Mod tranny ID

[VK7ZL]

Can anyone identify this mod tranny or guess at a rating for it?
The code number is A14806 which may not mean anything.
Resistance measurements between terminals:
1 & 2 = 80 ohms
1 & 3 = 165 ohms
4 & 5 = 46 ohms
6 & 7 = 85 ohms

[KL7OF]

It might be a Merit brand...It reminds me of a driver transformer

[KM1H]

National used that part # sequence also, and there are likely several others.

Carl

[W2PFY]

What is the reading between 1 and 8?

[VK7ZL]

What is the reading between 1 and 8?

On closer inspection the 8 is actually 6 so the bottom terminals are 6 & 7 which makes more sense.
It has 3 seperate windings, one has a CT, one of 46 ohms and one of 85 ohms.

[k4kyv]

Feed some voltage into the winding with the CT (use a filament transformer maybe?) or use a variac.   Measure the voltage that appears across the other windings.  That will give you an idea of what the transformer is.  Or put an incandescent lamp in series with the winding and apply mains voltage. I believe you have 240v 50~ mains voltage.  If the lamp just barely lights up, short out one of the other windings, and the lamp should light up to full brilliance.  If that is the  case, it is probably safe to apply full mains voltage to the midtapped winding.  That is likely the primary for a push-pull stage stage.

Also, it might be a power transformer.  The midtapped winding may be the secondary to feed a full wave rectifier, and the two other windings to be wired in series for 240v or in parallel for 120v.  That might be the case if the voltage that appears across the two windings is exactly the same when voltage is applied to the midtapped winding. Or it could be a mod transformer designed for multiple impedances, with two secondary windings that can be wired in series.  They could be wired in parallel if and only if the voltage output from the two windings is precisely identical.

[W2PFY]

My original thought  was that it may been from a Wilcox transmitter and may have been an auto type transmitter. If the resistance between 1-2 then 2-3 are pretty much the same, then terminal 2 would be the center tap and the other windings would be the secondary.

[VK7ZL]

Feed some voltage into the winding with the CT (use a filament transformer maybe?) or use a variac.   Measure the voltage that appears across the other windings.  That will give you an idea of what the transformer is.  Or put an incandescent lamp in series with the winding and apply mains voltage. I believe you have 240v 50~ mains voltage.  If the lamp just barely lights up, short out one of the other windings, and the lamp should light up to full brilliance.  If that is the  case, it is probably safe to apply full mains voltage to the midtapped winding.  That is likely the primary for a push-pull stage stage.

Also, it might be a power transformer.  The midtapped winding may be the secondary to feed a full wave rectifier, and the two other windings to be wired in series for 240v or in parallel for 120v.  That might be the case if the voltage that appears across the two windings is exactly the same when voltage is applied to the midtapped winding. Or it could be a mod transformer designed for multiple impedances, with two secondary windings that can be wired in series.  They could be wired in parallel if and only if the voltage output from the two windings is precisely identical.

I fed mains voltage via a 25W globe to terminals 1 & 3, no glow so I connected directly to the mains (250V)
Voltage between 1 & 2 or 3 & 2 is 125V
Voltage across 4 & 5 is 60V
Voltage across 6 & 7 is 150V
Secondary's in series (5 to 6) - voltage across 4 & 7 is 88 volts

[k4kyv]

I fed mains voltage via a 25W globe to terminals 1 & 3, no glow so I connected directly to the mains (250V)
Voltage between 1 & 2 or 3 & 2 is 125V
Voltage across 4 & 5 is 60V
Voltage across 6 & 7 is 150V
Secondary's in series (5 to 6) - voltage across 4 & 7 is 88 volts

It might be a modulation transformer.  Primary (1-2-3) to secondary (6-7) is 1.67:1 turns ratio.  About right for modulation percentage limited to 100%.

Connect secondaries in series (5 to 7 - voltage across 4-6) should be 210 volts, or connect to 4 and 6 with 5 and 7 tied together.  This gives a 1.19:1 turns ratio.  Would allow positive peaks to go substantially above 100% positive.

Given the size, it should be good for about 30-50 watts of audio maximum.

If you  have a signal generator, try running audio through it by applying audio to terminals 6 & 7 and measure voltage that appears across 1 & 3 over the 100~ 5000~ range to see what kind of frequency response you get.

[G3UUR]

Bob,

Looking at the style of your transformer, I wonder whether it was made by AWA.

Don has given you some good advice on checking out the transformer, but based on its size and the fact it's a custom-made transformer rather than a multi-impedance one , I would have rated it higher if it is a mod tranny. The one used in the Collins 618S is smaller than your transformer at 2.75"x3"x3.5", and is for a pair of 6159s (26V heater 6146s) modulating 3 in parallel in the PA. It's rated at 45 watts nominal and 90 watts peak. If it is a custom-made mod tranny, the other secondary (4-5) could well be for modulating the screen grid.

73,

Dave.
 

[VK7ZL]

Connect secondaries in series (5 to 7 - voltage across 4-6) should be 210 volts, or connect to 4 and 6 with 5 and 7 tied together.  This gives a 1.19:1 turns ratio.  Would allow positive peaks to go substantially above 100% positive.

Given the size, it should be good for about 30-50 watts of audio maximum.

If you  have a signal generator, try running audio through it by applying audio to terminals 6 & 7 and measure voltage that appears across 1 & 3 over the 100~ 5000~ range to see what kind of frequency response you get.

Don, you were spot on. The voltage across 4 & 6 was 210 v.
I picked up and audio sig gen at a small ham fest on Sunday but it has a fault so I will repair that and then do a freq. response check.


Dave, you could be right about it being AWA, their equipment is very common here in VK land.
I want to use it to modulate a pair of 1625's and it seems it won't be over stressed doing that.

Thanks to everyone for their input.

[W7TFO]

I have the iron out of an Aussie-built (factory) parts chassis.  The mod trans looks a lot like yours, same type of insulators & can but the arrangement is slightly different. 

It used a pair of 6L6's to an unknown RF load, probably close to 50W.

73DG