Ecc86 is a low anode voltage designed tube. There are lots of radio circuits that use it. There are more tube types of this type too, it is not just the ecc86.6.3V Anode Voltage is too low for ECC86. How it worked @ 6MHz ?? Are you sure ? What was the Anode current ?
It also depends on crystal specifications. There are variants for 455 kHz crystals and each one has a target application. There is no rule that every 455 kHz crystal will work, definitely no.
I have tried a 100k trimmer at the anode and a 1meg trimmer at the grid and varied them but I could not get it to oscillate. I have also tried a 10millihenry choke at the anode (100R self resistance) and no luck...try 100k => 1Meg
and 1k => 4k7
What is your anode voltage in your simulation?In Pierce configuration, is hard to make the circuit oscillate for crystals below 1MHz. Perhaps you are using a ceramic resonator, not a real crystal which is hard to get for frequencies below 1MHz.
The circuit attach, its a bit more complicate, but oscillates in any conditions, with any type of resonator.
Check the right polarity of L2.
Another option in your Pierce configuration, is to add a series 1mH inductor at the anode (series with the 1k resistor) and place a 122pF cap in parallel with the inductor (will be a resonant circuit on 455kHz). Needs a 100nF decoupling cap to ground at the connection of the 1mH inductor and the 1k resistor. Simulation shows that the circuit oscillates.
Unlikely both a crystal and a ceramic resonator to be dead at the same time.perhaps your Xtal is dead ?
What is the anode voltage in your simulation?ECC86 was designed for car radios. At that time, most of the cars use 6V batteries. The tube works with anode voltages between 6V and 25V.
The slope of the tube is not very high, only 2.6mA/V at 6V, compared to a 100V tube as ECC88 which has about 12mA/V. This make a challange the tube to oscillate without proper feedback.
Both approaches that I mentioned above, improves the feedback, but needs some experiments to make it work.
In addition, what are the crystal model parameters?What is the anode voltage in your simulation?
I tried this circuit at first and it did not work. I tried a 1meg trimmer at the grid, changing it's value to see if it will oscillate. I connected a 100pF fixed and a 5-50pf variable in parallel to the inductor, to bring it at exact resonance. I also tried to short the 1K. nothing...+6.3V
I was hoping to get this running with a tube, so as to match an old wooden radio and be used as a BFO for it. Now the wooden radio has already a HV, but It would be easier and cheaper to do it using just the heaters (rectified).I think you are simply seeing lack of gain. The 452KHz crystal (which should be its series resonant frequency, the 6MHz one was probably its parallel resonant frequency) will need more drive signal. Adding the tuned circuit would certainly help by increasing the impedance at the anode but still no guarantee there would be enough. Just a thought - try swapping the tube with a JFET, it might work better.
Brian.
I have connected a 470pF there as an experiment which did not work. I will reduce this and let you know.In your tube Pierce oscillator #14 you forgot to place a capacitor from Grid to ground. Simulation shows that a 100pF capacitor would be fine.
As I said, the slope of ECC86 is small, and if the tube is old with many working hours, could be even smaller.
If still not oscillating, the circuit posted in #6 will work for sure.
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