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New Novacron's - Feedback ?

50.80.123.193
Posted on April 30, 2013 at 17:38:16
vacuumtube1954
Audiophile

Posts: 245
Location: GA
Joined: December 24, 2009
 Just checking to see if someone here at the Asylum has a pair of the new ones and would share their views on them. A few photos would be nice. I understand Ralph has done a great job in upgrading them from the 1990's version. Thanks.

 

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RE: New Novacron's - Feedback ?, posted on May 6, 2013 at 13:13:38
Sue Kraft
 Can the M-60 amps be upgraded to Novacons? :-)

Those are "bucket list" amps to be sure. I would build a shrine around them. I would be interested in feedback on them also. How do they sound?

 

RE: New Novacron's - Feedback ?, posted on May 7, 2013 at 08:10:20
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 Ralph might want to comment, but off the top of my head, I would guess that the chassis of an M60 might require surgery in order to accommodate the sockets needed for 6C33Cs, because they are physically larger than the octal sockets used by 6AS7s. Also, the 6C33Cs are "fatter" tubes and might need more space around them, compared to 6AS7, for proper cooling. Those would be issues, in any case. Beefing up the filament supply in an M60 would be another; 6C33Cs require about 5A per tube.

 

RE: New Novacron's - Feedback ?, posted on May 7, 2013 at 10:40:41
Sue Kraft
 Hi Lew,

I really didn't think the M60 could be upgraded to a pair of Novacons. I've still got a closet full of the 6C33 output tubes from when I owned the Tenor amps. Tenor had the 6C33 tubes wired in such a way that when one exploded it took a second tube alomg for the ride. Always had to have plenty of spares handy.

 

RE: New Novacron's - Feedback ?, posted on May 7, 2013 at 13:48:16
vacuumtube1954
Audiophile

Posts: 245
Location: GA
Joined: December 24, 2009
 Hi Lew,

Have you had the chance to listen to the new Novacrons ? BTW great system you have put together my friend.

 

RE: New Novacron's - Feedback ?, posted on May 7, 2013 at 13:48:53
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 My MA240s used 6C33Cs until I converted them over to 7241s. The 6C33C is externally fused in the MA240, which saves the tubes from ever exploding in the first place. Before installing the 7241s, I had not appreciated that they are internally fused. To make matters worse, the 7241 has 3 cathodes that are not necessarily sharing the current equally. Even with separate cathode resistors, I have had a problem with cathode fuses blowing, which renders the whole tube rather less useful, since it becomes 2/3 of its former self in terms of current handling and etc. I am dealing with it.

 

RE: New Novacron's - Feedback ?, posted on May 8, 2013 at 01:30:45
Banat
 Hi Lew !

To solve problem of 7241 unequal three separate cathodes static & dynamic current sharing go with combined fixed & autobias scheme .

Best Regards !

 

RE: New Novacron's - Feedback ?, posted on May 8, 2013 at 06:34:58
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 Dear Banat,
First, can you explain why that would help?
Second, I have built these amps from the beginning so that I can separately bias each output tube. In other words, there is a separate driver stage for each tube. Each driver stage is a super-linear cathode follower (SLCF), in my amplifiers. It is no problem for me to set the 7241s or the 6C33Cs in the original build, so that each is pulling the exact same amount of bias current. With the 7241s, I also use a 6R resistor on each of the 3 cathodes per tube, to help equalize current under dynamic conditions. Ralph even suggested inserting a separate fuse as well on each of the three cathodes, in hopes that the external fuse would blow before the internal fuse on each cathode blows. But this is too much complication for me, and I would have no way of knowing whether one of those external fuses has blown except to dismantle the amplifier. Beyond that, I am not sure how your idea could help. It's not the total bias that is a problem or even the dynamic conditions; it's those internal fuse wires, one on each cathode.

In any case, this issue has arisen in only one of the two monoblocks, so I really suspect there is an occult problem with the one monoblock that is blowing tubes. The other monoblock works beautifully and sounds divine.

 

RE: New Novacron's - Feedback ?, posted on May 8, 2013 at 06:39:48
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 Have not heard the new Novacron (or any Novacron), but my own amplifiers started life as MA240s, a now discontinued model that used six 6C33Cs per monoblock. I have had them for 15-16 years, at this point. (It hardly seems possible so much time has passed.) Along the way, I have added many if not all of the upgrades that Ralph has come up with, plus a few of my own. So, it could be said that I have heard a Novacron-like amplifier.

Thanks for the compliment. In the last year, with the input of another -phile in Australia, I made some major changes to the input circuit of the Sound Lab 845s. This amounted to the most significant improvement I have ever heard in my system and literally brought a tear to my eye when I first heard my speakers after I did the mods.

 

RE: New Novacron's - Feedback ?, posted on May 8, 2013 at 09:00:39
Banat
 OK Lew !

