PATHÉ PROJECTOR AMPLIFIERS

These circuits are shown to assist anyone who may be restoring these amplifiers, they are intended only as a guide and no responsibility can be accepted for any damage or injury resulting from their use
Amplifiers of this type use high voltages, so repairs or modifications should only be made by suitably qualified or experienced persons.
If you don't know what you are doing, don't do it!


PATHÉ VOX

Original circuit

 

Modified circuit

Points to note:

Never run a valve amplifier with the loudspeaker disconnected, this will generate high voltages which could damage the output transformer or output valves.

If the original loudspeaker plug is not available, the amplifier can be tested by bridging the appropriate pins on the loudspeaker socket but make sure the choke terminals are solidly connected. If the choke terminals are open circuited, voltages in excess of 450v will appear between the metal cans of the smoothing capacitors and the charge will remain after the amplifier has been switched off. YOU HAVE BEEN WARNED!!!

Some capacitors followed the pre-WWII German practice of quoting the capacitance in centimetres. The conversion factor is 1cm = 1.13pf.

VR2 balances the drive to the output valves. It can be conveniently set up by feeding in a constant tone and adjusting VR2 for minimum signal appearing at the cathodes of V3 and V4.


PATHÉ SUPERVOX

Original circuit

 

Modified circuit

Points to note:

Never run a valve amplifier with the loudspeaker disconnected, this will generate high voltages which could damage the output transformer or output valves.

If the original loudspeaker plug is not available, the amplifier can be tested by bridging the appropriate pins on the loudspeaker socket but make sure the choke terminals are solidly connected. If the choke terminals are open circuited, voltages in excess of 450v will appear between the metal cans of the smoothing capacitors and the charge will remain after the amplifier has been switched off. YOU HAVE BEEN WARNED!!!


PATHÉ SON

Circuit of one amplifier 'as received', believed to be heavily modified.

 

Points to note:

Never run a valve amplifier with the loudspeaker disconnected, this will generate high voltages which could damage the output transformer or output valves.
The second valve appears to have originally been connected as a pentode but later modified to work as a triode; a suppressor grid decoupling capacitor is still in place but disconnected.
Speculation:  The tone control does not appear to function, I suspect it was originally in some sort of feedback loop which reduced the gain of the output stage, which was why the extra gain of a pentode was necessary.