Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Return to Tube DIY Asylum

Battery Bias; Are you using it? Why or Why not?

208.106.0.104
Posted on November 6, 2009 at 19:09:07
kellymon
Audiophile

Posts: 406
Location: N. California
Joined: September 30, 2005
 I'm finishing another amp build and I am seriously considering trying battery bias on the driver again.
Previously, when I tried it in another amp, it sounded ok, but I gave a "slight" edge to R/C cathode bias on a cap coupled 2 stage amp.
And I'm a little concerned about battery life, what happens when it fades and how do you know?
I've read most of the archives here and elsewhere.... it seemed like there was a flurry a few years ago, but not much discussion lately....

So I'm wondering, if you've tried it, are you still using it...why or why not?
robert
Suitable grid resistor for battery bias?, posted on November 8, 2009 at 02:58:39
andy evans
Audiophile

Posts: 997
Joined: October 20, 2000
 Hi - never tried this - what's a suitable grid resistor to use with battery bias for a preamp with a 26 tube?

RE: Suitable grid resistor for battery bias?, posted on November 8, 2009 at 09:26:51
Poindexter
Manufacturer

Posts: 2581
Location: Maui
Joined: November 29, 2000
 Andy, battery bias is 'fixed' bias.  Look at the device's rating for Rg-k under this service.  For directly heated valves, this rating is typically low (in ohms).  Evidently, they will draw some grid current.

Aloha,

Poinz
AudioTropic

RE: Battery Bias; OT, posted on November 7, 2009 at 10:34:58
FenderLover
Audiophile

Posts: 3309
Joined: July 31, 2007
Contributor
  Since: May 17, 2009
 Do batteries add any tonal signature to a system? Versus a conventional power supply.


Thanks!

Definitely, posted on November 7, 2009 at 12:02:21
danlaudionut
Audiophile

Posts: 3564
Location: Upstate NY
Joined: June 6, 2002

FL

The pink trace is the noise spectra of an unloaded battery.
The blue trace is the noise spectra of discrete low noise regulator.
The cyan trace is the battery with a load of 35mA.
Batteries do have noise under dynamic load.

Also read here and link below for more -
http://diyparadise.com/web/index.php?option=com_content&task=view&id=96&Itemid=5

DanL
much thanks, posted on November 7, 2009 at 23:08:39
FenderLover
Audiophile

Posts: 3309
Joined: July 31, 2007
Contributor
  Since: May 17, 2009
 Is there a sonic signature? One that a person could tell simply from listening to a unit with battery power?

RE: much thanks, posted on November 7, 2009 at 23:53:53
danlaudionut
Audiophile

Posts: 3564
Location: Upstate NY
Joined: June 6, 2002
 FL

Usually it is the lower noise floor
creating a blacker back drop for the music
which is less noise between the notes.
Some call it downward dynamic expansion.

DanL
The graph looks suspicious..., posted on November 7, 2009 at 14:34:32
Lee of Omaha
Dealer

Posts: 449
Location: Omaha NE
Joined: September 8, 2006
 The peaks correlate very well from source to source. There is no reason that I can think of that batteries and and other source should generate essentially the same noise spectra. It seems more likely that the battery is a better filter of extraneous noise. The 50 Hz peak is especially suspicious--were these spectra taken in Europe?

Lee

RE: Battery Bias Reliability, posted on November 7, 2009 at 05:56:17
Neff
 Place a dedicated volt meter on the chassis to monitor battery voltage or have test points with easy access using a remote meter.

External test points... great idea!, posted on November 7, 2009 at 14:53:10
kellymon
Audiophile

Posts: 406
Location: N. California
Joined: September 30, 2005
 Neff,
Thanks for that suggestion, I like the idea of a volt meter, but probably not on this amp.....but externally accesable test points for the battery bias is a fine idea.

