[imacdaddy757]

Good morning, all. I've done a ton of work rewiring the Philco 39-30 Code 121 because of rotted rubber-coated wiring and want to protect the set.

I've gotten answers to questions on putting in Safety caps inside the Bakelite cap, but where is the best location to put a fuze into the circuit?

Regards,
Clarence

[Dave]

Add your fuse in series with the A/C power cable, before the on / off switch. Many radio chassis have small holes drilled in them, I try to use one of the holes to bolt or rivit the fuseholder inside the chassis. You could also use a twist-lock style fuse holder and mount it to the back side of the chassis but that will require drilling about a 1/2" hole, which I wouldn't do to my radios, but that's just me.
Dave
[Image: http://i1100.photobucket.com/albums/g407...C02183.jpg]

[ipwizard]

You also want to fuse the hot side of the power cord. This would be the lead to the power switch. You might also consider using a polarized AC plug also so no one plugs it in backwards.

[codefox1]

Tell us the picture you posted is the "before" version. All those rotted out capacitors must go.

For ultimate protection, drill a hole and mount a fuse holder in back of the chassis, if you have room. Say, if 1 amp is about right, make it so. Nothing stopping you from adding a second fuse under the chassis, say 2 amps. That way if trouble arises and someone gets creative in replacing outboard fuse, you could prevent a total meltdown or fire hazard. This is standard practice in recently manufactured guitar amps.

[Dave]

Yes Codefox, the photo is of a work in progress, but it's intended to show how to wire the fuse. I like to put the fuse inside the chassis, so I don't have to drill large hole for a twist lock fuse holder. And let's face it, if the fuse does blow I'm going to pull the chassis out anyway to find out what caused it to blow. Since I don't restore radios for resell, I can get away with making things a little less user friendly for the average Joe. Again that's just my preference, and as they say, there's more than one way to skin a cat.
Dave

[imacdaddy757]

Thanks to all who replied. I do plan on using a polarized plug, and X-Y safety caps, one on each side of the incoming line.

If I'm only using one fuze, inside the chassis (prefer to keep mine hidden), is it better to fuze the
hot or ground of the wall cord?

Regards,
Clarence

[LASJayhawk]

ALWAYS fuse the hot side! Never fuse the neutral side

[imacdaddy757]

ALWAYS fuse the hot side! Never fuse the neutral side

Thanks much, Jayhawk. I was able to find X1/Y2 .01uf caps, at 250V.
Is that sufficient?
I tried several other vendors online, but they had just Y2 caps with PC pins at the
bottom for a connection, and were not X-Y.

Regards,
Clarence

[LASJayhawk]

yep thats what you want for max safety.

[imacdaddy757]

yep thats what you want for max safety.

Much appreciated. Sounded like 250V would be enough, but wanted to be sure.

Regards,
Clarence

[Arran]

It's really six of one half a dozen of the other, if I were to us a fuse holder in a set it would be in series with the B+ line coming off the cathode of the rectifier tube since that's where you are most likey to experience a dead short, that was likely what destroyed the tranformer in your set. You can fuse the primary but that won't really protect the HV secondary from burning up which is the main failure of a power tranformer, about the only thing that it would protect from is something like a lightening strike. I'm not sure whether the polarity really matters on the input side, it's AC in an AC set and it's the primary of a power tranformer, so other then through the line capacitors it is not connected to the chassis, but both line capacitors are connected the same way regardless of which way the set is plugged in.
Regards
Arran

[imacdaddy757]

Got the fuse holder in, and it all works, after having to replace a bad power transformer.
Used two X-Y rated safety caps for line isolation, inside the Bakelite housing that originally
contained two .01uf caps. After some searching, I finally found ceramic ones rated at 250v
that were physically small enough to fit into the Bakelite block. I'd previously used the big
square safety caps on the AC/DC sets I'd worked on.
I did install the polarized plug, though it probably doesn't make much difference as
someone here pointed out.

Got the set playing well on AM, and at a stopping point for now. I need to re-install the
push-button assembly, order a plastic dial cover, and order the longer version repro
push-buttons. And gently touch up the original finish of the cabinet.
I didn't get any signals on SW, but I'll check on that later on.

Many thanks to all who took the time to reply.

Regards,
Clarence