[lemonjelly]

 
Hi lemonjelly.
 
Are we really OK? As gibosi has mentioned, aren't they separate windings for anodes and heaters? I remember TrollDragon voicing concerns over the transformer if higher rated resistors are used...
 
Cheers!

Hmm I'm learning this stuff as I go, so I needed to check this a bit more carefully.  The VA rating above is correct for the entire transformer, so the transformer can handle that amount of power and the resultant heat, but obviously the question is whether the winding itself can manage.  Apparently if you don't use the heater windings, then it does mean you can use more current in the HT winding, as the transformer is cooler due to not using those windings.  It's pretty hard to work out exactly how much leeway this gives you however - it's definitely not as simple as I assumed above - but it seems like really about 50% extra or so would be realistic (so 150mA HT).  You're OK so long as no part of the transformer gets so hot that you can't keep your hand on it from the sounds of it (a transformer dies when it gets so hot the laminations between windings melt and the transformer shorts).
 
+ I know that I had the transformer at over 180mA and it was hot, I'd say probably fairly close to as hot as I'd want it, but it still worked fine.  And that's with my wooden/acrylic chassis whereas a stock amp would have the metal casing as a heatsink.  So yep it's still a risk, but I think it's much less of a risk than I thought before... as in the transformer is pretty close to being in spec (maybe slightly over but nothing like as over spec as I thought it was before) and the resistors probably also are over/@ spec, but they're likely to last for a decent amount of time (but this is where I'd expect failures really).  

 

[gibosi]

Is anyone getting bored? lol I have a suggestion for a new tube to try:
 
PCC85 / 9AQ8
 
This is a double triode with the same pinout as the ECC88, but 9 volt heaters! So you will need an adjustable external heater PS. From what little I can find on Google, it seems to be pretty good and I figure it is worth a look.
 
There are a few eBay sellers offering these for ridiculous prices, but there also are plenty of bargains to be had. I have a 1960's era Telefunken NOS/NIB coming my way for $10. And American brands can often be had for less than $5.

 

[lemonjelly]

  Is anyone getting bored? lol I have a suggestion for a new tube to try:
 
PCC85 / 9AQ8
 
This is a double triode with the same pinout as the ECC88, but 9 volt heaters! So you will need an adjustable external heater PS. From what little I can find on Google, it seems to be pretty good and I figure it is worth a look.
 
There are a few eBay sellers offering these for ridiculous prices, but there also are plenty of bargains to be had. I have a 1960's era Telefunken NOS/NIB coming my way for $10. And American brands can often be had for less than $5.

Agreed ... tldr it's not that much of a risk to run 6AS7s... but still a little bit of a risk.  And I don't have a horse in this race any more as I bought a cheap 165v HT transformer, and so am now running the 6080s I have at over 90mA, with a 6SN7 for about 100ma per transformer (the stock transformer for 1 channel, the 165v HT 1 the other).
 
There are so many good tubes to try... it's a bit scary really.  I've basically finished modding (I'll put in some DN2540s/IXY45s as CCS for plate load/cathode bias but that's a simple mod), so will be trying some of the tubes you guys have recommended soon.  The miniatures look interesting... and of course the c3gs at some point (but that's a bit more expensive), and I'm currently thinking about ordering some 6E5Ps, which are supposed to be good, but look like they pull a lot of current.  I don't think anyone has tried them yet?  If I try them I'll let you all know how it goes + if they're usable in a stock amp of course (be good to contribute something to this thread that I've lurked for a long time).
 
And currently burning in the final mod on my amp, which are some 100uF obligatto film caps in place of the stock 220uF/330uF output electrolytics - it's enough capacitance for my 300 ohm HD650s but probably wouldn't be enough with the bass rolloff on lower impedance cans.

 

[gibosi]

  ..............and I'm currently thinking about ordering some 6E5Ps, which are supposed to be good, but look like they pull a lot of current.  I don't think anyone has tried them yet?  If I try them I'll let you all know how it goes + if they're usable in a stock amp of course (be good to contribute something to this thread that I've lurked for a long time).

 
The 6E5P does indeed look interesting. However, building two clean and neat adapters to triode-strap these 9-pin tetrodes and convert them to a 7-pin B7G base may well be a challenge for some of us. (And you can count me as one of those!) I would be inclined to use two 9-pin breadboard sockets to accomplish the strapping and then route the triode elements into the LD through the existing 7-pin vectors, ugly and easy. lol
 
And if it turns out that these work well in the LD, and sound good, I am sure we could ask one of the Chinese eBay sellers to make converters for us, as they did for the C3g.
 
A couple more Russian tubes that might be worth trying are the 6N1P and 6N5P. These are double triodes with the same pin-out as a 6DJ8. However, they have 0.6A heaters, so an external PS is necessary.

