Need to run heaters in output tubes, remove plate and screen safe? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th February 2012, 11:49 AM   #1
diyAudio Member
 
Join Date: Apr 2010
Default Need to run heaters in output tubes, remove plate and screen safe?

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?

Last edited by Printer2; 12th February 2012 at 11:51 AM.
  Reply With Quote
Old 12th February 2012, 11:59 AM   #2
diyAudio Member
 
Rundmaus's Avatar
 
Join Date: Aug 2005
... 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
  Reply With Quote
Old 12th February 2012, 12:26 PM   #3
diyAudio Member
 
Join Date: Apr 2010
Quote:
Originally Posted by Rundmaus View Post
... 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?
  Reply With Quote
Old 12th February 2012, 12:28 PM   #4
GloBug is offline GloBug  Canada
Banned
 
Join Date: Jun 2011
Sounds OK to me.
  Reply With Quote
Old 12th February 2012, 12:37 PM   #5
diyAudio Member
 
Join Date: Aug 2005
Buy less efficient speakers?
  Reply With Quote
Old 12th February 2012, 01:20 PM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Do you mean too much gain, perhaps? How does one have "too much power"?
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 12th February 2012, 01:25 PM   #7
diyAudio Member
 
Rundmaus's Avatar
 
Join Date: Aug 2005
Quote:
Originally Posted by Printer2 View Post
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
  Reply With Quote
Old 12th February 2012, 01:29 PM   #8
jjman is offline jjman  United States
diyAudio Member
 
Join Date: Jan 2009
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.
  Reply With Quote
Old 12th February 2012, 02:08 PM   #9
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: South Florida
Quote:
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.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 12th February 2012, 02:39 PM   #10
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
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.
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]

Last edited by bear; 12th February 2012 at 02:43 PM.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Output Pentode Screen at half Plate voltage Andrewbee Tubes / Valves 32 2nd May 2012 11:41 PM
do tubes ever leak b+ into heaters? ryuji Tubes / Valves 25 7th July 2011 04:42 PM
150V plate output tubes engels Tubes / Valves 10 10th July 2007 05:01 AM
Safe to run IRF540 on +-42V? Fritzell Solid State 1 28th February 2007 04:46 PM
how to remove the words on the face plate? i_like_pie116 Everything Else 4 18th February 2007 02:53 PM


New To Site? Need Help?

All times are GMT. The time now is 11:02 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2