A loud pop! A bright orange tube, and a completely blown fuse.
That's what I get, and right in the middle of "Glass Onion" from the
"White Album" damnit!

I've got a Jolida Sj 302A that uses type El-34 Tubes. I've had it
for about 2 and one half years now. It blows tubes every six months.
I know this can't be right. After the last set of tubes went I called
Jolida, and asked them what they thought the problem might be. They
explained that my Svetlanas are not quite as reliable so I should
switch to Sovtek. My father's Conrad Johnson is going about 3 years
strong on the same set of Svetlanas, but I took the bait anyway. The
switch to Sovtek solved nothing. I follow the manufacturer's
guidelines, I check the bias frequently, and it couldn't have better
ventilation.

Any other Jolida users suffering the same problems? What causes
tubes to blow like this taking the fuse with them and all? I even
think I may have seen smoke! Is this typical when a tube dies, or
does it indicate a problem with the amp? The tubes in my guitar amp
always seem to die a quiet death, but the Jolida likes to make them go
out with a bang.

Thanks,
Robert

Is the loud "pop" from a speaker? If so then it is likely the
result of the fuse blowing.

We are not generally good at questions about branded amps because
must of us round here make our own. In fact I don't think we really
understand why some people have amps with names.

Some kind of circuit description is therefore necessary for a
sensible reply.

You have a problem of catastrophic bias failure that cannot be the
fault of the valves. I suspect you may be suffering a short
somewhere when the amp gets hot. If it is fixed bias, a trapped
wire can eventually short against the chassis when the insulation
creeps. That might have no effect other than to stop the bias to
one or more valves, resulting in the symptoms you describe. Such an
intermittent, temperature-sensitive fault can be very hard to track
down.

Or anything else in the power stage grid or cathode circuits that
might fail when hot...coupling capacitors, cathode resistor bypass
caps if it is autobias.

Most other faults would not be temporarily overcome by changing
valves. If you let the amp cool down, change the fuse, and power up
without changing the valves, does it work OK again for a while? I
don't recommend switching it on for more than a few moments until
you have established the cause of failure.

Jolida are being naughty if they say catasrophic failure is down to
the brand of valve. There may be a problem with some valves dying
slowly, but the bright orange scenario is an amp problem for sure.

cheers, Ian

"Robert Philbeck" wrote in message
om...
A loud pop! A bright orange tube, and a completely blown fuse.
That's what I get, and right in the middle of "Glass Onion" from
the
"White Album" damnit!

I've got a Jolida Sj 302A that uses type El-34 Tubes. I've had
it
for about 2 and one half years now. It blows tubes every six
months.
I know this can't be right. After the last set of tubes went I
called
Jolida, and asked them what they thought the problem might be.
They
explained that my Svetlanas are not quite as reliable so I should
switch to Sovtek. My father's Conrad Johnson is going about 3
years
strong on the same set of Svetlanas, but I took the bait anyway.
The
switch to Sovtek solved nothing. I follow the manufacturer's
guidelines, I check the bias frequently, and it couldn't have
better
ventilation.

Any other Jolida users suffering the same problems? What causes
tubes to blow like this taking the fuse with them and all? I even
think I may have seen smoke! Is this typical when a tube dies, or
does it indicate a problem with the amp? The tubes in my guitar
amp
always seem to die a quiet death, but the Jolida likes to make
them go
out with a bang.

Thanks,
Robert

Hi RATs!

Take your amp to a tech and get it fixed.

You are too far from the problem to solve it yourself.

It ain't the tubes

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead

"Ian Iveson" wrote in message ...
Is the loud "pop" from a speaker? If so then it is likely the
result of the fuse blowing.

We are not generally good at questions about branded amps because
must of us round here make our own. In fact I don't think we really
understand why some people have amps with names.

Some kind of circuit description is therefore necessary for a
sensible reply.

I'm not sure what a circuit description should encompass, but here is
a link to the specs. http://www.jolida.com/catalogue/jd302b.html

You have a problem of catastrophic bias failure that cannot be the
fault of the valves. I suspect you may be suffering a short
somewhere when the amp gets hot. If it is fixed bias, a trapped
wire can eventually short against the chassis when the insulation
creeps. That might have no effect other than to stop the bias to
one or more valves, resulting in the symptoms you describe. Such an
intermittent, temperature-sensitive fault can be very hard to track
down.

It is adjustable bias.

Or anything else in the power stage grid or cathode circuits that
might fail when hot...coupling capacitors, cathode resistor bypass
caps if it is autobias.

Most other faults would not be temporarily overcome by changing
valves. If you let the amp cool down, change the fuse, and power up
without changing the valves, does it work OK again for a while? I
don't recommend switching it on for more than a few moments until
you have established the cause of failure.

