Urei 1176LN limiter issue with power supply

[Randall]

Vintage blackface 1176LN, worth a lot of money. It's blowing it's 250mA fuse. It came in with the PT wires snipped off, among other things. I spliced them together and fired it up, now I have trouble. I have been over the wiring many times. I'm reasonably sure it is correct. Here is my situation,,

With the grey wire d/c from the middle of the voltage switch, disabling the bottom primary, I have the 30v supply from the top primary, and the unit pulls 40 mA.

With the grey wire connected, and the b/w wire d/c from the other middle of the voltage switch, disabling the top primary, I have my -9.6v supply. Unit pulls about 40mA.

But with both primaries connected, the unit pulls 500mA, twice it's rated fuse current. This is all with it on the LB limiter.

So, what's up? Why either supply, but not both?

page 55.pdf

[The Dude]

Either primary wired separately should result in roughly the same voltage out of the transformer. If I'm reading your post right, that's not the case. They are two roughly identical primaries in parallel for 120V and in series for 220V. The fact that they result in different output voltages makes me think at least one is shorted. They could be shorted to each other and the short is rendered partially irrelevant when one is disconnected. I would check resistance between the two windings when they are disconnected from each other to see if there is a short from one winding to another.

[nosaj]

Yes figure out the PT before even connecting it back to the circuit. There's a reason it was snipped out.
nosaj

[Enzo]

Your positive and negative DC supplies should both be there for either primary, and of course for both. One primary does not run just one secondary and the other the other. That is what your description sounds like. In other words with one primary connected, you should get both the +30 and the -10. Then changing to the other primary, the same results should occur.

What happens if you set the switch to 230vAC? I mean other than the secondary side will only be at half voltage.

[vintagekiki]

Index of /Manuals/UREI
Urei 1176LN 01.pdf
Urei 1176LN 02.pdf

Phasing PT ¹⁾
Disconnect 1176LN from mains voltage.
Remove both red wires from the PCB.
Input voltage selector set to 230VAC.
Connect source 10 - 20VAC voltage to red wires.
Phase both primary windings so that you get the highest primary voltage. When switch the input voltage selector to the 115V position, you should get half primary voltage.
Connect 1176LN to the mains. You should have two symmetrical voltages between red and red/yel wire.
Return both red wires to the PCB.
When the PT windings are properly phased and you still do not get the correct DC voltages, check the components in the power supply.

[Helmholtz]

That^^^^

Seems one of the primaries has its phase reversed.

If the primaries are connected out-of-phase, the total looks to the mains like a short.

[Randall]

Out of phase primaries were indeed the culprit. The wires to the PT were cut off very short, for some odd reason. This made splicing difficult, and caused me to make the error of confusing two of the primary wires. This is why I had such a time figuring it out, because I was working with the spliced ends, and not taking into consideration that the colors I was dealing with were not all exactly what was coming out of the PT.

And I learned something, because I did not realize out of phase primaries would act as a short. I'm still not clear as to why.

Anyway, it seems all good now. Once again, thank you all!

[Helmholtz]

And I learned something, because I did not realize out of phase primaries would act as a short. I'm still not clear as to why.

The opposing magnetic fields of out of phase wired primaries mutually cancel.This results in zero inductance and only leaves the DCR.

[The Dude]

I misunderstood the first post. I thought secondary voltages were different for each primary winding hooked up.

[Randall]

Dude,

No, that's what I thought also. I was pretty sure that was the case, but I can see now where that probably doesn't make sense. At this point I'm not really sure, but it is working now, so that is what is important.