Fuse Question

OK, yet another dumb question.

SP-8, passed the no-tube part of the smoke test last night.
12.5V on the filament circuit w/out tubes.
Went and got tubes for part II tonight but,
plugged the unit in, powered on, and immediatly blew the fuse.
No tubes in the sockets, just like last night.
Looked at the fuse, it's a 1.25A and doesn't say slo-blow.
I'll get some 1A slow blows and try again tomorrow but
is it the fuse?
Is there some other disaster I'm overlooking?
Argh! Help! I have angst!

Tom

(actually I didn't look up angst so I'm not sure if that's what I've got)

Yup, angst is what you've got all right.

thanks mang,
I was wondering....

Most likely a bad solder joint. Move the amp a little and it breaks or makes the connection. If it is blowing fuses then you need to check your build step by step.
Almost always a mistake you made in the build or soldering. Get someone else to look at it sometimes helps because you keep making the same mistake or do not see the error yourself.

Sounds like you may be overlooking something as a one amp fuse should be fine as most tube preamps dissipate 20-40W.

SP8 can use a GMC-1 or a GMC-1.25 fuse, those are medium delay
you've probably got a short or wiring error somewhere, or a shorted tube filament

Thanks all.
Went and got new fuses. Looked at everything for oops, found nothing.
Put new fuse in, no tubes. Power up, worked fine.
Power down, wiggle, jiggle, try to see if anything is wrong, nothing.
Power up, fine! Power down, tubes in. Fine!
Hook up to CD, music goes in one side, comes out the other. It's a miracle!
Unplug CD, just the faintest bit of 60 cycle hum with vol all the way up.
I'll need to work on that but caveat, it's playing through an old Technics integrated in the garage.
Cd first, then SP8, then the Technics pre and power (can't separate them),
so I have no idea if that's part of the hmmmmm.
Will try with an independent power amp this weekend but
in the mean time,
Beers all around. Tell 'em I said so!

Tom

You may want to do some power cycling and burn in using the garage system. Remeber that problems that go away by themselves can come back by themselves. Better to build up some confidence out in the garage rather than have an "event" while driving your Quad57s inside! I keep a pair of Radio Shack Minimus 77s and a NAD amp around just for this purpose.
...j

Good advice j. Thanks!

OK, found the fuse blowing problem. Kinda.
Was trying to find the minor ground loop hum and switching polarity of the plugs as Roy (I think) suggested in Ed's sp-12 thread.
Old Technics integrated is serving as the amp during the garage phase. It's a two prong plug.

Technics plug one side up - sp-8 blows fuse.
Technics plug other side up, reversed polarity - sp-8 makes pretty music.

I know I know, just keep the right side of the plug up

But maybe somebody could enlighten me on this condition and let me know if there's a common error I've made here?

Thanks as always!

Tom

Also, the ground loop hum is only evident when the Technics is cranked more than 1/2 way up. I can't wait to get the SP-8 on the real amp, that hum might just be invisible.
Hmmmm. I guess that should be inaudible.

I just quickly read this post but if the fuse blows depending which way you plug in your Technics amp... Houston, we have a problem..

You have a short somewhere, does the Technics amp have a capacitor from the line cord to ground, if so, that capacitor might have some serious leakage.

Sal

Houston to Sal:
Affirmative on the possiblity of the cap leak in the Technics.
Rumbles and grumbles on power up and down.
Will initiate diagnostic and workaround.
Houston out.

Tom