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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 55

post #811 of 8465
Over the weekend, I had some time to more closely compare the 6CB6As in my possession. I have 1960s era Sylvania, Tung-Sol and RCA, and 1970s or newer Raytheon (all consumer grade tubes), and Mil-spec GEs, dated 1962, and Sylvanias, dated 1978. I think I went a little nuts and bought too many of these! lol But they were cheap and it's been fun.
 
Anyway, all of these tubes, with the exception of the Raytheons, sound the same to me. If there are differences, they are too subtle for my old rusty iron ears and cheap headphones to detect. This is surprising to me, given that different brands of 6AK5s have such different sound characteristics. Actually, the Raytheons sound the same as the other 6CB6As too. The difference is that they are not as loud. This is too bizarre!. All the other 6CB6As, including the 1978 Sylvanias, are significantly louder than my Mullard CV4015s (date code 81-14). However, these Raytheons seem to be no louder than my Mullards, and as a result, I was able to more closely compare these two tubes without feeling the need to readjust the volume. To my ears these two tubes sound very similar, but there are some differences. However, I lack the experience and the vocabulary to be able to clearly understand and articulate just what I am hearing, so I think all I can safely say is the Mullards sound more musical to me.
 
And so ends my journey through the land of 6CB6As. lol 
 
Todays mail brought me a pair of Raytheon 6EW6s and a pair of RCA 6GX6s.  I did manage to briefly plug them into my LD  and I am happy to report they seem fine, and I hope to be able to spend more time with them later this evening.
 

 

 

 

post #812 of 8465
Quote:
Originally Posted by Acapella11 View Post

Hey Audiofanboy, just a brief update for now:

 

Oversampling / Upsampling:

 

"Oversampling is the process by which an analog signal is digitally sampled well above the Nyquist rate (2x it's real bandwidth). Upsampling is a process by which an already digitally sampled signal is sampled above it's original sampling rate."

 

In summary, upsampling seems not good for the signal, whereas oversampling is quite common and generally found to be useful. But, yes it does basically "interpolate" steps in the original signal curve. I am not sure what the context with jitter is. Oversampling is much older than the knowledge about jitter, think about the old and glorious Philips 4 x oversampling chips. There is a de-jittering mechanism in place for the M-DAC but to be fair I haven't yet researched how it works.

 

 

LD power

 

Excellent! I think if we manage 400 mW that would be a useful (surely not optimal, but still) amount of power. I heave read that - in theory - 6H30 tubes for example can do 4 W max, as well as 300 V, if the environment supports it. Now, I have to check on the 6N6P tubes, but even if it is just 1 W, and maybe even 500 mW in the context of the LD, then that's a reasonable to good value for the HE-500. Another question is whether the higher gain also relates to more effective power or just more loudness. I have read about this before. Usually, louder sounds better though it seems.

 

 

6N6P-IR

 

Yeah, it was an interesting finding. I would still wholeheartedly recommend to get one pair and then see for yourself :)

 

 

Other tubes 

 

Interesting stuff!

 

Interesting, I keep hearing about either Non-oversampling (NOS) DACs or the opposite, and their virtues about jitter-battling, but I never investigated whether that was at the digital or analog stage of things. I'll look further into this, out of curiosity. I know there are other "de-jittering" mechanisms, such as reclocking too. It's just the Beresford webiste mentions that about the Caiman DAC so I was a bit curious.


If the 6N6P/6N30P tubes in a class A push-pull can give 500mW per channel (@300-600 ohms), assuming that is with 6AK5 tubes, then we could expect some degree of extra power with more "powerful" driver tubes (higher filament current draw? Higher plate current? Higher transconductance or mu? I understand barely 10% of all this... Although higher transconductance seems correlated with higher listening pleasure to me so far with what little time I had to test my 8136 tubes today). The problem is, I do not know what essentially limits these amps... Still, I'm quite sure 300-400 mW total power is reachable @ 32-50 ohms with a few improvements.

