--------- Begin forwarded message ----------
From: km1h
To: measures@vc.net
Subject: Re: [AMPS] Band Switch Heath SB-1000
To: <amps@contesting.com>
Date: Sat, 26 Apr 1997 16:32:38 PST
Message-ID: <19970426.163531.8935.21.km1h@juno.com>
References: <19970426202131.AAB24433@[205.231.11.143]>
On Sat, 26 Apr 97 13:25:25 -0800 Rich Measures <measures@vc.net> writes:
>>Get the switch from Ameritron...it is a PnP replacement.
>>
>>Then quit underloading the amp; that is the major cause of zapped
>>switches. Load it up to maximum obtainable output with 100W of drive.
>>Then back the drive ONLY down until you have ~ 800W. Do not reduce
>power
>>with the amp controls.
>>There is something amiss in the basic design...same as the AL-80...
>that
>>causes zapped switches when underloaded.
>>
>>73...Carl KM1H
>
>This was apparently not the case in the zapped bandswitches whose
>photographs are available on my Web site.
>http://www.vcnet.com/measures
> Unless showered with spilt coffee, the AL-80 and the SB-1000
>bandswitches can withstand over 5500v.
I believe you are wrong about the switch specs Rich....those are simply
the old Centralab 2500 series as used in the SB220, etc. They are only
rated at 1500V AC 60 Hz much less 5.5Kv. Customized options such as fiber
shafts can raise the specs to 2500VAC max. I suspect you are confusing
the JV series switches. Both styles have new designations under
Electroswitch but I'm more comfortable with the old CRL designations.
The piv in typical use is
>under
>2900v. Statements about tank voltage soaring off into the heavens
>during
>mistuning makes zero technical sense to me. In a mistuning test, the
>measured piv increased a bit under 30% maximum. However, the settings
>to
>produce this condition were far, far removed from the settings that
>produced max. RF to the antenna, which is how most folks tune an
>amplifier.
That statement only holds true...with reservations....when you are
dumping into a purely resistive load. Reactances as are typical with some
ham antennas can transform that voltage to very high levels....if the
load is not absorbing power the tank voltage can approach that calculated
in the UNLOADED Q of the circuit...not the magic Q of 12. You were close
the other day when you mentioned the Tesla Coil effect. The actual
voltage can vary between both extremes.
>--.Carl: Have you measured the VHF suppressor resistance in an
>amplifier
>that came in for repair with a crispy-crittered bandswitch?
No, the old suppressor usually gets trashed anyway and I use my own
version for a replacement. Time is money and my customers bitch when I do
R&D on their nickle. After 5,10,20 years any carbon comp resistor is
going to change value when subjected to even its rated dissapation at DC.
Severe changes in value I have found, and mentioned here months ago with
nary a response, are usually indicitave of high levels of RF above
50MHz....parasitics, harmonics or whatever. Those 2W carbons just do not
like VHF heat period.
73....Carl KM1H
>Rich---
>
>R. L. Measures, 805-386-3734, AG6K
>
>
>--
>FAQ on WWW: http://www.contesting.com/ampfaq.html
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>
--------- End forwarded message ----------
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|