Stupid heater question...

[Geezer]

  Hoffman Amplifiers
    > Tube Amp Building - Tweaks - Repairs
        > Stupid heater question...      
 
<< Prev Topic | Next Topic >>  
Author  Comment  
Dbltlk44
Junior tube assistant
Posts: 3
(2/6/04 11:31 pm)
 Stupid heater question...
--------------------------------------------------------------------------------
 

Question for all you tube aces....

I know that a 12A*7 heater can run off on 6.3 or 12.6 volts; now, I'm assuming because just about every power tube common to gee-tar amps has a 6.3 heater, it's the reason that the 12A*7's are run on 6.3. ( makes sense )

Any worldly reason ya wouldn't want to run the heaters on 12.6? I mean the 12's of course, not the power tubes. I remember reading somewhere that a higher fil voltage can generate more noise and such. Anybody have any experience with this? I'm tinkering with a homebrew, and I'm thinking of using a 3A 12.6 fil tranny to light up my preamp tubes.

Any info or feedback would be most graciously appreciated!
 
6G6
Junior tube assistant
Posts: 72
(2/7/04 12:12 am)
 Re: Stupid heater question...
--------------------------------------------------------------------------------
 I've wondered about that too.
I decided it's another of those things you don't need to fix if it ain't broke.
They seem pretty happy with 6.3V on the heaters.
 
eddiejg
Senior tube assistant
Posts: 218
(2/7/04 12:53 am)
 heater question...
--------------------------------------------------------------------------------
 I can't help you on the noise / performance issue as I never tried it.
I can tell you that the 12AX7 is designed for 150mA of heater current at 12.6 volts when wired in series.
The common parallel wiring draws 300mA at 6.3 volts.
Just make sure that you wire the heater pins accordingly for the 12.6 volts.
Check the tube data sheet, but I think it's 1 heater wire each to pin 4 & 5 for series as opposed to 1 wire to both pins 4 & 5 & 1 wire to pin 9 for the usual parallel method.
-Ed
 
Andy Poupart
Senior tube assistant
Posts: 112
(2/7/04 1:40 am)
 Re: heater question...
--------------------------------------------------------------------------------
 There are two reasons not to run 12A*7 tube's heaters at 12.6V.

First, you'd need a separate 12V filament transformer, or another winding on your power transformer. Cost was certainly a major concern for Leo Fender.

Second, 12V heaters wired for 6V operation are humbucking. 12V operation is noisier.
 
bnwitt
Senior tube assistant
Posts: 274
(2/7/04 10:00 am)
 Re: heater question...
--------------------------------------------------------------------------------
 If I'm not mistaken, the 12.6 volt setup for these tubes was there for when a battery was the heater supply voltage. Seems like I read that somewhere.
Barry
 
Tiny Daddy
I will work on all amps
Posts: 479
(2/7/04 11:13 am)
 Re: Stupid heater question...
--------------------------------------------------------------------------------
 Reason for 6.3V is so you can ground the heater winding center-tap for less hum noise from the filament. With 12.6VAC the only option is to ground one side of the filament. But for DC filament operation there is no hum and the supply is easier to filter due to the lower current so 12.6V is used.
 
Dbltlk44
Junior tube assistant
Posts: 5
(2/7/04 11:36 pm)
 Re: Stupid heater question...
--------------------------------------------------------------------------------
 

Thanks for the replys guys!

I'd be using an additional transformer, as the PT I have is only good to light up 2 6V6's and a 12AX7...and getting a 12.6 is purty darn easy, but a 6.3 is a different story it seems these days.

DC circuit sounds like the ticket!


Again, much thanks for the replies...this newb really appreciates it! You guys are great
 
 
 << Prev Topic | Next Topic >>

 

 Topic Commands
 Click to receive email notification of replies
  
jump to:  Tube Amp Building - Tweaks - Repairs (New)New Product Suggestions (New)Praises - Complaints - Suggestions (New)Buy - Sell- Trade (New)Archives (New)    
 

- Hoffman Amplifiers - Tube Amp Building - Tweaks - Repairs - Hoffman Amplifiers -



Powered By ezboard® Ver. 7.32
Copyright ©1999-2005 ezboard, Inc.