Yes I understand perfectly that you have possibility of separate bias for each 7241 tube from asociated separate SLCF driver stage !
But if you look in to the Tung Sol tentative data they as 7241 tubes manufacturer strongly suggest insertion of Minimum 27 Ohm ( maximum 100 Ohm )separate cathodes power resistors for best mutual current share between three separate internal triode tube systems . ( graph nr.1 ) , and 1Kohm for optimum value of grid stop resistors .
Any way with insertion of Only of let`s say 27 ohm power resistors per each 7241 tube cathode output impedance of Amp will go up to much !, but if you insert 1000uF/35V/105C Elko`s in parallel with each of that 27 ohm power resistors than everything is OK , both Amp low output impedance & relative good mutual static & dynamic current share .
My opinion is that even better solution is to insert wire wound 50 ohm power trim pot in series with each 7241 cathode , alltogether with associated parallel Elko`s , where rough fixed bias adjustment is done in usual way from SLCF drivers stages , but fine adjusting of partially automatic bias network between each triode section is done by adjusting of each 50 ohm power trim pot separately .
Ralph idea of insertion of separate external 7241`s cathode fuses is very good !!! , control of each fuses condition can be done very simple by soldering of small LED diode in series with associated load resistors ,all that need to be soldered in parallel with each external fuse holder , so if some fuse accidentally blow associated LED diode will light on .
Any way if you feel that yours Amps works satisfactory than my suggestions can be ignored !

BTW ,
Friend of my just finished his DIY Circlotron Amps with 4 x 6c33c tubes /CH. , fully automatic biased via separate cathodes power trim pot`s , his Amps work rock stable , driving perfectly (as no any Amp before ) via 150/2 Ohm huge autoformer some very strange for me Apogee loudspeakers .

And yes , I apologize to thread starter -Vacuumtube 1954- for my non intetional thread jackin !

 

Thanks, Banat, posted on May 8, 2013 at 11:34:33
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 Those are interesting and creative ideas. The purist in me would not be so happy to have the audio signal traverse those 1000uF capacitors. I am aware of the 7241 data sheet, where it says to use minimum 27R resistors on each cathode. But that is when using the 7241 as intended, as a pass tube in a voltage regulator. I had hoped I could get away with lower value R so as to minimize the effect on output impedance. And in fact, I do appear to be getting away with it in one monoblock. Nevertheless, I will keep your suggestion in mind should I fail to "cure" the problem in the other monoblock.

A more knowledgable friend (Jim Dowdy) is using 7241s in a transformer-coupled amplifier. He uses 9R resistors in the cathodes and has no issues. But he is running higher plate voltage, lower current.

 

RE: New Novacron's - Feedback ?, posted on May 9, 2013 at 13:33:23
Sue Kraft
 How about if I just order a new pair? I just spoke with Ralph and it sure is tempting. Please send donations to...........just kidding on the donations. But I'll keep you guys posted with plenty of photos if I decide to pull the trigger on the new Novacrons. And will hang on to my M60s lond enough for a shootout if anyone is interested.

 

RE: New Novacron's - Feedback ?, posted on May 9, 2013 at 17:21:18
Catastrofe
Audiophile

Posts: 93
Location: St. Louis
Joined: August 10, 2002
 Why not order the Novacrons and have them shipped to me. I'll compare them to MY M60s. . . ;-)

 

RE: New Novacron's - Feedback ?, posted on May 12, 2013 at 12:14:14
David Lawrence
Audiophile

Posts: 315
Location: North Dakota
Joined: April 23, 2007
 I built and used M60 mk 1's in the mid 90's (the ones with the M60 mains transformers in M50 chasses). I was one of the first, if not the first, to build these with parts kits from Atma-Sphere, even before there were construction manuals, and I modified/upgraded them over a couple years, guided in phone conversations with Ralph. I no longer have the amps, which had many virtues, but that is another story. Anyway, I do not know if they are still available, but Ralph had sold me special adaptors that enabled one to plug 6C33's in the M60's. Basically, they were little black boxes with octal plugs on the bottom and 6C33 sockets on the top. I forget if there was anything inside them besides wires, and I also forget how many 6C33's I used in each monoblock. I thought they did sound better than the 6AS7's, but was also worried about the possibility of a 6C33 failure.
David

 

RE: New Novacron's - Feedback ?, posted on May 13, 2013 at 02:04:39
GFL


 
Thanks for this info....I would say 4ea 6C33's pr amp...would give close to 50-60 watts...an i would bet that 2ea M60s would sound vary sweet.
If you can live with less power.

 

RE: New Novacron's - Feedback ?, posted on October 29, 2015 at 22:19:42
njchurchill
Audiophile

Posts: 1
Joined: October 25, 2009



Beautiful amps which sound awesome. Similar to the M-60s with more authority. A lot beefier in the bass. They really are spectacular. They are not, however, easy to live with (sockets, tubes, fuses...are a challenge).
NJC

 

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