Mark IIb tube questions

Bill Assumpcao · Apr 19, 2006

Howdy folks,
I've been a member here for a coupla weeks and have yet to show my ignorance. So, here goes

a) Iffen I got my amp in 60 watt mode, supposedly only the 2 outside 6L6s are pushing the amp. Shouldn't they be glowing brighter than the inside tubes? Or would that only happen if I push the amp hard?

b) Iffen the outside 6L6s get the most work, would switching them with the inside 6L6s buy me some time if my amp started to sound a little weak?

Just a coupla "Gee, I wonder...."s
:roll: :lol:
BillA

Dirt123 · Apr 21, 2006

a) Can't help here, but I would assume you are correct.

b) Yes, if you run in the 60 watt mode all the time, swapping the tubes will buy you time.

Question: If you are in 60 watt mode, do you even need the other 2 tubes in the amp?

Dirt

Boogiebabies · Apr 21, 2006

A. No - What makes a tube light up is the heater element.

B. Yes - They will wear evenly if you rotate them.

Bill Assumpcao · Apr 21, 2006

G'morning Gents,
Thanks for responding

I'm gonna hafta try that swapping tubes thingie. Kinda like rotating tires :wink:

Dirt123 said:
Question: If you are in 60 watt mode, do you even need the other 2 tubes in the amp?

As I stated earlier, I'm pretty ignorant about this stuff. But, I think that I read somewhere (?) that there's some kinda reason to leave all the valves in. Maybe Boogiebabies knows why?
Thanks again,
BillA

Paul Secondino · Apr 22, 2006

I'm not sure if Simulclass wiring makes a difference. But if you pull tubes in an amp like a recto, you do change something.Aside from reducing the amp's headroom, you also effectively change the output impedence of the amp. So your 8ohm speaker out becomes a 16ohm speaker out.

Like I said, I don't know if this applies the same to a simulclass amp but I'd look into it for a definitive answer.And that way, you can protect yourself from too low of a speaker load.Your amp's output section wants to see an equal or greater load but never a lesser load.

Bill Assumpcao · Apr 23, 2006

How do Paul,
Thanks for the response

Paul Secondino said:
...Your amp's output section wants to see an equal or greater load but never a lesser load.

'Acause it'll overheat, right?
And if I run it into too high an impedence (16 ohms), it'll wear the tubes faster, right?
Since I don't know what I'm doing, I've been trying to do everything according to the instruction manual, and asking lottsa stupid questions.
I wouldn't wanna hurt my baby,

BillA

Boogiebabies · Apr 25, 2006

If you use a 60/100 or Simul-Class switch it shorts out the two middle tubes. The only thing still on is the heaters. Heaters glow, but never wear out. Simul-Class amos are not a push pull. They have a special output transformer that blends the outer sockets signal with the inner sockets signal through the primary of the OT. I would not feel comfortable pulling tubes from a simul. Just let the heaters glow. You will be fine. In general, a 60/100, when shorting the middle tubes it makes the plate voltage go up as there are two less tubes to draw current. They may run a bit hotter due to this.