Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: pullshocks on May 03, 2025, 09:33:18 pm
-
I include a convenience outlet in all my builds. I’ve always wired with the amp fused and the convenience outlet un-fused. The grounds are separate wires, bolted to the chassis together.
Should the convenience outlet be fused?
-
Safety regulators would probably say ‘yes’ as a belts and braces approach, but I say only if there is likely to be a danger to the user from the convenience. (Most conveniences that run off mains power will have their own mains fuse). YMMV
-
Without the outlet fused, your amp is acting like an extension cord. That cord should have a current rating. If it is 18awg, it could be rated as low as 10A. IMO, the outlet should be fused for the difference between what the amp is drawing and the cord rating, with the outlet labeled for maximum permissible load.
-
Always fuse. Not an option IMO.
--Pete
-
Should the convenience outlet be fused?
I think it really depends on your level of exposure to legal action in the event of an adverse event.
Personally, I do not fuse a convenience outlets if I use them. Nor did Leo, until Fenders stopped offering them (?when), and I assume this was a cost cutting measure -- reduced part count and less liability.
Mostly I use them in Dumble inspired amps with passive effect loops to allow for a Dumbleator. But I don't make it convenient either, by using Powercon connectors. And when I sell an amp, it is sold with a disclaimer of liability.
For a production amp with a true convenience outlet, I agree with DummyLoad. It is easy enough to fuse.
As you can tell, I am not a successful businessman. :BangHead:
-
Thanks for the responses. I only use the convenience outlet for my digital reverb wall wart, but I suppose when I'm gone, someone could use it as an extension cord for a table saw or something.
It is going to take some surgery to fit in a second fuse holder, but I'll work it out.
-
I think you can take the power from fuse "out":
In other words:
Mains in L ---> fuse "in" ---> fuse "out" ---> switch
---> convenience outlet L
This gives you a fused always on outlet. If you're just using this for a wall wart, you shouldn't need to change the fuse rating.
Honestly, although it's best practice to fuse this, if the amp were just for me I would NOT fuse it.
-
I am reworking that corner of the amp anyway, so might as well add the 2nd fuse holder while I have room....
-
I am a late arrival to "convenience" outlets. I added one to my practice amp (5F1) that I built. On mine, I interrupted the incoming A/C cord to the amp, and hard wired it to the household style outlet and receptacle box that I bolted to the back side of the speaker box the amp is housed in.
It never occurred to me to add one before.
If I were going to build more (plan is not to), I'd certainly give it more aesthetic consideration, but would have the main A/C-in cord running straight into my convenience outlet before supplying power to the amp. And I'd increase that cord to a minimum 12AWG.
I like the idea of being able to use the outlet without having the amp on. Or, being able to daisy chain other gear if it was in stage/performance use.
Being able to supply adequate power to other "unknown-future" gear would be a consideration for me. Ergo the 12AWG min spec.
And then add in finding a fuse or having one on hand?
Thinking about it, I'd really consider one of the below receptacle's.
(https://toms-shop.com/wp-content/uploads/2025/05/Breaker-e1746447867987.jpg)
~~~~~~~~~
I never introduced myself, so pardon the intrusion. I built a few amps out of sheer boredom, and finally had the time to do so. I ordered a kit initially, then just built from specs and diagrams. Bought a board from Hoffman. Having Fun. Sold everything I built. But, could tell it'd take years to be able to create a Biz outta of it.
Cancer came to visit me back in 2020. Got lucky. Am in remission. In my late 60's. I've worn many hats, from .mil, to Garage/s, to guns, to nurse, to A/V work. Still kicking.
-
Another option is to add an in-line fuse holder inside the amp - gives you protection but saves the hassle of adding another fuse holder to the chassis. Unless there is something else wrong with using those, the main drawback is that they are not convenient to change if they blow - but you only lose the convenience of having an extra outlet nearby and can still play the amp.
-
The surgery was looking good, maybe not up to the metal working standards of South Texas Amp Company, but not too bad for hand tools.
But.........
It seems I lost track of the width of the wall wart, and spaced the outlet too close to the fuse holders. Pullshocks' rule #1: When you screw up, do it over with a smile on your face.
-
what are you powering that needs 5A?
-
what are you powering that needs 5A?
probably a small welder :laugh:
-
what are you powering that needs 5A?
probably a small welder :laugh:
Beer fridge.
-
what are you powering that needs 5A?
As Astronomicum pointed out in post #3, it is a glorified extension cord. The cord itself is rated 10A, and the amplifier is fused at 1A, so I figured derating the outlet to 5A max would be a safety factor . I have not calculated what size beer fridge (Thanks Tubeswell) or how many daisy chained Ampeg SVT's it would take to blow the 5A fuse.
-
All better now