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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 488

post #7306 of 7491
Quote:
Originally Posted by mordy View Post
 

For some reason it appears to me that these tubes run cooler than the 6080s, although they are said to draw 0.84A each.

 

 

Electrially, the 6080 and 6AS7 are virtually identical including 2.5A heaters.Where did you get this 0.84A number? 

post #7307 of 7491
Quote:
Originally Posted by superdux View Post
 

A few pages ago, i offered my 12ax7 adapter but no one seems interested, so i was going to roll some 12ax7 next month and wanted to ask you if there is something i have to look out for to not harm my beloved LDMKIII?

 

EDIT: Mikelap just told me to look up the list on following page

http://www.head-fi.org/t/563884/little-dot-tube-amps-vacuum-tube-rolling-guide/4875#post_10229116

 

Yes, a number of us have  run 12AX7-type tubes in our LDs with absolutely no problems. Also, I ran a number of 5751, which I thought were pretty good.

 

You might find this to be an interesting read:

 

 http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html#12AX7

 

Edit: Also, if you are using an external heater PS, the E80CC is a great tube. There are the more common Tunsgram and Heerlen-made versions, and the more rare, and better to my ears, early Eindhoven and Hamburg versions. However, the heaters draw .6A when run in the 6.3V setting so again, an external heater PS is necessary. 

 

And another very fine tube that has the same pinout as a 12AX7 is the Brimar 13D3, but the heaters draw .65A at 6.3V, so again an external heater PS is necessary.


Edited by gibosi - 8/27/14 at 8:29pm
post #7308 of 7491
Quote:
Originally Posted by MMMan View Post

For example:

....snip.....


.....snip

The second two are a Ken Rad VT231 and a grey glass Sylvania VT231 I picked up from an estate auction for $15. A great deal... And fun finding a match for each on the cheap!

It is important for everyone to know that very good deals are out there. Perhaps not all NOS tubes, but still testing 'good'....

This is the match for the top left tube:



Total cost for the pair: $12. eBay was looking the other way... Very happy smily_headphones1.gif
post #7309 of 7491
Quote:
Originally Posted by gibosi View Post
 

 

Yes, a number of us have  run 12AX7-type tubes in our LDs with absolutely no problems. Also, I ran a number of 5751, which I thought were pretty good.

 

You might find this to be an interesting read:

 

 http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html#12AX7

hi gibosi,

thx for your advice, i read the site about 12ax7 and maybe want to try some 5751 out.Do they share same pin layout as with 12ax7?
As for the list they should all run at 350mA.Guess i'll have to look for a bargain tube on the bay.Mikelaps adapter doesn't work with external power supply, it combines the 2 front tube outlets of my amp, so i'll have to beware of not too high mA rates.

post #7310 of 7491

All the 12A-7's: 12AU7, 12AT7 and 12AX7 have the same pinout, and as the 5751 is just a ruggedized 12AX7, with slightly less gain, it too has the same pinout.

 

And now I remember, you are using Mikelap's adapter so no external l heater PS. But fortunately, all these tubes are perfectly safe to use in your rig.

 

Cheers

post #7311 of 7491

And on the chance you don't have one of these.... you can purchase an adapter which will allow you to roll 6DJ8/ECC88 tubes in a 12AX7 socket:

 

http://www.ebay.com/itm/1pc-gold-plated-6cg7-6fq7-TO-ECC82-12AU7-tube-adapter-6-3V-heat-/201083377532?

post #7312 of 7491

Hi gibosi,

 

i think a 6V tube won't work in mikes adapter as he told me only to use 12V tubes yesterday, so i'm not sure about that.

 

anyway we have something called sperrmuell here in germany where people put out their trash onto the street for pickup and i found an old german radio and picked out the tubes so if any of you like to take a look:

 

 

 

 

 

 

 

it says "Lorenz ECH81","Lorenz EL84","Lorenz EADC 80" and "Lorenz EF89" on them.

post #7313 of 7491
Quote:
Originally Posted by superdux View Post
 

i think a 6V tube won't work in mikes adapter as he told me only to use 12V tubes yesterday, so i'm not sure about that.