I installed another fuse and it blew the second I turned the amp on.
The culprit tube also lit up white. I changed the tube, put in a new
fuse, rebiased the amp and all seems fine. But I know It's running on
borrowed time based on past experiance.

Jolida are being naughty if they say catasrophic failure is down to
the brand of valve. There may be a problem with some valves dying
slowly, but the bright orange scenario is an amp problem for sure.

cheers, Ian

Thanks so much for your help. If the information I've given here
provides you with anymore insight to the problem please let me know.
I plan to take it to a tech, but just like to arm myself with as much
undertsnadin as possible regarding things like this. Thanks again.

Robert

"Robert Philbeck" wrote in message
om...
A loud pop! A bright orange tube, and a completely blown fuse.
That's what I get, and right in the middle of "Glass Onion" from
the
"White Album" damnit!

I've got a Jolida Sj 302A that uses type El-34 Tubes. I've had
it
for about 2 and one half years now. It blows tubes every six
months.
I know this can't be right. After the last set of tubes went I
called
Jolida, and asked them what they thought the problem might be.
They
explained that my Svetlanas are not quite as reliable so I should
switch to Sovtek. My father's Conrad Johnson is going about 3
years
strong on the same set of Svetlanas, but I took the bait anyway.
The
switch to Sovtek solved nothing. I follow the manufacturer's
guidelines, I check the bias frequently, and it couldn't have
better
ventilation.

Any other Jolida users suffering the same problems? What causes
tubes to blow like this taking the fuse with them and all? I even
think I may have seen smoke! Is this typical when a tube dies, or
does it indicate a problem with the amp? The tubes in my guitar
amp
always seem to die a quiet death, but the Jolida likes to make
them go
out with a bang.

Thanks,
Robert

(TubeGarden) wrote in message ...
Hi RATs!

Take your amp to a tech and get it fixed.

You are too far from the problem to solve it yourself.

It ain't the tubes

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead

Hi Alan. Who is RATs? I agree with you that I should take the amp to
a tech and plan on doing so asap. I would just like to arm myself
with as much knowledge as possible.

Thanks,
Robert

Thanks Xavier. Forgot about DrTube. Nice simple design.

cheers, Ian

"Xavier van Unen" wrote in message
...
Hi Robert and Ian,

Some kind of circuit description is therefore necessary for a
sensible reply.
See:
www.DrTube.com/audioamp.htm#Jolida
for a circuit of the 302 and 502.

Regards Xavier.

Almost certainly coupling caps, Robert.

Fixed bias is the same thing as adjustable bias, paradoxically :-)
It means that you have to fix it...it is not automatic.

If you look at the circuit diagram, the output section is the top
right-hand quarter.

All current passing through the power valves passes also through the
1ohm resistors, R17 and R18, at the cathodes. The test points are
shown, and you should be able to see that for each 1
mA passing through a valve, you get 1mV at the corresponding test
point.

The anode and screen of each valve is connected to the HT, or B+
supply, in your case around 500V. The cathodes are grounded via R17
and R18. All this part of your amp is OK.

Turning to the grids, the important points are the junctions of
C3/R9/R13, and C4/R12/R16. At each of these two points, the bias
voltage (via R9/R12) is combined with the signal voltage (via C3/C4)
and applied to the grids (via R13/R16).

The negative DC bias voltage at those points is adjusted with pots
RV2/RV3. As you vary the voltage, you change the current passing
through the valves, and hence the voltage at the test points. The
bias circuit is made to be reliable, fail-safe, and
temperature-stable. The pots can go open or short-circuit in any
combination and some bias will remain. If R9 or R12 fail to
open-circuit, or if they are shorted to ground, then you will lose
bias. This is unlikely IMO unless you have a wire touching the
chassis where it shouldn't.

And an EL34 should be able to cope with zero bias for a while.
Decent ones can get hot enough to melt the glass (and often do in
Marshalls) and still be OK (ish). So failed bias would probably not
explain why your valves fail. Oh...except I notice there are no
screen resistors, so I suppose you might be burning the screens.

On the other side of the coupling caps, C3/C4, you have over 400V
(C6 seems under-specified for voltage btw). If one fails to a short
or a low resistance then the grids will go positive and current will
flow through the delicate grid wires. Enough current can damage the
grid and if it burns who knows where it might dangle and what
fireworks might ensue. Without the grid you have a diode :-( You
are lucky that the output transformer seems to have survived all
that current.

This doesn't explain the regularity of your 6 monthly failures.
Perhaps it gets hot twice a year where you are? The technician
might ask what kind of replacement coupling caps you want. Perhaps
that will be your next question.

Oh, and rats is us. Should be ravs, I think.

cheers, Ian

"Robert Philbeck" wrote in message
om...
"Ian Iveson" wrote in message
...
Is the loud "pop" from a speaker? If so then it is likely the
result of the fuse blowing.

