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AudioNote Kit-1

68.225.198.26
Posted on July 13, 2013 at 20:53:01
rlyach


 
I have had my kit-1 for almost two months now and have experienced a tube failure. One of my Sophia Princess mesh plates no longer functions. At first the plate became bright red, and now it only buzzes at low volumes. I put a pair of JJ 300B's in the amp and all is well. The voltages are within reasonable values. Has anyone else had this problem? After a quick calculation I note that the Kit-1 runs the tubes close to 30 Watts. Is this too much for the Sophia mesh plates? The spec sheet says that they can handle up to 40 Watts. Just looking for some guidance. I have to say I like the sound of the JJ's better than the the Sophia mesh plats that I had. Perhaps one of them was bad all along. Sadly, I did not purchase the one year warrantee, so I am out $425 after only a little more than 4 weeks of listening.

 

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RE: AudioNote Kit-1, posted on July 14, 2013 at 11:32:27
rlyach@yahoo.com
Audiophile

Posts: 7
Location: Arizona
Joined: July 14, 2013
 One more question... What is the life expectancy of 300B tubes in the Kit-1

 

RE: AudioNote Kit-1, posted on July 15, 2013 at 10:02:42
jetrexpro@aol.com
Audiophile

Posts: 57
Joined: April 19, 2010
 I have read elsewhere on this site that Sophia Mesh 300B's should be biased between 60mA and 70mA and not going above 7omA. What is your Kit one bias set at? I think the Mesh Plates do not disapate heat as efficiently as solid plate tubes.

 

RE: AudioNote Kit-1, posted on July 15, 2013 at 10:22:25
rlyach@yahoo.com
Audiophile

Posts: 7
Location: Arizona
Joined: July 14, 2013
 I thought as much. The classic kit-1 biases the tube a little over 80mA. I could reduce the bias current but That will also affect a lot of other parameters, including the sound. I don't know if I want to experiment that much. To their credit, Sophia is going to replace the tube that went out. Thanks for the reply.

 

RE: AudioNote Kit-1, posted on July 15, 2013 at 10:54:20
jetrexpro@aol.com
Audiophile

Posts: 57
Joined: April 19, 2010
 I had my Sophia mesh 300b Tubes biased at 70mA and brought them down to 60mA and actually like the sound better. This is on my 91a homebrew amp with a B+ of 425v. Not sure what the Kit One would sound like at the lower bias. I would try a lower bias if you plan on using Sophia Mesh plates. If they dont sound good at 60-70mA in your amp you may have to sell them and try a solid plate 300b.

 

RE: AudioNote Kit-1, posted on July 15, 2013 at 12:59:26
rlyach@yahoo.com
Audiophile

Posts: 7
Location: Arizona
Joined: July 14, 2013






Thanks for all the advice. I think I will have to use solid plate tubes. I ran through all the calcs and at a lower bias the output power is lower and the distortion is higher. It appears that the kit one is biased perfectly for optimal performance of a classic 300B tube. I have attached the operating point for the standard 82mA bias using two parallel 1.8K resistors. When compared to a 60ma bias, the output power drops from 8.12W to 6.68W and the max distortion increases from 8.7% to 9.3%. I will have to see what I can do with the mesh plate 300B's, as it appears that I will not be able to use them. Thanks again for your help.

 

It may not be the tube, posted on July 24, 2013 at 01:35:27
Frihed89
Audiophile

Posts: 15703
Location: Copenhagen
Joined: March 21, 2005
 Ask over on the DIY forum what else you might need to do, to operate at these points. The decrease in power is understandable; the increase in distortion is not. In adopting this set of OPs (which many DIY pros have recommended) you've changed the impedance the OPT sees, correct?

 

RE: It may not be the tube, posted on July 24, 2013 at 06:40:57
rlyach@yahoo.com
Audiophile

Posts: 7
Location: Arizona
Joined: July 14, 2013
 Thanks for posting a reply. My conclusion were drawn from both measurements and consulting several people on different forums, and also speaking to a very experienced audiophile who has built many amps. Even the people at Sophia Electric recommended I switch to the Carbon Princess, which I did. The problem is not the lower current operating point in itself, it is trying to get an optimum operating point at a lower current using Kit-1. There are many factors that determine where the tube can and should be operated, including the B+ voltage and the output transformer load. Not just the cathode resistor. The AN Kit-1 is a self biased circuit and B+ is fixed at close to 450V with a 5U4GB rectifier. The output transformer has a DC resistance of about 130 ohms and a musical impedance of 2.7K ohms. Given these limitations just changing the cathode resistors does indeed increase the distortion at full power. If I could change the output transformers, or the B+ than that would be a different story. A higher output transformer impedance and lower B+ will indeed work very well at lower currents with lower distortion. If you have an suggestions on how to achieve a lower current without having to make major (expensive) modifications to my kit-1 I would be very appreciative. Thanks again for your guidance.

 

RE: It may not be the tube, posted on July 24, 2013 at 07:15:55
astrostar59
Audiophile

Posts: 250
Location: Almeria
Joined: February 11, 2006
 Hi
I am confused by this thread. The Kit1 has been sold for years, with many happy customers. Are we now saying that it is a tube eater? Or is the issue with the Sophia 300b tube?

