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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 23 May 2012, 07:42 
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I took the time to compare Don’s 300B with my Silver Dragon 300BSE both built to Matt’s schematic.

Look away if subjective audio comments offend.

I heated both amps up for one hour then played the first 2 mins of four different tracks through both, firstly through Dons amp then the Dragon. The tracks included; male voice, female voice/male voice, trumpet /male voice and violin. Music style was up-beat swing, cool jazz and classical.

The first time I played Don’s amp I felt it lacked top and bottom end extension and mids sounded veiled. I also though it may need some run in time. Though it has only had about three or four hours of play I have to give the amp back (its builder (Don) has not heard it yet and is anxious to do so). My opinion of the sound of the amp has not changed. After saying that it is a “nice” amp to listen to and if you had no other, a good axe to wheel in your listening room.
Compared to the Silver Dragon (at over three times the cost of parts) it doesn’t compare. BUT the Dragon is a very high performing amp so few amps, home grown or store bought, will ever compete! The big strength of Dons 300B is; 1 – It plays loud as heck (through 91db efficient 3 ways towers) and it is very compact.

Differences which may explain why the Dragon is so detailed with good extension at both audible frequency extremes compared to Don’s are: all Poly filter caps in the PS, very expensive TJ Full Music 300BSE (carbon plate) power tubes, over size Hammond OPTs (though Don’s Dyne OPTs are quite beefy), Silver Foil PIO ($341 each now) Audio Note inter-stage caps. Don’s 2A3 is a much better amp than this 300B and probably cost him no more.

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PostPosted: 07 Jun 2012, 07:54 
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Matt had designed a smart regulator cct. to provide clean DC to the 300B heaters in the amp. When the guy I built the amp for took delivery his friend replaced the high performance regulators with some cheaper units. This did not effect the sound but I though the DC was not floating any more. I got the original regs back and replaced some parts which had gone missing with the intention of replacing the simpler regs with the originals.

After checking weather the cheaper regs were grounded, which they weren't, I decided to leave them in. It would have been a big job to remove the regs which were in there and re-fitting the originals. I'm not sure there would have been any advantage. I can use the repaired good regs for another project.

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PostPosted: 24 Jun 2012, 18:08 
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I had the 807, Luciano amp, in my main listening area but decided to move it to my second listening area. I brought back the 300B amp (Silver Dragon) and went to turn it on. The switch felt lose and the amp failed to light-up after throwing the switch. OK a switch replacement is no big deal but the shear weight of the PS makes any work on it very difficult. The switch felt odd right from the start and was difficult to operate then one day became lose. Evidently it was failing and now completely broken.

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PostPosted: 24 Jun 2012, 23:14 
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Silly me: I made a comment about the 300B having a broken on/off switch. I was switching the standby switch on and off with the power switch off and wondering why the amp failed to work. Just saved myself an hour's work.

Silly Don: An rampant and tenacious amp building friend, Don, who must build close to a tube amp a month, brought around his 6A3 (2A3 with 6V filaments). It was not working and when he showed me the schematic it was evident why. The driver stage is inductor loaded and Don thought it better to leave the inductor out. I have suggested to replace the inductor with a 100K resistors. This is yet to be tested.

Don's best amp to date is his 2A3 which also didn't work but I fixed for him. Then again neither did the last three other amps he has built. Lucky in most cases they were simple fixes.

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PostPosted: 29 Jun 2012, 08:53 
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I recently swapped the 300B back into main system from the 807. Both excellent amps. While listening to the 300B there was a huge hum over all the music. I could not remember this from the last time I listened to it. I did remembered that if I have the preamp on the Oppo and in the middle it induces a hum into the preamp (must be over the power tranni). I had just upgraded to the BDP-95 from the 93 and would have move the preamp (sitting atop) to get the player in position. Moving the preamp heavily to the left of the player dropped all the hum to zero from the speakers.