 

[mordy]

Hi,
 
Found an interesting review comparing the MKIII to the MKVI. This was written in 2008 so I assume it refers to the first version of the LD MKIII. The relevance to me is that the the MK9 amp basically is half of a MKVI. Here is what the reviewer says:
 
"So, the question is: considering the price difference between the two amps, is the MK6 worth the $500 difference (excluding shipping difference)? After listening to both amps for extended periods of time, I can say that for $200, the MK3 is truly a very good amp. Although its sound is beat by the MK6 in almost all categories (as expected), it takes a much more expensive balanced setup to reaffirm just how good the MK3 is. The overall sound signature is almost identical to that of the MK6. It’s just that the latter sounded like two of the former combined. If you do not want to spend too much on headphones audio, I’d suggest sticking with the LD MK3. However, if you are an experienced audiophile and wish to try out how balanced audio sounds, the Little Dot MK6 would be a very good choice. If Little Dot could sort out the component(s) making the buzz and entirely eliminate the noise, the MK6 would be one of the best bargains in the audio market today. For me, let’s just say after going balanced, I do not ever want to go back."
 
It seems to me that with the mods we have found, using 6AS7/6080 power tubes and the great driver tubes discovered, the sound of the MKIII should be approaching the sound of the MK9 (MKVI). I do not understand how using a balanced set up with speakers will improve the sound.
 
If you want to see the entire review the link is here:
 
http://www.compudio.ca/2008/10/exclusive-review-little-dot-mk6.html

 

[lemonjelly]

   
The 6E5P does indeed look interesting. However, building two clean and neat adapters to triode-strap these 9-pin tetrodes and convert them to a 7-pin B7G base may well be a challenge for some of us. (And you can count me as one of those!) I would be inclined to use two 9-pin breadboard sockets to accomplish the strapping and then route the triode elements into the LD through the existing 7-pin vectors, ugly and easy. lol
 
And if it turns out that these work well in the LD, and sound good, I am sure we could ask one of the Chinese eBay sellers to make converters for us, as they did for the C3g.
 
A couple more Russian tubes that might be worth trying are the 6N1P and 6N5P. These are double triodes with the same pin-out as a 6DJ8. However, they have 0.6A heaters, so an external PS is necessary.

Yep I was thinking of something similar (to be able to try them).  I've got a 6080 tube that had stopped working, and so I smashed it and reused the base - soldering in wires to the wires going to the 8 pins (including the heaters).  As I replaced the 7pins with a single octal socket, I can then use it as an adaptor for any tubes I want to try.  I've just tried it with EF95s to see if it worked OK, and might eventually take readings with EF91/EF92/EF95 tubes just to compare what bias they run at compared to the 6SN7 I've got in currently (it'll be interesting to see what all of the readings etc are especially for the EF91s/92s).
 
Interesting review mordy... I'd agree I think with the changes to the tubes we've made that we probably are approaching similar quality to the mkVI.  But I have noticed that the sound with 2 transformers (so basically a little like a balanced amp in that there is reduced crosstalk as the channels aren't directly connected) is improved.  How much a properly balanced setup would improve on that I'm not sure - cos balanced is really meant when using long cable runs to reduce interference.

 

[mordy]

Hi lemonjelly.
 
I have a broken octal tube as well. How do I disassemble the octal bottom from the rest of the tube?

 

[lemonjelly]

  Hi lemonjelly.
 
I have a broken octal tube as well. How do I disassemble the octal bottom from the rest of the tube?

Um.... I just smashed it.  The 6080 I had has a metal base anyway (Thomson) so that stayed together... and then I just cut off the main body of the tube from the rest... and could solder wires to the wires coming off the pins.  Really it's just cos I had a broken tube and I wanted the octal base (cos I've replaced the 7 pins with the octal in my amp).  It's interesting to see all the makeup of the tube if you do that though, still think the workmanship etc that goes into tubes is amazing really.

 

[yomomma1]

Hijack!
 
I have buzzing coming from my left channel (mk4 SE) it starts after a short time or if the desktop is even gently knocked. HELP!

 

[lemonjelly]

  Hijack!
 
I have buzzing coming from my left channel (mk4 SE) it starts after a short time or if the desktop is even gently knocked. HELP!

Hi, the easiest thing to check first are the tubes.  You can swap the tubes from one side to another, and wiggle them a bit while you have the buzz to see if it is a dodgy connection with the tubes.  If it's that then cleaning the pins/changing the tubes will probably fix it.  After that it'll probably be a loose connection.  To find where it is you could see if you can move physically/flick/whatever the: volume control; headphone cable socket; and RCAs at the back of the amp, and just see where the problem seems to be (my bet going off the MKIII build would be the volume pot or RCAs).  It's easier if you can narrow down where the problem is, but it's probably a dodgy connection in one of those if it isn't the tubes.  
 