We are not generally good at questions about branded amps
because
must of us round here make our own. In fact I don't think we
really
understand why some people have amps with names.

Some kind of circuit description is therefore necessary for a
sensible reply.

I'm not sure what a circuit description should encompass, but here
is
a link to the specs. http://www.jolida.com/catalogue/jd302b.html

You have a problem of catastrophic bias failure that cannot be
the
fault of the valves. I suspect you may be suffering a short
somewhere when the amp gets hot. If it is fixed bias, a trapped
wire can eventually short against the chassis when the
insulation
creeps. That might have no effect other than to stop the bias
to
one or more valves, resulting in the symptoms you describe.
Such an
intermittent, temperature-sensitive fault can be very hard to
track
down.

It is adjustable bias.

Or anything else in the power stage grid or cathode circuits
that
might fail when hot...coupling capacitors, cathode resistor
bypass
caps if it is autobias.

Most other faults would not be temporarily overcome by changing
valves. If you let the amp cool down, change the fuse, and
power up
without changing the valves, does it work OK again for a while?
I
don't recommend switching it on for more than a few moments
until
you have established the cause of failure.

I installed another fuse and it blew the second I turned the amp
on.
The culprit tube also lit up white. I changed the tube, put in a
new
fuse, rebiased the amp and all seems fine. But I know It's
running on
borrowed time based on past experiance.

Jolida are being naughty if they say catasrophic failure is down
to
the brand of valve. There may be a problem with some valves
dying
slowly, but the bright orange scenario is an amp problem for
sure.

cheers, Ian

Thanks so much for your help. If the information I've given here
provides you with anymore insight to the problem please let me
know.
I plan to take it to a tech, but just like to arm myself with as
much
undertsnadin as possible regarding things like this. Thanks
again.

Robert

"Robert Philbeck" wrote in message
om...
A loud pop! A bright orange tube, and a completely blown
fuse.
That's what I get, and right in the middle of "Glass Onion"
from
the
"White Album" damnit!

I've got a Jolida Sj 302A that uses type El-34 Tubes. I've
had
it
for about 2 and one half years now. It blows tubes every six
months.
I know this can't be right. After the last set of tubes went
I
called
Jolida, and asked them what they thought the problem might be.
They
explained that my Svetlanas are not quite as reliable so I
should
switch to Sovtek. My father's Conrad Johnson is going about 3
years
strong on the same set of Svetlanas, but I took the bait anywa
y.
The
switch to Sovtek solved nothing. I follow the manufacturer's
guidelines, I check the bias frequently, and it couldn't have
better
ventilation.

Any other Jolida users suffering the same problems? What
causes
tubes to blow like this taking the fuse with them and all? I
even
think I may have seen smoke! Is this typical when a tube
dies, or
does it indicate a problem with the amp? The tubes in my
guitar
amp
always seem to die a quiet death, but the Jolida likes to make
them go
out with a bang.

Thanks,
Robert

Hi RATs!

Rec.Audio.Tubes

DrTube good!

Is it always the same tube?

If R9 or R10 is open, then if the VR, or RV, pot goes open, there is no bias.
Not good.

Good design, but, not everything in reality does what it was intended to do.

Well, except me

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead

Sounds like plate to grid cap is shorting. Bias supply may be bad but I dont
think it could cause this much damage so I lean more toward B+ from the
driver getting to the grids. There may be a problem in the screen circuit. I
dont know how they derive the screen voltage but if it suddenly shoots up to
the B+ value it could fry the tubes also. When I build an amp I put a big
zener diode from the screen to ground and a fuse in the screeen circuit. If
the voltage goes above the zener's cut on point the fuse blows. Tubes are
just to damn expensive not to protect them.


"Robert Philbeck" wrote in message
om...
A loud pop! A bright orange tube, and a completely blown fuse.
That's what I get, and right in the middle of "Glass Onion" from the
"White Album" damnit!

I've got a Jolida Sj 302A that uses type El-34 Tubes. I've had it
for about 2 and one half years now. It blows tubes every six months.
I know this can't be right. After the last set of tubes went I called
Jolida, and asked them what they thought the problem might be. They
explained that my Svetlanas are not quite as reliable so I should
switch to Sovtek. My father's Conrad Johnson is going about 3 years
strong on the same set of Svetlanas, but I took the bait anyway. The
switch to Sovtek solved nothing. I follow the manufacturer's
guidelines, I check the bias frequently, and it couldn't have better
ventilation.

Any other Jolida users suffering the same problems? What causes
tubes to blow like this taking the fuse with them and all? I even
think I may have seen smoke! Is this typical when a tube dies, or
does it indicate a problem with the amp? The tubes in my guitar amp
always seem to die a quiet death, but the Jolida likes to make them go
out with a bang.

Thanks,
Robert