 

I'd love to try some 6N6P-IR, does anyone live close enough to lend me a pair of these ;) . More seriously if I can find any cheap -xR type Russian driver or power tubes compatible (or that I can make compatible) with my LD amp, I will definitely try them!

 

Gibosi, I'm looking forward to your feedback on 6EW6 and 6GX6 tubes, until I get mine sometime this week. So far, I can say that the 8136 tubes hold great promise, not in the sense that they're more powerful or anything, but because of their transparency and great extension. The 6676 tubes, with a few hours of burn-in, seem interesting but less lively and extended than the 8136. But both seem less "fun" and liquid than the GEC CV4014. The 8136 really does seem to have some high qualities, as I was expecting (tube is used so should sound close to its normal sound without burn-in), with deeper bass and spikier treble (good for electronic music), good soundstage and very detailed. Will continue testing and report a bit more tomorrow.

 

What saddens me about tube rolling is how it is making me a tube cynic... I love my GEC CV4014, which are sort of my best happy private unexpected discovery, but now that I'm comparing them to other good high current draw tubes, I'm already starting to feel how the CV4014 are still a compromise, and how other tubes will most likely end up coming on top eventually...

post #813 of 8465
Quote:
Originally Posted by Audiofanboy View Post

 

Interesting, I keep hearing about either Non-oversampling (NOS) DACs or the opposite, and their virtues about jitter-battling, but I never investigated whether that was at the digital or analog stage of things. I'll look further into this, out of curiosity. I know there are other "de-jittering" mechanisms, such as reclocking too. It's just the Beresford webiste mentions that about the Caiman DAC so I was a bit curious.


If the 6N6P/6N30P tubes in a class A push-pull can give 500mW per channel (@300-600 ohms), assuming that is with 6AK5 tubes, then we could expect some degree of extra power with more "powerful" driver tubes (higher filament current draw? Higher plate current? Higher transconductance or mu? I understand barely 10% of all this... Although higher transconductance seems correlated with higher listening pleasure to me so far with what little time I had to test my 8136 tubes today). The problem is, I do not know what essentially limits these amps... Still, I'm quite sure 300-400 mW total power is reachable @ 32-50 ohms with a few improvements.

 

I'd love to try some 6N6P-IR, does anyone live close enough to lend me a pair of these ;) . More seriously if I can find any cheap -xR type Russian driver or power tubes compatible (or that I can make compatible) with my LD amp, I will definitely try them!

 

Gibosi, I'm looking forward to your feedback on 6EW6 and 6GX6 tubes, until I get mine sometime this week. So far, I can say that the 8136 tubes hold great promise, not in the sense that they're more powerful or anything, but because of their transparency and great extension. The 6676 tubes, with a few hours of burn-in, seem interesting but less lively and extended than the 8136. But both seem less "fun" and liquid than the GEC CV4014. The 8136 really does seem to have some high qualities, as I was expecting (tube is used so should sound close to its normal sound without burn-in), with deeper bass and spikier treble (good for electronic music), good soundstage and very detailed. Will continue testing and report a bit more tomorrow.

 

What saddens me about tube rolling is how it is making me a tube cynic... I love my GEC CV4014, which are sort of my best happy private unexpected discovery, but now that I'm comparing them to other good high current draw tubes, I'm already starting to feel how the CV4014 are still a compromise, and how other tubes will most likely end up coming on top eventually...

 

Just one more reason I'm happy i bought a pair of the GEC CV4014 tubes :)

 

Waiting on them to arrive from the UK to NY.

 

my collection keeps growing, currently breaking in my new 6N6P-IR tubes, they're very nice! can't seem to put my finger on the signature just yet compared to my 6H30Pi other that being much more transparent.

 

Curious to see what your research finds for the ER and XR 6N6P variants. Happy Hunting!


