well,ive fitted mullard oa47 diodes inn place of d3 and d4,its made no difference(the needle still sits at 20% deflection with input open,ive checked all resistor values,(they seem spot on ( all 5% tolerance),the voltage readings i get are as follows ,left to right,originals first,mine in brackets. 4.98(4.990) 4.56 (4.533) 2.42 (2.748) 1.29 (1.286) 2.80 (2.81) 2.78 (2.652) 1.29 (1.295),i will post some screenshots from the scope later,ok.,im pulling my hair out now!! lol,73 m3vuv.
M3VUV,
The DC voltages at the various points are correct. This means that all the parts that determine the DC voltages are correct.
The parts with the blue check marks are correct.
The circuitry in the emitter of the transistors, the 33
resistors and the 2.2uF capacitors impacts the AC gain of these amplifier stages.
These 2.2uF capacitors have been discussed before. I used ceramic capacitors in the prototype. Other people have used low ESR electrolytic capacitors. If you use electrolytic capacitors you can increase the value to get a lower ESR. If the ESR is too high it will reduce the gain of these amplifier stages. Try 47uF or 100uF 105C low ESR electrolytic capacitors.
Operating FrequencyYou say that the Tektronix 453 scope is set to 0.1ms/div. The UNCAL lights are on for the timebase and the vertical inputs:
The variable timebase slows the time/div by up to 2.5 times. So if the UNCAL light is on the timebase is between 0.1 and 0.25ms/div
To extinguish the UNCAL lights, turn the red knobs on the vertical controls clockwise. There is normally a click, a switch, and the lights will go off. Do the same with the red knob on the timebase.
x10 Horizontal MagnificationThe Tektronix 453 has a Horizontal magnifier. This should be set to off and the MAG light should be off:
Make sure that the Horizontal Mag is set to off.
If I assume that the timebase is 0.1ms/div, the period of the waveform shown is about 1.5 div or 0.15ms
This means the frequency is only 6kHz and 10 times lower than it should be. Check the value of C2 in the oscillator section. It should be 1.5nF, 1500pF.
Regards,
Jay_Diddy_B