Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 58

Dear Gibosi,

Here is a photo of the Raytheon 1945 6AK5 tubes that I have. They appear completely new, and are packaged in greenish felt lined paper. If anybody is interested, I would trade one pair of these Feb 1945 tubes for one pair of 6N6P-IR tubes.
 

This is just what I thought^^. My consumer 6EW6 also are also not that silent and inert against the environment. Do you mind posting a link or an information where you bought your military spec 6EW6? I am interested in those. Thanks in advance.

Quote:

Originally Posted by Acapella11 

 

This is just what I thought^^. My consumer 6EW6 also are also not that silent and inert against the environment. Do you mind posting a link or an information where you bought your military spec 6EW6? I am interested in those. Thanks in advance.

Sadly, it was a one-shot auction/buy now for both my 6EW6 and 6GM6, that was the seller only inventory for those tubes, and for many miniature types in general... Again, I'm pretty sure my 6EW6 aren't mil spec, but maybe just "selected" since the box mentions your typical US government contract name and such, but nothing about a special quality or military type, or even a JAN indication. Basically plain Jane tube for the US government agencies, possibly not even intended for the military.

On the other hand, I'd love to re-try some less consumer grade 6GM6 -as those were really good- provided someone finds some selected ones at least or the same kind of US government ones, for lack of JAN ones...

Quote:

Originally Posted by Audiofanboy 

Sadly, it was a one-shot auction/buy now for both my 6EW6 and 6GM6, that was the seller only inventory for those tubes, and for many miniature types in general... Again, I'm pretty sure my 6EW6 aren't mil spec, but maybe just "selected" since the box mentions your typical US government contract name and such, but nothing about a special quality or military type, or even a JAN indication. Basically plain Jane tube for the US government agencies, possibly not even intended for the military.

 

On the other hand, I'd love to re-try some less consumer grade 6GM6 -as those were really good- provided someone finds some selected ones at least or the same kind of US government ones, for lack of JAN ones...

there is a seller in Montreal that i bought some tubes from, went to his shop and he tested my tubes in front of me so the guy honest  and he has  the 6ew6 and 6gm6 tubes on his site email him for details heres is link      http://www.tubebazar.com   

There is a hunch of an observation respective the R at the end of the name of the Russian power tubes. I noticed a larger stage and deeper bass with the 6N6P-IR compared to the 6N6P-I. I think the 6N6P-I are fine tubes too, just they do not sound as "high-end" to my ears as the ones with R do.

Now, Audiofanboy described that the 6H30P-EV sound flatter and not as deep bassy as the 6H30P-DR tubes do. It makes me start to think that the low noise spec (R) generally could add a vaster stage and a more U shaped type of sound, thereby adding more substance to the deepest and possibly also highest frequencies in the spectrum. This would be an interesting rule of thumb.

Quote:

Originally Posted by Acapella11 

There is a hunch of an observation respective the R at the end of the name of the Russian power tubes. I noticed a larger stage and deeper bass with the 6N6P-IR compared to the 6N6P-I. I think the 6N6P-I are fine tubes too, just they do not sound as "high-end" to my ears as the ones with R do.

 

Now, Audiofanboy described that the 6H30P-EV sound flatter and not as deep bassy as the 6H30P-DR tubes do. It makes me start to think that the low noise spec (R) generally could add a vaster stage and a more U shaped type of sound, thereby adding more substance to the deepest and possibly also highest frequencies in the spectrum. This would be an interesting rule of thumb.

I can only speak for the -DRs but they definitely have much better upper end extension, and a much more linear and extended lower end - they are in essence very linear imo, it's the driver tubes that end up "biasing" them to a more or less U or V shaped signature. Basically, I'd say the R -low-noise- trait does exactly what it's supposed to, the lower noise level allows for much more clarity and transparency, and for micro-details (airiness and instrument separation in the highs), texture of sounds and realism of transients (mids and bass) to be that much better than their non-R counterparts. Of course, that low noise effect is more apparent the more transparent you gear is up to the power tubes, including driver tubes, but not only (software, transport, DAC).

