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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 331

post #4951 of 10502

Please don't thank me, I am more than happy to help whenever I can.

 

You are right by combining tubes you can get the benefits of different variants or types.

However you can get lots of enjoyment by rolling just the driver, some amps respond very well to it depending on the design.

post #4952 of 10502

Hi Gibosi and rosgr63,

 

I find it fascinating to read about combining two driver tubes, because this has been on my mind for quite a while. My present set up is a breadboard with an external PS using a dual triode of the 6SN7 family via 2 Vector adapters plugged into the LD MKIII.

 

If I have the 7 pin Vector sockets available to plug in two 7 pin tubes such as the 6HM5, and they are powered by the LD, is there anything untoward preventing me from trying this?

post #4953 of 10502
Quote:
Originally Posted by mordy View Post
 

Hi Gibosi and rosgr63,

 

I find it fascinating to read about combining two driver tubes, because this has been on my mind for quite a while. My present set up is a breadboard with an external PS using a dual triode of the 6SN7 family via 2 Vector adapters plugged into the LD MKIII.

 

If I have the 7 pin Vector sockets available to plug in two 7 pin tubes such as the 6HM5, and they are powered by the LD, is there anything untoward preventing me from trying this?

 

Mordy, I think fire and smoke is quite possible resulting from plugging anything into the Vectors while your 6SN7 is also running. Further, I doubt that the LD can support two stages of driver tubes without a huge amount of modification. However, what is very possible is using the one 6SN7 with external heater PS as a driver and then installing a pair of 6CG7/6SN7 as power tubes.

 

I remember that you tried using 6CG7s as power tubes driven by a single 6SL7, but that was not optimal, largely due to the 6SL7's borderline compatibility in the LD, I suspect. But running 6CG7/6SN7 in both the driver and power positions could work quite well.

post #4954 of 10502

Hi everyone,

  I Just tried running my  LD 1+ with  3 driver Tubes 1 6SL7 with separate PS and 2   6J1 so far no fireworks and no magic smoke.

 

 

 

 

 

post #4955 of 10502

I felt that using the 6CG7 tubes as power tubes ruined both the drive tube and the 6CG7 power tubes. The plate voltage was in the area of 218V. The heater voltage on my favorite 12AX7 tube read 0.34V on one side after this experiment.

 

I recall a comment that the 6CG7 is not compatible with the LD MKIII but the 6FQ7 is (perhaps from the Little Dot Forum).

 

Too scared to try the 6FQ7 as power tubes.

 

I have to wait for another way to combine tubes safely.

post #4956 of 10502

Hi i luvmusic2,

 

Congratulations! Looks really neat! Now, I have the LD MKIII, so it is not exactly the same setup. If somebody can vouch for the safety of my MKIII amp I would definitively try it.

 

The BIG question: How does it sound? Is there a real improvement?

 

Next: Your voltage regulator looks the same as mine. I am not able to adjust the LED readout to read 6.3V. The closest I get is 6.27V.  However, it seems that the LED readout is stepped, because I get 6.27V and next 6.43V. However, you can still turn the set screw within the 6.27V readout and see different voltages as measured at the output terminals on the voltage regulator. After a little fiddling and measuring with my multimeter, I can get a steady 6.30V. Sometimes the voltage fluctuates as measured, but minimally  (6.29 - 6.31V) - not that it should matter much.

post #4957 of 10502
Quote:
Originally Posted by mordy View Post
 

Hi i luvmusic2,

 

Congratulations! Looks really neat! Now, I have the LD MKIII, so it is not exactly the same setup. If somebody can vouch for the safety of my MKIII amp I would definitively try it.

 

The BIG question: How does it sound? Is there a real improvement?

 

Next: Your voltage regulator looks the same as mine. I am not able to adjust the LED readout to read 6.3V. The closest I get is 6.27V.  However, it seems that the LED readout is stepped, because I get 6.27V and next 6.43V. However, you can still turn the set screw within the 6.27V readout and see different voltages as measured at the output terminals on the voltage regulator. After a little fiddling and measuring with my multimeter, I can get a steady 6.30V. Sometimes the voltage fluctuates as measured, but minimally  (6.29 - 6.31V) - not that it should matter much.

IMO None.

post #4958 of 10502

Hi Mordy,

   I just tried my LD MK III running combined Driver tubes(same setup with my LD 1)again nothing happened no fireworks and no smoke,about the sound  IMO No changes . I hope these Help.

 

 

 

 

 

Thanks!

post #4959 of 10502

Hi i luvmusic2,

 

Thanks for trying the three driver setup on the MKIII. I was really hoping that there would be a sonic benefit, but you state that it did not make a difference. Maybe a different combination of tubes would change things.

 

Thanks for the help.

post #4960 of 10502
Haphazardly running random tubes in parallel is very careless and will prove to be entertaining...
popcorn.gif
post #4961 of 10502

HI TD,

 

Is this the entertainment you mean?

 

http://upload.wikimedia.org/wikipedia/commons/0/02/Imploding_vacuum_tube.JPG

post #4962 of 10502

 I will try 6HM5 and 6SL7 as a Driver tube on LD MK III.wish me LUCK,someone has to try it right. 'll be back in a minute.

post #4963 of 10502
No I mean this kind of entertainment...

This was from a bad capacitor but similar things can happen when good parts are overdriven.
Edited by TrollDragon - 2/8/14 at 8:28pm
post #4964 of 10502

I'm back,No worries LD 1,LD MK III and i are OK.Just tried 6HM5 and 6SL7 combined driver tubes with my LD1 and LD MK III and still no changes in sound and no fireworks.That's enough for me before i hurt my self.

post #4965 of 10502
Quote:
Originally Posted by mordy View Post
 

I felt that using the 6CG7 tubes as power tubes ruined both the drive tube and the 6CG7 power tubes. The plate voltage was in the area of 218V. The heater voltage on my favorite 12AX7 tube read 0.34V on one side after this experiment.

 

I recall a comment that the 6CG7 is not compatible with the LD MKIII but the 6FQ7 is (perhaps from the Little Dot Forum).

 

Too scared to try the 6FQ7 as power tubes.

 

I have to wait for another way to combine tubes safely.

 

Mordy,

 

The only difference between a 6CG7 and a 6FQ7 is the former has a shield and the latter does not, so if one is compatible then the other one is too. The 6SN7 is perfectly happy with a plate voltage of 250V, so 218V is well within spec. And the heater voltage for the 6SN7 is now controlled via your external PS, so that is no longer an issue. However, I certainly understand your reluctance.....

 

But I will say that this is far and away much safer than running two 7-pin tubes in parallel with your 6SN7!!!


Edited by gibosi - 2/8/14 at 8:24pm
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