logansays
86 posts
Sep 03, 2012
11:30 AM
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hi ,
I got a VHT amp head online..
the first thing i did is plugged the power cable in and switched on the amp..
the red light came on and and also a buzz/hum and then the light went off..tried again , it would come on ..( i dont have a cab to connect, ust wanted to make sure the amps working)..
i realised later, after reading, its a 120 v device and i plugged it in a 240 v power source!!
Have I done a lot of damage? need help please..my first time with a tube AMP and i have no idea whatsoever!!
Will appreciate any help.
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Rick Davis
643 posts
Sep 03, 2012
12:33 PM
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Never switch on a tube amp without having speakers connected.
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-Rick Davis
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logansays
87 posts
Sep 03, 2012
11:42 PM
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maybe ill take it to get checked...thanks for the response:: @rick:
" Never switch on a tube amp without having speakers connected"
whats the reason for that? even if the amp is in standby?
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5F6H
1334 posts
Sep 04, 2012
2:41 AM
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@ Logansays - Switching a tube amp on whilst no speaker is connected, even in standby, is asking for trouble. It's too easy to throw the standby into "play" mode & blow the amp. When tubes are in operation they need to see an appropriate speaker load at the speaker side of the output transformer (OT)- an open load (no speaker) will cause AC voltages to skyrocket and kill the tubes instantly and probably the OT too, punching through the insulation of the primary windings. A short/too small a load will cause the current at the OT secondary to skyrocket and possibly burn out the OT primary winding. Fender amps tend to have the speaker jack short out if the speaker is unplugged, this can buy you a little time before damage sets in but is definitely NOT recommended that you put this to the test!
If you have no speaker attached, you must also remove the power tube(s) before powering up to see if the amp will turn on. However, the value of doing this is somewhat limited, as all you learn from this is that the power transformer works...assuming the fuse doesn't blow that is.
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logansays
88 posts
Sep 12, 2012
7:05 AM
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@5F6H hey thanks for that info..well I think i did two things i wasnt supposed to do..
1) used a 240 V power source
2) no speakers attached..
i have to take it to a reliable source to get it checked..but i need to ask this, out of the two things i did to the amp which one would have caused more damage....
i have absolutely no idea about amps, tube amps and electrical stuff in general..trying to read as much as i can online!
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didjcripey
381 posts
Sep 12, 2012
7:12 PM
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I did a similar thing with an american (110 V) amp, though it was a combo so the speakers were attached. Took it to the local amp tech, who charged me a hundred bucks to put a new fuse in and tell me it was OK!
I reckon the fuse would have blown before the absence of speakers was an issue.
Save your dough, replace the fuse (same value) attach speakers, get a transformer and see how you go. This all the tech did and it cost me a hundred bucks! Amp techs often charge a fortune just to put it on their bench.
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Lucky Lester
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5F6H
1355 posts
Sep 13, 2012
1:37 AM
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@logansays - Using a higher than expected power source can blow: power transformer, rectifier, power tubes & output transformer.
Running without a speaker load will blow the power tubes, possibly take the output transformer out.
You either lose very big, or lose pretty big.
@didjcripey - Frankly, you were robbed! It shouldn't take more than an hour to get to the chassis, do a full voltage check & report back. If techs can charge $100/hour where you live, I'm moving! ;-) Any large bills like that should be itemised. One question though, if it was just the fuse, why didn't you fit one for a few cents & save yourself a trip to the tech?
Fuses are typically on the AC side of the power transformer & "slo blo" to save them popping during surges at power up. The power tubes are on one of the 2 or 3 secondary windings (sometimes has it's own fuse) and without a speaker can be overloaded in milliseconds. In short don't rely on the amp's fuse to save the day in the event of having no speaker attached. I have seen amps where the B+ primary winding (feeds the tubes) has completely failed but the amp will turn on without popping the fuse.
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didjcripey
385 posts
Sep 13, 2012
3:11 AM
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@5F6H: yep I know i was robbed! I said to him: '100 bucks for a fuse; you're kidding!" His response was a combination of being offended, aggressive and disdain. 'I didn't just change the fuse, I had to check it over and run it for a while to make sure it was OK' It was clear that I wasn't getting my amp till I paid him, so I sucked it up, and needless to say he'll get no business from me, and I have warned many others. This shop charges 90 bucks for a look (and ten bucks for a fuse!).
The reason I didn't just replace the fuse was because it was a few years ago and my first valve amp; like the OP, I was worried that replacing the fuse and turning it on might damage it further, and I had no idea the amp tech was such a thief.
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Lucky Lester
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