No speaker load on tube power amp...bad???

[m.oreilly]

i have a (late 80s ?) peavey classic rack tube power amp (60 watts rms) that i had been thinking of using in some sort of pseudo-portaflex-ish rig, but decided to see if using it for a tube overdrive would work. it does. bass into the eden pre, then pre out to the peavey input (cranked), then its direct out (turned way down) to the qsc, i get a very nice overdriven sound (beefy, not distorted in any manner. yet). will i run into issues if i am only using the peavey direct out, as opposed to having a speaker load and using the direct out? unit is fan cooled, and didn't break a sweat running for an hour or so.

[JimmyM]

it is extremely bad for tube power amps. tube amps have output transformers, which require some sort of impedance load while in operation. without this load, the ot sees infinite ohms, which causes the ot to blow. you may have gotten away with it today, but you won't get away with it much longer.

[m.oreilly]

ah dang. this is the best ever tube overdrive sound i have ever had (without breaking windows). i guess i'll have to find some low power/high sensitivity 15" driver to get some use out of the thing...thanks J.

[m.oreilly]

jim, if this is the case, how did swr do the interstellar od (had, i believe, an output tube or two in it to get the grind)?

[Govier966]

you could create a dummy load, which basically tricks the amp into thinking it has something connected to it

[Bassmec]

Originally Posted by m.oreilly

i have a (late 80s ?) peavey classic rack tube power amp (60 watts rms) that i had been thinking of using in some sort of pseudo-portaflex-ish rig, but decided to see if using it for a tube overdrive would work. it does. bass into the eden pre, then pre out to the peavey input (cranked), then its direct out (turned way down) to the qsc, i get a very nice overdriven sound (beefy, not distorted in any manner. yet). will i run into issues if i am only using the peavey direct out, as opposed to having a speaker load and using the direct out? unit is fan cooled, and didn't break a sweat running for an hour or so.

Just pull the output tubes then your output trans will be fine.
Surprised it still works though a higher power amp probably wouldn't unless the master was down and the direct out was
of course pre that.

[craig.p]

If you don't care that much about the amp, just stick a shorted phone plug into the speaker output, assuming it's a phone jack. If you've got screw terminals, just jumper the (+) terminal to the (-) terminal. Okay, okay, I know... it's not very elegant, but a helluva lot better than running an open circuit. Best solution, though, is to buy a noninductive dummy load that's the same impedance as your power amp's output, and rated 60 watts or more.

[JimmyM]

Originally Posted by m.oreilly

jim, if this is the case, how did swr do the interstellar od (had, i believe, an output tube or two in it to get the grind)?

it had no power tubes at all. the iod is a preamp only so it didn't need an output transformer.

govier, good point about the dummy load. i've tried it and it does work. however, the amp seems to run way hotter with a dummy load (at least it did with the dummy load i have), so nowadays i cheat and just use my vt deluxe

[billfitzmaurice]

Most tube amps short the output to ground when there's no speaker plugged in. The schematic will show that. If it has an effects loop that creates a place to tap the signal and prevent it from passing to the power amp section.

[kosmicwizard]

https://amptechtools.powweb.com/truload.htm

[m.oreilly]

thanks guys. bill, if this is true, would this be kosher for this unit? i have to see if i can find a pdf on this thing...

[JimmyM]

it should be fine for that amp. for an svt, no way, but for a 60w amp, sure.

[m.oreilly]

sweet. thanks. heck, those fake load things look good for the money.

[Jeff Scott]

Originally Posted by JimmyM

it had no power tubes at all. the iod is a preamp only so it didn't need an output transformer.

It does have a small power amp in it with a load resistor when no speaker is plugged in; take a look near the bottom of page 10:

http://www.swrsound.com/support/manu...rstellarod.pdf

[JimmyM]

Originally Posted by Jeff Scott

It does have a small power amp in it with a load resistor when no speaker is plugged in; take a look near the bottom of page 10:

http://www.swrsound.com/support/manu...rstellarod.pdf

apologies...totally forgot. it's been a long time since i saw one or read anything about it. i thought it was just a pre with no power amp.

well there you go, m...the iod does have a power amp and output transformer.

[madmatt]

Originally Posted by m.oreilly

i have a (late 80s ?) peavey classic rack tube power amp (60 watts rms) that i had been thinking of using in some sort of pseudo-portaflex-ish rig, but decided to see if using it for a tube overdrive would work. it does. bass into the eden pre, then pre out to the peavey input (cranked), then its direct out (turned way down) to the qsc, i get a very nice overdriven sound (beefy, not distorted in any manner. yet). will i run into issues if i am only using the peavey direct out, as opposed to having a speaker load and using the direct out? unit is fan cooled, and didn't break a sweat running for an hour or so.

No speaker load = bad.
That picture next to your name = really bad.

[m.oreilly]

Originally Posted by JimmyM

it had no power tubes at all. the iod is a preamp only so it didn't need an output transformer.

jim, this is what i was referring to:
http://www.amptone.com/swrinterstellaroverdrive.htm

The main circuit consists of a tube (2 times EL84) power amp which feeds into a pre-amp (12AX7 or similar)

[Passinwind]

Originally Posted by m.oreilly

jim, this is what i was referring to:
http://www.amptone.com/swrinterstellaroverdrive.htm

IIRC it uses an internal dummy load, like the Lexicon one also does.

[m.oreilly]

ah...thanks charlie
oops, didn't see the more recent previous posts...