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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 387

post #5791 of 10502
Quote:
Originally Posted by i luvmusic 2 View Post

 

Excellent ILM2, thanks for the pics!

 

Unfortunately there is no current ratings on any of the outputs.

 

Label reads as follows:

Power Transformer - 15VA

Import: 120V Black Red 120V Black Red

Export: 100V Brown Brown 15V*2 Blue Black Blue

             3.2V*2 Green Black Green / Ground Green (The one on the top I assume)

 

There is no current ratings on the individual winding and there is no way to figure it out from just the 15VA rating.

If there was a model number on the transformer and one had access to the national Chi-Nee transformer database, it could be figured out.

 

Since it is only 15VA there is NOT a lot of current to go around.

The more info we have on these Little Dots the better we can understand the limitations.

 

Thanks Again for the Pics!

:beerchug:

post #5792 of 10502
Quote:
Originally Posted by MIKELAP View Post
 

    On the first picture you see 3 pins (arrows) on the right side its the EF95 JUMPER SETTING so you would use the 2 pins on the right and if you want to use EF92 you use the 2 pins to the left and you do the same thing for the other channel. On the 2 nd picture the jumper is on the EF95 setting these peep holes are under the Littledot remember to put jumpers the same way on both channels                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     

 

 

 

010.JPG

 

Crystal clear now!! Thanks very much, M!

post #5793 of 10502

Not picking on you gibosi, your posts just quoted nicely. ;) 

 

Quote:

Originally Posted by gibosi View Post
 

And I would be very leery about trying to run one 6AS7 off the internal Little Dot heater circuit and the other off an external power supply. It is quite likely (TrollDragon please weigh in here) that the two power tubes are wired separately and drawing that much current through just one side may well overload your wiring (smoke and flames?). But for sure, if you are willing to go to the trouble of feeding one separately, it would be simple matter to feed both off the same external power supply (tie the tubes' heaters together, pin 7 to pin 7 and pin 8 to pin 8) as long as your power supply and regulator have sufficient capacity, I am guessing more than 5amps to be safe.

Yes indeed 2.5A max split between the two power tubes, I would not advise using the LD to power 6AS7's. As gibosi says, if you are going to the trouble to externally feed one heater, might just as well feed both with a proper power supply, yes greater than 5 Amps as tubes can draw triple the current for a brief moment when starting from cold. 
 

 

Quote:
Originally Posted by gibosi View Post
 

 

I think a single 6AS7 could be used. but it is not at all clear what it would sound like. As the LD runs the double triodes in parallel, the resisters used to bias the tube are sized accordingly, and they may be too far out of spec for a single triode. But even so, I think it may well be worth trying.


We can not run single triodes in the output stage as it is a Push-Pull, White Cathode Follower circuit.

 

This is basically the output circuit give or take a few components (Borrowed from Tube Cad Journal)

There is only the power tube from a single channel drawn here.

 

Also an article written by Alex Cavalli from Cavalli Audio about optimizing a WCF circuit in an OTL amplifier. (Heavy Math)

http://www.cavalliaudio.com/diy/docs/WCFOptimization.pdf 

 

:beerchug:

post #5794 of 10502
Quote:
Originally Posted by TrollDragon View Post
 

Yes indeed 2.5A max split between the two power tubes, I would not advise using the LD to power 6AS7's. As gibosi says, if you are going to the trouble to externally feed one heater, might just as well feed both with a proper power supply, yes greater than 5 Amps as tubes can draw triple the current for a brief moment when starting from cold. 
 

 


We can not run single triodes in the output stage as it is a Push-Pull, White Cathode Follower circuit.

 

This is basically the output circuit give or take a few components (Borrowed from Tube Cad Journal)

There is only the power tube from a single channel drawn here.

 

Also an article written by Alex Cavalli from Cavalli Audio about optimizing a WCF circuit in an OTL amplifier. (Heavy Math)

http://www.cavalliaudio.com/diy/docs/WCFOptimization.pdf 

 

:beerchug:

 

Thanks TD for your input re 6AS7 requirements...now just have to try and find a good (but not too expensive) hiA DC power supply here in the UK...

 

Had a quick look at that article - gave me the shivers (flashback to school days!). But what I did manage to grasp was the difficulty in getting the plate resistance just right in this kind of circuit - shades of artsi's concerns. So it really is going to be a question of just where they pitched these parameters in the MKIV SE - hopefully such that they are "jack of all trades, master of none"!.

Will certainly have to keep a very close eye on those resistors...wish I knew exactly where they would be located inside the unit, though...

 

Interesting/slightly worrying times ahead, methinks!...

post #5795 of 10502
Quote:
Originally Posted by hypnos1 View Post
 

Thanks TD for your input re 6AS7 requirements...now just have to try and find a good (but not too expensive) hiA DC power supply here in the UK...

