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VTL 450 mystery - please help


Hello Folks:

I am now the very proud owner of the VTL MB-450 monoblock. They were built in 1998 and upgraded with every available option in 2003. The seller has an impeccable reputation and I trust him. With that said, something very very upsetting is happening that I could use some advice on.

The first night that I used them, I brought them over to a friends home who has a new PS Audio Premier power conditioner and we plugged both of the amps in and listed for a few hours with no problems. Late that night, after I left, one of the amps B+ fuses blew out.

When I went over to run some tests, we found that both amps tube bias readings are about dead-on and while we were working on one of them with no signal, the other fuse in the other monoblock also blew and I thought I observed one of the tubes near the front of the unit glow unusually bright just before that happened.

The preamp that my friend has is passive, built by Creek and was not muted. The home also has one dedicated power line and one older power line that the other unit was running through.

Bea at VTL told me that sometimes power conditioners inhibit the amount of current that these amp's need to function. She also recommended that I buy a new set of tubes.

Can anyone help?!!

Thanks.

D.H.
danhirsh
Ag insider logo xs@2x
ncarv
983 posts
 
I had a similar problem with these amps when I plugged them into a power conditioner. They worked fine when plugged into the wall. The one tube may have had a short in it. Tubes can operate and test okay, until they don't. Try the amps without the power conditioner and, if you can, test the one tube, including for shorts (though this is not infallible either). You may want to just change that one tube. Also, be sure you are using fuses with the correct value. The liklihood that there is something wrong with the amps is doubtful, since the fuses blew in both.
zaikesman
3,017 posts
 
I don't believe that the Power Plant had anything to do with it. My MB-185's have blown more tubes and fuses than I would've liked to see. About half the time I've owned them they've been plugged into an ExactPower EP15A, but they also blew tubes and fuses before I used that, and in any case I know the EP doesn't limit current and the VTLs don't approach its amperage draw capacity. Tubes gone bad are the most likely culprit, but the B+ fusing of the VTLs seems touchy as well. Mine are '98's too, and have had the fusing upgrade done by the factory (600v ceramic), same as I'm sure yours have. I frequently check the bias with a digital meter. After my last couple of episodes with tubes lighting up and causing the fuses to blow (usually when playing at louder volumes), I've now reached a point where both amps seem to want to blow the fuse soon after turn-on regardless of tube replacement or playing volume, so they need to go to the repair shop for a diagnosis. My solution in the meantime has been to switch to a solid-state amp which I feel sounds better anyway (a McCormack DNA-500).
nrostov
199 posts
 
Just for the record if you call PS Audio they will tell you that their power conditioner's can't handle the VTL 450's. Too much power for them. I don't know if this would cause a tube to go bad but it will restrict the dynamics. I use the hydra 8 because a. it's passive b. it can handle my amps.

Usually when the B+ fuses blow it is a bad tube. The easiest way I found to test for a bad tube was to remove all the tubes, put in a new B+ fuse, and put one tube in at a time, until the fuse blows again.
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