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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 282

post #4216 of 10486
Quote:
Originally Posted by Ctritical Bill View Post
 

The instructions I gave were for the pins of a socket 7 tube. The principle is the same for any tube you just have to identify what each pin is connected to. The best place to take measurements is the most convenient to your setup so the breadboard connections would probably be best.

 

For me, it is easiest and most convenient to take these measurements off of the 7-pin Vectors because no matter what tube I use, be it 6DJ8, 12AX7, 6SL7 or 2C51, the measurements are taken at the exact same pins, namely 2, 3, 4 and 5. If I make measurements at the 9-pin socket, I have to pay close attention to how the two triodes and the heater are connected, as they are slightly different for each of these tubes. But of course, YMMV. :)

post #4217 of 10486
Quote:
Originally Posted by MIKELAP View Post
 

Now for the 12v. adaptor, if i remember correctly the 6su7 octal works both with 6v. and 12 v. am i wright ,and now for the 12ax7 tubes dont have any of those i wread the thread a bit and found the 5751 triple mica to be a good tube would anybody have any ideas regarding good 12ax7 tubes brand and style or are the 6DJ8 just better overall than the 12ax7 and they are not worth getting into. Thanks

 

In my opinion the 12AX7 / 5751 tubes, and even the 6SL7s, are not worth your time and money. I believe that the 6DJ8 are unquestionably superior, at least in our LDs, But again, this is only my opinion.... :)

post #4218 of 10486
Quote:
Originally Posted by gibosi View Post
 

 

Yes, 6.7v would seem to be a bit high, but if I understand things correctly, this is a function of the mains and the LD transformer, not the tube. I live in 120volt land and I measure 122v at the wall. Again, if I understand correctly, the transformer simply converts this to 6.7v. Perhaps if my mains was closer to 115VAC, the heater voltage would be correspondingly lower?

 

A 1960 Heerlen, Holland E188CC running in an LD 1+:
 
Heater  -  6.7v
Plate (R) - 81.5    Grid (R) - 3.1
Plate (L)  - 81.5    Grid (L)  - 3.1

 

Be that as it may, anything over 6.6V does strike me as "not so good over the long term"... Maybe a simple resistor on the heater wire path could eversoslightly lower that voltage?

 

Quote:
Originally Posted by gibosi View Post
 

 

In my opinion the 12AX7 / 5751 tubes, and even the 6SL7s, are not worth your time and money. I believe that the 6DJ8 are unquestionably superior, at least in our LDs, But again, this is only my opinion.... :)

Oh.

 

Well... I guess that just answers a few questions right there lol... Hopefully the 2C51 may be able to hold a candle to the all-mighty 6DJ8 so we can at least have some alternative?

 

Then again, I keep marveling at both how good the 6922 and 7308 are, all in all, and how well they work in my LD... I only have 10 hours on my - one of my two - Philips 1960 E188CC, and I can already tell how these how very very very rugged and nice tubes. Even after 3 hours, the detail in the treble and sense of air (see the comments on the RTC E188CC over on the Lyr thread) were impressive. I haven't had a chance to listen to the tube that critically yet, not with music at least, but after 10-12 hours, I am hearing something I like!

post #4219 of 10486

Can octals be used either in 6v.or 12 v. adaptors not shure .Thanks

post #4220 of 10486
Quote:
Originally Posted by MIKELAP View Post
 

Can octals be used either in 6v.or 12 v. adaptors not shure .Thanks

 

We need to know more about your system...

 

I purchased a 6SL7 to 12AX7 adapter. With that, I configured my breadboard socket to run a 12AX7 in 6volt mode, and simply plugged it in. If you have a similar adapter, then this is all you have to do. If you are using an actual octal socket, then it will be necessary to look at a data sheet to see how to properly configure that socket.....  

post #4221 of 10486
Quote:
Originally Posted by Audiofanboy View Post

 

Be that as it may, anything over 6.6V does strike me as "not so good over the long term"... Maybe a simple resistor on the heater wire path could eversoslightly lower that voltage?

 

I have been thinking the same thing, but before I start groping and fumbling around, I am hoping that Ctritical Bill and TrollDragon will weigh in on this....

 

Quote:
Originally Posted by Audiofanboy View Post
 

Well... I guess that just answers a few questions right there lol... Hopefully the 2C51 may be able to hold a candle to the all-mighty 6DJ8 so we can at least have some alternative?

 

I have made a few attempts to grab a Western Electric 369A, but each time I have been seriously outbid. I figure that eventually I will get lucky so will keep bidding until I can get one at a good price.

post #4222 of 10486
Quote:
Originally Posted by gibosi View Post
 

 

I have been thinking the same thing, but before I start groping and fumbling around, I am hoping that Ctritical Bill and TrollDragon will weigh in on this....

 

 

I have made a few attempts to grab a Western Electric 369A, but each time I have been seriously outbid. I figure that eventually I will get lucky so will keep bidding until I can get one at a good price.

 

Laugh all you want, but I actually had a Western Electric JW 396A at one point.

 

I got it in the same bundle of tubes I got that mil-spec "flying 12AT7" Mullard from. Perfect silk writing and pins, no reason to think it didn't work. So I put it up for sale fairly cheap, clearly stating that I didn't have the means to test it - and that I'd take it back if it didn't work.

 

Long story short, obviously, the tube didn't work properly (or so the buyer said, but he claimed that only one triode worked before explaining that the other triode worked when he flicked the tube, so I always had a doubt as to wherein the problem really lied), and I had to both pay the fellow back, lose the paypal and shipping fees, and not get my beautiful rare - albeit not functional - tube back...