 

Search eBay for "laptop power supplies". These typically have plenty of capacity. For example:

 

http://www.ebay.com/itm/AC-ADAPTER-POWER-SUPPLY-HP-PA-1900-18H2-P-N-463554-002-laptop-Charger-AMD-CPU-/400691844773?pt=Laptop_Adapters_Chargers&hash=item5d4b1856a5

 

This is listed as 65W (18.5V/3.5A). Divide the wattage by 6.3V and you get a bit more than 10A, so more than enough. And I would expect that you could find something similar at a local computer supply store there in UK.

post #5796 of 10502

It's too bad it's not enough info on that LD 1 Transformer.:(

post #5797 of 10502

Received a Brimar 6SN7GT today. Managed to pick it up for $5. Apparently the vendor didn't realize what he had and the picture quality was quite poor, so I was the only one who bid on it. :)

 

 

This appears to be the first version, according the 6SN7GT Identification thread, apparently the same as the STC/Brimar 6SN7GTY / CV1988, as it has the "small anode plate extensions" extending vertically above the top mica.

 

 

I have only just now shoved it into the LD, and I am happy to say that it lights up, it's quiet, and I hear music, A very good beginning. :)

post #5798 of 10502
Quote:
Originally Posted by i luvmusic 2 View Post
 

It's too bad it's not enough info on that LD 1 Transformer.:(

 

Even so, I think we can continue to assume that the LD 1+ can supply at most a total of one 1 amp shared between the two driver tubes. And to be safe, if we are going to use the internal heater circuitry, we should probably not exceed .450A per tube.


Edited by gibosi - 4/9/14 at 1:44pm
post #5799 of 10502

I think i may have burn my VOLUME POT when i was unsoldering it from the PCB but i need to reconnect it to be sure it  still working but if i need to replace it do i need one of those so called high end and am i gonna gain something from those?

post #5800 of 10502
Quote:
Originally Posted by gibosi View Post
 

 

Even so, I think we can continue to assume that the LD 1+ can supply at most a total of one 1 amp shared between the two driver tubes. And to be safe, if we are going to use the internal heater circuitry, we should probably not exceed .450A per tube.

As long as we use External Power Supply we should be fine i think.I have used 6AS7 and the LD 1 get a little warmer than usual that is all so IMO it is safe to use 6AS7 i did run mine for 6 hours straight to see how long the LD 1 can handle the 6AS7 and my amp still functioning properly.It depends on how comfortable you are using 6AS7.LD 1 can handle that tube no doubt in my mind.

post #5801 of 10502
Quote:
Originally Posted by gibosi View Post
 

 

Search eBay for "laptop power supplies". These typically have plenty of capacity. For example:

 

http://www.ebay.com/itm/AC-ADAPTER-POWER-SUPPLY-HP-PA-1900-18H2-P-N-463554-002-laptop-Charger-AMD-CPU-/400691844773?pt=Laptop_Adapters_Chargers&hash=item5d4b1856a5

 

This is listed as 65W (18.5V/3.5A). Divide the wattage by 6.3V and you get a bit more than 10A, so more than enough. And I would expect that you could find something similar at a local computer supply store there in UK.


Thanks gibosi...but that means a voltage regulator as well - was hoping to find something "all-in" (6V approx.) to keep things neat...you know I like things 'neat and tidy!'

 

Cheers.

post #5802 of 10502
Quote:
Originally Posted by i luvmusic 2 View Post
 

I think i may have burn my VOLUME POT when i was unsoldering it from the PCB but i need to reconnect it to be sure it  still working but if i need to replace it do i need one of those so called high end and am i gonna gain something from those?

 

You are going to mount it on a new case I think? If it isn't too expensive, why not? And at the least, this is the perfect opportunity to get one with a larger knob. I have always felt that the LD 1+'s knob is too small and too slippery to allow very fine adjustments.

post #5803 of 10502

Hey there mikelap...how are things with the Woo? Am sure I'm not the only one eager to hear how it compares to the LD!

 

Hope you can give us the low-down sometime soon...

post #5804 of 10502
Quote:
Originally Posted by gibosi View Post
 

 

You are going to mount it on a new case I think? If it isn't too expensive, why not? And at the least, this is the perfect opportunity to get one with a larger knob. I have always felt that the LD 1+'s knob is too small and too slippery to allow very fine adjustments.

Yes G i will be mounting it in a new Chassis but if that pot is still working i will still use it with a big KNOB i have the knob recycled from an old amp i don't know why i keep on using recycled materials am i going GREEN nah i'm just being CHEAP.:biggrin:

post #5805 of 10502
Quote:
Originally Posted by hypnos1 View Post
 

Thanks gibosi...but that means a voltage regulator as well - was hoping to find something "all-in" (6V approx.) to keep things neat...you know I like things 'neat and tidy!'

 

 

Well I am one of the best when it comes to easy and ugly. lol 

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