Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 56

Quote:

Originally Posted by Audiofanboy 

 

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.

Sylvania 6EW6 arrived, stuck in, burned in for just 1 hour, aaaaannnd... Nice! As you say more bass slam. Generally, these sound nicely warm but still balanced. Let's see how they develop. And there is the tube rolling fever back ;).

My volume dial went back quite a bit. These seem to kick the HE-500 quite nicely. With a gain of 10 I listen now at 9 to 9.30, tempted to reduce the gain to 5. These sound very promising already. Absolutely no regret there.

After the first impression, it sounds like what we were hoping for Audiofanboy ;)

100th post (101th...), at last I feel like I'm finally credible here lol.

I let my 6EW6 burn in for about a business day while I was at work today, but even listening after this, I feel that I can't quite reach a conclusion on these yet. I tried the GE 6AG5 really quickly earlier (which I don't expect to be using anyway as they aren't physically matched), my only conclusion would be that this family could show great promise, but not necessarily these old world 6AG5s. Still, I noted a nice slightly tube-y sound signature, and imagining a more selected/military model, I'm sure that family could reach great performance. Again, 6AK5 jumper settings for the 6AG5.

Speaking of changing jumpers, as I had to go from the EF92 setting to the 6AK5 one and back, I gave myself quite a scare testing my GE 6676/6CB6A earlier... I put them in, turned the amp on, heard a slight noise, and the driver tubes filaments took like 10 seconds to begin lighting up, and the power tubes also. I listened for a bit, and found similar impressions compared to my other CGE 6676 tubes. When I switched the amp off, it made a loud BZZZZZ sound for a few seconds, that had me pretty worked up. So I tried switching the amp on again with the same tubes, this time the filaments lit up right way but as soon as I tapped the amp with my finger, the 4 filament just went dark. I was literally convinced I had killed my amp by burning in a 400 mA filament current tube for the whole day... So, I reached for the plug to try and troubleshoot the issue, and it turns out the plug had come loose after fiddling with the amp to change jumpers twice. I put the plug back in, started the amp back up, it worked perfectly, I started breathing again. Lesson learned, check cables after putting the amp upside down a couple of times...

Anyway, after that heart-stopping problem, i resumed testing other tubes, and tested my fourth pair of tubes, the very odd spec-ed 6GX6/6GY6 (which actually has 6GY6 etched in the glass). Very high heater/filament current draw at 450 mA, but very un-audio like specs with transconductance and plate current (the specs I've convinced myself have the highest influence on "power") lower than a 6AK5, and meant to be a "dual control pentode" for FM detection, a far cry from nice sharp-cutoff pentodes well-suited for audio -as a pentode that is. It turns out these dual control pentodes once triode-strapped work very well in audio circuits for some mysterious design reason (look it up on google).

So, after a couple of hours with these tubes, I can say these are the best in my latest batch of non-LD certified tubes; outrageous performance for $3 a pair... And they aren't even burnt-in yet, holy schiit... Apart from the bass -which is a bit lacking in slam- and the volume (which is as high as a 8136 or a 6676, just low for a 450mA filament current draw), these are some of the best tubes I've put in my LD amp. They're just natural, basically. Sounds come in the most natural and detailed way from logical directions around your head, and proceed to give you constant small eargasms, that themselves sound like the most natural thing to be having while listening to music with these tubes. I'll hold off on describing these with real audiophile words until they're burnt-in, but seriously these are quite a discovery!

As a matter of fact, it's the use of "crappy" TV-intended very specifically designed dual control pentodes -and not signal pentodes- in audio systems that is interesting (again, google it), as they make extremely linear -and very inefficient- triode-strapped pentodes. I'll be looking for more tubes with specs like this, as there have been many made throughout the years, apparently

The last tube I intend to spend time with is the 6GM6 I got (high transconductance, very high plate current), which should sound glorious triode-strapped. That might have to wait until this weekend, as I end up not having enough time to actually test all my discoveries ;) ...

Now, pictures:

GE 6AG5 (two different structures)

GE 6GM6

GE 6676/6CB6A

GE 6GX6/6GY6

Military GE 6EW6

Edit: my only worry with the 6GX6/6GY6 triode-strapped is that I'm pretty sure it's way over its heat dissipation specs (it is meant for 1.7W plate dissipation, which is like half of a 6EW6) as the control/suppressor grid(s) no longer serve their purpose as they are tied to the anode. Just food for thoughts.

At this point David from LittleDot should be paying you for all your research!

Keep up the good work!

The 6AW6 do a good job so far, different from the CV4015 but worth listening if you like a little tubier but balanced type of tube, for example M8100 fans. For more details, I want to burn them in 20 - 30h but they surely are enjoyable.