 

I now regret even trying to sell the tube... Both for testing purposes, and also for "collection" purposes...

post #4223 of 10486
Quote:
Originally Posted by gibosi View Post
 

 

We need to know more about your system...

 

I purchased a 6SL7 to 12AX7 adapter. With that, I configured my breadboard socket to run a 12AX7 in 6volt mode, and simply plugged it in. If you have a similar adapter, then this is all you have to do. If you are using an actual octal socket, then it will be necessary to look at a data sheet to see how to properly configure that socket.....  

Yes i forgot about that i have 2 6SL7 to 12ax7adapters on the slow boat from China that i will plug in the 6DJ8 adaptor i just made so its 6 volts thanks gibosi.

post #4224 of 10486
Quote:
Originally Posted by MIKELAP View Post
 

Yes i forgot about that i have 2 6SL7 to 12ax7adapters on the slow boat from China that i will plug in the 6DJ8 adaptor i just made so its 6 volts thanks gibosi.

 

Since your shiny new copper adapter is configured for 6DJ8 tubes, I don't think this will work...  

 

The heater connections are different for the 6DJ8 and 12AX7. Since your socket is configured for 6DJ8 tubes, it will be necessary to reconfigure pins 4, 5 and 9 on your 9-pin socket to use 12AX7 and 6SL7 tubes.

 

Like so:

 

http://www.head-fi.org/t/563884/little-dot-tube-amps-vacuum-tube-rolling-guide/3630#post_9911760

 

Can you do this?

post #4225 of 10486
Quote:
Originally Posted by gibosi View Post
 

I have made a few attempts to grab a Western Electric 369A, but each time I have been seriously outbid. I figure that eventually I will get lucky so will keep bidding until I can get one at a good price.

 

Well color me surprised!  I just won one... and at a pretty good price - $12 plus $5 shipping. In a few days, I hope to be able to see how one of the best of the 2C51 compares to some of the best of the 6DJ8. :) 

post #4226 of 10486
Hey gibosi

Pricklely Peete in this thread has done some major mods to his amp improving the sound totally.

He also suffers from a mains voltage of 127V which brings his filaments up to 6.9 or 7. He solved this issue by putting a 1 ohm 3W resistor in series with the filament which dropped it .5V I think this is something you should look into as well to improve the longevity of your tubes. Running them at 6.2 or 6.1 will definitely make them last longer.

Here is the link, info is about halfway down.
www.head-fi.org/t/439449/little-dot-mk-iii-mods/15#post_5938548

beerchug.gif
post #4227 of 10486
Quote:
Originally Posted by gibosi View Post
 

 

Since your shiny new copper adapter is configured for 6DJ8 tubes, I don't think this will work...  

 

The heater connections are different for the 6DJ8 and 12AX7. Since your socket is configured for 6DJ8 tubes, it will be necessary to reconfigure pins 4, 5 and 9 on your 9-pin socket to use 12AX7 and 6SL7 tubes.

 

Like so:

 

http://www.head-fi.org/t/563884/little-dot-tube-amps-vacuum-tube-rolling-guide/3630#post_9911760

 

Can you do this?

Yes i can i have the shematics already ive waited so long to get the parts i didnt remember that anymore so thats why i had to make the 12v. adapter :confused_face(1): at least one of us is still with it .Thanks again for clearing that up my friend. 

post #4228 of 10486
Quote:
Originally Posted by TrollDragon View Post

He also suffers from a mains voltage of 127V which brings his filaments up to 6.9 or 7. He solved this issue by putting a 1 ohm 3W resistor in series with the filament which dropped it .5V I think this is something you should look into as well to improve the longevity of your tubes. Running them at 6.2 or 6.1 will definitely make them last longer.

Here is the link, info is about halfway down.
www.head-fi.org/t/439449/little-dot-mk-iii-mods/15#post_5938548

 

Thank you!! :)

 

To be sure I understand... Running just one double triode and supplying power to that tube as we have been doing through one of the Vectors, I would need only one of these resisters, connected in series to either Vector pin 3 or 4?

post #4229 of 10486
Quote:
Originally Posted by gibosi View Post
 

 

Thank you!! :)

 

To be sure I understand... Running just one double triode and supplying power to that tube as we have been doing through one of the Vectors, I would need only one of these resisters, connected in series to either Vector pin 3 or 4?

Yes that is correct, his voltage is 127 and yours is only 122 so the 1 ohm might be too much, you can also get .5 ohm ones or in a pinch you can join two 1 ohm in parallel to give you .5 ohm.

 

I would pick up some axial lead 1 Ohm 3 Watt 1% from a local electronics supplier or Mouser / Digikey or eBay similar to these.

 

You could use 5 Watt but they are starting to get a little large. ;)

post #4230 of 10486
Quote:
Originally Posted by TrollDragon View Post
 

Yes that is correct, his voltage is 127 and yours is only 122 so the 1 ohm might be too much, you can also get .5 ohm ones or in a pinch you can join two 1 ohm in parallel to give you .5 ohm.

 

I would pick up some axial lead 1 Ohm 3 Watt 1% from a local electronics supplier or Mouser / Digikey or eBay similar to these.

 

You could use 5 Watt but they are starting to get a little large. ;)

 

Thanks again! :)

 

I have a pretty decent electronic supply store close by, so hope to get these tomorrow.

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