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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 29th Sep 2020, 11:45 am   #1
livewireless123
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Default Unusual crystal

Just had a dig in an old bits-box and re-discovered this 10KHz GEC. crystal unit
on an octal base.I shone a torch through the glass and could just make out
lead outs to pins 2, 4, and 5. a cap' meter reads 10pF 2-5 and 4-5. and 5pF
2-4 so possibly 2 sections, centre tapped.
I wonder if anyone can suggest an osc' circuit to fire this up.
I might try to produce a retro digi clock using minitrons.
Mike.
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Old 29th Sep 2020, 12:00 pm   #2
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Default Re: Unusual crystal

Most likely a flexural mode one, with the weld-bonded wires at the points of no displacement.

Almost any of the classic circuits would do, but you may need some filtering to stop it going off at unwanted modes.

Meacham bridge oscillators were popular for VLF crystal oscillators

2^15 Hz crystals were designed for pseudo Pierce simplistic oscillators, with a frequency offset to compensate for the not-quite-right frequency due to the imperfect phase shift of the pseudo pierce. THe true Pierce has three phase shift sections (including the ESR) to make 180 degrees. THe aim was minimum component count and very low battery consumption with CMOS

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Old 29th Sep 2020, 1:46 pm   #3
ionburn
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Default Re: Unusual crystal

I have one of these GEC crystals, frequency 2800 c/s. I built an oscillator based on the attached (unclassified US military source) circuit. Other sources I have seen have had problems using these and they don't seem very active. I had no problems with mine but, perhaps due to low drive level, the oscillator takes (predictively) 50 seconds to startup.
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Old 29th Sep 2020, 1:50 pm   #4
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Default Re: Unusual crystal

I should add too that my oscillator works reliably on frequency but there is minor waveform distortion which would easily be removed either by filtering, or squaring for digital purposes.
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Old 2nd Oct 2020, 10:10 am   #5
livewireless123
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Default Re: Unusual crystal

Thanks for the comments on this, I also found some info on google.
I will try the triode circuit, I have plenty of 6C4s.
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