Quad ii fuse blowing

[Edwin]

The fuse on one of my quads blows, tried switching all the valves still
the fault is the same.

I'v just been all over it with my meter (valves removed) and cant find
any shorts to earth or any readings significantly diferent to the other
amp. I have paid particular attention to the mains transformer, output
transformer, the can type capacitor with the 2 x 16 uf caps inside and
the choke. can anyone point me in the right direction form here?

Thanks Edwin

Sevenoaks Uk

[Phil Allison]

"Edwin" > wrote in message
oups.com...


** Groper Alert !!

> The fuse on one of my quads blows, tried switching all the valves still
> the fault is the same.


** Err - what fault ??

You have not detailed WHEN the fuse is blowing - at power witch on, during
loud volume, purely randomly, with a loud bang through the speaker or
silently ??



> I'v just been all over it with my meter (valves removed) and cant find
> any shorts to earth or any readings significantly diferent to the other
> amp. I have paid particular attention to the mains transformer, output
> transformer, the can type capacitor with the 2 x 16 uf caps inside and
> the choke. can anyone point me in the right direction form here?


** Describe the fuses that have blown - rating and type.



........ Phil

[Patrick Turner]

Edwin wrote:

> The fuse on one of my quads blows, tried switching all the valves still
> the fault is the same.
>
> I'v just been all over it with my meter (valves removed) and cant find
> any shorts to earth or any readings significantly diferent to the other
> amp. I have paid particular attention to the mains transformer, output
> transformer, the can type capacitor with the 2 x 16 uf caps inside and
> the choke. can anyone point me in the right direction form here?
>
> Thanks Edwin
>
> Sevenoaks Uk

Is the fuse the correct value?

You don't say if the fuse blows at turn on or not.

I'll assume it blows even with no tubes plugged in.

This would mean you are not getting any B+ voltage.

You could have a shorted turn in a winding on the power transformer
which is causing a heavy current to flow in the primary winding
and thus cause the fuse to blow.
There may not be any short circuit to ground with this condition.

If the fuse blows after the GZ32 begins to conduct after about 12 seconds
and B+ tries to rise to some +ve voltage but falls again after the fuse
blows then you may have a defective rectifier,
or a shorted PS cap, or the screen supply choke or OPT windings arcs to
ground.

Measure the dc resistance of all transformer windings of the TWO Quad II
amps
when cold and see if any differences exist.

You may need to unsolder all secondary connections on the PT and
measure the input current to the primary.

A variac can be used to gradually increase the input supply voltage from 0V

while measuring the input current of BOTH amps.
If you don't own a variac, a lamp socket with a bulb can be used to
reduce or limit input current from the mains, and a bulb of 25 watts allows

104mA maximum input current even with a dead short circuit, but slightly
more
of not lit up, if the bulb remains slightly bright, measurements can be
taken
without a fuse blowing. Having 120V applied to the primary instaed of the
240V
will cause the bulb to run low, and also cause the tubes to conduct a bit,
so
its best to test with a bulb with all the tubes out at first. The bulb
might flicker at turn on then remain
unlit, indicating a low input primary current flow; if the bulb become full
brightness
you have a short circuit somewhere. If you bulb remains unlit and you then
plug in a rectifier tube,
the bulb may flicker when turned on, then go out, but you will have a
substantial B+
voltage present if all is well in the PS B+ supply.
With output tubes in the bulb will slowly turn on a bit as the B+
conducts and heaters cause a drain.


If there is a fault in a PT such as a shorted turn then the input current
will be much higher even when the input voltage is only 24Vrms
and well before any of the tubes warming enough to allow emission and B+
conduction.
Check to see if the GZ32 has a short between its anodes and cathode.

if you are blowing fuses there must be a reason why, assuming the fuse
value is the same for
both amps, and you must have missed something in your measurements.

Patrick Turner.

[Mike Coatham]

"Edwin" > wrote in message
oups.com...
> The fuse on one of my quads blows, tried switching all the valves still
> the fault is the same.
>
> I'v just been all over it with my meter (valves removed) and cant find
> any shorts to earth or any readings significantly diferent to the other
> amp. I have paid particular attention to the mains transformer, output
> transformer, the can type capacitor with the 2 x 16 uf caps inside and
> the choke. can anyone point me in the right direction form here?
>
> Thanks Edwin
>
> Sevenoaks Uk

The right direction for you, is to point your car at Huntingdon and deliver
the amp to the Quad Service Dept.

[Peter Wieck]

Patrick Turner wrote:
If you bulb remains unlit and you then
> plug in a rectifier tube,
> the bulb may flicker when turned on, then go out, but you will have a
> substantial B+
> voltage present if all is well in the PS B+ supply.


OK... just be careful that the unloaded PS does not damage your filter
caps. Verify that the B+ is OK, then turn the system off ASAP. Best be
there with the VOM, keep an eye on the current drain, and as the B+
starts to rise (presuming the fuse remains intact), shut it down there.


One more thing that I have not seen mentioned. Most such amps want
"dual-element" fuses (as distinct from Slow-Blow fuses... an invention
of the devil). If you have a standard fast fuse in place, it will pop
mostly at turn on when the current hits the cold filaments and causes a
momentary high draw.