On another topic, I'll be testing a whole new range of driver tubes very soon, the 6AU6 family of tubes to start with. Now, bear in mind these are not natively compatible with our LD amps; as pins 2 and 7 are inverted compared to a 6AK5 tube, so you'd have a floating cathode pin linked to nothing while a grid gets high voltage randomly.

I ordered two very nice pairs of these for starters:

- A matched pair of GE JAN 6AU6WC 6136 NOS NIB (special quality + military spec matched in a double government box, so matched in box basically (thereafter MIB), special quality 6136 etched in glass, how does that sound?)

- A matched pair of Tektronix 6AU6A 8425A NOS NIB (controlled filament heater special type + made for industrial and computer applications, MIB matched in double Tektronix box (selected by pairs by Tek for their scopes) with Tek tags on each tube and special Tek serial numbers; made by GE, 6AU6A etched in glass; could turn out to be even better than the ones above!)

Now comes the complicated part, as these are not natively compatible (yet perfectly suited for our amps), they need to be made compatible by linking pins 2 (grid 3 + shield) and pins 7 (cathode) soldering a very small wire between the pins very close to the glass so the tubes can still fit in the sockets, and then using the amp with the 6AK5 jumper setting or it will explode like 6AK5s on the wrong setting.

This has been tested to work in practice, now the difficult part is just to find the best stable and functional way to get those pins connected. An adapter could also be an option, but I think I'll try the solder solution first, as it is not that hard and has a lower footprint between the amp and tube.

If you have no idea what I'm talking about or about what pins I'm talking about or why I'm doing this in the first place, look back a few pages where I wrote a very long post with the details on what is compatible with the amp in what setting and why, and what pins do what on compatible tubes. I'll also be reporting -I assume with pictures- as soon as I get to try this myself (I tried and succeeded in soldering pins together on a dead tube but it'll take me a few days to have my 6AU6 with me to test on).

I anybody else wants to try this, I'd suggest staying away from all the basic types of 6AU6, as they are supposed to be very microphonic and noisy, especially the plain GEs, says Google. So, I'd go directly with the best special quality and or (if you can get both, why not?) military specs types, which really aren't that expensive anyway, or better yet get them MIB if you can find them.

Quote:

Originally Posted by Audiofanboy 

Meanwhile, I think I've made sense of this whole jumper business, pin out, and why some tubes are compatible or not in the LD MK III/IV, after reading through a number of datasheets (that I barely understand), other google sources, the pics of the LD amp PCBs on the LD website, and this document on google, that finally helped me makes sense of the whole thing.

 

http://www.kaponk.com/~yanyong/ETF06TS.pdf (pages 11 onwards)

 

The amp uses pentodes as driver tubes, strapped as triodes, meaning that instead of having a cathode, grid (1), grid 2 (screen), grid 3 (suppressor) and anode, it straps grids 2 and 3 to either cathode or anode, leaving only cathode+anode+grid = triode.

 

On the 6AK5 tube, this is pretty easy, as the grid 3 is internally connected to the cathode (pin 2 = k+g3 is connected to pin 7 = k+g3). On the amp PCB the grid 2 is connected to the anode (pin 5 = a is connected to pin 6 = g2), thereby forming a perfect triode strapped pentode we've learned to love, with a by the book execution (g3 connected to k, g2 to a).

 

On the EF92/91, things get more complicated as pins 6 and 7 are inverted (g2 and g3 are inverted), and no pins are hardwired together internally (k is not connected to g3). But on the LD circuit board, pins 5 (still anode) and 6 (now g3) are still connected, leaving g2 connected to nothing. This is where the jumper comes in handy. The jumper apparently connects pins 6 and 7 (g3 and g2) to pin 5 (anode), thereby creating another alternative triode strapped pentode by the book example with both extra grids connected to the anode.

