Dead PT

[txstrat]

Hi all,

I've built another copy of that ole B-15N as a head and yesterday there ought to be the first launch.
When I switched it on, the primary fuse blew (no tubes in). I disconnected all but the wires for the primary (230V) and the fuse still blew.
OK PT might be dead. Is there a way to test that? So far I've checked the secondary leads and each winding has s low ohms reading in the 0.6 up to 5.5 ohms range.

Thanks

[Enzo]

Are the primary wires correct? Does this have a split primary - parallel for 120v and series for 240v? If you get one of the series windings reversed, the thing will buck itself and blow fuses.

If that part is OK, I can;t think of a more definitive test than applying primary power with the secondaries ALL unwired. If that pops fuses, you PT is very troubled.

[txstrat]

No split primary. Two solder tags for the primary.
When I apply power to the PT (all secondaries unwired) the fuse pops = PT dead.
Thanks Enzo

[txstrat]

Turned out to be the power switch. DPDT. Had a short.
Found out when I tried a different PT with the same result of blowing the fuse. Changed the switch and... amp runs. Only thing is massive hum.
I'll open another thread for this.

[Enzo]

Ah, very good call. I usually connect the primary wires directly to the mains through clip wires for the test, but I never thought to say that. Sorry if I cause dany undue concern for your expensive transformer.



And lest I assume further, yes, through a fused and current monitored variac.

[txstrat]

No problem. Frankly I didn't think about my concerns but rather being happy it was the switch only.