 

I assure you that with an adapter, 6DJ8/EC88 tubes will work fine. The heaters in the LD are 6.3V, not 12.6V. The only reason 12AX7 tubes will work at all in the LD is that it is possible to wire these tubes to run on 6.3V. This is what Mike's adapter does. It is wired to run a 12AX7 on 6.3V. And the adapter I linked to above allows you to use a 6DJ8 in a 12AX7 socket that has been wired to operate at 6.3V.

post #7314 of 7491
Quote:
Originally Posted by MMMan View Post


This is the match for the top left tube:



Total cost for the pair: $12. eBay was looking the other way... Very happy smily_headphones1.gif

 

 

Quote:
Originally Posted by MMMan View Post

For example:




The first pic is from a lot of 5 6SN7s I bought for $35. These two tubes are both black glass NUs, that sell for $70 to $90 a pair. All were reported as 'test good'. A great deal.

The second two are a Ken Rad VT231 and a grey glass Sylvania VT231 I picked up from an estate auction for $15. A great deal... And fun finding a match for each on the cheap!

It is important for everyone to know that very good deals are out there. Perhaps not all NOS tubes, but still testing 'good'....

 

Sorry...think I got the postings the wrong way round!

 

Anyway, MMMan, your examples (and gibosi's...not to mention mordy's results after patient searches) have shown that 6SN7s can be found for reasonable money...which brings me to an update on my suggestion to the Feliks-Audio Espressivo-E people, in Poland, to consider changing those mediocre tubes for 6SN7 drivers and 6AS7G/6080 powers...AND THEY'RE GOING TO BUILD A PROTOTYPE!! ...WOWEE!...If they can manage to keep the price below the LD MK9 and LaFigaro 339, that should be a giant killer to say the least!! :biggrin:.

 

Will keep y'all posted...

 

Quote:
Originally Posted by gibosi View Post
 

 

Mordy, 

 

I too am curious how the Sylvania 7963 and the Sylvania 5687WA compare in your rig. In my LD+, they are very, very close.

 

Well, gibosi, I can see why you love the 5687...I have only just finished cobbling together (much against my usual principles, lol! ;)) your (and mordy's) "flying" monstrosities...my excuse being I needed to make sure they would be OK in my new Little Bear!

 

Given that the amp hasn't many hours on it, and the tubes/masses of wires even less...plus only my HD598s to test (until I patch into my 650s), to say I'm VERY impressed is understating things at the very least :bigsmile_face:. With one of my GEC 6AS7Gs in the hot seat, I am fairly confident already that this cheapie chappie will almost be a match for the LD III & IV with modded upgrades. And for less than $200 (free shipping), this is quite ridiculous!!

 

I am sure the 5687s are a major help here...although I was very UNDERwhelmed by their appearance (especially compared to the C3Gs!), I can tell already that they are all you say they are...EXCELLENT. The full potential is a ways off yet...but I am getting really excited at the prospect of what may come, after proper burn-in/proper (silver-wired!) adapters/650s in tow :L3000:.

 

And then will come the shoot-out with the fully-loaded LD...can't wait lol!

post #7315 of 7491
Quote:
Originally Posted by gibosi View Post

 The only reason 12AX7 tubes will work at all in the LD is that it is possible to wire these tubes to run on 6.3V. This is what Mike's adapter does. It is wired to run a 12AX7 on 6.3V. And the adapter I linked to above allows you to use a 6DJ8 in a 12AX7 socket that has been wired to operate at 6.3V.

