Hartley oscillator doesn't start anymore.

Thread Starter

patpin

Joined Sep 15, 2012
401
Hello, I had this oscillator working for months and after replacement of components after OUT2 the oscillator doesn' start anymore.
I did NOT changed things on the circuit as joined!
I scope on OUT0. I measured following:
Knooppunt (=node) A: 1.44V
Knooppunt B: 0.55V
Q1b: 0.88V; coll.8V; e 0.33V; so Q1conducts;
L2: 53µH; L1 14µH (Induction meter not sensitive enough below 20µH but measures as when it oscillated.)
C3 1083 pF (in circuit) (800 out circuit)
C2 100nF
Q1bc: 0,712 (reverse pol. 2.8); Q1be: 0.728 (reverse 2.7)
D1/D2/D3 all between 0.610 and 0.630; reverse 2.8
R1/2/6: values as diagram
over C6: 11K
over C1: 1.5Meg
Voltage over D1: 6.54 V
D2/D3: 0.57
Voltage over R1: 0.318 (sim was 0.255). I lowered the Q1 base voltage to 0.87 as in the sim by putting R 10K over R2: no help.
All grounds are checked.
Changing mutual induction L2-L1 : no help (it helped before this problem).
I would appreciate some help on how to proceed. Thanks.
 

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drc_567

Joined Dec 29, 2008
1,135
... If you were to remove the connection between out1 and R10, would you then have oscillation in the tank circuit? It seems that the Q2 section of the circuit is for amplification of the tank circuit signal. Maybe the Q2 section needs some adjusting or re-arranging.
 

Thread Starter

patpin

Joined Sep 15, 2012
401
... If you were to remove the connection between out1 and R10, would you then have oscillation in the tank circuit? It seems that the Q2 section of the circuit is for amplification of the tank circuit signal. Maybe the Q2 section needs some adjusting or re-arranging.
I have no oscillations at the collector of Q1 and I removed R4 too.
 

drc_567

Joined Dec 29, 2008
1,135
... Are you able to measure the DC voltage between the base and emitter of Q1? It should be about 0.7 volts DC, if Q1 is working correctly.
 

Thread Starter

patpin

Joined Sep 15, 2012
401
... Are you able to measure the DC voltage between the base and emitter of Q1? It should be about 0.7 volts DC, if Q1 is working correctly.
Base is 0.56 relative to emitter. There is a V. drop of 0.31 over R1.
When circuit functioned there was always a base V of 0.86 relative to ground.
 

drc_567

Joined Dec 29, 2008
1,135
... As a guess, either something is wrong with the Q1 biasing components, D1 or D2, or possibly there is something wrong with Q1 itself. What are the DC voltages across R6 and R2? ... Wondering if the current through either resistor is reasonable or not.
 

Thread Starter

patpin

Joined Sep 15, 2012
401
... As a guess, either something is wrong with the Q1 biasing components, D1 or D2, or possibly there is something wrong with Q1 itself. What are the DC voltages across R6 and R2? ... Wondering if the current through either resistor is reasonable or not.
Over R6 0.86 V; over R2: 0.3 V
PS. I have already replaced Q1 but no help..
 
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drc_567

Joined Dec 29, 2008
1,135
... That result indicates that there is more current flowing through R6 than through R2, which doesn't sound right.
... Can you measure the DC voltage across D1, D2, and D3? If they are working correctly, the voltage drop should be about 0.7 volts DC for each diode.
... edit ...meant to say more current through R2 than R6.
 
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Thread Starter

patpin

Joined Sep 15, 2012
401
Voltage over D1: 6.54 V
D2/D3: 0.57
All three as given by LTSpice.
I also add some plots of a starting oscillation (on sim)
 

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drc_567

Joined Dec 29, 2008
1,135
... still trying to understand why the Q1 emitter to base voltage is low, meaning Q1 is not completely turned on. Try reducing R1 to 500 ohms and see if Vb-e increases ... just another guess though.
 

Thread Starter

patpin

Joined Sep 15, 2012
401
... still trying to understand why the Q1 emitter to base voltage is low, meaning Q1 is not completely turned on. Try reducing R1 to 500 ohms and see if Vb-e increases ... just another guess though.
Base is 0.54 higher as emitter; over R1 there is a drop of.33V ; base to ground 0,87 instead of 0.88 AND IT OSCILLATES !!!! Congratulations for yr debugging effort! Freq is 657 Khz and Vpp is 8. (at OUT0); this is much less as on LTSpice where I get 15.7Vpp. I tried changing mutual induction but it only reduces the Vpp. Any idea?
 
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drc_567

Joined Dec 29, 2008
1,135
... Something else to try as far as increasing Vpp ... place a 100 μF capacitor in parallel with R1. This should increase the Vpp amplitude ... but may require adjusting. ... Not sure why LTSpice gives a greater Vpp amplitude ...
 
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