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my MG20 tweeter went out the other day

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Posted on January 24, 2016 at 15:06:53
Green Lantern
Audiophile

Posts: 16952
Location: San Diego, Ca
Joined: November 12, 2002
Contributor
  Since: June 17, 2003
 I was listening to some music the other day, cruising along at 55db (loud but not 'that' loud) and I began to notice the left tweeter was sounding a bit harsh. I wrote it off as dirty juice coming from the city lines until around 30 min into it the highs on the left completely vanished.
Well first thing I did of course was shut down the system. I didn't smell smoke which was a good sign I'm guessing, and I went out to the garage and grabbed my multi-meter. I popped out the fuse and it looked perfect (I was a little disappointed actually hoping that was the only issue)...and tested the continuity-it was good meaning the fuse was intact.

Well now I'm thinking wtf, now I have to f with the socks, remove the tweeter and send it off to Magnepan for a replacement, re-attach it, fumble with the sock again, etc.,and I'm mumbling 'why me, why me...'

I then decided to check my tube amp which powers that tweeter. Fired it up and all the tubes were aglow (disappointed again thinking it just might be a bad tube). Then I brought in my garage speaker, an old trusted Pioneer SP-BS21 Andrew Jones design. At $60 a pair it often doubles as my 'sacrifice' speaker in cases like this. Anyway I hooked up the amp into the speaker, fired up just the left side and again -no sound. Hmmm after double checking connections still no sound. Now I'm thinking I don't have a tweeter problem at all, this might be an amp problem. So I swap the right side tube amp with the left, and fed it into the MG20 tweeter, fired up the system and woola, sweet, magical sound coming from the tweeter. So now I'm happy it's not the tweeter but kind of muffed that it's now a tube amp problem. I hope it's just a bad tube (or two) in there, and not a transformer or other issue involved...I'll to have to get it checked out. I never learned to bias tubes and these amps weren't designed 'bias friendly'; at least not to a avg Joe like me.









 

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RE: my MG20 tweeter went out the other day, posted on January 24, 2016 at 16:26:17
j beede
Audiophile

Posts: 239
Location: NorCal
Joined: March 28, 2011
 No output, filaments glowing, and no "red plating" sounds like you lost B+. If your amps use tube rectification then swap rectifiers between your amps as a test. If your amps use GZ-34/5AR4 you could head over to your local guitar amp dealer and buy a JJ or Shuguang or Sovtek 5AR4 for $20-30.

 

RE: my MG20 tweeter went out the other day, posted on January 24, 2016 at 22:18:54
russ69
Audiophile

Posts: 951
Joined: December 13, 2009
 You really need to learn to bias your amps. In most cases it's not very hard at all.

 

One (possible) solution to tube-amp biasing problems..., posted on January 25, 2016 at 00:26:39
Audiophilander
Audiophile

Posts: 30200
Location: Fort Worth (D/FW Metroplex)
Joined: March 31, 2000

Well, in the long run, one like this worked for me..

My old tube amps are in storage, although I never had transformer issues or difficulty biasing the Transcendents (Bruce Rozenblit's tube amp designs were very user-friendly).

Cheers,
AuPh

 

RE: my MG20 tweeter went out the other day, posted on January 25, 2016 at 05:15:34
Green Lantern
Audiophile

Posts: 16952
Location: San Diego, Ca
Joined: November 12, 2002
Contributor
  Since: June 17, 2003
 good info thanks-









 

Bummer, but, posted on January 25, 2016 at 06:09:39
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 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!

 

RE: Bummer, but, posted on January 25, 2016 at 11:22:59
Norman M
 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.)

 

If replacing a fuse, posted on January 25, 2016 at 11:37:06
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 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: Well, you are walking on the wild side when ..., posted on January 25, 2016 at 12:31:12
andyr
Manufacturer

Posts: 12548
Location: Melbourne
Joined: September 2, 2000
 you use tubes with Maggies, IMO! ;-))

But seriously, you said "the highs on the left completely vanished". So bass was OK ... so you're bi-amping? Do you have ss or tube on the bass panels?


Regards,

Andy

 

RE: Well, you are walking on the wild side when ..., posted on January 25, 2016 at 18:39:13
Green Lantern
Audiophile

Posts: 16952
Location: San Diego, Ca
Joined: November 12, 2002
Contributor
  Since: June 17, 2003



Emotiva XPA-1s on the bass panels, biamp'ed thru a Marchand XM44. R'gds









 

RE: Bummer, but, posted on January 25, 2016 at 18:41:49
Green Lantern
Audiophile

Posts: 16952
Location: San Diego, Ca
Joined: November 12, 2002
Contributor
  Since: June 17, 2003
 Much appreciated









 

RE: Bummer, but, posted on January 25, 2016 at 19:29:51
Green Lantern
Audiophile

Posts: 16952
Location: San Diego, Ca
Joined: November 12, 2002
Contributor
  Since: June 17, 2003



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.









 

RE: If replacing a fuse, posted on January 26, 2016 at 10:34:54
Norman M
 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, posted on January 26, 2016 at 10:43:01
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 ...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, posted on January 26, 2016 at 12:21:21
Norman M
 .

 

I consider replacing fuses, posted on January 26, 2016 at 12:32:47
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 an example of pragmatism.

No mystery involved when the filament burns through: you lose conductivity.

 

RE: I consider replacing fuses, posted on January 26, 2016 at 13:56:28
Norman M
 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, posted on January 26, 2016 at 15:17:26
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 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.

 

RE: One (possible) solution to tube-amp biasing problems..., posted on January 27, 2016 at 10:06:56
airheadair
Audiophile

Posts: 393
Location: California
Joined: October 18, 2010
 It you had Transcendent's no wonder you had no transformer issues....aren't they OTL
(Output transformer less)? They are supposed to be great. Is the Magtech really similar-sounding?

I am interested because with my Stax electrostatic loudspeakers, which have a huge impedance in the midrange, no solid state amp that I tried sounded decent, and in fact only the Futterman OTL design really sang. I still have these, but I worry about the future.

 

Not OTL amps., posted on January 28, 2016 at 02:36:29
Audiophilander
Audiophile

Posts: 30200
Location: Fort Worth (D/FW Metroplex)
Joined: March 31, 2000
 My Transcendent amps are a pair of original Super Compact 150 monoblocks, built by Bruce before he started the DIY site. They worked flawlessly for years and were easily biased. The EL-509 power tubes for these are hard to come by these days, but I still have a reserve supply in case I decide to pull these little jewels out of storage. I'm sure that OTL's are fantastic, but I'm not sure they provide sufficient oomph for good sized planar speakers. It probably takes lots of $$$ power tubes for an OTL design with sufficient current for a thirsty pair of Maggies.

The Sanders Magtech amp is great, 900 wpc of clean power with little, if any sound signature of it's own. Plenty of headroom for a pair of Maggie 3.7(i).

Cheers,
AuPh

 

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