Little Dot Tube Amps: Vacuum Tube Rolling Guide

Finally back after a few days of vacation, and still no triodes on my doorstep, though I apparently have a package waiting for me at my local post office; could either be my second 8532W tube, or my last -major- order, that I placed last week just leaving for the airport.
 
Speaking of ordering tubes, and seeing how I'm still missing out on all the triodes and even heptodes fun, here is what I have on ice, ordered from an obscure UK tube company, and that should get to me within this week.
 
- Mullard 6BE6W (were originally Syvlanias, but turned out to be Mullard when the seller checked the stock, I'm not sure whether that's good news or bad news, I'd say good, since Acapella seems to have already found better 6BE6 tubes than the Sylvanias, making buying them a bit pointless)
 
- Brimar CV4012 (UK mil spec 6BE6 type, kind of curious as to what these even look like)
 
- Pinnacle EBC91 (European 6AV6 type, were supposed to be Telefunken and cheap-ish, but turned out not to be when the seller checked them, but could be sourced from any European brand from Mullard to Telefunken, or silly Russian tubes; Pinnacle seems to have a decent reputation depending on the rebranded tubes, so it's a bit of a gamble. Considering the same labeling/branding happened with the 6BE6W when the tubes were checked from the seller's stock (I've seen Sylvania tubes which were Mullard imports, so they might be Mullard made but Sylvania branded, hence the information in the stock list) I'm hoping the same holds true for these; there must be a reason why they had been entered in as Telefunken by the seller in the first place?)
 
- Telefunken EH900S (6BY6 type, similar to the 6BE6 and made by Telefunken, supposedly high grade tubes, can't be horrible can it...? Could have gold pins or not, both versions seem to have existed)
 
- Mullard CV4070 (UK mil spec EC91 type -that I think I may have mentioned here before unofficially- possibly dual labeled M8099, ground-grid triode like the 6J4 with even more interesting characteristics, the mil spec versions of the EC91/6AQ4 seem to be hard to come by, hence my not having made these official yet)
 
- Mullard CV5311 (UK mil spec 6J4 type, possibly dual labeled M8248, not from the same -unique ebay- seller as gibosi though, hopefully very nice tubes)
 
So I can -finally- get back on the tube rolling band wagon and start giving impressions again; this, despite my still being absolutely mesmerized by the Tung-Sol 6485... These are a very, very, clear-cut grade above all my other tubes, and that's saying a lot.
 
About those socket adapters, did the Chinese ebay seller ever mention sizes? Basically, I'm trying to figure out if I could even fit an adapter on MK IV SE sockets without "modifying" the golden tube protectors that make it look so pretty in the first place, which I probably wouldn't do...

Burning in some tung-sol 6BE6 they seem to be lighter on the bass but maybe more detailed i like the violins on these tubes .Soundstage is good . What are your impressions.                                          

I ordered a pair yesterday he didnt mention the diameter but he said that it would fit the mk3 When i get the sockets will measure the exterior and post. i asked for 6ak5 to 6au6 socket adaptor hope i get them soon but like i said to gibosi if its anything like Russia its going to take a while anyways ill keep you guys posted                            

http://www.ebay.co.uk/itm/300630722142?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
 
http://www.ebay.co.uk/itm/2-Stk-ECC99-JJ-Tube-Rohrenverstarker-Rohre-HighEnd-12BH7-matched-Paar-NEU-/200775278980?pt=R%C3%B6hren&hash=item2ebf23a184
 
I started searching for power tubes, 6n6p ir, I have a few from different years and some with the gold pins.  Very happy with them but in the spirit of tube rolling i thought i would extend the search to include the ecc99 and found these. do you guy's think they will work, i haven't ordered them yet though I have asked Yen if he thinks they would work.

Quote:

acapella11 said:

Hi Mikelap, Agree on great stage and detailed. Two big points. With respect to bass: Also agree with this not being a bass heavy tube. I would almost say the frequency spectrum is slightly skewed to mids and treble, not in a bad way though. To give a bigger picture, IMO they were so clean that there was no bass "coloration" when no bass was produced and once bass kicked in, its quality was actually really good  - well articulated and punchy. After tube and brain burn in, I didn't find them bass light. Why I found the tube special really was, because it just sounds so clean with a black background. Every other tube slightly distorted on certain transients and broke small details in the imaging, listening to violins for example (as you mentioned them), but these didn't. Details...

IMO and generalized, the 6BE6 signature matches approximately that of CV4015 and TS 6485, more inclined towards the TS 6485.

 

Gibosi, OK. Good luck sorting out your sockets!

