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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 27th Apr 2024, 1:59 pm   #1
trobbins
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Default Vertical output transformer - re purposing

I've just been checking out a vertical line transformer from a late 1960's aussie B&W TV, with only 3 wires exiting it. The part is marked 43340A, and is shown as TR301 in AWA's TV schematic for the 50-00 series chassis: https://www.kevinchant.com/uploads/7...00_series..pdf

The vertical output stage uses a 6GV8 7Wdiss power pentode in single ended mode with 205V B+ and the vertical output transformer has a non-isolated secondary winding with a small number of turns (23:1 turns ratio).

The inductance of the primary winding measures 19H at 20mAdc with 6Vac, reducing to 11H at 60mAdc at 12Vac, so this transformer would happily function as a filter choke, and would likely be happy at 80mAdc idle (DCR=370, 2.5W) as this part is a fair size.

Another use would be as the output transformer in a single-ended cathode follower output stage audio amp, as the primary winding would present a 4kohm SE load, for an 8 ohm secondary load. The inductance is not huge, but for a cheap and cheerful guitar amp it would likely be fine.

Would that type of vertical output transformer been common in B&W TV's ?
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Old 27th Apr 2024, 7:07 pm   #2
Ed_Dinning
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Default Re: Vertical output transformer - re purposing

Hi Tim, I believe most UK types were double wound transformers, but a few sets used auto transformers.
Double wound gave the scan coils insulation an easier time.

Others may be able to name makers/ sets that used auto transformers in the UK market

Cheers, Ed
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Old 27th Apr 2024, 10:19 pm   #3
kalee20
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Default Re: Vertical output transformer - re purposing

I've used frame output transformers as mains transformers even! The insulation isn't to be relied upon to meet modern safety requirements - but I still have a radio I made out of old TV bits - the frame O/P transformer giving about 19V AC which supplied a PCL82 with a low-voltage lamp in series, and also an EF80 with a 12V lamp in series, in a live-chassis design.

And yes, a few manufacturers did have the frame output transformer as an autotransformer - maybe it worked out slightly cheaper to leave out the primary-secondary insulation, and put it in the frame deflection coils instead.
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Old 28th Apr 2024, 1:31 am   #4
trobbins
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Default Re: Vertical output transformer - re purposing

I have two of these vertical output transformers so will aim to set one up in a prototype amp and check out what plentiful TV style output stage valves would be practical, as well as a suitable driver stage to adequately swing a cathode follower to its limits.
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