22-10-2018, 06:33 PM
Hi
Does anyone recognise this Standard Telephones & Cables Oscillator type 74330B.
I posted this on UKVRRR but I would be interested to know if anyone here has any information.
My guess is it would have be used for injecting signals into PO private transmission lines for testing, or equipment prior to leaving the factory.
The selenium rectifier is visible in the last photo.
The left hand knob, which is marked "P.S." has the following settings;
300 400 500 800 1400 1600 1800 2000 2200 2400 2600 2800. It isnt clear but I am assuming this is marked in cycles per second or Hz.
The right hand knob is marked "D.B. Send" and is calibrated in.
-30 -20 -10 0 +10.
The 2 black thumb screw terminals top right are marked with AC symbol "~" I would assume this the output.
The black knob under these terminals is just a handle for lifting as is the black knob opposite on the left under the earth terminal.
The black thumb screw terminal top left is marked with earth symbol.
The centre knob at the bottom is marked "OSC"
The 2 fuse carriers are marked "0.25 Amp" they are very nicely made and slide down before lifting off, they have standard type fuse wire fitted between the terminals.
There does not appear to be any other cable entry points and the insides to me look complete.
I imagine the centre calibrated meter is used to set a prescribed level.
There is a 50's style electrolytic fitted, which looks to be a replacement.
I have given it a try, and it works, I first disconnected the very leaky HT electrolytic and a 250uF 12v one which I believed was in the cathode circuit across a 300 ohm resistor, and tacked in some temporary replacements.
It worked OK giving about 3v output with no load, and about 1.3v into 600 ohms.
But it has a strange HT supply, I believe it is a voltage doubler as the transformer HT winding is only 90v. There was about 150v on the final HT.
The dual variable resistor does set the level, which is slightly short of the set point on the higher frequencies.
I have been wondering about the year of manufacture. The capacitors look like paper in wax/bitumen types encased in a metal can. Similar to those used in late 20's to mid 30's radios. There is a 250uf 12 volt cap in a tall rectangular metal can with a Bakelite moulded top. The resistor immediately to the right of the valve in photo 2 is one of those with fuzzy colour bands as if they have been spayed on. There is the dog bone resistor on the right. There is a black moulded mica capacitor just behind and to the right of the dual ganged pot.
The resistors associated with the DB level control are wire wound on tall ceramic bobbins.
Here are some photos;
thanks
Mike
Does anyone recognise this Standard Telephones & Cables Oscillator type 74330B.
I posted this on UKVRRR but I would be interested to know if anyone here has any information.
My guess is it would have be used for injecting signals into PO private transmission lines for testing, or equipment prior to leaving the factory.
The selenium rectifier is visible in the last photo.
The left hand knob, which is marked "P.S." has the following settings;
300 400 500 800 1400 1600 1800 2000 2200 2400 2600 2800. It isnt clear but I am assuming this is marked in cycles per second or Hz.
The right hand knob is marked "D.B. Send" and is calibrated in.
-30 -20 -10 0 +10.
The 2 black thumb screw terminals top right are marked with AC symbol "~" I would assume this the output.
The black knob under these terminals is just a handle for lifting as is the black knob opposite on the left under the earth terminal.
The black thumb screw terminal top left is marked with earth symbol.
The centre knob at the bottom is marked "OSC"
The 2 fuse carriers are marked "0.25 Amp" they are very nicely made and slide down before lifting off, they have standard type fuse wire fitted between the terminals.
There does not appear to be any other cable entry points and the insides to me look complete.
I imagine the centre calibrated meter is used to set a prescribed level.
There is a 50's style electrolytic fitted, which looks to be a replacement.
I have given it a try, and it works, I first disconnected the very leaky HT electrolytic and a 250uF 12v one which I believed was in the cathode circuit across a 300 ohm resistor, and tacked in some temporary replacements.
It worked OK giving about 3v output with no load, and about 1.3v into 600 ohms.
But it has a strange HT supply, I believe it is a voltage doubler as the transformer HT winding is only 90v. There was about 150v on the final HT.
The dual variable resistor does set the level, which is slightly short of the set point on the higher frequencies.
I have been wondering about the year of manufacture. The capacitors look like paper in wax/bitumen types encased in a metal can. Similar to those used in late 20's to mid 30's radios. There is a 250uf 12 volt cap in a tall rectangular metal can with a Bakelite moulded top. The resistor immediately to the right of the valve in photo 2 is one of those with fuzzy colour bands as if they have been spayed on. There is the dog bone resistor on the right. There is a black moulded mica capacitor just behind and to the right of the dual ganged pot.
The resistors associated with the DB level control are wire wound on tall ceramic bobbins.
Here are some photos;
thanks
Mike