 

Hypnos, 6N6P gold grid? Agree with Mikelap, that's really standard stuff. Pop them in. They should be fine. Depending on year of production, which I guess is more critical than the gold grid, you may find them more or less useful. If I remember correctly, Mordy uses 6N6P gold grid from the Cold War times.

 

Audiofanboy, WB and your new tube menue looks very yummy indeed.

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With time hopefully my descriptions will improve as for your description its on the money thats what i am earing.

Hi everybody,
first of all thanks to all of you for this amazing an super informative thread. My wallet is not so happy after all the new found tubes, but my ears definitely are 
 
I have a question regarding the 6BE6, 6CS6 group, for which I've not yet got any tube: did anybody had a chance to try (or ordered) the Mullard EH90 ? They should be very similar to the 6CS6, but I'm not 100% sure.
 
By the way, I confirm that almost all tubes mentioned in the table on page 77 are also working perfectly in the Little Dot MK II+ amp. I said "almost all", as I have not tried the 6BE6 family and the "modified"6J4 / 6AV6 ones... yet.

Quote:

vic2vic said:

I have a question regarding the 6BE6, 6CS6 group, for which I've not yet got any tube: did anybody had a chance to try (or ordered) the Mullard EH90 ? They should be very similar to the 6CS6, but I'm not 100% sure.
 

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Yes, and in fact, the 6CS6 and EH90 are the same tube. EH90 is the European designation for 6CS6, and thus you will often see it used in reference to European manufactured tubes. Oh, but no, I haven't tried it....
 
This site is very helpful in sorting out what is equal to what:
 
http://www.radiomuseum.org/tubes/tube_6cs6.html

Quote:

mikelap said:

 
 

1.  
2.  

[size=1.5em] Re: Little Dot Mark IV SE tubes compatibility[/size]

by Chocki » Jul 7th, '12, 17:17

[size=1.3em] Well my 6N6P Gold grid power tubes arrived this morning, I've had them in all day circa 12 hrs playing while I've been working doing the kitchen up.
Impressions are very favorable, they are as good as the 6H30PI's but last a lot longer being military ruggedised. They start off completely silent at max volume with no imput (Remember my headphones are much lower resistance than sennheiser HD 650's so everything is much louder), but after 12 Hrs, they also exhibit some slight static noise but nothing like like the 6H30PI's, not that I ever listen at max output and it really is faint, while checking this out what I did notice though is that the LD DAC_1 suffers from crosstalk!. With IN2 playing, selecting any other input, you could still hear IN2 (RCA SPDIF) very faintly at max volume. Again not the slightest bit worried as I only intend to listening to one source.[/size]


Found this on Littledot site and its dated july 2012 did they change the model after that.

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Hi mikelap.
 
Thanks for the quote/link. Chocki didn't seem to have any problem with the 6N6Ps, and I think the only modification was to hardwire so as to remove the  jumper option.
I can only assume the LD people found (or presaged) a possible problem with long-term use....Whatever, he found the 6H30Pis a better match for the Senn HD650, which I have, so methinks I would be foolish to take any kind of risk - everything is sounding so darned good now (up yet ANOTHER notch with just 15 more hours on the tubes - is it the 6485s or the DRs? Both probably...).
Am almost afraid to even try the 5750s, I'm so star-struck!! This rolling can be a bit of a roller(sorry!)coaster ride, to say the least. Ah well, 'agony and ecstasy' is obviously not restricted to just artists!

Quote:

mikelap said:

I ordered a pair yesterday he didnt mention the diameter but he said that it would fit the mk3 When i get the sockets will measure the exterior and post. i asked for 6ak5 to 6au6 socket adaptor hope i get them soon but like i said to gibosi if its anything like Russia its going to take a while anyways ill keep you guys posted                            

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Thanks to Mikelap's considerable efforts, you can now order 6AU6 to 6AK5 tube adapter socket converters on eBay!!
 
http://www.ebay.com/itm/1x-6AU6-to-6AK5-tube-adapter-socket-converter-/290917075011?pt=Vintage_Electronics_R2&hash=item43bc024843

Quote:

gibosi said:

 
Thanks to Mikelap's considerable efforts, you can now order 6AU6 to 6AK5 tube adapter socket converters on eBay!!
 
http://www.ebay.com/itm/1x-6AU6-to-6AK5-tube-adapter-socket-converter-/290917075011?pt=Vintage_Electronics_R2&hash=item43bc024843

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Well, color me impressed; that's actually kind of cool to have our very own custom adapter! Next step would be the "adapter" that disables pins 5 and 6 at the tube level, yet cleanly links pin 7 to either of those at the socket level (so we can use all those cute triodes (6J4, EC91) and double diode-triodes with the EF95 setting and with no "pin modification" bloodshed, or was it metalshed?).
 
