On Sun, 27 Dec 1998 12:24:46 -0800 Rich Measures <measures@vc.net>
writes:
>
>>
>>
>>
>>On Sat, 26 Dec 1998 09:39:32 -0800 Rich Measures <measures@vc.net>
>>writes:
>>>
>>>>
>>>>
>>>>
>>>>On Sat, 26 Dec 1998 19:50:02 +0800 Alek Petkovic
><vk6apk@eon.net.au>
>>>>writes:
>>>>>
>>>>>Hi All,
>>>>> A friend of mine in Virginia is having the following
>>>>>nightmare
>>>>>with his SB220. Can anybody help?
>>>>>My SB220 contains a small transformer with two windings. One
>winding
>>>>>supplies the filament voltage for the 3-500zs and the other
>supplies
>>>>>bias and relay voltage at 120volts. One side of the relay coil is
>>>>>connected to this little half wave supply. The other side of the
>>>>>relay
>>>>>coil goes a jack on the back of the linear. When this jack is
>>>>>grounded
>>>>>it closes the relay and the linear goes into the transmit. From
>the
>>>>>banded end of the diode rectifier, a 20ufd, 160 volt electrolytic
>>>>>capacitor is connected from this point to ground. Without this
>>>>>capacitor the relay will not close. It just chatters from the
>>>>>pulsating dc voltage. Just what you'd expect.
>>>>>
>>>>>I have gone through at least 10 capacitors, and each one explodes
>>>>>after>a short time.
>>>>
>>>>Starting with the obvious, you have checked or replaced the diode?
>>>>
>>>>>Six of them were supposedly new stock.
>>>>
>>>>Brand and date code?? That is a 1/2 wave supply and the ripple may
>
>>>be
>>>>too much for some bargain brand caps.
>>>
>>>Ä The original capacitor was a cheapo and it worked ok, Carl.
>
>>Worked OK until it leaked or shorted, that cap was always on the
>edge,
>>particularly the early ones in the brown/tan case.
>>>
>>>>Have you actually MEASURED the voltage?
>>>>Are R4 and R5 OK and in the ckt? If not the voltage will rise
>quite a
>>>>bit and can exceed the cap rating.
>>>
>>>Ä The secondary winding is 80Vrms. How can the peak-V exceed 160V?
>>
>>
>>Easy since you are incorrect about the AC rms voltage a half wave ckt
>with no
>resistive
> >load.
>
>? I measure 122vdc, no load. That's c.86Vrms. Are you contending
>that
>Vrms x the square root of 2 does Not = peak-V?
>- later, Carl
That is not what I said.
Later yourself
Carl
>
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>
>
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>
>
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