Bottom Line: Make sure you have the Correct TYPE as well as the Correct
RATING for the fuse you use.

Presuming the correct fuses and so forth, Patrick is right on the money
in terms of disconnecting the secondaries on the transformers. This
will separate a transformer problem from a load problem. Just hope it
is the load, not the iron.

Peter Wieck
Wyncote, PA

[Patrick Turner]

Peter Wieck wrote:

> Patrick Turner wrote:
> If you bulb remains unlit and you then
> > plug in a rectifier tube,
> > the bulb may flicker when turned on, then go out, but you will have a
> > substantial B+
> > voltage present if all is well in the PS B+ supply.
>
> OK... just be careful that the unloaded PS does not damage your filter
> caps. Verify that the B+ is OK, then turn the system off ASAP. Best be
> there with the VOM, keep an eye on the current drain, and as the B+
> starts to rise (presuming the fuse remains intact), shut it down there.

The Quad II amp can be tested without audio tubes plugged in.
B+ without a load connected should be 1.4 times the ac Vrms voltage across
each
1/2 of the HT secondary windings.
Each arm of the CT HT sec should have equal AC voltage.
The B+ without a load should be just under the voltage rating of the
electros, and the B+ surges to about 440V before the output tubes pull the
B+ down to
a loweer working level.

>
>
> One more thing that I have not seen mentioned. Most such amps want
> "dual-element" fuses (as distinct from Slow-Blow fuses... an invention
> of the devil). If you have a standard fast fuse in place, it will pop
> mostly at turn on when the current hits the cold filaments and causes a
> momentary high draw.
>
> Bottom Line: Make sure you have the Correct TYPE as well as the Correct
> RATING for the fuse you use.

I try to use the minimum value slo blow fuse without getting constant
nuisance blowings.
This is usually less than the Quad value of fuse, even with
very large value PS caps and silicon diodes.

>
>
> Presuming the correct fuses and so forth, Patrick is right on the money
> in terms of disconnecting the secondaries on the transformers. This
> will separate a transformer problem from a load problem. Just hope it
> is the load, not the iron.

Rewinding Quad II amp PTs isn't a real easy job.
One needs to be sure about just what is wrong and what one is measuring.

Patrick Turner.

>
>
> Peter Wieck
> Wyncote, PA

[Edwin]

Thanks for somuch advice. the fuse that blows is the main fuse on the
end of the quad ii power amp and blows at power on.

the fuse value originaly was 1A not sure if slow or fast as i dont
think it was speced on the fuse or maybe just hard to read.

last night I tried removing gz 32 and powering on with a larger fuse (i
know this was stupid), the pre amp powered up for about 3 seconds I
heard some fizling before the fuse blew, I think I may have blown one
of the caps in the pre amp but cannot see anything obvious.

As soon as I have more time I will run some more checks on the tranny,
I do have a vary ac so can run low power tests.


Patrick Turner wrote:
> Peter Wieck wrote:
>
> > Patrick Turner wrote:
> > If you bulb remains unlit and you then
> > > plug in a rectifier tube,
> > > the bulb may flicker when turned on, then go out, but you will have a
> > > substantial B+
> > > voltage present if all is well in the PS B+ supply.
> >
> > OK... just be careful that the unloaded PS does not damage your filter
> > caps. Verify that the B+ is OK, then turn the system off ASAP. Best be
> > there with the VOM, keep an eye on the current drain, and as the B+
> > starts to rise (presuming the fuse remains intact), shut it down there.
>
> The Quad II amp can be tested without audio tubes plugged in.
> B+ without a load connected should be 1.4 times the ac Vrms voltage across
> each
> 1/2 of the HT secondary windings.
> Each arm of the CT HT sec should have equal AC voltage.
> The B+ without a load should be just under the voltage rating of the
> electros, and the B+ surges to about 440V before the output tubes pull the
> B+ down to
> a loweer working level.
>
> >
> >
> > One more thing that I have not seen mentioned. Most such amps want
> > "dual-element" fuses (as distinct from Slow-Blow fuses... an invention
> > of the devil). If you have a standard fast fuse in place, it will pop
> > mostly at turn on when the current hits the cold filaments and causes a
> > momentary high draw.
> >
> > Bottom Line: Make sure you have the Correct TYPE as well as the Correct
> > RATING for the fuse you use.
>
> I try to use the minimum value slo blow fuse without getting constant
> nuisance blowings.
> This is usually less than the Quad value of fuse, even with
> very large value PS caps and silicon diodes.
>
> >
> >
> > Presuming the correct fuses and so forth, Patrick is right on the money
> > in terms of disconnecting the secondaries on the transformers. This
> > will separate a transformer problem from a load problem. Just hope it
> > is the load, not the iron.
>
> Rewinding Quad II amp PTs isn't a real easy job.
> One needs to be sure about just what is wrong and what one is measuring.
>
> Patrick Turner.
>
> >
> >
> > Peter Wieck
> > Wyncote, PA