User`s manual

"Ticking" noise:
Some tubes (particularly JJ ECC83) tend to exhibit a low-level "ticking" noise right after
the amplifier is taken off standby. The noise stops after a second or two, when the tube
has had a chance to stabilize, and is not indicative of a problem.
Ringing noise or feedback that occurs with no guitar plugged in:
If the amplifier exhibits a "ringing" noise, especially when tapping on the chassis, or if it
makes a howling or whistling feedback noise when the volume is turned up but no guitar
is plugged in, there is probably a microphonic tube in the amplifier, likely in the first
position (the small tube closest to the input jacks), or in the reverb recovery position.
Remove the shield and lightly tap on the tube with the volume turned up. A small amount
of noise is normal, but a loud, ringing noise indicates a microphonic tube, which should
be replaced. In a emergency, you can swap the other 12AX7/ECC83 preamp tubes
around until you find the least microphonic one to put in the first position. Typically, the
phase inverter tube is the least susceptible to microphonics, so the most microphonic
tube should be used in this position. The least microphonic tube should be used in the
first position, and the next least microphonic tube should be used in the reverb recovery
position. When purchasing tubes, be sure to purchase tubes that have been tested for
microphonics. Many vendors do not test for microphonics, and you could end up wasting
your money on tubes that are unsuitable for use. Combo amps are more susceptible to
microphonics than heads, because the sound field coming from the back of the speaker
can excite the tube into oscillation. In rare cases, the EL34 output tubes can be
microphonic, particularly if they are at the end of their lifespan.
Fuse blowing:
An amplifier typically has two fuses - one for the "mains" or AC supply, and a second one
for the "HT" or high-voltage section of the amplifier. It is perfectly normal for a blown
mains fuse to shut the entire amp down. That's the fuse’s job - to shut the amp off to
protect it in the event of a short circuit. Sometimes a fuse will blow for no apparent reason
(called "nuisance" fuse blowing). An amplifier has large filter capacitors that can draw
quite a bit of inrush current when the amp is first turned on and they are fully discharged,
and this can occasionally cause a fuse to blow, particularly if the fuse is old. If your amp
blows a fuse, you should replace it with one of the same type and rating. If it still blows
the fuse, the amp needs further servicing. The HT fuse should be a fast-acting type, and
the mains fuse should be a slo-blo type.
If your Sabre blows the HT fuse, it is most likely caused by a bad EL34 output tube, or
incorrect bias setting (usually accompanied by red glowing plates in the tubes and a very
hot running amplifier). If it blows the mains fuse, immediately on power up every time, it
is most likely a bad rectifier diode. If it just occasionally blows the mains fuse, you may
want to go up one size in fuse to prevent this “nuisance” blowing. If you are using a 2A
fuse, try a 2 ½ or 3 amp fuse, but don’t go any larger or you may damage the power
transformer in the event of a real failure.
Troubleshooting steps:
(1) First pull out both EL34 output tubes and put in a new fuse. Turn the amp on. If the
pilot light comes on, the power transformer and wiring and rectifier diodes are fine. Let it
run for a few minutes to make sure the fuses don’t blow again. Then proceed to
troubleshooting step 3.