Then it'll probably mean a visit to a repair shop, returning to LD, or opening the amp yourself if you're handy with a soldering iron.  If opening the amp, leave music playing and turn the amp off (so leave the source connected) and wait for the sound to go as quiet as possible.  Then the voltage in the amp should be dissipated mostly (but will dissipate more if you can leave it overnight), but still avoid touching any of the capacitors unless you either short the terminals first or use a resistor across the terminals to get rid of any of the voltage (you shouldn't need to be dealing with any of the capacitors though).  Then you might be able to see where the loose connection is easily, or just resolder any of the connections that look dull on whichever component it is that seems to be causing the problem. 
 
I wouldn't be too worried though, the difficulty will be finding where the fault is rather than the fixing of the problem.  + ofc let us know how it goes !

 

[yomomma1]

Cheers pal. I have changed tubes over and ran as a pre-amp so not tubes or HP socket. Will check other options, I started to take it apart but chickened out and put it back together, I'm not confident with that so will poss take it in somewhere?
 
Thanks again.

 

[lemonjelly]

  Cheers pal. I have changed tubes over and ran as a pre-amp so not tubes or HP socket. Will check other options, I started to take it apart but chickened out and put it back together, I'm not confident with that so will poss take it in somewhere?
 
Thanks again.

It's probably a good plan .  The problem with taking the amp apart - as you probably found - is that it's pretty shoehorned in there.  I should've said that if you do that then you have to be really careful cos you could break connections just because it's such a hassle to pull it out enough to work on it.  But kinda forgot as I've not worked in that chassis in so long !  If you do take it somewhere it should be a simple job for them... I would think the volume potentiometer or input RCAs are the most likely places where the dodgy connection is as before.
 
Edit: saw your post about the preamp thing as well so I'll just tag a reply on here.  The problem when using the LD as a preamp is with DC coupled amps, so long as your amp isn't DC coupled (which I think is fairly rare, but more common in audiophile stuff) then there aren't any problems.  It's cos DC coupled amps don't have a blocking capacitor to stop DC (less capacitors in the signal path and all that) and there's a chance the LD will pass some DC voltage across, that will then get amplified by the amp and possibly blow the speakers (some DC coupled amps will have a protection built in to prevent it even then though).  LD and from the looks any manufacturer of DC coupled amps just flat out say it's not a good idea for them to be used together.

 

[MIKELAP]

  It's probably a good plan .  The problem with taking the amp apart - as you probably found - is that it's pretty shoehorned in there.  I should've said that if you do that then you have to be really careful cos you could break connections just because it's such a hassle to pull it out enough to work on it.  But kinda forgot as I've not worked in that chassis in so long !  If you do take it somewhere it should be a simple job for them... I would think the volume potentiometer or input RCAs are the most likely places where the dodgy connection is as before.
 
Edit: saw your post about the preamp thing as well so I'll just tag a reply on here.  The problem when using the LD as a preamp is with DC coupled amps, so long as your amp isn't DC coupled (which I think is fairly rare, but more common in audiophile stuff) then there aren't any problems.  It's cos DC coupled amps don't have a blocking capacitor to stop DC (less capacitors in the signal path and all that) and there's a chance the LD will pass some DC voltage across, that will then get amplified by the amp and possibly blow the speakers (some DC coupled amps will have a protection built in to prevent it even then though).  LD and from the looks any manufacturer of DC coupled amps just flat out say it's not a good idea for them to be used together.

Thats exactly what i was told when i wanted to use my LD mk3 with my 70's Pioneer. I was told tough that the LD MK9 can be used with DC coupled amps .

 

[mordy]

Hi yomommo1,
 
Another source of hum not be overlooked could come from electric interference, especially portable phones and appliances. If you have a portable phone or base station near your amp, see what happens if you move it away or turn it off. I found that I can reduce hum by moving and repositioning the various breadboards and adapter wires that I am using with my LD MKIII.
 
Hi lemonjelly,
 
I have a DC coupled receiver that I cannot use with the MKIII.  Do you know of any kind of circuit or outboard unit that can be added to block the high DC voltage?

 

[yomomma1]

Hmm....well I ran it through a lovely Denon amp )yes they do exist) and more recently through my Marantz 610 but it hummed (which is defo not a phone related issue, don;t have a phone near it and it occurs if I even tap on the desk) I turned the amp off when it buzzed and the 610 almost blew! Popped and went off, couldn;t switch it on for a while, thought I'd killed it!!!