Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: frank57 on January 25, 2013, 08:23:03 am

Title: Did I wire this fuse right to the live?
Post by: frank57 on January 25, 2013, 08:23:03 am

Did I do this right?
I might just put it back to the neutral like they had but is it wired right for the live?

Title: Re: Did I wire this fuse right to the live?
Post by: jjasilli on January 25, 2013, 11:28:10 am

If I understand your drawing:

1.  The fuse is wired right.  In series with the hot wire before the SW is OK.  Just one fuse in the neutral line is the worst case:  though it "works", the whole amp remains "hot" even if the fuse blows.

2. The 2 things labeled 103 appear to be caps.  These are wired wrong, because they're in parallel with the Hot and with the Neutral leads.  So they will pass current with the SW Off, and get shorted-out and do nothing with the SW On.

If the caps are for filtering / noise suppression, they need to be shunted, NOT parallel.  They also need to be properly rated.  Alternatively, don't use them at all.

Maybe checkout Merlin's (Valve Wizzard) website -- fuse section.  DPDT SW is good and can be fused in Both lines.

Title: Re: Did I wire this fuse right to the live?
Post by: frank57 on January 25, 2013, 12:33:03 pm

So it doesn't matter where the live from the plug goes on the fuse?
Top of the tab or the other tab?

Originally it was wired to the neutral.(see pics)

The caps are 103/630v.
Are they to protect the contacts?

The power switch has 4 tabs similar to this marshall one but with plastic dividers between the tabs.

Title: Re: Did I wire this fuse right to the live?
Post by: punkykatt on January 25, 2013, 02:08:11 pm

The fuse holder should be wired so if the fuse blows and you go to remove the dead fuse with the amp still plugged in to the wall recptical  you dont get a shock.

Title: Re: Did I wire this fuse right to the live?
Post by: frank57 on January 25, 2013, 02:31:58 pm

Is it wired right or wrong?
Why on earth would you keep the amp plugged in with a blown fuse?

Title: Re: Did I wire this fuse right to the live?
Post by: jjasilli on January 25, 2013, 02:37:11 pm

So it doesn't matter where the live from the plug goes on the fuse?

Ditto to punkykat.  The fuse will function either way.  But the hot wire should first go to the "rear" lug, furthest inside the amp on the fuse holder.  Otherwise, the outside contact, closest to the user, of the fuseholder will be live.  So, if you pull or insert a good fuse, then the end you're holding will go live when the other end of the fuse touches the outer contact of the fuse holder.  Hence, only the inner contact of the fuse holder should be hot-wired.

Why on earth would you keep the amp plugged in with a blown fuse?
Murphy's Law.  Proper, safer wiring is a desirable safeguard.

Title: Re: Did I wire this fuse right to the live?
Post by: smackoj on January 25, 2013, 04:47:02 pm

why ask why? I do stupid stuff all the time and leaving the amp plugged in has happened more than once.....

 :icon_biggrin:

Title: Re: Did I wire this fuse right to the live?
Post by: frank57 on January 26, 2013, 11:42:08 am

So wire it like this?
Otherwise I can go back to what they did with the neutral.
I got this about the caps:

If they are across the contact they are for arc suppression. If they are across the mains they are for noise suppression.