Had the same problem in a few different models of similar
amplifiers. Turns out to be a power supply electrolytic
failing after an amount of "on time." Power off and the
faulty cap un shorts itself. Repeats the same each power
up... good for a number of minutes and poof.
-
Same problem in two Alphas I've repaired...
cheers
skipp
On Wed, 2 Oct 2002 14:18:02 -0400 "John" <hydro@naturecoast.net> writes:
> Hi all
> I have a very interesting problem with my SB-1000 Heathkit
> .....This is the
> same amp as the ameritron AL80a with a single 3-500z
>
> Hears what happen.... I turn the amp on to use it, Talk on it for a
> few
> minutes, The amp blows the fuse for no reason while in receive... no
> pops,
> cracks, nothing ...just went dead while in standby
>
> I pull the tube test ....still blows fuse.... Test diodes...Check
> out OK,
> but replace them anyway..Still blows fuse...Check caps .....Seem
> ok... just
> for test I leave them out .Still blows fuse with NO caps in amp....
> Put it
> all back together, disconnect the B+ ....No dice
>
> So I am just about stumped.... I disconnect the HV negative from
> chassis
> ....Power it up
> It comes on .... Now the power supply is totally isolated from the
> amp....
> As soon as I connected the negative HV from the power supply to
> chassis
> ground it blows the fuse.....
>
> So the only thing I can come up with is the transformer must have
> some kind
> of internal short, Because there is no problem in the diode board or
> caps &
> the power supply will work as long as you do not connect the HV
> negative to
> the chassis
>
> Any ideas .....Richard or Tom ???
>
> thanks john
>
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>
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