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THÖRESS
845 Single-Ended Triode . Mono . Power Amplifier
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"SE845 Mono"
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I N S T R U C T I O N
M A N U A
L.............
Thank you for purchasing the
SE845 Mono Power Amplifiers!
THÖRES
Our SE845 Monoblock has been tailored around
the famous 845 filamentary
power triode in single-ended (class-A) operation mode for an output of 20 watts into
a 4, 8 or 16 ohm load. The amplifier is built with meticulous hand construction using
our proven point-to-point wiring techniques. Much care has been taken in arranging
each aspect of the internal construction to ensure low noise performance, ease of
service and the highest reliability for many years to come. Please read the following
explanations and instructions carefully to get the most out of your SE845 amplifier!
CATHODE POINT BALANCE
The 845 power triode is a filamentary tube (FT) with a brightly glowing 10V/3.25A
filament which has been developed in the early times of vacuum technology. It
consumes a considerable amount of heating power, 32.5W=10Vx3.25A. The filament
of a FT consists of a thin thoriated tungsten wire mounted with spring suspensions
to mica supports pressed into the glass envelope. The electrons which constitute the
anode (cathode-to-plate) current are emitted by the glowing wire itself (directly) and
not by a cathode pipe insulated from the filament as in case of the more widely used
indirectly heated tubes. The anode current flows through the filament along with
the heater current!
FTs require a specific cathode point implementation outside the vacuum envelope in
order to separate the signal current from the subsidiary heater current!
In the inception of vacuum technology (when semiconductor rectifiers were not in
existence) FTs were AC heated with the aid of dedicated windings on the mains
transformer whereas a M.IDDLE T.AP of the winding served as cathode point (ACMT
cathode point implementation). In our mono block the 845 tube is DC heated
whereas the cathode point is given by the junction of a two-resistor (RR) voltage
divider bypassed with a balance potentiometer (BALPOT, mounted on the rear
panel) connected in parallel with the filament. We call this arrangement DCRR
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Summary of Contents for THÖRESS SE845 Mono
- Page 1 I N S T R U C T I O N M A N U A L…..Thank you for purchasing the SE845 Mono Power Amplifiers! THÖRES Our SE845 Monoblock has been tailored around the famous 845 filamentary power triode in single-ended (class-A) operation mode for an output of 20 watts into a 4, 8 or 16 ohm load.
- Page 2 cathode point implementation. The BALPOT allows to balance the cathode point of the amplifier with respect to the filament of each individual 845 power tube in order to ensure equal current flow through both ends of the tube filament. Optimal cathode point balance is attained when the hum induced in the wanted signal via residual ripple of the heater voltage vanishes (reaches a minimum).
- Page 3 Tube microphony is especially critical when highly efficient loudspeakers are involved, for obvious reasons. Place the SE845 Mono Amplifier on a rigid rack, shelf or platform carefully decoupled from the floor in order to keep the signal free of noise artifacts due to tube microphony!
- Page 4 LOUDSPEAKER LOAD MATCHING The SE845 Mono Amplifier allows for precise 4, 8 or 16 ohm loudspeaker load matching by way of jumpers soldered to the secondary terminals of the OPT according to the patterns given below. Each of which pattern corresponds to a specific (primary versus secondary) turns ratio of the OPT.
- Page 5 It is not advisable to use a 8-ohm rated speaker on the 16-ohm load pattern of the OPT! FUSE The SE845 mono amplifier draws a current of about 0.7/1.4A from the 230Vac/115Vac mains corresponding to a power consumption of 160W. It is protected with a 2A slow-blowing 5x25mm fuse inside the power inlet module.
- Page 6 SETUP To set up a pair of SE845 Mono Amplifiers power off all devices of the setup and proceed as follows. Do not connect the amplifiers to the mains until steps 1 to 5 have been taken! Do not connect the amplifiers to the preamplifier until steps 1 to 8 have been taken! 1.
- Page 7 accomplished. 8. Balance the cathode point of the R-channel monoblock with respect to the filament of the installed 845 tube in a similar manner. Power off the R-amplifier after the balancing procedure has been completed. Check the amplifiers for correct cathode point balance from time to time and finely tune the balance if necessary! Always re-balance the L+R amplifier after changing the 845 power tube! 9.
- Page 8 • Dimensions: 150x595xH330 mm, 330=20/feet+210+150/tube over case, 595=575+20/speaker terminals, weight 18 Kg (each monoblock). • Dimensions of the shipping crate: 950x400xH460 mm..............THÖRESS... A Tribute to Professional Audio Components from the Golden Age of the Electronic Tube ..............
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