From my recollection of working on the tube B+
supplies many years ago, another possible cause is an
open or leaky decoupling capacitor on the grid of the
comparator tubes (6AU6). Check to see if your scope
has a very small value (.001-.1 uF) capacitor in the
grid circuit across the grid input to ground. When
these go bad, the power supplies become unstable.
Jim Reese
--- "JOSE V. GAVILA (EB5AGV/EC5AAU)" <eb5agv@...>
wrote:
Hello!
After another small trip (why do women _love_ to
travel so much???), I am
again at home. And, just today, I have got an
original 545B manual in the
mail. Sometimes, eBay is great; I got it for just $8
+ shipping. And it has
taken only three days to arrive to Spain (it was
dated 18th)
So, armed with the manual, I have been looking again
at the power supply...
to find that, yes, there is a trouble. -150V is
good, as is +100V and +225V
(less than about 5mVpp ripple on them). BUT +350V
and +500V show no less
than about 20Vpp ripple!. As the +500V is based on
the +350V supply,
culprit should be on that last supply. But I have
not yet been able to
locate the ofending part. Obvious things, as the
+350V electrolytic cap
filter and the 6080 rectifier are fine. Also, the
6AU6 comparator is good
(I have checked in both cases with good tubes).
Although they check fine
on-circuit, I suspect one of the solid state
rectifier diodes just after
the transformer winding could be bad so the power
supply has not enough
available current and voltage drops on the 'bad'
semicycle... But I need to
check this. Anyway, is there any idea from your
side?
About the 1A1 plug-in, it is of the 'old' type (6
nuvistors on it). It
seems to work fine. Hope it keeps going, as the
nuvistors are not cheap
items ;-)
Regards,
JOSE
----------------------------------------------------------------------
73 EB5AGV / EC5AAU - JOSE V. GAVILA
La Canyada - Valencia (SPAIN)
EB5AGV Vintage Radio Site:
European Boatanchors List:
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