Radio Interference Measurement Receiver

[geeoboeh2s]

I have a Post Office designed Radio Interference Measurement receiver. When last used with its dedicated power supply it worked perfectly. However I no longer have the power supply.
The operating manual states that the power supply provides 250Vdc and 6.3Vac so I didn't anticipate any issues with evaluating its performance.
Power is provided to a 4 pin Jones plug and I readily determined the 3 pins for ht, heater supplies and common ground. The 4th pin is connected to the suppressor grid of the mixer valve, V4 on the circuit diagram. I need to determine the potential applied to this pin.
If anybody has the relevant power supply or a circuit diagram perhaps they could help or perhaps somebody has experience of mixers with the oscillator voltage taken to the suppressor grid.

Chris

[Leon Crampin]

It looks to me as though the suppressor grid of the mixer receives the local oscillator output in order to function as a mixer. I suspect that the decoupled link to the Jones plug is there to enable the local oscillator to be disabled from the front panel, either to facilitate finding the source of any unusual "birdies" during measurements - or else possibly as an aid to the alignment of the IF stages of the receiver.

This looks like a very high gain receiver - what's the valve line-up?

Leon.

[ms660]

The connection to the suppressor grid will be for the bias voltage...11 volts -ve so far as I can make out.

Lawrence.

[geeoboeh2s]

Leon,
The receiver has 11 valves,
R.F stages, amplifier, mixer, oscillator are CV1091
If Amplifiers, CV1053(2) and CV1065 (1)
Meter detector CV1054
Calibration oscillator CV172
DC amplifier CV587
Audio CV587
BFO CV587

The unit is designed to detect and measure the amplitude of levels of interference, conducted and radiated. A rod aerial is included for the measurement of field strength in чV/m.

Lawrence,
Perhaps you could tell me how you arrived at -11Vdc for the suppressor voltage. It seems a sensible figure but I can't follow how you calculated it.

Chris

[ms660]

Originally Posted by geeoboeh2s

Lawrence,
Perhaps you could tell me how you arrived at -11Vdc for the suppressor voltage. It seems a sensible figure but I can't follow how you calculated it.

Chris

Section 2.2.8 in report page 8 here:

http://www.digitalarchives.bt.com/Ca...B_226_2388.pdf

Lawrence.

[geeoboeh2s]

Thank you very much for the link to the Post Office document. It is far more comprehensive than the one supplied with the test set that merely says that the supplies are 250Vdc and 6.3Vac. A very confusing statement.
A 180R resistor in the grounded end of the ht line should suffice.

Chris