Please help!....My Marshall JCM800 Lead head enjoys eating fuses.
Michael Dyke
Dear tube experts:
I have a Marshall JCM800 Lead Series head that has blown the 500mA
fuse three times in the past week. Is this an indication that the
tubes need replacing, or could it be a more sinister problem?
I don't know if this is just coincidence or not, but each time the
fuse has blown, I have had my ART SGX2000 Express preamp/processor
plugged in. It has never blown when I was running the guitar straight
into the head or when I used my pedal board.
Please forgive my ignorance on the tube amp subject, but this is the
first tube amp that I have ever had the pleasure of owning. I am
really pleased by the sound I get, but this problem is a bit
troubling.
Thanks for your help.
Michael Dyke
Hompage: http://www.planetc.com/users/dykemw
Email:dyk...@planetc.net <---Change net to com
Strat1995
>I have a Marshall JCM800 Lead Series head that has blown the 500mA
>fuse three times in the past week. Is this an indication that the
>tubes need replacing, or could it be a more sinister problem?
It could be either. Try replacing the tubes and see if it stops the fuse from
blowing.
DB>
Hi Micheal -
You may need to have the bias checked, and or new tubes, depending on
whether the tubes are new or old.
Dave Blackhurst
Blackhurst Custom Guitar
Michael Dyke wrote in message <34fab4f4...@news.planetc.com>...
>Dear tube experts:
>
>I have a Marshall JCM800 Lead Series head that has blown the 500mA
>fuse three times in the past week. Is this an indication that the
>tubes need replacing, or could it be a more sinister problem?
>
Norm Berube
Strat1995 wrote:
> It could be either. Try replacing the tubes and see if it stops the fuse from
> blowing.
Try bringing it to a repair shop and see what they think before you go replacing
shit....the tubes could be fine. I'm BY FAR not a tube guy, either, but I always
have my gear checked out before I replace parts. Let's see what Lord Valve has to
say...He knows his shit.
--
...................................
Norm Berube
comp...@ma.ultranet.com
http://www.ultranet.com/~compound
...................................
"patgtrfr...@hotmail.com
Norm Berube wrote:
>
> Strat1995 wrote:
>
> > It could be either. Try replacing the tubes and see if it stops the fuse from
> > blowing.
>
> Try bringing it to a repair shop and see what they think before you go replacing
> shit....the tubes could be fine. I'm BY FAR not a tube guy, either, but I always
> have my gear checked out before I replace parts. Let's see what Lord Valve has to
> say...He knows his shit.
hey this is simple blowing fuses???
pull all the tubes replace the fuse
insert tubes one at a time till the fuse pops
youv'e found the bad tube !!!
cost a 5 pak of fuses and the replacement tube
for best results replace your outputs in complete sets
if the fuse dosn't pop ... how
old are your output tubes ??
over 2 years replace them anyway
then
leave the amp on for a couple of hours to check it out
pat
"patgtrfr...@hotmail.com
patgtrfrk(remove)@hotmail.com wrote:
>
> hey this is simple blowing fuses???
>
> pull all the tubes replace the fuse
>
> insert tubes one at a time till the fuse pops
> youv'e found the bad tube !!!
>
> cost a 5 pak of fuses and the replacement tube
> for best results replace your outputs in complete sets
>
> if the fuse dosn't pop ... how
> old are your output tubes ??
>
> over 2 years replace them anyway
> then
> leave the amp on for a couple of hours to check it out
>
> pat
there is anther phenomena that needs a mention here
in CANADA in winter we see a lot of marshall fuse popage
although fuses pop is usually a sign of an amp problem
in winter in CANADA it can be the result of a sever cold start
especially with jcm 800's which have many many fuses thru the amp
as temperatures drop the internal components of the amp drop in
resistance especially the heater lines and the ht line at startup ...
you might think your amp isn't too cold but you switch it on and pop
....
when giging in canada in winter i usually try to arrive early at the bar
and set up my amp first...
plug it in and turn on the power but leave the standby off
i will let it warm like this forever till we actually go on
after a few minutes i will flip the standy to play then back again this
allows some current to flow then shuts the flow off again .. the filters
charge up a little so the turn on isnt as hard as it might be ...
with jcm 800's in particular when cold or left unused for a while this
soft start technique will keep an otherwise good condition amp from
popping fuses ...
some local players even re-fuse the heater fuses with slightly higher
values (slighly) for this reason ... though higher value fuses are
always risky and one should never raise the value of the mains or ht
fuse
pat
Skip May
Michael Dyke (dyk...@planetc.net) wrote:
: Dear tube experts:
: I have a Marshall JCM800 Lead Series head that has blown the 500mA
: fuse three times in the past week. Is this an indication that the
: tubes need replacing, or could it be a more sinister problem?
What's the time constant on that fuse your using? slow blow/fast blow or
something special?
What model JCM 800 is it...?
Do you know what type output tubes are in it? 6550/6L6/EL-34
: I don't know if this is just coincidence or not, but each time the
: fuse has blown, I have had my ART SGX2000 Express preamp/processor
: plugged in. It has never blown when I was running the guitar straight
: into the head or when I used my pedal board.
:
Yes, there could be a relationship, but a little more info would help.
: Please forgive my ignorance on the tube amp subject, but this is the
: first tube amp that I have ever had the pleasure of owning. I am
: really pleased by the sound I get, but this problem is a bit
: troubling.
