[TrollDragon]

Hey mordy,

Tubes will still conduct quite a while as they cool down... If the tubes were cold then what you are hearing is probably conducted through the LD's feedback circuit...

Did you turn the LD up 2 notches or your receiver? Try the same experiment with cold tubes and don't turn on the PC supply to the outputs.

 

[mordy]

The power tubes are completely cool - have been going for over an hour without power. The LD is turned up all the way, which is where I keep it with the 6AS7/6080 power tubes due to the low amplification factor. (All the way up with RCA 6AS7 and RCA 6080, almost all the way up with the Chatham 6080).
 
The 5687 is running off a 5A voltage regulator set at 12.6V.

 

[TrollDragon]

Very Cool...

So it is my guess the the feedback circuit in the LD is passing the audio along, I think you would find it not to work if you powered the output filaments instead of the driver.

 

[joshk4]

Hi,
 
Sorry my bad, forgot to mention that I was using the Hifiman ef2a, I'm guessing this would be the same to the little dots?
 
Thanks guys for helping me out.
 
Josh

 

[genclaymore]

   
They are the same, that is 6ZH1P-EV = 6J1P-EV.
 
Purchasing matched pairs for the Little Dot is a waste of money. I purchased two pairs from this vendor:
 
http://www.ebay.com/itm/2-pc-6J1P-EV-EF95-6F32-6AK7-Gold-Platinum-grid-NIB-/130436695928?
 
$3 / pair, plus $12 shipping to the US.

I would had did that but I did not trust ordering tubes from outside of the usa, because I didn't want to go thru the hassle of getting a bad tube and sending it back. Plus I wouldn't had like it if I gotten a fake. So I got both my pairs in the usa to ease my mind, I know i spent too much but it put my mind at ease as if something went wrong  or sent bad ones I could easy send them back. Instead of paying a lot to ship them back outside of the usa. I also don't have any way to test them as I don't have a tube tester, plus one of you guys said power tube matching on little dot is pointless but I read conflicting stories that it could damaged or shorten life of the tube amp if it wasn't matched and I wasn't about to take that chance and would not look forward to my Little dot burning out which would mean i would be out of luck for months.

 

[bbmiller]

   
 
Nice Schematic as well, I have a hand drawn MK IV version that I cobbled together.
 

Spoiler: MK IV Rough Schematic

 

Do you think from looking at the way TrollDragon draws the 6.3 volt portion of the power supply that in its on modified form the little dot MK four headphone amplifier uses AC rather than DC voltage and current to heat its tubes and an alternative way to modify this amplifier to supply more current to the power tubes would be to drill a hole in the chassis and simply remove the wires from the press and transformer supplying the 6.3 AC and replace it with the more hefty external AC step down transformer with no regulation or rectification?

 

[TrollDragon]

Yes bbmiller you could very easily drill a hole in the backplate of the amplifier and run a higher current 6.3V into the tube filaments from am external power supply. The only thing is large current transformers are rather big, heavy and not cheap.

That is why all the guys here use a Switching Power Supply and an external regulator. But if you have access to a filament transformer then that would be an easy conversion, just unsolder and tie off the current filament leads coming from the LD's transformer and hook up your own.

 

[TrollDragon]

I would had did that but I did not trust ordering tubes from outside of the usa, because I didn't want to go thru the hassle of getting a bad tube and sending it back. Plus I wouldn't had like it if I gotten a fake. So I got both my pairs in the usa to ease my mind, I know i spent too much but it put my mind at ease as if something went wrong  or sent bad ones I could easy send them back. Instead of paying a lot to ship them back outside of the usa. I also don't have any way to test them as I don't have a tube tester, plus one of you guys said power tube matching on little dot is pointless but I read conflicting stories that it could damaged or shorten life of the tube amp if it wasn't matched and I wasn't about to take that chance and would not look forward to my Little dot burning out which would mean i would be out of luck for months.

There are quite a few good Eastern Block eBay sellers that have a 100% rating who will not send you bad tubes, also they are cheap enough that one should order 3 or 4 just incase someone drops kicks the box during transport...

They don't fake tubes like the 6J1P A's it is really not worth the time to do so. It would be like someone counterfeiting $5 bills, they go after the tubes that are in high demand that they can get $100 for from uninformed new tube buyers.

Matched tubes are recommended for amplifiers that have parallel output power tubes which the Little Dot has none. There is only one output tube per channel and they are not a power tube although we label them such.

So unmatched tubes will not harm the LD amplifier and paying extra for them is just money wasted. But if you do have lots of extra dosh to splash around there is probably a matched pair of $80 Telefunken 6AK5's on Yenaudio that they would just love to sell you...

 

[MIKELAP]

 
I would had did that but I did not trust ordering tubes from outside of the usa, because I didn't want to go thru the hassle of getting a bad tube and sending it back. Plus I wouldn't had like it if I gotten a fake. So I got both my pairs in the usa to ease my mind, I know i spent too much but it put my mind at ease as if something went wrong  or sent bad ones I could easy send them back. Instead of paying a lot to ship them back outside of the usa. I also don't have any way to test them as I don't have a tube tester, plus one of you guys said power tube matching on little dot is pointless but I read conflicting stories that it could damaged or shorten life of the tube amp if it wasn't matched and I wasn't about to take that chance and would not look forward to my Little dot burning out which would mean i would be out of luck for months.

