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Bummer, but

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In Reply to: RE: my MG20 tweeter went out the other day posted by Green Lantern on January 24, 2016 at 15:06:53

I think there may be an easy answer - replace the B+ fuse. Manley/VTL amps fuse the high voltage so that if a tube does go supernova, it doesn't take out fellow components on the board. The only bad news is that those 600V fuses are a bit pricey. I keep a stock of them on hand just in case. When tubes age, they tend to require a higher level of bias and sometimes they get cranky and blow the B+.

Bias procedure is also pretty straight forward requiring only a basic VOM and a few minutes of your time.

The Manley website has legacy manuals online. From appearance, it appears you have the "Lab Series 100 watt monos". Click here for the manual.

Good luck!

Follow Ups:

RE: Bummer, but - Green Lantern 18:41:49 01/25/16 (0)
Much appreciated
RE: Bummer, but - Norman M 11:22:59 01/25/16 (8)
Perhaps keep some SS (more reliable) amp/s "on hand just in case". :-)

(Yeah, yeah I know about and heard the reported advantages of tubed equipment, after all starting in this so called high-end hobby with Tympani 1Cs, ARC D-76As SP-3A-1 and EC-2A, and am also aware that tubed equipment has made some advances since back then. Nevertheless those advantages were reported upon and also heard back then.)
- RE: Bummer, but - Green Lantern 19:29:51 01/25/16 (0)
  Well I have a pair of UPA-1 mono blocks I use on my Gunned MMGs in another room. I guess I'll have to see how they sound on the TRT.
- If replacing a fuse - E-Stat 11:37:06 01/25/16 (6)
  is beyond your ability, I would agree with your suggestion.
  
  Yeah, yeah I know about and heard the reported advantages of tubed equipment
  
  If you don't hear the advantages, then by all means choose SS.
  - RE: If replacing a fuse - Norman M 10:34:54 01/26/16 (5)
    For GL's sake I hope there's nothing amiss in his amp which caused it to blow a fuse. If such a problem does exist, any and all replacement fuses might also go bust.
    
    I'm happy being able to write that my ability to replace a fuse in an amp
    or device containing an amp has never come under test, since no such fuses have ever blown during 50+ years in this hobby.
    - Congratulations - E-Stat 10:43:01 01/26/16 (4)
      ...since no such fuses have ever blown during 50+ years in this hobby.
      
      More than one amp I've used over the years has blown a rail or B+ fuse. Just replaced them and went on. :)
      - Mysticism? NT - Norman M 12:21:21 01/26/16 (3)
        
        In Reply to: RE: Congratulations posted by E-Stat on January 26, 2016 at 10:43:01
        
        .
        
        I consider replacing fuses - E-Stat 12:32:47 01/26/16 (2)
        
        In Reply to: RE: Mysticism? NT posted by Norman M on January 26, 2016 at 12:21:21
        
        an example of pragmatism.
        
        No mystery involved when the filament burns through: you lose conductivity.
        
        RE: I consider replacing fuses - Norman M 13:56:28 01/26/16 (1)
        
        In Reply to: RE: I consider replacing fuses posted by E-Stat on January 26, 2016 at 12:32:47
        
        Yup, I'm trying to visualize you opening up your big Bryston, Classe, Krell or Mark Levinson (in alphabetical order) to replace one of their fuses as a matter of "pragmatism", despite your very nice great loudspeakers. :-)
        
        In fact, I can't even see your opening up one of their cabinets!
        
        I was expecting to read you write somewhere or other 'power surge' or 'dirty power'; standard explanations I've come across when a person hasn't even the faintest idea why something happened.
        
        RE: I consider replacing fuses - E-Stat 15:17:26 01/26/16 (0)
        
        In Reply to: RE: I consider replacing fuses posted by Norman M on January 26, 2016 at 13:56:28
        
        Yup, I'm trying to visualize you opening up your big Bryston, Classe, Krell or Mark Levinson (in alphabetical order) to replace one of their fuses as a matter of "pragmatism", despite your very nice great loudspeakers.
        I'll be happy to assist with your understanding. First of all, most manufacturers that I'm aware of (and use) conveniently locate fuse holders on the back panel for easy access. Surely the companies you mention also use that common approach.
        Here, for example, is a shot of the backside of a VTL Mb-450 like mine (and similar to GL's smaller amp).
        
        On the angled panel at the 2:00 position from the IEC socket is the gray "Main fuse". This type, like that found on my previous Threshold Stasis requires a flat blade screwdriver to remove. Inside, you'll find a standard "3AG" fuse. On the flat side just to the right of the VTL label is the black B+ fuse holder. It is of the knurled knob design and large enough so that you can twist it open with your hand. Returning to the Green Lantern's original post, it is this fuse that I think might have opened up.
        In the fifteen years I've owned these amps, I've probably replaced about a dozen B+ fuses. Some of which has simply been a learning curve in that when a tube ages and the bias needs to be increased, it can cause one to pop. I've since learned to retire them earlier! I've also experienced two 6550 output tubes catastrophically fail and go "supernova". In the space of say five seconds the tube starts glowing increasingly brighter and following a brief flash goes dark as it dies. That will open a B+ fuse. You replace the fuse, replace and rebias that tube and you're back playing music again!
        Likewise the backplates (power supplies) on the U-1 speakers have an easily accessible fuse. It is labeled "bias" and is located just above the IEC socket.
        
        edit: One time, I spent the longest time trying to find a fuse on a GamuT CD-1. Come to discover it was located in a small drawer located on the IEC socket itself underneath the jack! Push in, then release and the drawer opens.
        
        Edits: 01/26/16

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