VTL MB 250 schematic

[Lightloopy]

I have a pair of these beasts that are giving me some trouble. One repair technician advised me to call it a day and shelve them. I have an EE friend who has worked on them but a schematic would be a great help. Bea Lamm wants me to send them to VTL and has no local repair recommendations on the East coast.
Appreciate any help from the group or direction.
Thanks!

 

[roberto]

Can you explain the problem? Are both exhibin the same problem?

 

[Lightloopy]

Hi Roberto,
My friend went through 1 mono and updated everything he could find in Jan. It has been working fine until it started popping the B+ fuse. Last week one of the tubes glowed very brightly and the B+ went. I replaced the tube and fuse but it was making a intermittent static pop so I shut the whole thing down. The other mono is starting to blow it's B+ but has not been gone through its restoration.
My friend wants to evaluate them again but has done this all without a schematic.
This weekend I was able to find a copy of the VTL book on Ebay which has some basic information and schematics.
I will keep you posted as things develop.
I can tell you the 11A works well with lower powered amps but the CLSII turns its nose up at them.

 

[roberto]

Lightloopy, Can I ask which power amp are driving the CLS and the 11A? I do know about the magic in the CLSs...I had all the models...and I was a CLS user for over 26 years.

But my ear tells me that the 11A are more dynamic, with more extension and more easy to set them up. They are very picky with electronics. Not all electronics do a good job on them.

Happy listening!

 

[Lightloopy]

Hi Roberto,
I used VTL MB250 w/ the SL3 for 12 years w/ complete satisfaction. I got the 11A when the sale came along. As you know, I was disappointed in the sound initially but in the last few weeks they have really opened up and showing all the strengths you have talked about. I am currently using an MFA D75 stereo amp that sounds great but I still love what the triodes do.
The CLSII has 30 yo panels but I still like what they do with the VTL amp until they broke . I think now that the 11A is warming up it will show the difference between the VTL and D75.
It's like our member with the CLS and CLX- 2 different flavors with strengths and weaknesses.
Thanks!

 

[caoauto]

Hi all MLO lovers,
I am a new bee to this side, I own the VTL mb750 which is very much the same problem with MB250 here. I call Bea Lamm no help no luck? wonder any one know how to get the schematic? I can pay high money for it,
Here is my amps problem right now, I bought these and the guy is a scammer big time, I plug them in find out the B+ burn out, I test all the tube, find out more than haft are bad, order a set of brand new tubes put them in turn on both working for about one hour but there are hum in it and other channel is noise in it than B+ burn again open it inside find one of resistance and one capacitor in the bias circuit of the power tube are bad, and under one of the power tube socket is burn out, replace them clean out the main board and rewire couple wires and put together, the other channel is one of the input circuit loose, fix those now they are working good but the hum still there?
I do have scope and VOM meter but schematic? Please help!

 

[Steelhead]

Not sure if EveAnna can help but VTL and Manley were closely associated at one point and Manley MAY be able to secure schematics and work on the amp.

I have had my Manley 100/200's refurbed last month and they were and are a great company to deal with.

Check with Manley and see if they can assist.

Good Luck.

 

[Leporello]

has no local repair recommendations on the East coast.
Appreciate any help from the group or direction.
Thanks!

Really? I would think Audio Classics of Binghamton, NY could help. I recall there used to be a tech named Cliff there, I don't know if he still is.

Manufacturers have gotten stingy with schematics. But there isn't really all that much to a tube power amp that you can't deduce without a schematic. Unless their designs changed radically since the VTL book was published, they're basically one dual triode with the sections paralleled for voltage gain, a long tailed differential phase splitter and ultralinear power stage with fixed bias. Rectification was solid state. If you know the tube pin outs, which are readily available, you pretty much know everything you could find from a schematic.