Here is a pic:

I also ordered already a pair of 6GX6/6GY6 tubes. gibosi's and your positive impressions make me really look forward to these.

Stripping down pentodes is the way forward ;) Exciting LD tube rolling times and keep us updated!

Edit: They sound crisper and pair very well with my 6H30P-EV.

Yes, I noticed that my 6GX6s seem to run pretty hot....  Might it be reasonable to infer that these tubes will have to be replaced more often? A heat-shortened lifespan?

On the other hand, when I have 408As installed (20 volt rather than 6.3), they too are similarly pretty hot, so maybe this is not a problem....

Quote:

Originally Posted by Acapella11 

The 6AW6 do a good job so far, different from the CV4015 but worth listening if you like a little tubier but balanced type of tube, for example M8100 fans. For more details, I want to burn them in 20 - 30h but they surely are enjoyable.

 

Here is a pic:

 

 

I also ordered already a pair of 6GX6/6GY6 tubes. gibosi's and your positive impressions make me really look forward to these.

 

Stripping down pentodes is the way forward ;) Exciting LD tube rolling times and keep us updated!

 

Edit: They sound crisper and pair very well with my 6H30P-EV.

Interesting about the 6EW6. I just couldn't make up my mind whether they were very good or average good earlier after 8-9h of burn-in. Just too hard to differentiate from the 8136 and 6676 tubes I'd been testing right before without placebo-ing myself, and I don't want to give any false impressions either... It's good you tried them also with 6H30P tubes, which often sound pretty different.

Meanwhile, I'm having quite the experience with my MK IV SE and its 6GX6/6GY6 strap-on pentode. They're not quite perfect yet, but they seem to do everything well, as in no musical style gets annoying after a couple of songs (as it often does when I'm testing more spiky or grainier tubes). And as is often the case during burn-in, the bass seems to be settling in a little.

Out of curiosity, which brand did you go for? Actually dual labeled? Thank for the pic of the 6EW6 tube; pics really are valuable when you go tube hunting yourself.

Gibosi, I honestly am not sure what running with a higher heat dissipation could do to those tubes. I mean, you'd think if they were made to run off of a 450 mA heater, they should be somewhat heat resistant, but the cathode might not be... Still, it's more the amp I'm a little worried about, but these don't seem to run *that* much hotter than a lot of EF91s I've tested. I guess it's fine, so long as the indoor temperature doesn't rise too much (the amps runs *much* hotter in the summer -without A/C).

Quote:

Originally Posted by Audiofanboy 

Meanwhile, I'm having quite the experience with my MK IV SE and its 6GX6/6GY6 strap-on pentode. They're not quite perfect yet, but they seem to do everything well, as in no musical style gets annoying after a couple of songs (as it often does when I'm testing more spiky or grainier tubes). And as is often the case during burn-in, the bass seems to be settling in a little.

 

Out of curiosity, which brand did you go for? Actually dual labeled? Thank for the pic of the 6EW6 tube; pics really are valuable when you go tube hunting yourself.

 

GE, 6GX6/6GY6 labelled (dual). Details I can report once they have arrived.

I ordered a pair of Raytheon 6GX6/6GY6, i'll report back on the sound once i get them.

Ahh, the power tubes :)

I found an informative post on the diyaudio forum from a member called dotfret respective 6N6P tubes. It explains some nice bits as the 6N6P super tube, some about the impulse tubes and the 6N30P tubes:

About heat dissipation:

The EF95 family tubes I use do not generate that much heat, but I remember burning in some EF92 type tubes that made the whole amp really hot to touch.

As mentioned, the amp runs hotter when the ambient temperature is higher in the summer. As for myself, I put up my amp on metal Hi-Fi cones to allow for cooling through convection - seems to work fine.

I remember one post from Australia who said he used a fan from a PC to blow on his amp. It seems to me that you could take out the power supply from any old computer and also take out and connect a fan from the same PC to cool the Little Dot amp. Any suggestions, or did anybody try this?
 

Quote:

Originally Posted by mordy 

About heat dissipation:

 

The EF95 family tubes I use do not generate that much heat, but I remember burning in some EF92 type tubes that made the whole amp really hot to touch.

As mentioned, the amp runs hotter when the ambient temperature is higher in the summer. As for myself, I put up my amp on metal Hi-Fi cones to allow for cooling through convection - seems to work fine.

 

I remember one post from Australia who said he used a fan from a PC to blow on his amp. It seems to me that you could take out the power supply from any old computer and also take out and connect a fan from the same PC to cool the Little Dot amp. Any suggestions, or did anybody try this?
 

I noticed the extra heat dissipation as soon as I put in EF92's. My 6N6Ps easily burn skin with these higher powered tubes.