Edited by mab1376 - 3/4/13 at 2:21pm
post #814 of 8465
Quote:
Originally Posted by Audiofanboy View Post
I'd love to try some 6N6P-IR, does anyone live close enough to lend me a pair of these ;) . More seriously if I can find any cheap -xR type Russian driver or power tubes compatible (or that I can make compatible) with my LD amp, I will definitely try them!

 

 

If you come to the Head-fi headphone meet on the 27th of April in London, we could do some tube rolling action ;)


Edited by Acapella11 - 3/4/13 at 2:43pm
post #815 of 8465
Quote:
Originally Posted by Acapella11 View Post

 

 

If you come to the Head-fi headphone meet on the 27th of April in London, we could do some tube rolling action ;)


Oh, you know that's actually not a bad idea, it never occurred to me; that and I hadn't figured out or forgot you were British ;) .

 

mac1376, about the Russian tubes and the -xR, I meant "x" as any letter lol, I only know of "DR" and "ER" tubes so far, but I meant I'd be willing to test any Russian tubes with the low noise "R" characteristic.

 

Listening to the 8136 intently, after a few hours of burn-in/try-every-couple-hours of the 6676. So far, I would say that the 6676 have a very pleasant sound signature, kind of like quality transparent sound in a large bubble, nice for vocals, but with a slight lack in upper and lower frequencies, a lack of fun and punch basically, but pretty good nonetheless. The 8136, on the other hand, while not perfect, are showing great promise, the bass on these is nice and punchy without sounding silly and obtrusive like other tubes I've had so far, and the flying airy non-annoying highs remind me of what I like in the EF91 family. I'm starting to think that what I find odd about these is that they sound somewhat un-tube like, a bit SS-like actually, much less liquid than the GEC CV4014 at any rate, which I liked precisely because they were liquid-sounding. Still, a very interesting tube that would complement my CV4014 for electronic music because of this. I haven't quite wrapped my head around these 8136 yet though, they keep surprising me...

post #816 of 8465

Received 6EW6s and 6GX6s yesterday and decided, based on Alain's strong recommendations, to put the 6GX6s in my LD to start. After about 10 hours of burnin my first impressions are that Alain was spot on. The first thing I noticed about these tubes is they are very quiet. Against such an utterly quiet background the music is detailed and crystal clear with a very liquid presentation. Again, these are first impressions, but in my opinion, this tube is a keeper and and I encourage everyone to get a pair of these.

post #817 of 8465
Quote:
Originally Posted by gibosi View Post

Received 6EW6s and 6GX6s yesterday and decided, based on Alain's strong recommendations, to put the 6GX6s in my LD to start. After about 10 hours of burnin my first impressions are that Alain was spot on. The first thing I noticed about these tubes is they are very quiet. Against such an utterly quiet background the music is detailed and crystal clear with a very liquid presentation. Again, these are first impressions, but in my opinion, this tube is a keeper and and I encourage everyone to get a pair of these.


And in terms of gain, or volume, how would these compare to the classic EF92 and EF91? As the specs shows a very high filament current draw, but not that much power output (pentode connected though, which is why I'm curious about its behavior triode-strapped).

post #818 of 8465

About DACs....

 

The purpose of oversampling is to simplify filter design, which makes it easier to design a better sounding filter (and cheaper to build it). At the 44.1 sample rate used on CDs, you need a very steep filter right above 20 kHz, which tends to be a poor compromise. By interpolating samples, the sample rate is raised, which raises the Nyquist frequency, which allows the designer of the DAC to use a filter that cuts in more gradually and at a higher frequency. This filter is both easier to design and build and easier to design such that it doesn't degrade performance in the audio band. Other than that, oversampling per-se shouldn't change the sound.

