[AMPS] SB220 problems

[km1h@juno.com]

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.
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. Later resistors used by Heath can fail
open with no outward sign. 

73  Carl  KM1H

  

Last week I took
>one of these "new caspacitors" and preconditioned it by putting it
>across a dc supply which I increased from 20volts to 125 volts 20 
>volts
>at a step, leaving it for 2hours at each step. I installed this
>capacitor yesterday morning and spent most of the day dxing on twenty
>meters. I gave that ------- linear a workout like it ain't had in 25
>years. Got reports from all over the world from S9 to "loudest signal 
>on
>the band". I thought I had it made when at 3:45 local time that
>capacitor let go like a shot gun blast. Blew pieces all over the 
>-------
>living room.
>
>I am at my wits end. You mentioned you were "dropping a couple in the
>mail" If you have done so, bless you. If you have not get your ------- 
>---
>--- to the sodding post office and do so. I'll pay, whatever it
>cost. I'm ------!
>73, de KC4DWI
>
>
>Any Ideas?
>
>73 de Alek, VK6APK.
>
>--
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>
>

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