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Old 28th March 2013, 12:21 PM   #671
Desmo is offline Desmo  Denmark
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To clearly identify if the noise is from the preamp or from a component like your dac, you can connect one of the inputs on the preamp to ground and then listen to the noise on that input... If the noise is the same, then it's from the preamp. If the noise is lower, then it indicates that the noise you hear is from earlier in the chain... And good that it's no longer a problem like it was earlier.
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Old 28th March 2013, 01:06 PM   #672
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I will try this Morten
jep happy the noise is so low now
best Bjarne
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Old 28th March 2013, 01:13 PM   #673
Desmo is offline Desmo  Denmark
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It still puzzles me that you have (or had) this noise with the other rectifier... I have no noise with any of my rectifiers, but maybe my Full Music 2A3/SE are just less sensitive for induced noise/hum from the rectifier, than the JJ's you are using.
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Old 6th April 2013, 10:38 AM   #674
Desmo is offline Desmo  Denmark
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Time for some Mu tube rolling I have used the Russian version of the 6AS7 (a bit warm sounding), but most of the time I have used the Cunningham 6AS7 (a bit leaner than the Russian and more open sounding).

I have been trying to get a idea about what is considered the good sounding 6AS7, and as usual the one that are considered ''best'' are the very rare and expensive ones. I can't help but think, that because these nos tubes are considered so good is -partly- because they are so exotic... When reading comments on the Internet I noticed that many consider Chatham Electronics 6AS7 amongst the good sounding ones, and they are reasonably prices. Apparently Chatham Electronics was acquired by Tung-Sol, so later on these tubes was named; Chatham / Tung-Sol.

I have bought a nice pair of Chatham Electronics 6AS7 and it will be interesting to hear, if they make any difference in sound. Beautiful tubes with their copper posts..!!!
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Old 6th April 2013, 09:45 PM   #675
ktuuri is offline ktuuri  Canada
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The 2399 can sometimes be substituted in a 6AS7 circuit. Here are a few other tubes that might be considered.

6080 - low gain @ 2

7236 - medium gain - great bass, fast and dynamic.

5998A - medium gain in straight bottle. Plate construction like 6AS7.

5998 - medium gain at 5, full-bodied sound, same current load as 6AS7

421A - same as 5998 but with matched plates/sections

6AS7G - low gain, the standard tube for most, plentiful

6AS7GA - low gain, like the standard 6AS7G in striaght bottle

6520 - premium 6SA7G, sometimes with 5998 plates

6H13 - russian 6AS7G equivalent. nothing magical with these

ECC230 - european 6AS7G equivalent. haven't seen one in person

6528 - equiv to 5998 but very high gain at 9, twice the current load. Make sure you amp can handle it

6336 - like 6528 but low gain at 2, still twice current load. Make sure you amp can handle it
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Old 6th April 2013, 10:12 PM   #676
kazap is offline kazap  Australia
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Yes, there's lots of choice for the Tram2 "mu" tube.

Just be aware that the sonic comments in the list above like "great bass" probably refer to the tubes used in OTL headamps ,where its low output impedance allows direct output. So the sonic comments might be meaningless to the Tram2 application.

Ive got a heap of 6AS7 tubes from my own headamp. In the Tram2 I used a black plated RCA 6AS7G with very good results. This is a plentiful and inexpensive tube. As Morten noted its quite possible such a cheap mu tube might out perform the rare and pricey NOS offerings.

If anyone can borrow and listen to the expensive NOS mu tubes do let us know if the sound changed for the better or worse?
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Old 6th April 2013, 10:32 PM   #677
ktuuri is offline ktuuri  Canada
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Yes they were used in OTL headamps.
and could have a different affect in the Tram circuit.
I had the info in my computer, I did not do the testing myself, just wanted to let other know that there are a few other tubes to roll if one wishes.
It's nice to have options, but it can be a curse as well.
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Old 7th April 2013, 04:37 AM   #678
kazap is offline kazap  Australia
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Does anyone know if the Tram2 Mu tube needs to have a 6AS7G specific rated doubling amplification factor for compatibility?
Click the image to open in full size.

6AS7G Mu = 2, Gm = 7000, Rplate = 280 ohms
6080 Mu = 2, Gm = 6500-7000, Rplate = 280-300 ohms
6520 Mu = 2 (1.9-2.4) Gm 6400 - 7600
6H13C Mu=2.4 ?????
5998 Mu = 5.4 Gm = 15500, Rplate = 350 ohms,
7236 Mu = 4.8 Gm = 12500, Rplate = 350 ohms

Last edited by kazap; 7th April 2013 at 04:58 AM.
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Old 7th April 2013, 09:38 AM   #679
Desmo is offline Desmo  Denmark
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Quote:
Originally Posted by ktuuri View Post
Yes they were used in OTL headamps.
and could have a different affect in the Tram circuit.
Yes, the application is totally different in the Tram where the 6AS7 is in the final stage of the power supply doing voltage/current regulation of the B+ voltage before the triode. In those headamps the 6AS7 is in the signal path. This is also why I don't just rush out and buy one of those rare and expensive tubes mentioned as the holy grail when used in headamps. I have the Chatham up and running now, it should (for headamp use) be on the lean and detailed side of the fence, whereas the Cunningham I normally use should be fuller sounding - in headamps. If I hear the same pattern in the Tram, then maybe the experiences from headamp use can be transferred...
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Old 8th April 2013, 06:05 PM   #680
sjs is offline sjs  United Kingdom
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Quote:
Originally Posted by Desmo View Post
the 6AS7 is in the final stage of the power supply doing voltage/current regulation of the B+ voltage before the triode.
My reading of the circuit is somewhat different. I believe that if the circuit is traced out, 2a3 - modified CCS and 6AS7 together form what Thorsten refers to elsewhere as a Super mu follower circuit.

if you look at Richard sears circuit: 845 SE Triode the one with the choke is similar to what we have in the Tram2, but with the high impedance of the choke replaced by the modified CCS, as discussed by Thorsten here: The Super Mu Stage (No Bovine Jokes please).... - Thorsten - Bottlehead Forum

Some background on the mu follower can be found here: Mu Stage Philosophy 1993 Alan Kimmel

This suggests to me that the 6AS7 "mu tube" is just that, part of the modified mu follower stage, and not part of the power supply. Its role is to help isolate the audio stage from the power supply, but I would suggest that it is likely to remain audible, particularly there are so many reports that the rectifier tube remains audible.

In other uses I prefer 6080 over 6AS7, but unfortunately they are tricky to use in the Tram2 due to the size of the base on most 6080s.

best of luck
Simon
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