Puzzled about original location and type of fuse holder for Vox JMI-era AC-15

[dchang0]

On the Vox AC-15 schematic OA-031 from the early 60s, there's clearly a 3A slo blo fuse.

But in the few gut shots I've seen of AC-15s from that era, I don't see any such fuse.

I'd heard from ebay listings that they use a Beiling Lee 1/2" hole panel-mount fuse holder, but I don't see any such hole in the chassis for where one might be installed. A block-style, chassis-mount holder would be pretty obvious in photos, but no photos I've seen have that either.

Where exactly did Vox/JMI originally put the early 60s AC-15's fuse holder, and what type was it? Photos would help a lot if you have any.

(Currently I am considering using free-hanging in-line fuse holders for my build.)

Thanks in advance!

[Enzo]

I can't answer the question, but why on earth would you install hanging inline fuse holders? Whether the original had a fuse holder on the panel or not, why not install one on yours anyway? Then you could change a fuse without pulling the chassis, and it will be more secure than a wired thing hanging.

[dchang0]

Oh, it's because I have a period-correct replica of the original JMI-era copper faceplate and chassis, and there is no space or location for the fuse holder, even if I were to be willing to drill the 1/2" hole. (There is a functional, safe, modern Schurter 30mm rotary voltage selector switch where the giant hole is for the unsafe and illegal vintage voltage selector, so I can't put the panel-mount fuse holder there.)

Here's a listing of one that's also period correct: http://www.ebay.com/itm/Accurate-Rep...item2ca124d4eb

The photo shows the tight-quarters around the power switch, pilot lamp, and voltage selector. No room for another 1/2" hole. And given the insane price of another replica panel, you can understand why I'm reluctant to drill it at all.

So, the cleanest/neatest choice* is probably a block-style one screwed down to the chassis on the inside, but those are hard to change at a gig. Putting the fact that I'd have to unscrew the entire back panel aside and focusing only on the act of changing the fuse, it always seems that a screwdriver will break the glass first before prying the cartridge out of a block-style fuse holder. So I figured an ugly but easy-to-use in-line twist-lock fuse holder would work well without requiring any drilling. I could change fuses with just my fingertips (again putting aside the fact that a screwdriver would be necessary to remove the entire back panel, but at least removing the back panel is hard to mess up).

I'm not married to the idea, of course. I'm curious about what JMI did at the time and will give more weight to their solution due to historical accuracy.

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* One of the most elegant ideas I had was to get a 30mm Schurter rotary voltage selector switch with an integrated fuse holder, but these are impossible to find with the correct voltages for the Classictone AC-15 PT. They would have to be special-ordered in boxes of 25, and at $20 each, that's $500 worth of switches just to get one for my build. So I got just the rotary voltage selector from an ebay seller in Europe and will have to figure out where to put the fuse holder.

[Enzo]

Fair enough.

I wasn't thinking front panel anyway, and if the rear panel lacks space, how about on the underside of the chassis? You don't need access to them like to a volume control.

So you are planning to leave the inline fuse dangling outside the chassis? Unsafe and it sure ain't period correct.

If you can't bring yourself to mount a fuse clip inside, consider mounting it outside with an insulated cover. One or two screws would free the cover and the fuse is easily changed.

Don't pry a fuse from its clip in the center, put your blade near one end, and twist it so the fuse is contacted right next to its cap. But I always try to get under a cap anyway. I use a hook tool placed between the tabs of one of the end clips and pull up. Like one of these from harbor freight:



A small screwdriver will get in there too.

[dchang0]

Hmm. Good advice. I'm reconsidering my aversion to block-style fuse holders.

I'm okay with mounting the fuse holder inside; that was the plan all along, even with the inline one.

I'm a bit surprised the inline ones are unsafe. They are fully-encased in thick plastic and rated for 500V at 20A, and there is no chance of touching any metal components while changing the fuse. The only danger I could imagine is if the thick red insulated wires are cut somehow by the chassis, but my plan was to keep the inline holder completely inside the chassis, hanging just below the power switch. You are correct--absolutely not period-correct. But the trade-off was that no holes would have to be drilled in anything, so I could always change it to whatever is period correct later on.

I especially like your idea of the insulated cover on a block-style fuse holder, but it is probably not necessary since the plan is to install it inside the chassis. I'll use the screwdriver trick you mentioned to change it out.

Thanks--but I am still curious what the period-correct fuse holder was, so if anyone knows, stop me before I order the block-style fuse holder in a week or two...

[Enzo]

Well if you planned to mount the hanger inside, you are back to having to pull the chassis, and so a clip would be far preferable. My objection to an inline was if it were hanging down outside the chassis. The wire could easily get cut through the insulation, or caught on something and the wire ripped loose. And when you open it, the contacts are exposed, so someone could shock themselves. Inside, everything is exposed so the inline would be no more danger than anything else in there.