 

Are you following me so far? I barely am. So, this is what the jumper does to make the amp work with the usual types of tubes. Enter, 6CB6 tubes, and most of the other tubes I want to try for that matter, pins 1 to 5 are still the same, but pin 6 is now g2 again and pin 7 is g3 (like for the 6AK5), but nothing is hardwired internally (like the EF92/91), so it won't be triode-strapped with the EF95 jumper setting (and sound all flabby like when you tried your EF92 with the wrong jumpers). With the EF92 jumper setting, again pin 5 (a), 6 (g2) and 7 (g3) are connected, and you should get a normal triode strapped pentode, which is the only reason it works in the amp in the first place. The alternative solution to use these tubes with the 6AK5 setting, would be to hand-wire pin 2 (k) and pin 7 (g3), perhaps with a small flat wire soldered between the pins, which might offer better or similar triode performance like a real 6AK5, different noise rejection and such (and connect the internal shield to the cathode which should be better theoretically).

 

This explains, why EF92 tubes with the 6AK5 setting don't explode (they just don't work well) and why 6AK5 tubes on the EF92 setting light up and try to kill themselves (anode and cathode become connected through internal and PCB wiring, which can't be good).

 

One last thing, I've seen a few tubes with a 7 pin base and the right filament voltage, where the cathode (k) is wired to pin 7 and g3 to pin 2 (pins 2 and 7 are inverted basically), and not hardwired together. The 6AU6 tube (0.3A, sharp-cutoff pentode), which a lot of people like to use in DIY circuits, is like this. With a simple flat wire soldered between pins 2 and 7, and using the 6AK5 jumper setting (EF92 setting would make it explode again), these types of tubes could perfectly well work in the LD amps.

 

If you have no idea what I'm talking about or haven't understood any of this, either ignore my post, or pull up a few tube datasheets from google and look at the pin layout for the tube, it might make much more sense then.
 

EDIT: 6AG5 tubes are wired the same way as 6AK5s. That is, pin 2 (k+g3) is hardwired internally to pin 7 (k+g3), so it should work fine with the 6AK5 jumper setting as a triode-strapped pentode, but will surely explode if used with the wrong EF92 jumper setting (cathode and anode connected = bad).

 

EDIT 2: The 6J38P tubes also have their cathodes connected to grid 3 (pin 2 connected to pin7). I should therefore be used with the 6AK5 setting, unless you want to see some pretty fireworks...

You sir, are a gentleman and a scholar.

I didn't get all of that, but after reading http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm, I at least know what universe you are in.

So I got my GEC CV4014 tubes today. Changed the jumpers and plugged them in and the left channel sounded dull, a few moments later heard the super loud pig squeal type noise they nearly deafened me. I'm pretty sure the jumper is just a little mangled from the pliers I used, but jeez; that friggin' hurt.

This was with the 6N6P-IR power tubes, with the 6H30PI tubes it just stayed muffled and never went all crazy like that.

Quote:

Originally Posted by mab1376 

So I got my GEC CV4014 tubes today. Changed the jumpers and plugged them in and the left channel sounded dull, a few moments later heard the super loud pig squeal type noise they nearly deafened me. I'm pretty sure the jumper is just a little mangled from the pliers I used, but jeez; that friggin' hurt.

 

This was with the 6N6P-IR power tubes, with the 6H30PI tubes it just stayed muffled and never went all crazy like that.

The only reason I could think of for this to happen is that, indeed, the jumper did not strap pin 7 (grid 2, pretty important, unlike grid 3, the suppressor grid) to pin 6 (aforementioned grid 3) and pin 5 (anode), which would mean that the screen, grid 2, was just floating in there accumulating god know what kind of potentials, that eventually made that squeal that nearly deafened you. On the other hand, I see no reason why the power tubes would have an effect on this; if anything the 6N6P-IR are pretty much made for this kind of torture (pulse) so if the power tubes had an effect, it should have been the other way around.

