Peavey Ultra Plus - pull tubes?...

[Twangmaster]

does anybody know if I can pull two output tubes on my Peavey Ultra Plus head (4x 6L6), which I always play at low volumes, and I want to use just two output 6l6's. Can I pull them like on my Fender Twin - and just double the speaker impedance? Or is there a danger if I flip the ½ power switch - or is that switch doing just that?

Can one of you knowledgeable guys help out here?

Thanks,
Olav

[Twist]

The half power switch is disconnecting the cathodes of V7 and V8. Without physically looking inside the amp, I'm not sure which two. If you dont want to open up the amp to see then switch it to half power mode, plug in one tube at a time until you discover the two active sockets. I'm sure someone on here can tell you which two to use. As far as speaker impedance, if your running only two tubes then a 4 0hm tap would become an 8 Ohm tap, 8 Ohm tap would become a 16 ohm tap and so on.

[stokes]

Olav,if as Twist says (I dont have a schem for that amp) the half power switch is lifting the cathodes of two of the tubes,which is the most likely scenario,there is no reason to pull two tubes.The switch will disable two of the output tubes.As to which two are being disabled it is usually the two inner or the two outer tubes.A word of warning about pulling 2 tubes on your Twin,simply changing the output to an 8ohm isnt enough,when you pull 2 tubes you increase the current in the tube you leave in enough to cause considerable damage to the tubes and the amp.

[Enzo]

How would that happen? Pulling tubes is the same as shutting them off at the cathode.

[Jag]

Thanks for asking Enzo that. I thought there must be something I was missing.

[Enzo]

That is why it was a question, in case we are both missing someting.

[Twangmaster]

Just to be sure....

if Twist is right - I am safe to pull the two tubes, and nothing will happen to the amp, if I by accident switch in full power? Is it possible for somebody to verify this, by looking at the schematic?

Thanks,
Olav

PS: My twin sounds great with two tubes pulled, and a set of 16 ohm Celestion G12H (30w) from '76 in parallel...

[Enzo]

I think you are missing the point. There are four power tubes. Tha half power switch turns two of them off. This is the same as pulling them. That switch does exactly what you are trying to do, it just leaves the unused tubes in there. So pulling two tubes is the same as flipping the switch.

Now you COULD flip the switch AND pull two tubes. One of two things would happen. You might pull the two tubes that get turned off by the switch. In that case you would be half power all the time, and the switch would make no difference. On the other hand, you might pull the two tubes that don't get switched. Now that is more interesting because when the switch is on high power, you would only have two tubes running and teh amp would be on half power. But flip the switch to half power and it switches off the only two tubes you have in there. The amp would then have zero power tubes running and zero sound would come out the amp.

Bottom line is this: The half power switch already is there and does the same thing as pulling two tubes.

[Twangmaster]

I didn't explain myself...

I want to pull the tubes, to be able just to have 4 quality 6L6's between my Twin and Peavey. This instead of having 8 tubes sitting there - and only wanting power from 4 tubes...

[Enzo]

In that case, leave the switch in high power and pull the two end tubes.

[Twangmaster]

Why not...

leave them in the two sockets which are not connected to the ½ power switch - I guess this would kinda leave ½ power switch out of function - at least nothing will happen if somebody flips it by accident?

[Enzo]

If someone flips the switch, either nothing happens or it finds the only two tubes and turns them off leaving it tubeless, which won't hurt it.

it would be easy enough to figure out which sockets turn off if you want, turn on the amp on LOW and stick one tube in a socket. One tube won't sound great, but all we want to know is sound or no sound. Now move it over one, repeat until you have tried all four. WHichever two sockets work are the ones that work. That was why I suggested just leaving the switch in HIGH.