 

While various types of DACs are more or less sensitive to jitter, that is not "the big draw" with NOS DACs. (If you use some method to remove jitter, then it doesn't matter how sensitive your DAC is to it - within reason.) The main argument put forth by "the NOS DAC camp" is usually that certain NOS DACs "sound good" - and this difference tends to be attributed to the fact that "they use the original samples/data rather than fiddling with it". (They will say it in rather more creative ways, but that is the gist of it. It appears to me more like they prefer the sound of a specific chip, and then rationalize that it is somehow "better" *because* it is a NOS type chip.) In general, sigma-delta DAC chips generally perform better in all measurable ways than NOS DAC chips.... whether because the technology is always better or simply because most modern DAC chips are of that type. There are claims that S-D DACs are more affected by jitter but, as I said above, if you're keeping jitter low, and/or removing it entirely, then this is unlikely to matter. The fact is that many of the "beloved" NOS DAC chips perform very poorly in terms of noise and distortion.

 

Jitter is a specific phenomenon, and is not specifically related to the type of DAC you use. Jitter is caused by problems in data transmission or generation, and there are various ways of controlling or eliminating it. (Basically, you reclock the signal with a clean clock: either by having an asynch USB interface - which most better USb DACs do these days, or by removing it after the fact using a good PLL - common in older DACs, or an ASRC - common in newer DACs like Benchmark DAC-1 and Emotiva XDA-2, or some other similar mechanism - like in most newer Sabre DACs.)

 

Quote:

Originally Posted by Audiofanboy View Post

 

Interesting, I keep hearing about either Non-oversampling (NOS) DACs or the opposite, and their virtues about jitter-battling, but I never investigated whether that was at the digital or analog stage of things. I'll look further into this, out of curiosity. I know there are other "de-jittering" mechanisms, such as reclocking too. It's just the Beresford webiste mentions that about the Caiman DAC so I was a bit curious.


If the 6N6P/6N30P tubes in a class A push-pull can give 500mW per channel (@300-600 ohms), assuming that is with 6AK5 tubes, then we could expect some degree of extra power with more "powerful" driver tubes (higher filament current draw? Higher plate current? Higher transconductance or mu? I understand barely 10% of all this... Although higher transconductance seems correlated with higher listening pleasure to me so far with what little time I had to test my 8136 tubes today). The problem is, I do not know what essentially limits these amps... Still, I'm quite sure 300-400 mW total power is reachable @ 32-50 ohms with a few improvements.

 

I'd love to try some 6N6P-IR, does anyone live close enough to lend me a pair of these ;) . More seriously if I can find any cheap -xR type Russian driver or power tubes compatible (or that I can make compatible) with my LD amp, I will definitely try them!

 

Gibosi, I'm looking forward to your feedback on 6EW6 and 6GX6 tubes, until I get mine sometime this week. So far, I can say that the 8136 tubes hold great promise, not in the sense that they're more powerful or anything, but because of their transparency and great extension. The 6676 tubes, with a few hours of burn-in, seem interesting but less lively and extended than the 8136. But both seem less "fun" and liquid than the GEC CV4014. The 8136 really does seem to have some high qualities, as I was expecting (tube is used so should sound close to its normal sound without burn-in), with deeper bass and spikier treble (good for electronic music), good soundstage and very detailed. Will continue testing and report a bit more tomorrow.

 

What saddens me about tube rolling is how it is making me a tube cynic... I love my GEC CV4014, which are sort of my best happy private unexpected discovery, but now that I'm comparing them to other good high current draw tubes, I'm already starting to feel how the CV4014 are still a compromise, and how other tubes will most likely end up coming on top eventually...

post #819 of 8465

Oversampling is used to simplify filter construction - it is NOT a technique to minimize jitter. (Depending on how it is done, it may increase or decrease sensitivity to jitter). There are several methods for reducing jitter: asynch USB interface, reclock by PLL, reclock by ASRC, and the one Sabre uses (which is sort of a digital PLL). The USB interface itself is notoriously HIGH in jitter, so some sort of jitter reduction is always a good idea with USB. By far the most common way of eliminating jitter (although it is specific to the USB interface) is to use an ASYNCHRONOUS USB INTERFACE, which re-clocks the USB data to a local clock at the point where it is received. Most high-quality USB-to-S/PDIF converters these days (and most good DACs with USB inputs) are asynch USB.