I am no amp historian, but if it came from the UK, didn't they put mains fuses in the wall plug?

And to be sure, I certainly don't mean to talk you into drilling holes where you don't want them.

[Jazz P Bass]

Wasn't the fuse & fuse holder on the circuit board?

The VOX Showroom - Vox AC15TB and AC15TBX Amplifier - A Look Under the Hood

[dchang0]

Ah, I see. I am perfectly okay with taking the back cover off just to change the fuse--that probably didn't come across clearly enough in the original post.

So yes, the plan was always to have the fuse holder inside of the chassis and not out.

Wall plug! You are probably right--I'll look into that. Not that it would matter in that I couldn't do the same thing here in the US with a 3-prong plug, but confirmation of the fact would give me the excuse to use whatever I want.

[dchang0]

That's a different era. I'm looking for early 60s. This is the one I'm looking for the historical location of the fuse for:

The VOX Showroom - Vox AC-15 Amplifier - 1961 Model

The gut shots are too small. I see that someone converted this amp to a 3-prong cable with the white and green wires clearly shown, so whatever they chose for the fuse holder is probably not historically-accurate either.

Attached is a gut shot that I found on an ebay listing of an unmodified, working AC15 from that era that has no fuse whatsoever inside the chassis:



I tried updating the title of this thread to reduce confusion about the date period, but no-go.

[Ted]

On the Vox AC-15 schematic OA-031 from the early 60s, there's clearly a 3A slo blo fuse.

But in the few gut shots I've seen of AC-15s from that era, I don't see any such fuse.

I'd heard from ebay listings that they use a Beiling Lee 1/2" hole panel-mount fuse holder, but I don't see any such hole in the chassis for where one might be installed. A block-style, chassis-mount holder would be pretty obvious in photos, but no photos I've seen have that either.

Where exactly did Vox/JMI originally put the early 60s AC-15's fuse holder, and what type was it? Photos would help a lot if you have any.

(Currently I am considering using free-hanging in-line fuse holders for my build.)

Thanks in advance!

I've seen early AC15 (late 50s) which had no fuse at all and later (60s) ones which had the AC30 style front panel Bulgin fuseholder.

[dchang0]

Thanks, Ted.

It does appear that Enzo's hypothesis that the fuse may have been in the plug is probably true:

From Wikipedia https://en.wikipedia.org/wiki/AC_pow...d_types)#Fuses

"June 1947: BS 1363:1947 "Fused-Plugs and Shuttered Socket-Outlets" published.

May 1950: BS 1363:1947 Amendment 3, title changed to "Specification for two-pole and earthing-pin fused-plugs and shuttered socket-outlets for A.C. circuits up to 250 Volts (not intended for use on D.C. circuits)"."

"There are two common misconceptions about the purpose of the fuse in a BS 1363 plug, one is that it protects the appliance connected to the plug, and the other is that it protects against overloading. In fact the fuse is there to protect the flexible cord between the plug and the appliance under fault conditions."

What is probably the case is that, as you say, the late 1950s models "cheated" by relying on the fuse in the plug and had no fuse in the amp at all, and this was probably true for the early 1960s models too, and then in the mid-1960s they stopped cheating and put a fuse in the amp in addition to the one in the plug.

All we need is for someone who actually owns an early 1960s AC15 to confirm this to be sure...

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One thing that is still puzzling: the OA/031 schematic from 1960-1961 has the 3A slo blo fuse positioned between the power switch and the voltage selector, and there clearly is not any fuse in that position in ANY of the gut shots I have seen. There is no fuse in the schematic dated 1959, so they had to have added the fuse to the schematic on purpose. Why did they bother to draw it there if they weren't going to actually install one?

[loudthud]

I've been looking through Jim Elyea's book trying to find info on this subject. It's a little fuzzy but on page 233 it says that amps with power ratings below 30W did not have fuses on or in the chassis up until about 1960. In fact, it seems that up until that time the amps were shipped without a mains plug. The user installed a plug that was compatible with whatever mains outlet was available at the point of use. At that time in England there were five non compatible versions of the BS546 plugs/outlets in common use. It's not clear but it seems some or all amps had a detachable cord with a round Bulgin type plug and a socket on the back of the amp.

The early schematics "Amplifier Model A.C.1" (no number) March 4, 1958 and "AC/15 Amplifier No.2" (OS005) Dec 4, 1959 do not show a fuse.

[dchang0]

Very cool. Vox Showroom also says something about the late-1950s amps using a detachable cord with a Bulgin plug on one end and the mains plug on the other. Given that everything adds up, I think it is safe to say that everything you just wrote about the 1958-1959 amps is correct.

Does Elyea's book show where the fuse was located in amps from 1960 to 1964? I'm guessing you've already looked through and through and no luck...