[Milsurplus] [ARC5] BC-348 PSU questions

[Kenneth G. Gordon]

On 2 Oct 2015 at 10:43, Ian Wilson wrote:

> a puzzle. I have disconnected everything from its leads. Apart from
> two black AC input leads, we have:
>   - Red1
>   - Red2
>   - Yellow (possibly red/yellow originally)
>   - Green1
>   - Green2
> 
> All the transformers I've seen like this before have a centre-tapped HT
> winding
> and a heater winding. This one is different. I measure 6.3VAC across G1/G2
> with AC mains applied to Black/Black, as expected. But the DC resistances
> are odd:
> 
>   - Red1 - Green1 or Green2: 62 ohm
>   - Red2 - Yellow: 56 ohm
>   - Red1 - Red2: no connection
>   - Green1 - Green2: 0.2 ohm

Red1 is very odd. SInce the resistance between it and the two greens is 
(apparently) identical, that suggests some sort of CT, but it can't be. It could 
be a HV winding which is "on top of" the filament winding, and the low 
filament resistance simply makes it LOOK like the resistance to both is 
identical. Perhaps measuring the voltages with AC connected to the black 
wires would give a more accurate reading of their true relationship.

Red2 and yellow (possibly should be Red-Yellow and Yellow) is a HV 
winding of some sort, but no CT.

Green/green is filaments.

I suspect three differing possibilities: 1) the transformer is actually an audio 
transformer of some type and not a power transformer, or 2) there are some 
sorts of weird internal shorts taking place, or 3) that which I mentioned above

In any case, if that thing was mine, I would either throw it away, or dismantle 
it for rewinding.

Ken W7EKB