When I put in the 6GX6/6GY6 tubes the heat was worrying. I also noted that the filaments in my power tubes were much brighter as well.

I really haven't burned in any of the tubes that I own but in my experience, with my setup the 6GX6 sound signature was not better or worth the risk of heat damage.

I'm also not trying to drive orthos and my cans are 64ohms so 450ma tubes are overkill.

I'm thinking about taking some vinyl coated wire (similar to coat hanger wire) and bending it around the back and sides of the transformer cover, then upward in a way that would hold a very quiet 80mm computer fan above the tubes. Power is easily supplied using a 12v wall adapter.

So far I still really enjoy the tubey goodness of the Ultron EF92's but the 1964 RCA 6676/6CB6A tubes I received today are quickly becoming my current favorite.

The 6676 are quite clear and the bass is excellent. Slightly less bass loudness than the Ultrons but that's a good thing because it can be fatiguing with those tubes. Their overall tone is simply awesome for vocals. Voices are very direct and detailed. Overall detail is very good though sometimes the highs can be harsh. Dimensional placement is good but no other tube so far has come close to the 6J1P-EV's 3D effect. At some point I'm going to order a few pairs of 6N6P-IR power tubes and hopefully those can accent and extend the perceived placement of sounds.

I've got a few more on the way, GE 6CB6A and soon GE & RCA 8136 tubes.

Seriously, Audiofanboy deserves a lot of credit. He's put so much time into research and listening that it's fundamentally changed this thread from "what's available in the EF95/EF92/EF91 tube families?" to "what tubes can we use with LD amps?". Spectacular!

My 6J38P-EV Russian Tubes arrived today! According to their datasheet, this tube is configured like an EF95. I am also expecting some 6BC5/6AG5/6J3Ps which are also configured like EF95s this week, so will change jumpers and start burning these in...

Great gibosi, tell us what you think of those 6J38P with no western equivalents, when you get a chance!

Meanwhile -shameless plug-  I finally got around to posting a classified for a pair of NOS 6N30P-DR from 1980 and a pair of lightly used EH 6H30Pi Gold pins, if anyone's interested.

http://www.head-fi.org/t/654419/supertubes-matched-nos-6n30p-dr-electro-harmonix-6h30pi-gold

Now, back to topic, I finally got my -currently- last order of tubes in today, a whole bunch of Russian 6J3P-E, from three different years: 1972, 1977 and 1978. Each with the best military quality control, OTK1 and <> rhombus. 6AK5 setting, currently burning in. First impressions are a little ambivalent, but I can definitely hear a specific house sound with quite a bit of warmth compared to some of the slightly sterile tubes I tried this week. With so many interesting tubes and so little time to actually listen to them, it's a little difficult to give unbiased feedback...

Anyway, meet our new friend, the 6J3P-E

Quote:

Originally Posted by inphu510n 

I noticed the extra heat dissipation as soon as I put in EF92's. My 6N6Ps easily burn skin with these higher powered tubes.

When I put in the 6GX6/6GY6 tubes the heat was worrying. I also noted that the filaments in my power tubes were much brighter as well.

I really haven't burned in any of the tubes that I own but in my experience, with my setup the 6GX6 sound signature was not better or worth the risk of heat damage.

I'm also not trying to drive orthos and my cans are 64ohms so 450ma tubes are overkill.

 

I'm thinking about taking some vinyl coated wire (similar to coat hanger wire) and bending it around the back and sides of the transformer cover, then upward in a way that would hold a very quiet 80mm computer fan above the tubes. Power is easily supplied using a 12v wall adapter.

 

So far I still really enjoy the tubey goodness of the Ultron EF92's but the 1964 RCA 6676/6CB6A tubes I received today are quickly becoming my current favorite.

The 6676 are quite clear and the bass is excellent. Slightly less bass loudness than the Ultrons but that's a good thing because it can be fatiguing with those tubes. Their overall tone is simply awesome for vocals. Voices are very direct and detailed. Overall detail is very good though sometimes the highs can be harsh. Dimensional placement is good but no other tube so far has come close to the 6J1P-EV's 3D effect. At some point I'm going to order a few pairs of 6N6P-IR power tubes and hopefully those can accent and extend the perceived placement of sounds.

 

I've got a few more on the way, GE 6CB6A and soon GE & RCA 8136 tubes.

 

Seriously, Audiofanboy deserves a lot of credit. He's put so much time into research and listening that it's fundamentally changed this thread from "what's available in the EF95/EF92/EF91 tube families?" to "what tubes can we use with LD amps?". Spectacular!

I to received some tubes today 1958 hit ray 6cb6a  and i agree with you they were suprising very punchy clean tubes

Really curious to hear your thoughts on the 6J3P-E and 6J38P-EV!

Keep up the good work everyone!