Re: VOX AC30/6 TB

N Cook <diverse8@xxxxxxxxx> wrote in message
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DaveM <masondg4499@xxxxxxxxxxxxx> wrote in message
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"N Cook" <diverse8@xxxxxxxxx> wrote in message
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All valve, no solid state devices, probably made 2002 from barcode
date?
and
2001 date on Sovtek 5AR4.
Powered on for about 5 seconds with cracks and bangs then HT light
went
out
and dead.
Inside looks and smells fine but "gently" blown HT fuse. I've not
tested
the
valves yet.
1 of the 22K 1/3W HT R/C dropper resistors slightly discoloured and
all
4
EL84 1/2W, 100 ohm grid resistors slightly discolured. Someone has
crudely
cut one of the 2 grounds to the pcb, presumably trying to reduce hum
when it
was working.
All DVM DC resistance measurements of the transformers seem ok.
Any pointers to known problems with this version?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/



First question back to you is.. is the HT fuse after the rectifier or
before it?
Or, are you really talking about the AC mains fuse?

If the fuse is really in the AC mains line, then almost all my bets are
going to
be on a shorted power transformer or a shorted MOV or line bypass
capacitor.
If the fuse is after the rectifier, then you should pull the rectifier
tube,
replace the fuse, and see if the fuse blows again. If it blows again,
then
check to see if maybe one side of the power line is shorted to ground...
possibly caused by a shorted MOV or line bypass capacitor. Or a stray
piece of
wire, or other malady.
If the fuse doesn't blow again, then you have a bit of troubleshooting
to
do.
Most likely a shorted B+ filter capacitor or shorted tube. Be sure to
keep your
eyes peeled for stray wire clippings.

Cheers!!!!

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate
characters
in the
address)

Life is like a roll of toilet paper; the closer to the end, the faster
it
goes.



MOV= metal oxide varistor ?
Probably the most diagnostic feature is the 500mA HT fuse, on the DC side
of
the rectifier tube, is a small gap in the fuse filament with a glob on one
broken end, both remnants axially present in the barrel, no staining
inside
barrel at all.
Last gasp rather than catastrophic failure.
I'm struggling with sticky needle on my valve tester , again.
I know if i poke around in the meter I will totally bugger up the movement
,
so no use rather than problematic use with a lot of case tapping.

As an aside anyone know when barcodes started appearing on electronic kit
or
components? for age determination assistance. Mid 1980s is my recollection
but googling has not helped


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




the third EL84 tested , started out normally then rapidly accelerated off
the scale. I've never had the protection relay on my Avo CT 160 dropping out
before.
I had to get inside to manually reset it and took the opportunity to sort
out the meter needle sticking problem, much easier to get to and into this
meter movement than I'd thought.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


.

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