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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 287

post #4291 of 10574

Hi TD,

 

Try measuring the grid voltage when playing something. Sometimes I had to switch the leads and use the other lead for ground.

post #4292 of 10574
Quote:
Originally Posted by gibosi View Post

According to Ctritical Bill, when the tube is idle, the grid is 0 volts, but measuring the cathode voltage when the tube is idle amounts to the same thing.

http://www.head-fi.org/t/563884/little-dot-tube-amps-vacuum-tube-rolling-guide/4200#post_10034489
Thanks gibosi!
I don't know how I missed that bit the first time around, that will teach me to skim posts. wink.gif
Quote:
Originally Posted by mordy View Post

Hi TD,

Try measuring the grid voltage when playing something. Sometimes I had to switch the leads and use the other lead for ground.
Thanks mordy!
I had tried that but thought no, as the volume of the music should have an impact on the voltage.

Then I heard a loud scratching noise in the beyer's on the table while I was using the probes and quickly unplugged them.

My old vintage part DIY B9A to octal adapter is not the easiest to get measurements from. biggrin.gif
post #4293 of 10574

Hi TD,

 

Measured grid voltage on my 6N23P tube on 0 volume, 1/2 volume and full volume (close to clipping) at the LDIII and could not find any significant differences. The voltage could be a fraction higher or lower (2.67v vs 2.69V). With this tube I cannot see any volume dependent changes in measured grid voltage.

post #4294 of 10574
Quote:
Originally Posted by mordy View Post
 

Hi TD,

 

Measured grid voltage on my 6N23P tube on 0 volume, 1/2 volume and full volume (close to clipping) at the LDIII and could not find any significant differences. The voltage could be a fraction higher or lower (2.67v vs 2.69V). With this tube I cannot see any volume dependent changes in measured grid voltage.

Excellent!

 

Thanks mordy that is good to know.

post #4295 of 10574
Quote:
Originally Posted by Audiofanboy View Post
 

 

A more difficult question now : how hard would it be to make and use a battery-powered supply for the driver heaters (a 6.3V 0.5-1A DC power supply) and could it bring somekind of an improvement to the way the driver tubes function (less hum or noise, better and more stable current supply...)? I can't imagine it would be hard to make, I'm more curious about what it would change. I'm pretty sure I've read examples of people preferring a DC battery power supply to an AC transformer power supply for heating their tubes...

 

 

This is something I am currently working on. I am thinking of using a wall adapter and a simple/cheap voltage regulator to bring it down to the required DC voltage. I can't see it making much difference to the sound but will get around the possible limitations of the LD transformer. Should be able to set up it up to run 12 volt tubes too.

post #4296 of 10574

I picked up a 1 ohm 3 watt resister, put it in the heater circuit and now have a data-sheet perfect 6.3 volts! When I was talking to the old-timer who owns the electronics store, he pooh poohed the notion that 6.7 volts was too high. He told me that when 6.3 volt tubes were used in cars, the heater voltage was often as much as 8 volts and the tubes were fine. So.... maybe my tube isn't happier..... but I am happier. :)

post #4297 of 10574
Quote:
Originally Posted by Ctritical Bill View Post
 

 

This is something I am currently working on. I am thinking of using a wall adapter and a simple/cheap voltage regulator to bring it down to the required DC voltage. I can't see it making much difference to the sound but will get around the possible limitations of the LD transformer. Should be able to set up it up to run 12 volt tubes too.

Nice!

 

I am looking into the "Wall Wart" idea as well with a LT1085 or LM338 type device as the regulator.

 

This circuit here would be great, it automatically adjusts from 12AX7 to 6DJ8 by itself. :smile:

The article about the above is here at The Valve Wizard.

:beerchug:

post #4298 of 10574
Quote:
Originally Posted by gibosi View Post
 

I picked up a 1 ohm 3 watt resister, put it in the heater circuit and now have a data-sheet perfect 6.3 volts! When I was talking to the old-timer who owns the electronics store, he pooh poohed the notion that 6.7 volts was too high. He told me that when 6.3 volt tubes were used in cars, the heater voltage was often as much as 8 volts and the tubes were fine. So.... maybe my tube isn't happier..... but I am happier. :)

Nice! You could probably run it at 7 volts for years but why take the chance when it is easy to make right.

 

I just love the Old-Timer's and their logic, as back in the day the 6681, a mobile version of the 12AX7 designed to run by battery and designed to take a +/- 1.3V variation in the heater voltage could be bought brand spanking new from any corner drug store for $1.75... :D

 

Old GE Tube Price Chart 1960

post #4299 of 10574

Adjusted for inflation, $1.75 in 1960 would be $13.71 today in Canada and $12.25 in the USA. Would you pay that much for a 12AX7 tube? I have been paying between $0.99 and $7.00.

 

I guess I might pay that for an Amperex based on Gibosi's logic......LOL

post #4300 of 10574
Quote:
Originally Posted by mordy View Post
 

Adjusted for inflation, $1.75 in 1960 would be $13.71 today in Canada and $12.25 in the USA. Would you pay that much for a 12AX7 tube? I have been paying between $0.99 and $7.00.

 

I guess I might pay that for an Amperex based on Gibosi's logic......LOL

There always has to be one of you in the crowd... :tongue_smile: :D

Unfortunately wages didn't scale equally with the inflation... 

 

I picked up my two JAN Sylvania 5751's for $10 locally with a pair of GE mystery 5751's thrown in for free...

TubeDepot wants $30 for the exact same tube. http://www.tubedepot.com/nos-5751.html

:beerchug:


Edited by TrollDragon - 12/9/13 at 1:04pm
post #4301 of 10574
Man I've been following this thread for a while... And soon... Very soon I will actively be rolling tubes again... I have a ton of 6DJ8's and a few 12AX7's here... I just need the time to really sit down and listen/tinker... I'll be building an adapter to run these during my upcoming Christmas vacation... I feel like I have a ton of catching up to do...
post #4302 of 10574
Quote:
Originally Posted by kvtaco17 View Post

Man I've been following this thread for a while... And soon... Very soon I will actively be rolling tubes again... I have a ton of 6DJ8's and a few 12AX7's here... I just need the time to really sit down and listen/tinker... I'll be building an adapter to run these during my upcoming Christmas vacation... I feel like I have a ton of catching up to do...

 

And I think you now have a Lyr in the family?  If so, I for one, would be very interested in your impressions of your LD running a 6DJ8 compared to the Lyr. Cheers. :)

post #4303 of 10574
Quote:
Originally Posted by gibosi View Post
 

 

And I think you now have a Lyr in the family?  If so, I for one, would be very interested in your impressions of your LD running a 6DJ8 compared to the Lyr. Cheers. :)


I do! BUT I'd have to pry it away from my wife for an extended period of time lol

post #4304 of 10574
Quote:
Originally Posted by kvtaco17 View Post
 


I do! BUT I'd have to pry it away from my wife for an extended period of time lol

 A little bribery... and a little trickery....  Perhaps you can find a way?  lol :)

post #4305 of 10574
Quote:
Originally Posted by gibosi View Post
 

 A little bribery... and a little trickery....  Perhaps you can find a way?  lol :)


It won't be an issue lol She can used the o2 or little dot lol

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