Hello Jac, I'm sure this will turn out to be a truly excellent receiver. But before that happens every stage of the circuit will have to be traced out and documented. Tomorrow, I might be in a position to test the timebase panel in isolation from the main chassis. The attachment shows a rather rough and ready circuit diagram of the frame timebase.
Till Eulenspiegel.
The Ever-Ready experimental transistor TV set was developed with participation of the Thorn laboratories. Compare the circuit of the frame timebase circuit of the 1961 Ferguson 743T with the FTB of the ER set.
The timebase repetition rate is determined by C117 and R134, R134 and R135. Note the isolation diode W7, also the damper diode W6. The sawtooth forming capacitors are C121 and C122.
Till Eulenspiegel.
Those 2G302 transistors close to the line output transistor are used in the frame and line sync blanking circuit. Ref. to previous post.
Having established what the transistors do I'll move on to tracing out the sync separator stage.
Till Eulenspiegel.
The sync separator stage.
It can be seen that the sync separator transistor is in a conductive state and will be turned off when positive going sync pulses are applied to the base.
Till Eulenspiegel.
Attention is now turned to the line oscillator and the indirect sync system.
The line oscillator has three windings. Two are the collector and base windings in the blocking oscillator, the third winding is the base drive for the 2N1046 line output transistor.
The method of controlling the frequency and phase of the oscillator quite different to anything I've ever seen in a domestic television set.
A 2G302 transistor accepts the differentiated sync pulses and conducts on the negative going leading edge. The transistor shares the same 22Kohm collector load resistor with another 2G302 transistor. This transistor accepts the flyback pulse from the line output transistor. It's here where the strangeness begins. Common logic would suggest the that voltages on the common load resistor will provide the control of the line oscillator. Not so, instead the controlling voltage is derived from the 15K emitter load resistor. In series with the base winding of the line oscillator transformer is an adjustable inductor, this is obviously a key component is the flywheel sync system, if one can call it that.
Later today I will submit my interpretation of the line oscillator and sync circuits. A diagram and more suggestions on how the circuit works.
Till Eulenspiegel.
The circuit of the line sync system. I reckon it's a comparator. The transistor which receives it's drive from the line output transistor is effectively shunted across the sync amplifier transistor. The control voltage is developed across the 15Kohm emitter resistor. The adjustable inductor is possibly the phasing coil. Adjust to centralise the picture.
Till Eulenspiegel.
Testing the timebase panel.
Power supplier was set for 8volts and connected across the 5000uF capacitors.
20mS sawtooth waveform at the collector of the OC200 frame output transistor.
The waveform across the sawtooth forming capacitor in the line blocking oscillator.
The line timebase is running too slow.
Waveforms are present at the base and collector of the 2N1046 line output transistor.
Till Eulenspiegel.
How slow, is it waiting for sync?
Frank
How slow, is it waiting for sync?
Hi Frank, that may well be the matter. The line sync discriminator is not the usual balanced type and may well need the presence of sync pulses to bring it up to the correct operating frequency. According to the oscilloscope the repetition rate is 443Hz. As the EHT is generated by separate circuits the free running line timebase frequency is not important.
Till Eulenspiegel.
Mod Note: Fixed post formatting ?
Monitoring the emitter current of the line output transistor. The resistance between the emitter and chassis is used.
The waveform confirms that the sawtooth current is flowing through the high impedance line scanning coils. The waveform applied to the base of the line output transistor consists of a short duration positive going pulse and flat negative going scan period. Conduction takes place during the forward scan and the ramping up takes place in the scanning coils.
The IF board appears to be almost identical to the same in the Ferguson 743T.
Till Eulenspiegel.
Power supplier connected direct to the battery plug, output set to 10 volts.
The results so far.
The EHT generator is working but the regulation is bad. The timebases are way off frequency. Attention will be turned to the IF board. Information for this part of the receiver can be found in the 1961/62 Radio and Television servicing book.
Hi Peter, I've been working on the IF board all afternoon in my isolation workshop.
The power supplier is set for 10 volts. Aurora and tuner to Channel 1. Scope reveals nothing at the video detector load resistor. Soon discovered that the tuner derives it's power from a separate 10volt supply. Connect tuner to the IF board -10V line. The four stage sound IF amplifier and detector is now working. Sine wave waveform present across the detector load. No sound from the loudspeaker because the audio amplifier is supplied from a separate power supply source. But still nothing at the video detector load resistor. The vision IF amplifier has five amplifier stages. Sound and vision IF amplifiers in this set employ Mullard AF114 transistors. Voltage measurements reveal one of the vision IF transistors has almost zero volts on it's collector, it's that well known tin whiskers fault again. An AF124 will be used as the replacement.
I'll report my findings tomorrow after the set has been reassembled.
Till Eulenspiegel.
The replacement AF124 transistor has been fitted. To gain access the IF board was completely removed from the chassis, not an easy job.
With the PCB still removed from the chassis the power supplier was reconnected. Simple voltage measurements indicate all the vision IF transistors are drawing current. Base voltage of each VIF transistor is 0.2V above the emitter volts.
Checked a Hunts 1mfd 150V capacitor and found it had a 10Kohm leak. There's two more Hunts capacitors to test. One has a value of 0.25mfd and the other a value of 0.1mfd. Will check those tomorrow.
Till Eulenspiegel.
AF114 and AF124.
The EHT generator units. Any info about Oliver and Randall?
I guess one disadvantage of working on an experimental model is that you're pretty much in uncharted territory, and very much walking alone. I can't say that name rings any bells, but then your knowledge is way beyond anything I could even dream of.
It's definitely an interesting little set, and an interesting project to follow!
Hi Marion,
at least we have a brief description of the power supply arrangements. From page 122 of the December 1964 Practical Television magazine.
The Ever-Ready prototype Mk5 405 line transistor TV receiver. Extract from the description of the set.
"A separate blocking free-running oscillator feeding a five stage Cockroft-Walton multiplier provides EHT. A metrosil is employed to regulate EHT and give focus potential.
The particular triumph of the circuit is the stabilised power generator which maintains the battery volt-ampere product substantially constant. This employs three transistors, five diodes and a high ratio transformer with complicated suppression and smoothing."
On a small PCB we find a Mullard OC35 power transistor, an Ediswan XA701 and an unknown transistor in the regulator circuit. Also two stud type diodes, an OAZ703 Zener diode and two small diodes, the types of those will be determined after further examination of the board.
The tripler lives in one of the Oliver and Randall boxes and I assume the EHT blocking oscillator is in the other box.
Till Eulenspiegel.