As a side note, it looks like it could fit on an MK IV, though I would prefer a more brassy or aluminum feel to the adapter for that kind of amp... Oh well, can't win them all.

Quote:

gibosi said:

 
Thanks to Mikelap's considerable efforts, you can now order 6AU6 to 6AK5 tube adapter socket converters on eBay!!
 
http://www.ebay.com/itm/1x-6AU6-to-6AK5-tube-adapter-socket-converter-/290917075011?pt=Vintage_Electronics_R2&hash=item43bc024843

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HOLD THE PRESSES. mordy is responsible for that considerable effort he found the site for those sockets in the first place but i still would like to thank my mother ,father and my wife whithout whom none of this would be possible Thank you .

I have to say as a long term tube roller this is one of the best threads I have come across (took me days to read as well!). I think I will buying a LD to roll in the near future.
 
From my perspective I would be after 7 pin adapters for 7 / 1 pin and 2 / 6 'mods'' for an amp. This is far better than buttering old gems
 
If you guys like rolling 6AU6s you need to investigate 7543 tubes (mine are sylvania but a common type that when I bought was dirt cheap). These were a SQ type that was a low hum, low microphonic version of the 6AU6.
 

Quote:

mikelap said:

With time hopefully my descriptions will improve as for your description its on the money thats what i am earin

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Mikelap, Don't worry. Great we agree =)
Amazing, you got that socket sorted!
Yes, the pin 5-6 pin disconnect socket adapter and even an adapter for EF91/92 compatibility would be useful ("pesky jumpers") and then maybe later one for 12BH7 power tubes =)
 
Quote:

vic2vic said:

I have a question regarding the 6BE6, 6CS6 group, for which I've not yet got any tube: did anybody had a chance to try (or ordered) the Mullard EH90 ? They should be very similar to the 6CS6, but I'm not 100% sure.
 
By the way, I confirm that almost all tubes mentioned in the table on page 77 are also working perfectly in the Little Dot MK II+ amp. I said "almost all", as I have not tried the 6BE6 family and the "modified"6J4 / 6AV6 ones... yet.

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Vic2vic, Haven't tried them yet and I will update the table on page 77 accordingly. Thanks for the info.
 
Quote:

zedmeco said:

http://www.ebay.co.uk/itm/300630722142?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
 
http://www.ebay.co.uk/itm/2-Stk-ECC99-JJ-Tube-Rohrenverstarker-Rohre-HighEnd-12BH7-matched-Paar-NEU-/200775278980?pt=R%C3%B6hren&hash=item2ebf23a184
 
I started searching for power tubes, 6n6p ir, I have a few from different years and some with the gold pins.  Very happy with them but in the spirit of tube rolling i thought i would extend the search to include the ecc99 and found these. do you guy's think they will work, i haven't ordered them yet though I have asked Yen if he thinks they would work.

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Zedmeco,
Quote:

ECC99 is similar to 12BH7A, and is a drop-in for most applications. Please note that on some amps, 12BH7A is used in power supply circuits and ECC99 is not a drop-in. If you are not certain, please check with the amp manufacturer first. (http://www.boiaudioworks.com/12bh7)

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duncan1 explained the mod required to operate in post on page 75, post 1125. I have posted the pin layout and the 6N6P layout in comparison above duncan1 on the same page and down here. Here is duncan1's post, I have highlighted the practical bit:
Quote:

Look on the heaters as 2 resistors connected together at the center tap the  current flow through both will be the same 2 equal resistances connected in parallel the total resistance is HALVED[more current used] if connected to the other heater connection at the center  tap.    Applying  12V across -4+5 without using the CT will reduce the amount of current through them for use in other equal current heater circuits.by INCREASING the total resistance[lower resistance=higher current].[higher resistance=lower current]
                    So "double connect"-IE- shorted together 4+5 and the other heater connection to 9-AFTER you have removed the earth connection to it.

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I was about to consider this an easy mod: Connect 4-5: fine, then connect to 9: fine, AFTER you remove the earth connection to it: Hmm, how do I remove the earth connection from 9?
 
Nic Rhodes, welcome to the thread. Thanks for pointing to the 7543 tubes, I will update the table on page 77 with this info as well. A quick ebay search brought only one tube from this type. Do you happen to have a good source for these?

Just a quick note. I cut off pins 5 and 6 on a pair of Mullard EC91/6AQ4 and rolled them in, using the EF92 jumpers, as we have for the other triodes, and right out of the box, they sound very good. But then, all of the triodes I have tried recently sound very good, so not a big surprise.