tube power amp output jack type / wiring

[funkydiplomat]

ok, gang... here's one for you. My buddy has a supro taurus amp. the output section on these guys is a little unusual. first of all, it's two pairs of 6l6s, each with their own output tranny driving their own 8 ohm loads. The head connects to the cabinet piggy-back style and uses a 1/4" trs connector wired like you would wire a headphone-style connection. one amp uses the 'tip' the other the 'ring' and they both return on the sleeve. I opened up the amp today to work on some other stuff, which i think i have under control, however i noticed the female, chassis-mount output connector was not mating properly with the cable-mount trs that goes to the cabinet. when plugged in, the tip and the ring touch presenting a 4 ohm load to the two amps which are now connected in parallel. I think it's been working this way a while. i dunno. i just noticed it tonight. I tried the old trs connector that's wired to the cabinet, and also a modern neutrik type. neither fit. So... i want to put in a new connector. The amp has, and the schematic specifies, a switching-style jack that shorts the outputs to ground when the speaker cable is not attatched.

On this type of amp is it safer to have the output shorted to ground or open when there is no speaker connected?

I've been pretty careful to always have the cabinet plugged in anytime the amp is on. But, sometimes... usually drunk at a club gig or something... we'll power the amp up without it connected. I want to replace it asap. I have access to regular TRS jacks but would have to order a switching one. What do you guys/gals think??

thanks in advance,

joe

 

[CJ]

The output x-formers might pop if the amp is being driven hard and there is no load. A dead short is much closer to 4 ohms than infinite ohms.

1/4 inch jacks are a terrible way to connect spks to iron, but they have been getting away with it for years.

Not meant to handle anywhere near the power that they hopefully transmit, especially at the bass frequencies.

If you can butcher the amp, I would drill another hole and run two new shorting mono 1/4 inch jacks and two plugs, one for each speaker. The TRS is even worse than a 1/4 inch mono in my opinion.

If you were really on the stick, you would rig up some type of custom jack that is meant for high power. I used to run my Twin Reverb thru a three phase industrial power connector, you know, the ones with the three curved prongs. Never had a problem. Hefty spk wire also. 600 volt 30 amp stuff.
If I were an audiophool, I would swear it sounded better, but who can tell the difference with 100 watts in some poor fool's livingroom at one in the morning after a couple of gallons. :razz:

 

[BYacey]

XLRs make good speaker connectors, just mark it well so people don't try and plug a mic into it.

If you want to stay with the 1/4 inch jack, get a switching type and wire a couple of 4 ohm power resistors so they are switched to the outputs of the amps when nothing is jacked. This at least will provide a level of protection in the event of a speaker load not connected.