Power transformer; the original microwave

Reeltarded · Post by **Reeltarded** » Mon Oct 07, 2013 5:29 pm

I have this amp. It runs. Here's how it went...

This amp runs hot. It ate a fuse and made a tube dying noise. I changed the fuse and the output tubes. The one closest to the PT was white. The screen resistors were perfect. New fuse.

Damn. This thing runs really hot. Tubes look good. Runs 40 minutes. Fuse pops. It is so hot it's almost scary to flip the switch located on the IEC inlet. The PT is freaking hot enough to bake with. Fender small format combo width headbox with cathode bias 6L6 output.

Is my PT internally shorted, or should I be looking for something before the output section that is sucking enough current to put a giant robot down?

mhartman · Post by **mhartman** » Mon Oct 07, 2013 5:34 pm

How does it run when you don't have any tubes installed?

Reeltarded · Post by **Reeltarded** » Mon Oct 07, 2013 5:47 pm

Aha. Haven't tried that, but 40 minutes or so with.

So, in your mind if I ran it ten minutes without tubes and see if.. totally get that. Good one. I'll see if the evidence of current draw is missing and then start looking at resistors in the output section if the transformer is cold. Excellent.

Is there a way that a preamp tube causes a big draw with anything that wouldn't make it sound bad? I am looking for any reason to swap those out.

Firestorm · Post by **Firestorm** » Mon Oct 07, 2013 9:30 pm

Gotta be shorted turns. If it was shorted primary to secondary, the fuse would blow right away. Keep running it hot and it will get there, too.

M Fowler · Post by **M Fowler** » Mon Oct 07, 2013 9:50 pm

The last PT I ruined sounded like I was out in kitchen frying bacon.

Reeltarded · Post by **Reeltarded** » Mon Oct 07, 2013 9:57 pm

Ok but still haven't pulled anything.

If there is an internal short the PT will heat up with no load, corrightly?

Phil_S · Post by **Phil_S** » Mon Oct 07, 2013 10:08 pm

This showed up in the OT thread that's active. It will work for you, too.
http://www.geofex.com/FX_images/xform_test.gif

Leo_Gnardo · Post by **Leo_Gnardo** » Mon Oct 07, 2013 11:37 pm

Reeltarded wrote:If there is an internal short the PT will heat up with no load, corrightly?

Absorootly, that is what we're suspicioning.

Had one of them "boiling-over" types in an Ampeg Gem II last week. Swapped in a Ruby/Magic PT intended for Vibrolux (changed bells to standup type) and all is well. Hope yours will be soon too!

katopan · Post by **katopan** » Tue Oct 08, 2013 12:22 am

Definitely pull the valves and test by itself.

Reeltarded · Post by **Reeltarded** » Tue Oct 08, 2013 2:46 am

Phil_S wrote:This showed up in the OT thread that's active. It will work for you, too.
http://www.geofex.com/FX_images/xform_test.gif

Thanks, Phil!!

i am going to put that on a switch in all my future builds.

Just kidding.

Damn.

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Power transformer; the original microwave

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