HT fuse
The HT or ‘High Tension’ fuse protects the high voltage for the valve supply. If this fuse blows, the first
step is to replace it with an identical T250mA 20x5mm fuse. The HT fuse may sometimes blow due to
‘flash-over’ inside an output valve. This is where during the manufacturing process, not all of the gas is
removed from the glass envelope and the ‘getter’ inside the valve, usually made from barium or
magnesium oxide, will burn or evaporate these remaining gasses resulting in the common silvered
internal surface of the valve. This process, which is more likely to happen with new equipment, draws
high current momentarily and can blow the HT fuse. It will rarely cause any damage so just replacing the
fuse is sufficient to get the amp running normally again.
However, if the HT fuse blows again, it may indicate a serious valve failure where internal parts of a
valve are shorted and in this case the amplifier needs to be checked by a qualified engineer to assess the
problem.
Speaker outputs
PLEASE NOTE: The lightning flash with arrowhead symbol, within an equilateral triangle, is intended to
alert the user to the presence of uninsulated ‘dangerous voltage’ within the product’s enclosure that
may be of sufficient magnitude to constitute a risk of electric shock. Terminals labelled as “Speaker
Outputs” must be connected to a speaker cabinet of the designated load rating using an un-shielded two
conductor cable for speaker use at all times during operation. Never use a guitar cable to connect the
amplifier to a speaker as this presents the amplifier with a ‘capacitive load’. This can cause instability or
oscillation which may seriously damage valves and/or the expensive output transformer.
The output transformer in the RD1 has 2 separate secondary windings; a 16 Ohm and an 8 Ohm. This
makes it easy to connect different combinations of speakers. There are three speaker output jacks: 2 x 8
Ohms, (wired in parallel) and 1 x 16 ohms.
So here are the possible combinations:
1.
For a single 8 Ohm cabinet, use either of the 8 Ohm sockets.
2.
For a single 16 Ohm cabinet, use the 16 Ohm socket.
3.
For a pair of 16 Ohm cabinets, use both of the 8 Ohm sockets.
It is possible to use a pair of 8 Ohm cabinets with the RD1 but a special series lead needs to be used.
Over the page is a diagram of how this is achieved:
