1959 Vibrolux 5F11 Fender Fuse rating and 3-prong ground questions

[DrGonz78]

So I am doing some work on a beautiful 1959 Fender Vibrolux 5F11 and I have two questions. First, the fuse that is in it currently is a 5A 32v fuse, so obviously that is wrong. On the amp is says 1 amp fuse but does not indicate slo blo or fast. Also, on the schematics it shows a 2 amp fuse. Just need to know what fuse rating is best to put in it.

Secondly, I am attaching a 3-prong AC power cable. I am going to snip out the death cap and it's ground connection it attached to one of the screw mounts of the PT. I have always read that it is not good to attach my ground lug to the PT mounts. Also, I really don't want to drill a hole into this amp. So, I am thinking to attach the ground lug to the bolt that holds the chassis to the cab. This will allow the ground wire to be longest and last to disconnect if the cable is ripped out by accident. Any better ideas where to mount the ground lug? Thanks as always for reading and the advice.

[Leo_Gnardo]

I'd fuse that at no more than 2 amps, and 1 1/2 may be a good choice. If you can monitor the VLux's current draw at full rip, fuse at the next higher conveniently available value.

I use a PT bolt to connect ground in old amps, with a solder lug in place, no wrapping the wire around the bolt and hope for the best. Clean up the chassis surface below that lug so it will make good contact. You can apply a tiny dab of thread-lock or use a pal-nut if you're worried about the nut backing off. I just use the usual keps nut & tighten well, haven't found one loosening up yet. Another solution for the ground wire is to solder it directly to the side wall of the chassis, near but not exactly at the site where hi voltage center tap and possibly filament center tap are.

[DrGonz78]

Thanks for the reply Leo!! I am still not sure if I should put in a slow blow or fast acting fuse. My gut says to go with a slow blow but does anyone know?

[Enzo]

If it doesn't SAY slow blow, then assume it is not.

[Tom Phillips]

...I am thinking to attach the ground lug to the bolt that holds the chassis to the cab. This will allow the ground wire to be longest and last to disconnect if the cable is ripped out by accident. Any better ideas where to mount the ground lug? ...

That would violate the rule that prohibits using a safety ground attachment point that depends on hardware that could be removed for any reason during service or parts replacement. Don't do that!

Soldering directly to the chassis would be best if you don't have a dedicated screw hole available and don't want to add one.

[Chuck H]

Tom is right. The chassis ground should not be able to be disconnected by any unintentional means. But it's also a pedantic rule THAT IS IMPOSSIBLE TO IMPLEMENT WITHOUT MODIFICATION TO THE AMP IN QUESTION which I'll assume you do not wish to modify in any permanent way. Even an extra solder blob might be a deal breaker for a collector. And you say the amp is in beautiful condition. Anyone who SHOULD be working on the amp should also know what they're looking at if they remove a PT bolt mounted ground ring. So, with no disrespect at all intended toward Tom, I'd mount the ground by solder blob if you think it's ok with the owner and you have a big ass gun to do it with. Otherwise I'd mount it on the PT bolt with a proper ring lug as per Leo .

Most of the 2A fuses I've seen spec'd for amps are designated slo (slow). Enzo is probably right about using a standard fuse if it's unspecified. It could be an oversight in the designation. IMHE if you use a standard fuse on a guitar amp you should carry plenty of spares and be prepared to accept glares from band mates and audience I'd probably use a 2A slo blo (but I'm ready to get beat up for it).

[Tom Phillips]

It's hard to balance the issue of complete originality vs. full "as new" performance. Even if the amp is in great cosmetic condition you need to replace parts to make it a good player. Extra holes in the chassis should be avoided of course.

Are you planning on leaving the selenium bias supply rectifier in place? If not then that will free up a hole in the chassis for a dedicated ground lug with locking screw / nut hardware.

[Tom Phillips]

Regarding the fuse value. It's interesting to note that the 5E11 schematic specifies a 3/4 Amp fuse and the 5F11 schematic shows the 2 Amp value as discussed above. The minor circuit changes that were made for the 5E11 to 5F11 upgrade do not themselves create the need to increase the fuse value. Perhaps, the fuse value change was to resolve nuisance blowing. I'll toss in my vote that the original 5F11 fuse was a fast blow type. However, that doesn't mean it is the optimum choice.

I am the lucky owner of a 1959 5F11 and the fuse value silk screened on the chassis is "1 Amp." I use a 1 Amp Slo-Blo in my amp. That's my personal choice anyway.

Cheers,
Tom

[Leo_Gnardo]

I am the lucky owner of a 1959 5F11 and the fuse value silk screened on the chassis is "1 Amp." I use a 1 Amp Slo-Blo in my amp. That's my personal choice anyway.

That's likely where this will end up. Let's think about what was available in the 50's when Tweeds were built. Lots of towns had a mom n pop radio repair shop, but 3/4 amp fuses a bit of a rarity, can't expect to stock everything. Same for slo-blo. Regular-blo fuses in integer values, easily found, even at hardware stores or Woolworths' back then.

An awful lot of 40's-50's-60's small amps Fender and otherwise, had 2 amp fast blo fuses. But most of them would have been in deep doodoo before they drew 2 amps from the AC line. IMHO it makes sense to use slo-blo fuses for tube gear, remembering there's a pretty good current "bump" upon switchon while filaments are warming up, and to size the fuse so that (we hope) it will open if the amp starts drawing lots of current in a failure scenario. If you want to protect your amp, and have no "false alarm" fuse blowing, this may mean making a change from "original values" or manufacturer's suggested values. By no means am I suggesting anyone should put in way oversize fuses. Use your brain & experience, and if you're worried about making an error, make it on the safe side. We'd still rather have false alarm fuse popping than melting-down amps.

I like landing the ground cable at the selenium rectifier location, good suggestion. For those who elect to solder to chassis, I suggest the Weller 80 watt "pencil", way easier to use than any solder gun I've found and cheap at $30 or so. If you don't think 80W can do it, surprise! And if you still don't, there are 120 and 160W versions available too.

[DrGonz78]

Great information as always!! This gives me some great opinions to weigh on how to proceed. Right now I am just going to go the simple route of connecting the ground lug to the PT mount. I figure that there was a mounted virtual ground at that exact location for over 50 years, and it is less intrusive than a solder blob. Mainly, I don't really have a good solder gun to get the job done and that will be something to buy soon. Yeah the idea of mounting the ground onto the bolt that holds the chassis to the cab was a bad one, I figured. So I will have to look at what start up current this thing is pulling and then determine a conservative approach for the fuse. Will start with 1 amp and no more than 2 amps. I am thinking standard fuse and then see if if it needs a slo blow. Thanks for all the feedback!

Also, the amp has had all the caps changed not too long ago and is in great shape. Just attaching a 3 prong AC cord and testing it out for a positive inspection.

[Chuck H]

On a side note, what neat little amps those are. Those and the Tremolux too. With low-ish power, shallow cabinets, a single 10" speaker and no master volume they fall into the slot "too loud for bedroom practice but not loud enough for a gig". And what a cool, woodie, reedy sound they have both clean and dirty. I've never worked on one (though I've met a couple that I wished the owner would service), but whenever I get close to one I try to plug in because I just can't get the smile off my face whenever I hear them.

[Tom Phillips]

...the amp has had all the caps changed not too long ago and is in great shape. Just attaching a 3 prong AC cord and testing it out for a positive inspection.

Does the amp still have the selenium rectifier in the bias supply as originally fitted? If so, are you familiar with the characteristics & aging issues with those devices?

[Leo_Gnardo]

Mainly, I don't really have a good solder gun to get the job done and that will be something to buy soon.

Here's one case for sure where the pencil is mightier than the gun. Get the Weller 80W "pencil" - you'll be glad you did. I have 300W Weller "gun" that don't do the trick. It has to do with the mass of the tip: the pencil's massive tip carries the heat to the chassis with extra to spare, while the skinny tip on the gun may get hot all right, but can't transfer that heat to chassis efficiently.

[Chuck H]

Great consideration! When attempting chassis soldering (more often DEsoldering) I always think "gun". I don't have one because I just haven't needed one so far for what I do. There have been a couple of times when I wished I had one. Need two like buttons yet again because your observation makes so much sense and I never considered it. Like an old cast iron skillet vs. a slick copper bottom stainless steel pan (which do YOU make pancakes in). Gotta choose the right tool for each job. The amount of heat inertia is relative to the tips mass. I'm going for the pencil!

[Justin Thomas]

I'll second the 80W giant iron instead of a gun. The one that comes woth the tips for making stained glass windows! And be careful when it's on a stand - it's tip-heavy and slow to cool. But does a great job. It rarely gets used, but it's a lifesaver when needed. Usually I use it for 1ohm resistors, those ground jumpers from board to chassis, and melting huge gobs of old solder where about 20 leads meet. If I'm feeling lucky I'll ground to pot backs with it, but you have to be REALLY careful if there's any plastic parts,which is most, nowadays... Putting that mains ground on a steel chassis will be no problem.

Justin