 

 

Quote:

Originally Posted by Audiofanboy View Post


So you use an oversampling DAC, I hear that doesn't always mix well with USB-Digital interfaces (DAC oversamples to reduce the effects of jitter as it is, so further optimizations may not help much); I guess we use different strategies, hopefully with similar good results!

 

Speaking of SS and extra power, I finally managed to find out whether the output power specs of the LD amps are for both channels or for each. Good news: it's for each. So, that's a minimum of 200 mW total @ 32 ohms, hopefully a bit more at for orthos with a slightly higher impedance rating and with higher current draw tubes. Maybe something like 300 mW total in practice on a HE-500 (far from the recommended 1W, but getting closer as things get optimized).

 

About the 6N6P-IR, I just figured it might be a useful piece of information before splurging and buying a huge stash of them (or to go ahead and buy a stash of them just in case they don't last that long, either way lol).

 

After -E, -EV/EB, -I, -IR, -DR, I've discovered there are also -ER Russian tubes (long life / high reliability, low noise like all the best power tubes we like).

 

I just got three different types of tubes in the mail today, the first of a loooong list I intend to investigate. Mullard CV5377 from 1968 (special quality CV4014, which were special quality 6AM6, which are sp... You get the point), Canadian GE 6676 made by US GE 6CB6A/6676 (NOS, so burn-in required before any serious listening), and GE 8136 (instrument version of the 6DK6) used so I should report back about these soon.

post #820 of 8465
Quote:
Originally Posted by kLevkoff View Post

Oversampling is used to simplify filter construction - it is NOT a technique to minimize jitter. (Depending on how it is done, it may increase or decrease sensitivity to jitter). There are several methods for reducing jitter: asynch USB interface, reclock by PLL, reclock by ASRC, and the one Sabre uses (which is sort of a digital PLL). The USB interface itself is notoriously HIGH in jitter, so some sort of jitter reduction is always a good idea with USB. By far the most common way of eliminating jitter (although it is specific to the USB interface) is to use an ASYNCHRONOUS USB INTERFACE, which re-clocks the USB data to a local clock at the point where it is received. Most high-quality USB-to-S/PDIF converters these days (and most good DACs with USB inputs) are asynch USB.


Thanks for the explanation, I do remember reading about how some people feel very highly for their NOS DACs and will defend them to death. I personally would tie most differences and feelings to the type of chip used and its implementation, as you said. For example, I like the sound of Wolfson DACs, but knowing my tastes, I'm pretty sure I would let it go for a good Sabre DAC if everything I've read about the chip is true. About the evils of jitter, I do the first two or three things you mention, namely, asynch USB, quality data clocking at the S/PDIF conversion stage, and my DAC reclocks the incoming digital signal before sending it the DAC chip, which I'd say matters the least in the chain so long as it's decent in the first place -at least this is what my experience so far has tended to show me, as I have not managed to reach the "limits" of my desktop DAC yet and it still improves every time I improve something at the USB / S/PDIF stage (unlike my portable DAC, which uses the same WM8740 chip, and has reached its limits depending on what I've thrown at it).

 

Back to topic, I'm still waiting for my other tubes to go halfway around the globe and reach me, so I can only show pics of the tubes I've received and tested up to here.

 

The CGE 6676 (see the vertical etched "6CB6A" somewhere on the tube, that shows a US GE making, although it doesn't really show on the picture...)

 

 

The Mullard Mitcham-made CV5377 and a dirty box that came with them

 

 

And my current favorite, the GE 8136 (that has not dethroned the GEC CV4014 though)

 

post #821 of 8465
Quote:
Originally Posted by Audiofanboy View Post


And in terms of gain, or volume, how would these compare to the classic EF92 and EF91? As the specs shows a very high filament current draw, but not that much power output (pentode connected though, which is why I'm curious about its behavior triode-strapped).

