Identifying primary and secondary on Transformer

[Richardgr]

Hi Joe, thanks for the comments. I did compare with the transformer suggested for the ECL86 schematic you posted, and that one was 140mA, but 275-0-275 and valve rectified. But writing this now I can see the flaw in my thinking! 109-0-109 @ 150mA is less than half the power, unless one the 275-0-275 one is defined as the total current for the whole winding, and the 109-0-109 one is the current for each half of the winding.

Picture attached. It has a bigger core than the other one, that was not so far away from what I needed, which makes me think it is possible.

I think maybe I need to connect it to a suitable load (e.g. 60W lightbulb) and see how it behaves, working with the principle that 10% reduction of the unloaded voltage is close to to the normal working point. I can use the actual heaters to test the other secondary.

Cheers, Richard

[Ed_Dinning]

Hi Richard. It looks like a simple transformer to dismantle, and is wound on a bobbin.
If you are feeling brave you could try rewinding it.

Ed

[Richardgr]

Hi Ed - It would be interesting one day to have a go at winding my own transformer. I am always impressed with these guys who say 'needed a winding for this, so stuck N turns of X guage wire around the bobbin'.


I decided to try and evaluate this transformer with some real load, to see if it is viable.

ECL86 filament is 6.3V @ 700mA, so approx 10R load and 5W dissipation. As luck would have it I had a bunch of 10R 5W resistors, so I connected them a 2 parrelled on each side of the CT 8V winding, and then 3 in parallel (= 3.3R) between them to get the voltage down to 6.3V.

On the 109-0-109 winding I put a 60W bulb, which would require 250mA approx if the voltage was around 240V.

So ... it all looked very promising! Unfortunately my 5W resistors were a bit marginal since they were dissipating 5W, and they were starting to smoke so I did not want to leave it running to see how the transformer reacted after a few minutes. However the voltages all looked OK, close to 10% of the unloaded voltages, which I think is a reasonable safety margin.

Input voltage 235V

Unloaded 109-0-109 248V
Unloaded 8-0-8 18.2V

Loaded 109-0-109 216V
Loaded 8-0-8 16.1V (6.3V across the paralelled 10R).

Before I start drilling my chassis, does this seem like a reasonable test?

Cheers, Richard

[Ed_Dinning]

Hi Richard, looks like you could get away with it.
I'm a bit surprised at the poor regulation of the 109-0-109 winding. 218v nominal, 248v off load and 216v on load

Ed

[Richardgr]

Hi Ed, thanks for that. It could have been the variac was not on the same spot, and maybe the loading of the other secondary winding could affect the voltage? Plus the 60W bulb (250mA) is a bit more of a load than the final amp should be (180mA ish).

[Ed_Dinning]

Hi Richard, try it and see. Keep a close eye on the transformer temp. It should not get more than hand hot (45C) in an hour.

If all else fails it looks as if it would be easy enough to rewind

Ed