: Thanks for your help.
: Michael Dyke
But not a big deal Michael. Just make sure to keep replacing the fuse with
the proper value and type.
The we can give you some things to think about.
cheers
skip
nosp...@juno.com
TimVictor
FWIW: When I got my JCM800 a few years ago, it'd blow one of the internal fuses
any time I turned it up to 10. I don't remember which fuse was going out, but I
noticed that it was a fast-blow type. I replaced it with a slow-blow fuse of
the same rating which hasn't gone out yet.
Tim Victor
TimV...@aol.com
In article <34fab4f4...@news.planetc.com>, dyk...@planetc.net (Michael
Shredder
Michael Dyke wrote:
>
> Dear tube experts:
>
> I have a Marshall JCM800 Lead Series head that has blown the 500mA
> fuse three times in the past week. Is this an indication that the
> tubes need replacing, or could it be a more sinister problem?
>
Check the speaker output(s). I had a JCM 800 once that was eating fuses
because the output was shorted.
dst...@ibm.net
Hi Mike. That kind of intermittent fuse blowing problem you describe seems to
plague Marshalls pretty often for some reason. One thing I've found is that
sometimes one of the output tubes actually has an intermittent internal
short/arcing problem. The amp will be playing along fine, then a flash of
light appears in one of the tubes and the fuse blows. You can replace the fuse
and once again, the amp works fine... for a little while! Eventually, the
short develops into a "hard short" and the fuse blows consistently. This is
why we tech types use current limiters when we're confirming customer
complaints! :)
I recommend you take the amp to a competent tech. If the problem is NOT in the
tubes themselves--for instance, a "carbon track" that may have formed on one
of the sockets, or an intermittent short inside the amp--you could ruin your
new tubes and still be stuck with the same problem as before.
--Dave Stork
Stork Audio
http://members.aol.com/StorkAudio
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Danny Russell
patgtrfrk(remove)@hotmail.com wrote:
>
> there is anther phenomena that needs a mention here
> in CANADA in winter we see a lot of marshall fuse popage
> although fuses pop is usually a sign of an amp problem
> in winter in CANADA it can be the result of a sever cold start
> especially with jcm 800's which have many many fuses thru the amp
SNIP
I've noticed that the heater fuse on the JCM600 models has a tendency to
surge-blow at cold turn-on. I believe that these suffer from an
under-value fuse. You can watch the element groan and arch it's back
till it almost touches the glass and comes probably within a few
milliamps of popping, and then recovers. Don't recall off hand what the
stock value is (6.3A Slo-Blo w/ (2) 5881 I believe), but it should
really be 1 amp larger than it comes supplied. -Danny
Dr. Stereo
>TimVictor wrote
>. I replaced it with a slow-blow fuse of
>the same rating which hasn't gone out yet.
>
Tim :
That is probably the best answer.....I replace every fast blow fuse with a
slow blow as I find them.... I have not had a blown transformer yet....(over
60 repairs a month).....If you want to check for arcing tubes, put a 500 w
lamp in series with the AC line.....With all controls down, tap on each
tube... The bad tube will cause the lamp to light up but wont blow any
fuses.....If you have a arcing blue capacitor, this is about the only way to
track it down.... The cap will arc (light bulb flashing bright/dim) until it
finally shorts out, than you find it with your voltmeter.... The lowest DC
volts is the bad cap.....I don't need any flames here.... This system has
worked for me for over 10 units with this failure mode.... Your approach
could be better.....
Cordials
Dr. Stereo
Michael Dyke
I would like to thank everyone that replied to my prior question.
This has to be the best group on usenet! I post regularly in a few
other groups, but I must say that on average the people here in a.g.a
have to be the most courteous and helpful.
I have decided rather quickly that I am out of my league when it comes
to servicing my own amp. Until I learn more about it ( I'll continue
to be educated by the best here in a.g.a), I'll just take it to a
competent repair person and concentrate on my playing : )
I found someone that works on tube amps in the town in which I work,
and he went through a list of much the same possibilities as you did.
I'm going to take the head in asap. I'll let you know what the
problem is when I find out.
Thanks again for all your help, and I look forward to your great posts
in the future.
Sincerely
Lord Valve
In <19980302220...@ladder03.news.aol.com> stra...@aol.com
(Strat1995) writes:
>
>>I have a Marshall JCM800 Lead Series head that has blown the 500mA
>>fuse three times in the past week. Is this an indication that the
>>tubes need replacing, or could it be a more sinister problem?
>
fuse from
>blowing.
Lord Valve Speaketh:
While you're at it, check the sockets for burn marks between pins two
and three. If you find any, replace the socket AND the tube that was
in it. You'll have to look on both the top and the bottom of the
sockets to be sure. Have a look at the tube pins also...again, check
for burn marks between pins two and three. Make sure your speaker cord
is in good condition, and that you are operating the amp into the
correct impedance. If you don't know the impedance of your cabinet,
have someone check it with an ohmeter; running the amp into a higher
impedance than you have the selector set for will often cause burned
sockets. Power your amp up, take it off standby, and allow it to heat
for five minutes. Observe the power tubes IN THE DARK; look for orange
spots or stripes on the plates. (The plates are the large grey
structures inside the tubes.) If you see this, you either have a bad
tube or loss of bias voltage.
Lord Valve
Website at: http://www.freeyellow.com/members2/lord-valve/
"Sacred cows make the best hamburger." - Mark Twain