Need to run heaters in output tubes, remove plate and screen safe?

[Printer2]

A relative has too much power in their amp and wants to run two tubes in the output section rather than four. The transformer has a tap to take care of the impedance change needed in only running two tubes but the output tubes are run in series with six volt heaters running on 12v. I figure I could remove the plate and screen pins on some old tubes he has and pop them in there to complete the heater circuit. I would like to keep the grid and cathode pins in in order to give the tubes some mechanical stability but am not sure if electrons will collect on the grid and cause trouble when the amp clips. So is it safe to leave the pins connected or not?

[Rundmaus]

... how the hell can someone have too much power output from a tube amp?

Isn't there a volume pot somewhere in the circuit? I would rather turn the volume down a little than castrate tubes or circuit...

Greetings,
Andreas

[Printer2]

Originally Posted by Rundmaus

... how the hell can someone have too much power output from a tube amp?

Isn't there a volume pot somewhere in the circuit? I would rather turn the volume down a little than castrate tubes or circuit...

Greetings,
Andreas

I knew that was coming. Well given the case, any other answers?

[GloBug]

Sounds OK to me.

[mace1337]

Buy less efficient speakers?

[SY]

Do you mean too much gain, perhaps? How does one have "too much power"?

[Rundmaus]

Originally Posted by Printer2

I knew that was coming. Well given the case, any other answers?

Sorry, could not resist.

But I still do not understand the need for disabling two output tubes. If it's 'too loud', use the volume control. If there's too much gain, as SY suggested, this should be cured by making the appropriate changes to the driver stage.

Could you explain in more detail why there is 'too much power'?

Greetings,
Andreas

[jjman]

Guitar amps often have "too much power" since output clipping, at a volume below earthquake levels, is often a goal. I think they sometimes switch the cathodes on 2 tubes.

Half the watts is not half the volume so the difference may not be significant enough depending upon the goal.

[tubelab.com]

How does one have "too much power"?

4 X KT88 in PPP will do it

I assume that this is a guitar amp and the player likes the sound of the amp as it enters clipping / compression or as it operates just short of meltdown ( my preference)......however his neighbors don't.

The common path is a resistive attenuator between the amp and speaker, but it just doesn't sound the same. Turning off two output tubes is also somewhat common. In my amps I just switch the screen grids to ground to disable 2 tubes. That seems to work, but as suggested doesn't make the amp that much quieter.

Another path that works well in lower pwered amps is the VVR. It is a variable voltage regulator usually made with a mosfet that allows turning down the B+ to reduce the power and the point at which the amp enters distortion. It can be done on a big amp, but it will be a big mosfet on a big heat sink.

[bear]

Another way, other than just running "dummy tubes" is to regulate the 12vdc after rectification down to the required 6.3vdc... or use a dropping resistor (you could put it
on an octal plug in socket (assuming an octal tube).

I'd be surprised if the output transformer "has another tap" - that would be unusual on the primary side. One could use another secondary side tap, IF there is the right one.

A bit more information on precisely what the amp is and what the taps are could get you some much more precise answers.

_-_-bear

EDIT, actually none of that is required. You just have to use the proper two sockets, or rewire the filaments so that the pair of output tubes used are in series. I am assuming they put one primary "side" tube pair with filaments in series, rather than sharing between both sides. But there's really not a problem that i can see in running tubes on opposite sides of the primary with filaments in series (not for DHTs of course). These are indirectly heated tubes. So, rewire the filaments if need be.