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B&W TV Pineapple standards converter and David Looser modulator.

Black & White Television

Last Post by Till Eulenspiegel 2 years ago

4 Posts

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Till Eulenspiegel

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The first attachment shows the recently repaired Bush TV22 connected to the modulator unit and my Pineapple field store converter along with a 625 line Test Card C generator which bought some twenty years ago from HS Publications.

The original 1988 PCB artwork for the David Looser modulator.

Till Eulenspiegel.

Posted : 14/02/2023 12:21 pm

Lloyd and Nuvistor reacted

Till Eulenspiegel

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Posts: 4943

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Circuit diagram of the vision modulator and oscilloscope waveforms. The settings for the upper and lower traces are 20mV/division and the timebase is 20uS/division. The video bias control setting is for the sync tips to be as close to zero modulation as possible.

Till Eulenspiegel.

Posted : 14/02/2023 5:12 pm

Till Eulenspiegel

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Having proved my Pineapple standards converter still works my attention was turned to Derren's converter which today was made ready for testing. The small internal modulator unit was discarded and the converted baseband video output connected to a BNC socket. 1volt P - P video will be supplied to the modulator. Video input has a 75ohm termination resistor.

Till Eulenspiegel.

Posted : 14/02/2023 9:28 pm

Till Eulenspiegel

(@till)

Posts: 4943

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The modulator which was previously used with the Pineapple converter.

The integrated circuit which was a surface mounted device had failed and it wasn't possible identify it's type. What we do know about the circuit design is that the IC was intended for negative modulation systems with intercarrier sound. In fact the AM sound carrier was generated by a 3.5Mhz oscillator and mixed with the baseband 405 line video. Performance of this modulator was never satisfactory because intercarrier sound is not suitable for positive video modulation systems because of the interruptions to the carrier signal during the period when the synchronising pulses are in the video signal. Intercarrier sound is possible with negative modulation systems because the signal carrier does not go down to zero or near zero level.

Till Eulenspiegel.

Posted : 15/02/2023 11:12 am