mystery power transfomer - measuring voltages across all secondaries

[boroman]

I have some 6F6 pentode circuit radio that I resuce some parts from. One of them is power trabsformer. It has 2 green wires, 2 brown wires and 1 red wire. I suppose that:

- brown are HV (thick wire)
- green are screens (thin wire)
- red? (thin wire)

How to test it properly without soldering simple circuit? Red might be center tap from sreens or HV? I already connected power switch with fuse, and ran it through variac, but I'm getting low voltages between browns, but high voltages between brown and red (like 120V when hitting 200 on variac). So is there any way to test everythig here? I will reuse this transformer in a 6V6/6L6 circuit if test it right

[Enzo]

There are not enough wires. Clearly there must be primary side wires we cannot see. Are there others?

If those five are all we get, then I would start by thinking greens were the 6v for heaters, and maybe the red was center tap between browns for the high voltage winding. Maybe?

[boroman]

Primaries are already connected to power switch (and then to fuse and my variac) - those pictured are all 2nd.

[Helmholtz]

Typically there is no separate screen winding.
From the wire gauges I would guess that the brown wires are the heater winding, green/green is HV and red maybe the CT.
Use your Ohmmeter to see which wires belong to the same winding and measure DCR.
Heater winding should have a very low DCR.

Once windings are identified just measure the voltages. Expect them to be at least 10% higher than with load.

[g1]

I have some 6F6 pentode circuit radio that I resuce some parts from.

Do you know the make and model of the radio?

[boroman]

Do you know the make and model of the radio?

Tjerneld 188V
https://www.radiomuseum.org/r/tjemeld_188v188.html

From the wire gauges I would guess that the brown wires are the heater winding, green/green is HV and red maybe the CT.
Use your Ohmmeter to see which wires belong to the same winding and measure DCR.
Heater winding should have a very low DCR.

So,
- between thin green wires I have: 530 ohms
- between (each) green wire and thin red: 260 ohms
- between thick browns: 0.4 ohm
- nothing between red and browns

So... that would lead to 3,15-0-3,15 (green-red-green), and 0-HV (brown-brown)? Might be?

[eschertron]

You have that backwards. the brown wires are the heaters, green/red/green is the HV.
now that you have rung it out, carefully(!) apply power and check voltages to confirm.

[The Dude]

^^^^^ That. The lower resistance winding would also be lower voltage.

[boroman]

You have that backwards. the brown wires are the heaters, green/red/green is the HV.
now that you have rung it out, carefully(!) apply power and check voltages to confirm.

OK, So brown heaters (0 - 6,3), green HV (HV - 0 - HV), right?

Now the tricky part.... :-(
This transformer operated 4 different voltages: 110, 120, 220, 240V but the switch was broken and it just fell apart in my hands. Now I am stuck with few colored primary wires. To run it at 220 or 240V where I live I am supposed to join two of them, right? which ones... I don't know. Yellow, red, brown, brown/yel, green... Will post a photo later!

[Delta362]

Take resistance readings on the primary windings like you did for the secondary and post those please.

[boroman]

Take resistance readings on the primary windings like you did for the secondary and post those please.

OK, here's the photo of the primary side (s)
I'm takie measurements from one side primary (red/left side) to the others (coloured/right side)

from the top:

brown/black - no reading
yellow - no reading
green - 8 ohm
black - 9.5 ohm
brown - 7 ohm

there's continuity between left (red) side and green, red and black, red and brown.

[catalin gramada]

OK, So brown heaters (0 - 6,3), green HV (HV - 0 - HV), right?

Now the tricky part.... :-(
This transformer operated 4 different voltages: 110, 120, 220, 240V but the switch was broken and it just fell apart in my hands. Now I am stuck with few colored primary wires. To run it at 220 or 240V where I live I am supposed to join two of them, right? which ones... I don't know. Yellow, red, brown, brown/yel, green... Will post a photo later!

Better to look for 220v tap. Keep an eye for heaters voltage under load first.

[g1]

Is there a resistance between brown/black and yellow?

[boroman]

Is there a resistance between brown/black and yellow?

It's 3.6 Ohm

[g1]

So brown/black to yellow is it's own separate winding. It could be primary or secondary, there is nothing that says all primary have to be on one side physically. Some transformers have secondary wires on both sides, etc.

Like eschertron suggested above, you need to apply voltage somewhere and measure voltage at all the windings. For safety, it is preferable to start with a low AC voltage applied, like a 6.3V heater supply from another amp, or a low voltage AC wall wart type adapter.