Vertical output transformer - re purposing - UK Vintage Radio Repair and Restoration Discussion Forum

trobbins · 27th Apr 2024, 12:59 pm

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/7/1/0/8/7108231/chassis_50-00_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 ?

Ed_Dinning · 27th Apr 2024, 6:07 pm

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

kalee20 · 27th Apr 2024, 9:19 pm

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.

trobbins · 28th Apr 2024, 12:31 am

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.

27th Apr 2024, 12:59 pm	#1
trobbins Octode Join Date: Oct 2009 Location: Melbourne, Victoria, Australia. Posts: 1,041	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/7/1/0/8/7108231/chassis_50-00_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 ?

27th Apr 2024, 6:07 pm	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,681	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

27th Apr 2024, 9:19 pm	#3
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,545	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.

28th Apr 2024, 12:31 am	#4
trobbins Octode Join Date: Oct 2009 Location: Melbourne, Victoria, Australia. Posts: 1,041	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.