Pub mains supply problem?

[Ron(UK)]

N Cook wrote:

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:gRbvk.236116$ah4.201281@newsfe15.ams2...
"N Cook" <diverse8@gazeta.pl> wrote in message
news:g9ivba$i5l$1@inews.gazeta.pl...
I can understand lager chillers or lighting triacs causing clicks and
bangs
and noises off but blowing fuses on 2 Marshall valve amps at the same
time
and no other pub mains problem showing itself.

The 1987X from 2006 in front of me kept blowing 500mA HT fuses after the
initial failure. Not doing so now its in front of me, not fully checked
out
yet. Mains fuse always ok , just the HT one repeatedly failing after 4
seconds or so. At the same time as this HT one failed the mains fuse
failed
on another Marshall connected to the same supply - that one just
required
a
change of mains fuse and is still ok.

Could a fault causing failure of HT fuse on one amp cause the failure of
mains fuse on another amp , with no pub wiring problem at all, even
problem
local to the power ring/spur to the stage.


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



Absolutely certain that the supply is not losing the neutral outside
anywhere - particularly if an overhead supply to a country pub ? A friend
of
mine had a similar problem at a remote monitoring station for water
treatment that he had to look after, and the mains kept randomly shooting
up
to 440v. That would certainly cause the secondary voltage of the mains
tranny in the amp, to go up hugely, which would likely blow the HT fuse
and
/ or the mains fuse. Might account for why a similar problem is happening
to
two unrelated items of equipment, simultaneously ? Have they had any
problems with light bulbs failing, particularly any of those new-fangled
eco
things ? Otherwise, I can't think of anything that takes out the HT fuse
on
one amp, doing the same to the mains fuse on another.

Arfa




City pub in Pompey
Owner didn't notice anything else wrong in the room at the gig and
confronting the landlord he said he'd had no problems.

I asked the owner if he used a nasty plastic extension lead and he did not
really reply but even a problem there could not put a surge on to the kit.

Checked the valves and transformers , caps etc and everything seems hunky
dory , no wavering of HT of about 440V on dummy load. I looks as though it
will have to be replacement 500V, twin 50uF electrolytics although no
suspicious heating or bulges /weeping, unless an indisputable reason can be
found. Fuses blew to black interior, ie not soft blown.

Does these amps have valve rectifiers? GZ34 usually. The cheap Sovtec
ones have a habit of flashing over internally and that sees the mains
fuse off big time.

If the fault is repeatable, you might be able to sort of prove it by
temporarily fitting the amps with diode rectifiers for a couple of gigs.

2x 1n4007 in an old valve base (you can parallel up three a side if you
are worried) I always have one on my bench for testing, I see a lot of
duff valves these days.

Ron(UK)

 

[Dave]

"Ron(UK)" <ron@lunevalleyaudio.com> wrote in message
newssqdneoc5LKq-yDVnZ2dnUVZ8sjinZ2d@bt.com...

Does these amps have valve rectifiers? GZ34 usually. The cheap Sovtec ones
have a habit of flashing over internally and that sees the mains fuse off
big time.

If the fault is repeatable, you might be able to sort of prove it by
temporarily fitting the amps with diode rectifiers for a couple of gigs.

2x 1n4007 in an old valve base (you can parallel up three a side if you
are worried) I always have one on my bench for testing, I see a lot of
duff valves these days.

Ron(UK)

SS diodes in a tube rectifier receptable require a dropper resistor in
series as the tube rectifier drops ~50V whereas the diodes drop ~0.7V.
Otherwise your plate voltages will be too high.

Dave

 

[Ron(UK)]

N Cook wrote:

According to Regulation 27 of ESQC Regs 2002, UK mains should be
230V +10% - 6%, which gives a range of 216V to 253V.

I variaced up to 250V , switching on and off a few times, giving HT1 of 464
, nicely stable with amp under load.

A thorough inspection of all components only revealed slightly loose nuts
holding the iron laminations on the filter choke, which I cannot see as a
problem. Otherwise inside and out it looks brand new, only some of the large
binding post (lead-free of course everywhere ) solder joints looked grey but
otherwise sound.

Whats the teams opinion of adding 300mA axial (so quickblow) fuses in each
of the two EL34 anode supplies as well as the 500mA (T) regular fuse ?

Why?

Ron(UK)

 

[Eeyore]

N Cook wrote:

Eeyore wrote in message

Brief surges ?

I had a JVC TV blow its internal mains fuse every 2 years or so even when
not active (but in standby). Eventually a plug-in surge suppressor stopped
it.

Bet it occured at night.

I don't recall any particular pattern to it. It may even have had a transorb
itself - and it was over sensitive. Putting another effectively in parallel took
the load off it.

Graham

 

[nobody >]

N Cook wrote:

Very few power stations/generator sets are needed to power the grid in the
middle of the night. At some point it becomes necessary to start up another
one and what happens to the grid at that time ?

Generating systems don't just get "slapped on line" at startup, at least
here in the USA. I don't believe you'd find that in any but third-world
countries.

The generator is brought up to speed/frquency and voltage (and
stabilized) to match that of the grid before it's brought on line. Only
then does the plant operator raise output in conjunction with the rest
of the grid providers. It's a constant job to maintain the grid at
nominal levels and requires constant voice and data transfers amongst
the providers.

I'm not going to say that surges don't happen when abrupt loads are
dumped on or dropped, but that's another subject too long to explain in
one post.

 

[Eeyore]

N Cook wrote:

I can understand lager chillers or lighting triacs causing clicks and bangs
and noises off but blowing fuses on 2 Marshall valve amps at the same time
and no other pub mains problem showing itself.

The 1987X from 2006 in front of me kept blowing 500mA HT fuses after the
initial failure. Not doing so now its in front of me, not fully checked out
yet. Mains fuse always ok , just the HT one repeatedly failing after 4
seconds or so. At the same time as this HT one failed the mains fuse failed
on another Marshall connected to the same supply - that one just required a
change of mains fuse and is still ok.

Could a fault causing failure of HT fuse on one amp cause the failure of
mains fuse on another amp , with no pub wiring problem at all, even problem
local to the power ring/spur to the stage.

Brief surges ?

I had a JVC TV blow its internal mains fuse every 2 years or so even when not
active (but in standby). Eventually a plug-in surge suppressor stopped it.

Graham