>
>
>
>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
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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