On Jun 7, 2006, at 1:22 PM, Joe Subich, W4TV wrote:
> What do you base the 390 V and 2600 V peak?
Measurements with an oscilloscope and a 49.9-ohm termination, sending
50wpm dits on the SSB tap.
> 1500 W peak is 274 volts peak SQRT(1500*50).
Hams and the FCC - do not measure peak W, they measure PEP, which is
an RMS measurement. For example, 400v-pk into 50-ohms = (0.707 x 400)
^2 / 50-ohms = 1600w PEP.
> If you
> want to allow for SWR, 2:1 VSWR represents 548 volts.
> The voltage across the open tap of the band switch will
> depend on circuit Q, number of shorted turns as well as
> the mutual coupling between those turns and the rest of
> the coil ... and don't forget any mistuning. If the
> antenna relay is dirty, doesn't make good contact, or
> is mistimed the voltage across the band switch can reach
> as much as 5 KV even without any VHF parasite.
How did you measure the 5kV? The original Tune-C in a SB-220 has a
measured BD-V of c. 3600vdc at sea level. How could "as much as 5kV"
get past the Tune cap, Joe? A famous amplifier expert claimed that
10kV could appear across the bandswitch if a 220 is overdriven. Do
you believe that?
> 4900 volt DC breakdown simply doesn't cover it at 15
> or 20 meters.
It's true that BD-V decreases as f increases, but the question is how
> ... Joe, W4TV
>> -----Original Message-----
>> From: firstname.lastname@example.org
>> [mailto:email@example.com] On Behalf Of R L Measures
>> Sent: Wednesday, June 07, 2006 5:32 AM
>> To: firstname.lastname@example.org
>> Cc: email@example.com
>> Subject: Re: [Amps] SB-220 Plate Tuning Capacitor
>> On Jun 6, 2006, at 9:03 AM, Peter Chadwick wrote:
>>>> From what Colin told me in a private email, it seems to me that
>>>> the SB220 bandswitch is right on edge for the kW input power
>>>> level, and too small at 1500 watts for safety.
>> The measured breakdown potential of a SB-220 bandswitch is c. 4900v
>> at sea-level. At 390v peak output into 50-ohms, the actual
>> potential across open bandswitch contacts is c. 2600v-pk.
>> R L MEASURES, AG6K. 805-386-3734
>> Amps mailing list
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