To solve the jumper issue, I use extended computer jumpers that have an extra tab to hold them, and glued some matches (without the flammable part) to them so that they poke out ever so slightly out of the holes in the amplifier. Saves me from massacring them with pliers every time...

For changing jumpers:

http://www.ebay.co.uk/itm/VETERINARY-8-ANGLED-TWEEZERS-200mm-SURGICAL-INSTRUMENT-/160909646601?ssPageName=ADME:L:OC:GB:3160

=)

Interesting info, I did clean the contacts with deoxit before installing the tubes since the pins were a tad blue. I guess it's possible one of the pins had poor contact due to all the rolling I've done.

I'll definitely look into those tweezers, thanks for the link!

Hi folks,

In order to prepare for a set of 6CB6A tubes that I ordered, I decided to install a set of Mullard EF92 tubes. I dread changing the jumpers, and sure enough the assorted long nose pliers I have were hard to maneuver and I dropped one jumper. Inside the LD MkIII. Luckily, I was able to shake it out. Then I thought of using a stainless anti static tweezers that I had. (See link below). This turned out to be a good move, and I was able to change the jumpers very easy with the aid of a flashlight,

http://www.meritline.com/high-precision-anti-static-stainless-steel-tweezers---p-43059.aspx

Today these sell for $2.99, but I paid 69c, and I have seen them even cheaper on sale by Meritline. This is a reputable company, and I have bought from them many times. Customer service is very good, and their sale prices are very inexpensive, and most items are free shipping. You can check out their daily deals every day; the tweezers go on sale often.

One more question: What is the difference between the CV4015 and my Mullard EF92 tubes?

And speaking of power tubes, a new listing appeared today on EBay of what seems to be gold grid 6N6P-IR tubes. A little bit pricey at $24 each including shipping. In the past I bought my gold grid 6N6P tubes from this guy in Siberia but these new listings are much more expensive.

Quote:

Originally Posted by mordy 

Hi folks,

 

In order to prepare for a set of 6CB6A tubes that I ordered, I decided to install a set of Mullard EF92 tubes. I dread changing the jumpers, and sure enough the assorted long nose pliers I have were hard to maneuver and I dropped one jumper. Inside the LD MkIII. Luckily, I was able to shake it out. Then I thought of using a stainless anti static tweezers that I had. (See link below). This turned out to be a good move, and I was able to change the jumpers very easy with the aid of a flashlight,

 

http://www.meritline.com/high-precision-anti-static-stainless-steel-tweezers---p-43059.aspx

 

Today these sell for $2.99, but I paid 69c, and I have seen them even cheaper on sale by Meritline. This is a reputable company, and I have bought from them many times. Customer service is very good, and their sale prices are very inexpensive, and most items are free shipping. You can check out their daily deals every day; the tweezers go on sale often.

 

One more question: What is the difference between the CV4015 and my Mullard EF92 tubes?

 

And speaking of power tubes, a new listing appeared today on EBay of what seems to be gold grid 6N6P-IR tubes. A little bit pricey at $24 each including shipping. In the past I bought my gold grid 6N6P tubes from this guy in Siberia but these new listings are much more expensive.

Mullard EF92s are consumer grade tube, whereas CV4015 are the military version of the M8161, which are the a special quality EF92. They're also called 6065, and are the successor of the CV131, an older special quality EF92, also called 6CQ6. It gets very confusing for some tubes...

I thought all 6N6P-IR had "gold grids"? Or gold-platinum whichever. They have been getting more expensive on fleebay lately (all things considered) at $25+ a pair, and without that many offerings.

Has anyone ordered tubes directly from Russia before? I ask because I purchased a set of tubes from a high rated seller on Ebay almost a month ago but still didn't arrive yet (Russia to USA). Googling the issue it seems like there is a customs delay in Russia but just wanted to ask here if anyone has ordered from Russians before.