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?!!


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.
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).
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.
I have an st-85 as a loaner while my st-150 is being built at VTL..Whenever I put this little guy in triode mode it does exactly what is described in this thread. I saw a glow in one of the tubes on the respective channel of that fuse then the fuse blows (.5 A).

I have this amp plugged directly into the wall on a dedicated cirucit, not a power conditioner. I have never plugged my amps into a PC and wouldn't anymore than would put my fridge on a PC. Prior to this little amp I had a Krell FPB 400cx plugged into the same cirucit, never a problem. I suspect the amp needs new tubes and it is about the same generation of the ones described here.

Hopefully my new amp will not have this issue, that would be disappointing.
Yep, plugging a tube amp of that magnitude into a power conditioner is a sure fire way to ask for trouble. At the very least, the sound will suffer greatly. And that's reason enough for me to plug 'em straight into the wall.

Hey Oz/JC51373,

I have to respectfully disagree with you. I plug both my VTL's into my Shunyata Hydra 8 and have dramatically better sound than when I plug them into the wall. Now I have to say that plugging them into a Shunyata is like going straight to the wall except you get surge protection and noise free power.

Do you have a line dedicted to your system?

If it works for you by all means go for it, I just wouldn't try it. Maybe Shunyata is the exception...I still would not do it.
No I don't. When I got my Shunyata I a/b'ed with the wall outlet. There was a dramatic(and I am talking night and day difference here) increase in dynamics when I plugged my amps into the Shunyata Hydra 8.
agree w/ everyone else. just bad tubes, definitely happens, and actually happened to me just this wkend. replace the tubes that blew (in matched pair) and keep the left over for spare, and you should be good to go.
Also your friend might have his PS Audio Premier set for Multiwave and this is not good for you tube amp... check that..

I have experienced that after shipping (moving), I've had problems with tubes that worked perfectly before hand.. the flaring up is a sure sign of a tube problem.

The Shunyata is passive versus these regenerators and balanced conditioners.. so it won't limit current typically.
Just so people know, there is a rolling update on these amplifiers that lowers the voltages and makes them more "friendly" to modern production tubes. Local dealers can do this, Mine in Minneapolis did... I have lots of VTLs and have had occasional problems with tubes failing, but only when they were old and weak,
Also I have had the MB300 and the MB450 and what you need to know is that the updated, fat ceramic fuses used in the newer Signature series are better than the skinny ones in the older series, like the MB300. That being said, the only time I had a fuse go over on the mb300 is when they were played on led zeppelin late night. The fat fuses don't seem to blow unless tubes are bad. This holds true in my system for both the MB-450 and the Wotan. I will update my MB-300 eventually to the fat ceramic fuses.
Hello, my friend overseas has two MB450 Signature III and just had two 6550 blown. A last one blown along with fuse. Local dealer overseas told him to use ONLY the VTL supplied tubes and asking way too much money (300% profit for sure).
The US VLT guys are not helpful at all. Is this a true that VTL only tubes supposed to be used or I can use any good ones?
Many Thanks!
Danhirsh, I have a Amplitrex 1000 tube tester. The best in the business. If you want I would be willing to test all your tubes and send them back to you. Jeff
I previously owned VTL 300 Deluxe MB’s for many years. I had them fully upgraded in the early part of this Century. I took the amps to VTL myself and was given at tour of the factory. I met and have talked to the owners many times over the years. Truly, stand up people.

Once I tried plugging the 300’s into a PS Audio PPP and they sounded anemic and recessed and quickly plugged the amps back into my dedicated 20 amp outlet and they sounded normal again.

My advise is to buy a set of tubes from VTL and establish a business relationship with them. While you are getting to know the amps you may have questions and they have the answers. Every time I’ve called with questions. The first question from Bea’s is “Where did you get the tubes?” It helps to answer “From You!” Yes, you will pay a little more but you will be a customer.