New Fuse Blowing Problem

[EWBrown]

If you have disconnected everything and it still pops the fuses, it is a very high probability that the tranny has shorted, the Primary DC resistance reading of 2.7 ohms seems very low. If I remember corectly it should be around 40-50 ohms DCR.

Triode has been good about replacing bad trrannies, drop them a line and let Uncle Ned know about it.

/ed B in NH

[Shannon Parks]

My amplifier has been working fine with daily usage for about 4 months. However, it now it blows fuses upon power-up. I disconnected all the secondaries and the behavior was the same. I disconnected the power indicator lamp and the fuse still blew. Disconnecting the primary saves the fuse, but is of limited utility.

This is the same route I would have gone, too. Are you sure you had all the secondary connections isolated after disconnecting them (just to be sure you didn't go from one shorting condition to another)? And the filaments, too?

I'm using the Triode Electronics PA-774. I measured a primary DC resistance of about 2.7 ohms. Does anyone know what is normal? Any ideas other than replacing the power transformer?

Thanks,

Andy

I just checked an old PA-774, and it is indeed around 3 ohms on the primary. I would also check the high voltage secondary's resistance - both from tap to tap and the taps to the center tap. Should be around 160 ohms across and 80 ohms to the center tap.

WES (what Ed said). I would drop a line to Ned.

Shannon

[EWBrown]

OOps I wa sthinking of HV secondary resistance... Too early in the morning, too much darn snow on the roads, too little caffeine, etc...

I have a couple of new PA774s slated for a new project, in progress, I can check them out and report if there is any resistance discrepancy.

/ed

[Shannon Parks]

I forgot to mention checking the diodes, too.

Shannon

[Guest]

Thanks for the suggestions. I wrapped electrical tap around each secondary, so no shorts there (also recommended for personal safety!)

Diodes seem to be OK (I used a 9v battery & 200 ohm resistor, no measurable current one way and ~40 mA the other...)

I've sent a note to Ned (it seems wise to do WES...)