Though the preamp sits on top of a thick natural marble slap with many felt feet to help deaden the Oppo case, there is no magnetic isolation from the Oppo. The 95 uses a Rotel custom made power tranni (different from the 93) but both will induce hum into components directly above them. My BoZSE is in a Hammond extruded AL case which is heavy Al and bitumen lined but magnetic coupling will still occur if directly above. All better now.

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PostPosted: 29 Jul 2012, 07:35 
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I had a couple of audio critics around for an Opera afternoon. We played my 300B Silver Dragon against Don's 6C33C. I hate to admit but Don's amp was better. Better detail and greater musical depth. And as much a muscle amp as 12W will allow.

There is only one thing to do now. Build my own 6C33C. While the tubes are dead cheap just the iron will cost about $AU1000.

http://www.diyaudioprojects.com/Gallery/displayimage.php?pid=719

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PostPosted: 23 Aug 2012, 07:29 
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Don, "Mr Amps" claims you can drop a 6SL7 in for a 6SN7 even if the schematic is deigned for 6SN7. I know the 6SL7 has higher gain and pin for pin compatible but are there any draw back to this severe tube roll technique. What about bias points etc?

On the other end of the design stick which tube is better sonically - 6SN7 or 6SL7??

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PostPosted: 24 Aug 2012, 20:50 
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mwhouston wrote:
... which tube is better sonically - 6SN7 or 6SL7??
Hands down, the 6SN7 is sonically a much better tube that the 6SL7. It has lower noise, lower distortion, and better intermodulation characteristics. However, this is not to say that the 6SL7 cannot be a great tube in it's own right. You just have to be careful about how you pick your bias points and how much voltage swing to try to achieve.

As to whether you can tube roll between the 6SN7 and the 6SL7, this depends on the characteristics of the circuit. If your loads are appreciable (I'd say greater that 100k) and you have sufficent bias, then you could probably swap the two. However, I would be very careful before attempting such a swap.

Just my opinion.

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PostPosted: 25 Aug 2012, 03:57 
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Suncalc wrote:
mwhouston wrote:
... which tube is better sonically - 6SN7 or 6SL7??
Hands down, the 6SN7 is sonically a much better tube that the 6SL7. It has lower noise, lower distortion, and better intermodulation characteristics. However, this is not to say that the 6SL7 cannot be a great tube in it's own right. You just have to be careful about how you pick your bias points and how much voltage swing to try to achieve.

As to whether you can tube roll between the 6SN7 and the 6SL7, this depends on the characteristics of the circuit. If your loads are appreciable (I'd say greater that 100k) and you have sufficent bias, then you could probably swap the two. However, I would be very careful before attempting such a swap.

Just my opinion.

I'm being goaded by my friend Don to move to 6SL7 "directly in place of 6SN7" for more gain. Personally I like the 6SN7 and can get all the gain I like from my BoZ preamp. So I'm staying with with sonic(s) over over gain. Thanks Matt.

I have most of the parts for the upcoming EL34/KT88 amp based on change of passives as suggested by yourself and Bruce. My question now is can I swap the El34 for :KT88 (I think the answer is yes here), 6L6 and 5881. Do you see any problem with a plug and play with these tubes with no passives change?

And in the schematic with suggestions what would be the best sounding tube?

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PostPosted: 31 Aug 2012, 02:57 
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When I re-claimed the Silver Dragon it came back with a pair of Shuguang 50 Year Treasure 300B-Z ($496/pair) with the distinctive, black glass, ceramic base and gold pins. I played then for a short time but from what I could remember of the original sound of the TJ Full Music SEs I felt them inferior. So I swa[[ed them out.

The wife's away tonight and when the wife's away the music does play. I have dropped the Treasures back in for a long listen. Now it is an all "Treasure" amp with the 6SN7 also being of similar grade. I'll cook them for an hour with HT on because they have not been "on" for a long time. Also these days I play iTunes downloads (purchased) from hard drive through my Oppo - 95 after a conversion to a 24Bit 96K wav by "Switch". I have found when I "up convert" them they sound a lot better than the 16Bit/44.1K versions. I will report back.
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Attachment:
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