Anybody have any details on this type of wiring to wire a 12 V filament tube to run on 6 V is this possible with many 12 V tubes?

post #7316 of 7491
Quote:
Originally Posted by gibosi View Post
 

 

I assure you that with an adapter, 6DJ8/EC88 tubes will work fine. The heaters in the LD are 6.3V, not 12.6V. The only reason 12AX7 tubes will work at all in the LD is that it is possible to wire these tubes to run on 6.3V. This is what Mike's adapter does. It is wired to run a 12AX7 on 6.3V. And the adapter I linked to above allows you to use a 6DJ8 in a 12AX7 socket that has been wired to operate at 6.3V.

Its been awhile i didnt remember that but when i looked  at the octal to 9 pin adapter that goes in copper adapter it is marked 6.3 v on it so my bad and thanks gibosi for pointing that out .

post #7317 of 7491

Was just checking this out on page 267 and this is what gibosi told me back then i tought it sounded familiar .post 4004

 

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

 

And 6 volts is correct. Fortunately, the 12AX7 can be used with either 12 volt or 6 volt heaters. The Little Dot heater supply voltage is 6 volts, so we wire the 9-pin socket (by using pin 9) to run the 12AX7 on 6 volts. And since the 6SL7 is also a 6 volt tube, it works flawlessly.

 

post #7318 of 7491

Thx @gibosi and @MIKELAP, i'll guess then i'll do some more tube rolling in the future. There are so many tubes to roll with MIKELAPS adapter and i hope i'll find a special one.

post #7319 of 7491
Quote:
Originally Posted by bbmiller View Post
 

Anybody have any details on this type of wiring to wire a 12 V filament tube to run on 6 V is this possible with many 12 V tubes?

 

It's easy. In 12V mode, you would connect the heater supply directly to pins 4 and 5. But of course, this requires that you have a 12V heaters. In an amp with 6V heaters, first, you connect the heater supply to pins 4 and 9 (heater center tap). And then you need to tie pins 4 and 5 together. Fortunately, the triode elements, cathode, grid and anode, are identical for 6DJ8 and 12A-7 tubes, so the only change necessary to switch between the two of them is the heater wiring. This will work for 12AU7, 12AT7 and 12AX7, as well as E80CC and 13D3 (these last two need an external heater PS), and there might be others that I am overlooking....

 

5687, 7044 and E182CC/7119 are similar, in that they can also be wired for 12V or 6V, but the wiring is slightly different. In these tubes, pin 8 is the heater center tap. (However, these need more current than the LD can provide, so an external heater PS is required.) To run these in 6V mode, tie pins 4 and 5 together, and connect the heater supply to pins 4 and 8.

 

In the 6DJ8, pin 9 is attached to the shield. In the 12A-7, pin 9 is attached to the heater center tap. Otherwise, the triode sections, cathode, grid and anode, are wired identically. So to switch between 6DJ8 and 12AX7, the only change necessary is for the heaters. For the 5687 tubes, the triode-section wiring is not quite the same as a 6DJ8. so it is also necessary to rewire pins 6 and 9 if switching between 6DJ8 and 5687.

 

Below, a pic of my 9-pin socket wired to run 5687 tubes in 6V mode. The fat wires are the heater supply, and you can see that I have bridged pins 4 and 5.

 

 

 

 

 

Have fun! :) 

 

Edit: typo


Edited by gibosi - 8/28/14 at 5:20pm
post #7320 of 7491

Hi hypnos 1,

 

"update on my suggestion to the Feliks-Audio Espressivo-E people, in Poland, to consider changing those mediocre tubes for 6SN7 drivers and 6AS7G/6080 powers...AND THEY'RE GOING TO BUILD A PROTOTYPE!! ...WOWEE!...If they can manage to keep the price below the LD MK9 and LaFigaro 339, that should be a giant killer to say the least!! :biggrin:.

 

Will keep y'all posted..."

 

When you are communicating with the Feliks people, please ask them to design and incorporate a protective circuit so that a direct coupled  (DC) amp can be used. I assume that the amp will not only be a headphone amp, but could be used as a preamp as well. I would be happy to evaluate the amp as well....

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