I have ordered tubes at least 35 times from abroad and the tubes always got here just check for sellers that have a good reputation and everything should be alright . And i also dont use matched tubes ive had my MK3 for several years now and all is find .

 

[bbmiller]

Yes bbmiller you could very easily drill a hole in the backplate of the amplifier and run a higher current 6.3V into the tube filaments from am external power supply. The only thing is large current transformers are rather big, heavy and not cheap.

That is why all the guys here use a Switching Power Supply and an external regulator. But if you have access to a filament transformer then that would be an easy conversion, just unsolder and tie off the current filament leads coming from the LD's transformer and hook up your own.

You said above an external power supply not simply a step down transformer to 6.3 AC as the complete package. Is my assertion that the on modified little dot MK IV runs on AC filament voltage correct?

 

[mordy]

Hi genclaymore,
 
Agree completely with all the above comments about not having to worry about buying tubes from inexpensive reputable sources. The Little Dot MKIII that I have experience with is very sturdy, and I cannot remember people ruining the amp no matter what they threw at it.
 
As a rule, there are two types of tube sellers on Ebay - those who make a living from it, and those who sell tubes as a side income. The commercial sellers will try to make you think that their tubes are much better and thus deserve very high prices, but the truth is that the grand daughter who is selling off her grandfather's stock of old tubes for a fraction of the price, is selling the exact same tube as the high priced one.
 
By all means, it would be nice just to pick high priced tubes without worrying about the cost, but since the people on this forum bought thousands of tubes (collectively), and many of us have several hundred tubes, it makes financial sense to avoid the highest priced sellers, especially since they do not offer anything better than lower priced sellers of the same tube.
 
The 6AK5 family of tubes were produced in enormous numbers, and should somebody want to replace the stock GE 6AK5 tubes that came with the LD MKIII with a new pair, there is no problem - you could buy 10,000 of them! ($1.20 each, incl shipping, or best offer)
 
http://www.ebay.com/itm/MASSIVE-LOT-10-000-NOS-NIB-GENERAL-ELECTRIC-6AK5-6AK5W-5654-5654W-6J1-403A-TUBES-/301210986229?pt=Vintage_Electronics_R2&hash=item462192e6f5
 
Yen Audio will happily sell you a pair of GE 6AK5 for $73.50 incl shipping......
 
http://www.ebay.com/itm/2x-GE-Mobile-Radio-6AK5-Matched-Pair-Little-Dot-Amp-Mk-/290581310456
 
Good luck!

 

[TrollDragon]

You said above an external power supply not simply a step down transformer to 6.3 AC as the complete package. Is my assertion that the on modified little dot MK IV runs on AC filament voltage correct?

Hey bbmiller,

I am really not sure what you are trying to do or understand...

The LD amps have two separate windings on the built in power transformer to provide filament power to both output and driver tubes. There is a 6.3V 2.5A winding divided between the output tubes, and a 6.3V 1A winding divided between the driver tubes. This filament voltage is AC on an unmodified LD amplifier.

The guys here use both driver and output tubes that can draw more filament current than the LD transformer will safely provide, so this requires an external power source of some type for the filaments.

Since a higher current filament stepdown transformer ie 110VAC to 6.3VAC @ 10A is not easily or cheaply available, they run the filaments on 6.3VDC via a switching power supply and a 5A or 10A voltage regluator that can be adjusted down to 6.3VDC.

You could even run either pair of tube filaments in series from a 12.6V DC or AC source as well, but I don't wish to confuse the issue.

Has this answered your question?

 

[bbmiller]

 

You said above an external power supply not simply a step down transformer to 6.3 AC as the complete package. Is my assertion that the on modified little dot MK IV runs on AC filament voltage correct?

Hey bbmiller,

I am really not sure what you are trying to do or understand...

The LD amps have two separate windings on the built in power transformer to provide filament power to both output and driver tubes. There is a 6.3V 2.5A winding divided between the output tubes, and a 6.3V 1A winding divided between the driver tubes. This filament voltage is AC on an unmodified LD amplifier.

The guys here use both driver and output tubes that can draw more filament current than the LD transformer will safely provide, so this requires an external power source of some type for the filaments.

Since a higher current filament stepdown transformer ie 110VAC to 6.3VAC @ 10A is not easily or cheaply available, they run the filaments on 6.3VDC via a switching power supply and a 5A or 10A voltage regluator that can be adjusted down to 6.3VDC.

You could even run either pair of tube filaments in series from a 12.6V DC or AC source as well, but I don't wish to confuse the issue.

Has this answered your question?

Yes that answered it. thanks

 

[i luvmusic 2]

I finally finish my CRACK after 12 hours.......time for bed.

 

[CollectoR13]

Pictures please!
Very interested in how it looks (and sounds )!