Did an A/B between these and the GECs to quickly compare gain, and I can detect no difference. I do notice that both tubes have big bass and good highs, and they match up very well, I think. But, no, it appears that in this case, at least, 450mA versus 300mAs does not get you any increase in gain. That said, it might be worth noting that the 1+ uses an op amp instead of power tubes on the chance it might be a factor?

post #822 of 8465

Audiofanboy, what is the rank order in terms of power output of these 'new' tubes?


Edited by Acapella11 - 3/5/13 at 3:16pm
post #823 of 8465
Quote:
Originally Posted by Acapella11 View Post

Audiofanboy, what is the rank order in terms of power output of these 'new' tubes?


CV5377 (=CV4014) > 8136 >= 6676

 

The 8136 and 6676 have a bit less volume than the very high gain EF91 tubes, and I'd say that the 6676 have a bit less than 8136, but it's half volume and half the way the sound is staged. Up to now, my highest gain 300mA filament draw tubes are still the CV4014.

 

Finally today, a few of the tubes I was expecting came in. So as a supposed GE fetishist (as I suddenly realize it's ALL GE tubes lol), I'll be testing:

 

- GE 6EW6 in military boxes, dated 74 and 75, which is smack in the range I wanted (mid-60s to late 70s), they're going in first

- GE 6GM6 in normal boxes, datecode CA, so early since you don't get letter codes in later 50s, 60s and 70s datecodes, these look pretty sturdy actually

- GE 6AG5, plain Jane tubes, 1958 and 1962 (passively confirming that the above tubes could be from the late 50s, these look 60 years old), the two tubes have different colored markings and getter structure (which saddens me... But it's ok, I bought these more as a test of the 6AG5 family)

- GE 6676/6CB6A, both RN datecode, so sometime in the 50s or early 60s I guess, I'll take this chance to point out that these look strictly identical to my Canadian GE made by US GE 6676, internal structure, getter and etched 6CB6A marking, tube is dual labeled 6676/6CB6A

- GE 6GX6/6GY6, JE and NI so again 50s probably, the boxes sure look like they survived the 60s onwards, tubes are dual labeled 6GX6/6GY6

 

Voila, I have the 6EW6 in for burn-in for a work day, first 15-minute impressions are that it is "interesting", and different from all the other tubes. Definitely a bit more powerful on the HE-500 with more bass slam, and a tad more volume than the CV4014, and quite more than the 6676 and 8136.

 

I have to say, up to here I don't regret buying the tubes I tested. Those are all ultra-precise top-tier tubes, which makes it quite difficult to compare them. Fascinating world really, and cheap cheap cheap! (Much cheaper than buying $25 M8100, waaayyy overpriced...)

 

I'll try to get some pictures up at some point, as it makes it easier to know what to expect when you shop.


Edited by Audiofanboy - 3/6/13 at 6:30am
post #824 of 8465

After seeing  Audiofanboy's pictures that look like they belong in an art gallery, I thought I should try to up my game. lol

 

While still not good enough to put up in an art gallery, these are a bit better....

 

While his tubes are GE, these are RCA 6GX6s. I assume the MM is some sort of date code. I really like these tubes.

 

 

 

And these are Raytheon 6EW6s. The left one is stamped made in Japan. These are currently burning in.....

 

 

post #825 of 8465
Quote:
Originally Posted by gibosi View Post

After seeing  Audiofanboy's pictures that look like they belong in an art gallery, I thought I should try to up my game. lol

 

While still not good enough to put up in an art gallery, these are a bit better....

 

While his tubes are GE, these are RCA 6GX6s. I assume the MM is some sort of date code. I really like these tubes.

 

 

 

And these are Raytheon 6EW6s. The left one is stamped made in Japan. These are currently burning in.....

 

 

_FILES/RCA DATE CODES.pdf . try this link i saw your MM code.

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