As a matter of principle, every electrolytic cap should be replaced. That's been done, right? An ESR meter could help youpinpoint which ones are actually bad, without having to unsolder them (but might not tell you if they're breaking down under voltage). If the supply voltages--plate and bias--look reasonable (Manley liked to run his B+ on the high side) and tubes are still red plating and dying, could be a short in the output transformer. That would be unfortunate since the OTL is the most outstanding component in a VTL, and guaranteed to be the most expensive, if you can get them at all. But check those other things first. A Variac could be extremely helpful.

 

[Leporello]

p.s. unplug the tubes, power from a Variac (necessary because the voltages will rise substantially without the plate current load) and see if you can get up to reasonable voltages (the plate may have been designed to run as high as 600V on the plates, screen taps and bias) without popping the fuse. I don't know if VTL ever used filter chokes but if so that's another short circuit possibility.

A tech at a TV station I used to work with long ago used to say "There are only two possibilities: it's either the supply or the load". He was joking, but in this case they're words of wisdom.

 

[caoauto]

Not sure if EveAnna can help but VTL and Manley were closely associated at one point and Manley MAY be able to secure schematics and work on the amp.

I have had my Manley 100/200's refurbed last month and they were and are a great company to deal with.

Check with Manley and see if they can assist.

Good Luck.

Thanks Steelhead for the information but I like to do it my self first until I give up. Will see what happen

 

[caoauto]

p.s. unplug the tubes, power from a Variac (necessary because the voltages will rise substantially without the plate current load) and see if you can get up to reasonable voltages (the plate may have been designed to run as high as 600V on the plates, screen taps and bias) without popping the fuse. I don't know if VTL ever used filter chokes but if so that's another short circuit possibility.

A tech at a TV station I used to work with long ago used to say "There are only two possibilities: it's either the supply or the load". He was joking, but in this case they're words of wisdom.

Thanks Leporello for very help full information, this is a lot information, I will try to go step by step, as far as out put transformer is not available as I call Manufacturers so I dont know how dealer replace if they have to? " As a matter of principle, every electrolytic cap should be replaced" These I haven't done yet so these will do first then keep you guys in post.
Thanks again for the input.

 

[caoauto]

Thanks again Leporello for very help full information, this is a lot information, In the mean time I try to redraw the diagram my self from looking at the board and post it in here so many people can see if I miss some things we can try to correct it, probably the manufacture VTL don't like it but I did call them for help and buy the parts they do ignore and said they are not selling any parts or any information about the amp because it is too old (17 years old?) I also did ask them about the out put transformer in case it go bad that is the last thing I will check, the answer was no and not available?? and I try to search in the internet about VTL find out the service is very BAD!
Any way, for replace all the electrolytic cap, any one know where do to buy them? ebay? or any webside?
Thanks all in advance.

 

[BigGuy]

From a fellow audiophile who owned VTLs... May be of some help?!

My research lead me to a Martin Logan DIY website that had been discussing a problem that I had also dealt with. Namely the use of a newer B+ fuse which subsequent generations after the David Manley era were designed at the factory. Once that modification is done they become much more reliable. To Peter’s point, the company had an achievement of making an output transformer that was not harshly limited to one output impedance. They were able to use more wire for better compatibility with all different kinds of speakers without loss of output performance. That was a major selling point. And it makes a profound difference, with upgraded capacitors with any speaker I heard them prior to purchase.

 

[Lightloopy]

As far as VTL support , you are on your own with these amps. Between trying to identify a reputable repair shop, shipping costs etc, it wasn't worth it for me. My EE friend has been working his way through them and ended up buying them from me. The B+ fuse kept blowing but has settled with a higher quality fuse. He loves them with my SL3's he purchased. The good news he will loan them to me over the summer- makes his room too hot! They are amazing amps-as long as you have the skill ( or a reputable shop) to keep them running.
Suggest you honestly assess your skill level with this project. Some shops will not accept "previously worked on equipment" ie SoundSmith.
Best of luck.