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   Home » Melquiades Amplifier » Melquiades For Dummies™ - step by step. (29 posts, 2 pages)
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  »  New  Building Melquiades: Chronicle of full-range..  VR2 issue leading to jump in current on 6C33 tube...  Melquiades Amplifier  Forum     44  411962  06-09-2006
  »  New  “Melquiades” amplifier: a year later...  Considerations about Melquiades’ layout....  Melquiades Amplifier  Forum     33  318670  10-05-2006
  »  New  Full range Melquiades implementation..  Solved...  Melquiades Amplifier  Forum     81  522884  02-23-2011
  »  New  Building Melquiades: questions and answers...  PeaceMAT XS™...  Melquiades Amplifier  Forum     96  530116  10-09-2007
07-29-2019 Post does not mapped to Knowledge Tree
Terry Maddocks
United Kingdom
Posts 5
Joined on 04-04-2017

Post #: 26
Post ID: 25534
Reply to: 8025
Getting on board... Finally
I'm a little late to the party here, but better than never I suppose!  I'm getting there with parts acquisition, I have valves and output transformers, chokes on order. Next will be power transformers, and finally.. everything else.. Decoud did you ever get your Melquiades finished? 


"Music is enough for a lifetime, but a lifetime is not enough for music" Sergei Rachmaninoff
06-20-2023 Post does not mapped to Knowledge Tree
anthony
Posts 335
Joined on 08-18-2014

Post #: 27
Post ID: 27127
Reply to: 8019
6c33c heater wiring
A small word of advice regarding wiring the 6c33c heaters.

My DSET's have now have several thousand hours of use and I love them to death.  I've not heard any amplifier able to do what they do.  The first amp has over 10,000 hours now and has never failed.  The second amp has fewer hours (still 10,000 hours or so) and has failed twice and I now know the very simple cause and offer it as advice to those still contemplating building this amplifier or any amplifier using 6c33c tubes.

The first failure I attributed to a tube that failed in a way to short circuit the 6c33c heaters which caused the transformer to short circuit, push crazy amps into the wiring, melt some insulation, release a little bit of the magic smoke and because I was out of the room when it started eventually damaging the heater transformer.  This was an incorrect diagnosis.  I replaced the wiring and transformer considering it a freak event and happily listened to that amplifier for about another 6,000 hours.

A couple of days ago the same thing happened six hours into the days playlist.  Mmmm...a freak should not happen twice...there is obviously a design or implementation issue.  After much thinking I got out the FLIR thermal camera and poked it around inside the DSET that has never failed and the underside to the 6c33c socket, including the adjacent section of wiring was running at about 100 degrees celcius, which is very warm, certainly warmer than I expected.  The heaters have been wired with an 18AWG solid core with ultra thin mPPE insulation.  I chose ultra-thin so that the two conductors would be very close together when twisted thus aiding AC field cancellations.  The datasheet rates this insulation at 105 degrees celcius which is roughly the temperature underneath the 6c33c sockets.  Bingo!

What has been happening, in my estimation at least, is that at some point the insulation eventually runs warm enough to begin to weaken or melt and when that melt reaches the twisted section of wiring a short circuit is created and the whole thing runs away from there.  Considering the sheer amount of time these amplifiers have been turned on, I may be fortunate that it has only happened twice now, but the solution is very simple:  the amplifier filaments to all 6c33c tubes is to be re-wired using wire with teflon insulation which has double the temperature rating (200C) of the original wire I used.  Builders should be careful to route all wiring so that is is not close to the 6c33c tubes and also consider a fuse on the secondaries of any heater transformers just in case.
06-21-2023 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,049
Joined on 05-28-2004

Post #: 28
Post ID: 27129
Reply to: 27127
If it good for my hand it good for my amp.
Anthony,
  
I feel that 18AWG is a bit too weak for the filaments. I usually use 12. I do not know if you allow to have any ventilation around the 6C33C, I did. In my full range amp, I had holes around the 6C33 panel.
 
http://www.goodsoundclub.com/Site_Images/MakeMelq9.jpg

The 6-Ch version with 3x6c33 has the same holes a cooling fan

http://www.goodsoundclub.com/Site_Images/SuperMilqInside.jpg

Yes, certainly the Teflon insulation will help but generally you should have some kind of outlet for hot air outside of the chassis. I typically follow the rule that the temperature on a sealed tube amp inside after a few hours of operation should be comfortable for my hand.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
06-21-2023 Post does not mapped to Knowledge Tree
anthony
Posts 335
Joined on 08-18-2014

Post #: 29
Post ID: 27130
Reply to: 27129
Amp still open
Romy,
My DSET amps are still open (no top plate) so are fully ventilated, but I have left vents in the top plate around all of the valves and installed two computer fans (running very low speed) that push air from the bottom and out the vents on the top plate.  Teflon coated 14AWG wire is inbound to make the repairs next week.

My FLIR thermal camera shows that the bottom of the tube socket is a little hotter than 100C which translates to plenty of heat in the first couple of inches of wire but quite cool after that.  The only other warm things in the amp are the final resistors in the B+, but nowhere near as warm as the base of the 6c33c tube sockets.

Rgds,

Anthony 
Page 2 of 2 (29 items) Select Pages:  « 1 2
   Target    Threads for related reading   Most recent post in related threads   Forum  Replies   Views   Started 
  »  New  Building Melquiades: Chronicle of full-range..  VR2 issue leading to jump in current on 6C33 tube...  Melquiades Amplifier  Forum     44  411962  06-09-2006
  »  New  “Melquiades” amplifier: a year later...  Considerations about Melquiades’ layout....  Melquiades Amplifier  Forum     33  318670  10-05-2006
  »  New  Full range Melquiades implementation..  Solved...  Melquiades Amplifier  Forum     81  522884  02-23-2011
  »  New  Building Melquiades: questions and answers...  PeaceMAT XS™...  Melquiades Amplifier  Forum     96  530116  10-09-2007
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