Short in power section

[farbio]

O.k I've built me an amp. Alot of work since I knew stuff all about electronics
and all thumbs on both hands. It was fun for a while reading, learning, planning, doing ect. Now I'm at the 1st power up stage and keep blowing fuses. I can power up with standby on thus far since I removed the faulty relay transformer which caused the fuse to blow as soon as I switched the amp on. The SS rectifier ckt and bias ckt seem o.k.
AS soon as I hit the SB switch it blows a fuse (1 amp fastblow), which means somethin' aint right.
I'm powering up with no tubes installed (2 x6L6, 3 x 12ax7)
what do i look for?
1. B+ shorting to ground in filter section?
2. B+ shorting to ground in preamp section?
2. a bad choke? how do i test it?
Can faulty components cause the fuse to blow.
Anymore suggestions would be greatly appreciated as I'm losing sleep and sanity.
thanks

[Tom Phillips]

Tube amp debugging page

farbio,
Yes, you can have faulty components. Also wiring mistakes. Especially with a new build. I could start giving suggestions but I'd fist say just reference the tube amp debugging page. See the section under "Pops fuses". The web address is: http://www.geofex.com/ampdbug/ampdebug.htm
Regards,
Tom

[Enzo]

First place I would look would be at the filters. One wired backwards will do just that. Certainly check for shorts to ground from any and all B+ nodes. CHances are the preamp is not at fault, since the dropping resistors usually provide enough stretch for the fuse to hold. If you think the choke is arcing, disconnect it and put a wire in its place. So what if the filter action is reducced. All we care about at the moment is soving the fuse blowing. If the choke blows fuses and the wire doesn't, the choke is bad.

If nothing else, you can disconnect the B+ circuits so there is nothing after the rectifier., then add them back in one thng at a time until it pops a fuse, and then you know where the problem lies.

ANd don't overlook silly things like a little extra wire sticking through the terminal on the standby switch and touching the chassis just out of sight.

[Bill Durham]

trouble shooting

Enzo said it pretty well.. You have something shorted or shorting under high tension. If you are popping fuses with no tubes installed, there isn't anything there to pull current, except a short. At this point, any cap wired to ground from the rail should be suspect... either bad or backwards..talking electrolytics here. I agree that it is most likely not a preamp issue.

Good luck with it

BD

[farbio]

Thanks Tom, Enzo, Bill you guys are the best.
I've taken the advice and checked carefully. Thanks for the link to the debugging page.
This fault has been strange as it was intermittent. I would turn the amp on ( standby on standby) turn off then back on again, the fuse would blow even with a 1amp slo-blow. Disconnected everything from PT and reconnected one at a time. Now is fine even with standby in play mode. Still have a long way to go.Will try it with tubes tomorrow and check back but for now will have a glass of wine and drink to your health.
Thanks again
Farbio

[Enzo]

If you disconnected everything and now reconnected it, and it now seems to work, then it sounds like you might have had a solder bridge which was cleared away in the process.