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6j6 tube in 19j6 amp?

post #1 of 7
12/22/10 at 1:21am
Thread Starter 

I have a whiplash starving student amp that uses 19j6 tubes.  One tube is noisy and has been getting slowly worse for about a year.  I swap the tube to the other socket and the noise follows it.  I am frustrated and would like to replace it as I can hear the noise during listening.

 

I tried ordering 19j6 tubes from tube depot and they were back ordered for 3-6 weeks or something like that.  I've read other posts that they never show up.

 

I saw someone talking about a 6j6 tube.  Everything is the same physically, but the voltage and current are way different.  It plugs into the same socket...can they be used in my amp without causing harm?

 

Mechanical Data

Bulb .......................................... T-5 1/2
Base .......................................... Miniature Button 7-Pin
Outline ....................................... 5-2
EIA Base ...................................... 7BF
Mounting Position ............................. Any

Electrical Data

Heater Voltage ................................ 6.3 V
Heater Current ................................ 0.45 A
Maximum Heater-Cathode Voltage
Heater Positive with Respect to Cathode
DC Component .............................. 90 V
Heater Negative with Respect to Cathode
DC Component .............................. 90 V

 

vs 19j6

 

Mechanical Data

Bulb .......................................... T-5 1/2
Base .......................................... Miniature Button 7-Pin
Outline ....................................... 5-2
EIA Base ...................................... 7BF
Mounting Position ............................. Any
Electrical Data

Heater Voltage ................................ 18.9 V
Heater Current ................................ 0.15 A

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post #2 of 7
12/22/10 at 8:38am

Seems to be that R = V / I

 

18.9/0.15 = 126 ohms

 

6.3/0.45 = 14 ohms

 

14 = 18.9 / I

 

I = 18.9/14 = 1.35 amps

 

 

Hopefully you see by now that, that seems like a poor idea.

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post #3 of 7
12/22/10 at 8:55am
As nullstring is pointing out, those are radically different tubes.

Did you give Dale and Roy a call?

http://www.vacuumtubes.net/

They have a toll-free number.
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post #4 of 7
12/22/10 at 9:02am
Quote:
Originally Posted by jdkJake View Post

As nullstring is pointing out, those are radically different tubes.


I wouldn't go that far.

They are, in fact, almost exactly the same.

 

The only difference is the heater.

 

But the difference is certainly significant.

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post #5 of 7
12/22/10 at 9:07am
Fair enough. Perhaps I overstated a bit.

Since the op did not build the amp, I figured modifying the amp to accommodate the difference in heater requirements was pretty much out of the question.
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post #6 of 7
12/22/10 at 10:20am
Thread Starter 

I did go to my old friend from physics 133 and found the resistance to be different by almost a factor of 10.  I just thought I'd try and ask ;)

 

I may have found some tubes on the forum here for sale, but if that falls through I will call Dale or Roy.

 

Modifying the amp is not out of the question, but that is a very last resort.

 

Thanks guys :)

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post #7 of 7
12/22/10 at 10:23am

Yep - they are the same tube from a plate/grid standpoint and even share the same datasheet (along with the 5J6).  However, the fact that the heater in the 6J6 is 6V means the current is over 3X the 19J6 tube.  In an amp design such as the Starving Student, where the output MOSFETs use the heater current (and voltage!) to bias the MOSFETs, it simply makes the design unworkable with that tube.

 

Unlike the 19J6, there are tens of thousands of the 6J6's available at prices of $2 and less.  I've had some tube dealers tell me that "we" (as in the "headphone community") were too ignorant to know how to re-design the amp to use the 6J6.  As if Pete Millett or Dsavitsk didn't know how to design tube amps - HA!!  If it was a regular tube amp - no big deal, just change the heater supply from 19V at 0.15A to 6V at 0.45A.  Nothing else changes because plate (B+) supplies are always separate anyway (usually hundreds of volts).  As a hybrid though, with those MOSFETs biased by the heaters, it changes everything.

 

 

P.S. There is something exciting coming - very soon - that will use the 6J6, but it in no way resembles the Starving Student. biggrin.gif


Edited by tomb - 12/22/10 at 10:27am
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