I should have thought of that myself, main amp is a Dynaco ST70 and it gets checked every month or 2 via the external test points...
robert

RE: Battery Bias; Are you using it? Why or Why not?, posted on November 7, 2009 at 05:09:11
JANDG
Audiophile

Posts: 1564
Location: Washington State
Joined: February 27, 2004
 In the cathode position I have not had a NiMH read bad yet & even after 2-3 years.I allways after listening on kitchen table when building choose the NiMH for drivers it seems over R/C on cathode. Also had good luck with useing Dewalt power tool batteries ran in series if needed on cathode of outputs & even on g1 fixed bias. I like the sonics better eathier way useing batteries.
Joe
Wisdom for today.........
A GREAT tube amp or speakers will allways be GREAT & bieng relevant today is irrelevant.
Cool, thanks! (nt), posted on November 7, 2009 at 14:55:30
kellymon
Audiophile

Posts: 406
Location: N. California
Joined: September 30, 2005
 nt

RE: Battery Bias; Are you using it? Why or Why not?, posted on November 6, 2009 at 21:18:10
gluca
Audiophile

Posts: 749
Location: SomeWhere Islands
Joined: February 17, 2005
 Do you mean you want to bias the tube at the grid (1) or with a battery at the cathode (2)?

(1) it would last many many months ... I check them every 6 months and they are OK. The voltage fades away slowly so you are on the safe side

(2) get a rechargeable (capacity = 10x the bias current) and you are fine "for ever"

RE: Battery Bias; Are you using it? Why or Why not?, posted on November 6, 2009 at 21:32:27
twystd
Audiophile

Posts: 1663
Location: Austin,Texas
Joined: December 9, 2000
 I run a NiMh, on the cathodes of my 6SL7 driver, really like it, I change the batteries out about once a year to be on the safe side.

twystd

RE: Battery Bias; Are you using it? Why or Why not?, posted on November 7, 2009 at 14:57:23
kellymon
Audiophile

Posts: 406
Location: N. California
Joined: September 30, 2005
 Thanks for that, I saw in past posts that you had used it, but I wasn't sure how well it stood the test of time with you.
Good to know you still like it:)
robert

RE: Battery Bias; Are you using it? Why or Why not?, posted on November 6, 2009 at 21:30:57
kellymon
Audiophile

Posts: 406
Location: N. California
Joined: September 30, 2005
 Hi,
That would be replacing the cathode resistor/cap with a battery, in my case a NiMH @ about 1.2-1.3v.
Yes, the general rule with batteries in most applications seems to be at least 10X battery capacity vs current.
No problem there, my Duracell pre-charged (slow self discharge) NiMH says 2000 mAh and I'm only drawing 7.3 ma.

Can I assume from your reply that you use this form of bias and like it?
thanks,
robert

no, posted on November 7, 2009 at 13:14:59
gluca
Audiophile

Posts: 749
Location: SomeWhere Islands
Joined: February 17, 2005
 I always have the cathode at ground and bias the grid negative by the batteries (via the secondary coils of the input transformer). I do prefer going this way.

gianluca

Agree, posted on November 8, 2009 at 04:24:02
Naz
Audiophile

Posts: 1186
Location: Sydney
Joined: September 2, 2005
 Grid bias using lithiums makes the most sense to me. Virtually no current provides for an extremely stable and virtually noise free bias source and is out of the direct signal path where the most damage is done.

Naz

Eager to try that, posted on November 8, 2009 at 12:10:15
pix
Audiophile

Posts: 166
Location: sweden
Joined: March 18, 2006
 Hi Naz
I haveŽnt tryed that yet, byt eager to try.
Do you remove the output shunt resisistor (often 1M) om the previous stage to save battery capacity, or do you add a input cap?

Does it really make any difference if the Li-battery is serial connected to the grid leak resistor, or right on the grid
The signal circuit is the same?

Regards
Pix
Sweden
RE: Eager to try that, posted on November 8, 2009 at 14:59:32
Naz
Audiophile

Posts: 1186
Location: Sydney
Joined: September 2, 2005
 Hi Pix,

If you're not using an IT like Gluca, then this typical circuit shows a couple of examples of wiring so there is no DC idle current from the battery.



Rgds,
Naz

Page processed in 0.051 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2009, Audio Asylum, all rights reserved ] [ Go Green ] [ Take5 ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]