The hotter it gets, the more
>>resistance. Cooling air is helpful.
>>
>>> Hans and I are in agreement....there is a limit to how small you can
>>>make an RF deck.
>>>
>>>The same is true about band switches. One must take into consideration not
>>>only the voltage and current rating, but also the distance between contacts
>>>when selecting the proper component.
>>>
>>? Measuring the actual withstanding voltage is not a bad idea.
>>
>>cheers, Phil
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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