Should I use a shorting speaker jack for saftey?

[elipsey]

I just noticed that my 5F2A schematic uses a plain jack, instead of a switching one to ground the OT hot lead when unplugged.

Do you guys add this when a plain jack is specified?

Do you warn people not to turn the amp on with no load?

[pdf64]

The best protection seems to be to wire a resistor permanently across the secondary, with a value about 30 x the nominal load, eg 220 ohms across an 8 ohm output.
EDIT Power rating about 10-20% of amp's nominal power rating.
eg Vox AC50 uses 470 ohm 3 watt across 15 ohm output http://www.backfromthesixties.co.uk/Pages/Vox_AC50.aspx
Several versions of the Traynor YB1A use 180 ohm 20 watt across the 8 ohm output http://www.lynx.bc.ca/~jc/YBA1Schems.pdf
Switching jacks fail, speakers voicecoils can fuse etc but the resistor will always be there.
Pete

[Enzo]

If you got yourself an old Ford Model A auto and fixed it up to drive around town, would you also install seat belts and airbags and a bitchin stereo? Or would we appreciate it for what it was?


I'd say don;t worry about the jack. The shorting contact is useful and does what we claim it does: it helps protect the amp against an empty output jack. But thousands and thousands of old amps never had that protection, yet they lived. I always install one with a shorting contact when I install a jack. it isn;t some ideology, I just stock the jacks with contacts, same as I use at the input.

I can see a head forgetting to plug in, but no one unplugs their combo speaker really, so I doubt the empty jack even comes up much. I think we can rationalize: what if the protection fails, we need to do MORE. OK, add a resistor. or don;t. Frankly, how about just making sure your stuff is all connected before turning it on?

We warn people ALL the time that a tube amp MUST have a speaker load. We need to keep doing that. On the other hand some folks STILL don;t wear their seat belts.


Oh, and the Model A would be even BETTER with side air bags too....


and a roll bar...

[Jazz P Bass]

And some "Bitchin Wheels'.

And chrome headers.

[The Dude]

Don't forget the "real" accessories.



Edit: Sorry Enzo. I couldn't find Carol Merrill with a Model A.

[Jazz P Bass]

How about a Model T(Bird)

Along with Tiffany Coyne & Carol Merrill.

[g1]

Judging from Carol's right hand, I'd say Enzo's hopes are dashed . Or maybe not...

[Enzo]

Double your pleasure
Double your fun
Get yourself
Two broads
Instead of just one.



Come on guys, be fair. If you are going with headers, then OF COURSE you use a shorting jack.

[loudthud]

A vintage car should have a vacuum tube AM radio powered by a vibrator power supply.

[Tom Phillips]

Don't forget the "real" accessories.

[ATTACH=CONFIG]28584[/ATTACH]

...

Too bad that the custom mods done to the model aren't up to the workmanship standards applied to the hot rod.

[Enzo]

I have to admit, that surely did not go the direction I had imagined...

[elipsey]

Funny.

Since I'm building it, and it makes no appreciable difference in cost I used a shorting jack.

I do worry about what will happen to the amps I build once they get out there in the real world. What if they unplug the speaker? What if a speaker wire breaks? What are all of the concievable edge case consequences to all permutations of fuse/power switch/mains wiring? What if half of the outlets at the bar are wired with reverse polarity? What if the guy's todler tries to unwind a coat hanger and shove the whole thing inside the amp while it's on through the input jack? What if dude plays it in the rain powered by an un-earthed generator? What if the coupling caps fail shorted, and catch on fire at the personal injury lawyer convention brunch?

What if ...&c.?

I guess I have a hyperactive super ego...

[Leo_Gnardo]

I do worry about what will happen to the amps I build once they get out there in the real world. What if they unplug the speaker? What if a speaker wire breaks? What are all of the concievable edge case consequences to all permutations of fuse/power switch/mains wiring? What if half of the outlets at the bar are wired with reverse polarity? What if the guy's todler tries to unwind a coat hanger and shove the whole thing inside the amp while it's on through the input jack? What if dude plays it in the rain powered by an un-earthed generator? What if the coupling caps fail shorted, and catch on fire at the personal injury lawyer convention brunch?

Good rant! Better weld those amps into steel boxes and never let anyone see 'em or touch 'em or know that they're in there. Heave 'em into the depths of the ocean. And then you can stop worrying.

[Justin Thomas]

But what about when the lead content spikes in the water where they're dumped, or some endangered whale ir shark or whatever takes a bite and chips a tooth? Better to just build a Suicide Shuttle & "Set The Controls For The Heart Of The Sun." Hmm... maybe Cygnux X1.
I'll shut up now!

Justin

[Leo_Gnardo]

What if ...&c.?

What if you install a GFI into an amp . . . damn things shut off the line voltage even before you feel a shock.