I would have thought the circuit design of the Kit1 is correctly figured for optimum standard fair 300b tubes to run within tolerance.

I am wondering if your particular Kit1 build has an issue? It might be worth doing some voltage an current checks and pinging Brian for advice on that. Also bear n my (in my experience) that tolerances can go out of wack if feeding speakers with wild impedance swings or none tube friendly 3 way designs.

And I presume you have the amp in a cool environment with no shelf above to reduce air flow. Tubes amps don't like getting too hot or beyond there normal operating ambiant temp of 30°C max.

 

RE: It may not be the tube, posted on July 24, 2013 at 07:47:15
rlyach@yahoo.com
Audiophile

Posts: 7
Location: Arizona
Joined: July 14, 2013
 The kit one is great! The problem is that the mesh plate tubes can't handle the same dissipation level as solid plates. I bought the mesh plates because they had a good reputation and they looked cool, but I have since discovered that they must be run at a lower bias power. The bias points of kit one are indeed optimum and I have very happy with my kit-1. The folks at Sophia upgraded me to Carbon Princesses and they sound excellent. The bias point of Kit-1 is:

B+ ~450 w/ 5U4GB
B+ ~430 w/ 5U4G
V-plate ~360 w/ 5U4GB
V-plate ~340 w/ 5U4G
I-plate ~85mA w/ 5U4GB
I-plate ~82mA w/ 5U4G
V-cathode ~77V w/ 5U4GB
V-cathode ~73V w/ 5U4G

All these measurements were made with Sophia Carbon Princesses. JJ 300B's gave a slightly lower I-plate. If you calculate the power dissipation at these levels you get:

W-Plate ~31 Watts w/ 5U4Gb
W-Plate ~28 Watts w/ 5U4G

Notice that I included numbers for both 5U4G and 5U4GB. The 5U4G is a better choice in my opinion but the GB version is usually included in the kit, so I included these numbers for reference.

From what I have read, the mesh plates can't handle this continuous power. All the solid plates can, and I have had no problems with Shuguang, Psvane, JJ, and Sophia Carbon Princesses. I am currently running the Carbon Princesses. They seem to open up the sound a little more.

kit-1 is indeed a great circuit and I am very happy with it. I only ran into trouble with Sophia Mesh Plates.

here are a few pics of my build. Notice that the mesh plates are indeed running a little hot:

https://dl.dropboxusercontent.com/u/109856281/17-Finished%20A0.jpg
https://dl.dropboxusercontent.com/u/109856281/17-Finished%20A2.JPG
https://dl.dropboxusercontent.com/u/109856281/AN-K1-2.jpg
https://dl.dropboxusercontent.com/u/109856281/IMG_0255.JPG

 

OK, posted on July 24, 2013 at 22:19:27
Frihed89
Audiophile

Posts: 15703
Location: Copenhagen
Joined: March 21, 2005
 Sorry, didn't know what else you knew. I wish i could answer your question since you pinpointed the two things I was thinking about. I am not that familiar with the kit. A suggestion: post a schematic on the DIY forum and ask the same question.

 

RE: OK, posted on July 25, 2013 at 06:31:26
rlyach@yahoo.com
Audiophile

Posts: 7
Location: Arizona
Joined: July 14, 2013
 I believe I will just keep my system running where the original designers intended it to be run. There is a reason why this kit has been around for so long :-) There is an easy modification that I could try if I wanted to lower the operating current. Simply put a series resistor in front of the choke to drop B+ to a lower level. I don't believe this will be compatible with the output transformers however. If I decide to build another amp I may try using custom parts and target 70mA or so. As for my kit one, I will enjoy it as it is using solid plates. I really would like to hear a pair of KR 300Bs in this system. The KR tubes are rated at 50 Watts and 120mA, so they should work very well. Thanks for all the help and comments.

 

RE: AudioNote Kit-1, posted on August 14, 2013 at 09:37:15
IkeH
Audiophile

Posts: 152
Location: Vienna
Joined: March 31, 2004
 Hi,

I am sure that the tube life would also depend on the tubes... but if my experience may help you...

I've owned my Kit 1 for over 5 years now. Most recently, I have been using Chinese made Shuguang 300B-SB balloon shaped “mesh”plate (more precisely, a perforated metal plate) in my Kit 1 for about a year and a half without any problem. Before that, I used Emission Labs 300B XLS for over two years without any issues. I use my Kit 1 two to three hours a day on average. My rectifier tube is 5AS4 (5U4GB equivalent).

In the past, only tube that failed was one Emission Labs 300B tube but I think it was a problem with that specific tube because I bought it used and though the seller stated it had less than 200 hrs, the date stamp indicated that it was more than 5 years old.

Ike

 

RE: AudioNote Kit-1, posted on August 16, 2013 at 19:26:02
Wojciech
Audiophile

Posts: 4120
Joined: June 23, 2009
 I also have those balloon shaped perforated plate 300Bs and they are OK but nowhere near the KR 300Bxl . I had similar problem with EML 300B in identical circumstances.They were advertized as an improvement over WE 300B and should last well over 10.000 hrs mine lasted a tinny fraction of this. They had lot's of quality problems at that time which are supposedly well sorted out now.

 

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