Topic: Question on UL tap and tube getter

[wipeout]

Question lang about OPTs, specifically the UL tap.  Usually it is at 40% tap.  If the full winding tap of the primary is at ex. 100 ohms, 40% tap is with respect to which terminal?  B+ or Plate?  Is it directly translated as 40 ohms from B+ terminal? (if that's the answer to my previous question).

Another thing about tubes.
When does the getter activates?  When you buy a brand new tube, does it have the mirror-like area on the glass envelope?  Or it happens only after you initially powering it up in a circuit?  Or does it have that mirror like look on the glass after leaving the factory?

I had a power tube (KT88) which has 3 getters.  One on top, and 2 on the sides.  The one on top has a good mirror look.  Those on the sides look as it just about to activate, slightly smoky and only occupies a small area compared to my other healthy tube and you can still see the getter inside.  I believe that when the mirror portion had turned to white, there could possibly be a leak in the tube and is unusable.  Can you tell if the tube is considered faulty?  Pics are attached below.


Side view of the side getters


top view of one of the side getters


In comparison with a healthy tube (right)


In comparison with a healthy tube (right) showing the other side getter

Thanks a lot 

[ATJr.]

http://www.electronicslab.ph/forum/index.php?topic=25478.new#new

[qguy]

The getters are supposed to absorb any left over gasses inside the tube, overtime the side getter  gets smaller and smaller. An instant turning to white means a crack or leak.   My 9 month old GL KT88 tubes has the same condition as the ones you posted.   The GL tubes side getter seems to shrink faster than my Tungsol 6550 tubes.

Qguy wonders why the top getter does not seem to change for both Tungsol 6550 and GL KT88

[ATJr.]

over time also the getter get spent up, that happened to one of my 6bq5's, the getter did not turn white, is just faded away, the filament still lights up, but tube function is gone....

could also mean an impending loss of the tube...better use it while there is still life left in the tube....

tubes fail anyway eventually....this getter business is just one way tube dies...

[juanbote]

ULTRA-LINEAR OPERATION, also known as DISTRIBUTED LOAD OPERATION, is a term when applied to push-pull audio amplifiers, that describes the particular output stage configuration whereby the Screen Grids (Grid 2) of Tetrodes, Pentodes or Beam Power Tubes are fed from a tapping in each half of the primary of the output transformer - typically 43% turns or 18.5% impedance when measured from the centre-tap, instead of from a DC supply either independent or common to the anodes.

The sonic properties of the ultra-linear output stage configuration - albeit single-ended or push-pull design - are midway between triode and tetrode/beam power tube "tone".

Some audio-engineers describe the sound of triodes as "smooth, sweet, mellow, natural" and tetrode/beam power tubes as "clean, bright, sharp, punchy".

[ATJr.]

^good to see you here john......

additional info: http://www.aikenamps.com/UL.pdf

i have built 2 ultra-linears and 2 pentode push-pull amps, and the comments by those who heard them was that pentode seems to give better bass.... and i will attribute that to a well regulated screen grid or G2 voltage....

[juanbote]

Hi Tony,

It is true that speed, attack and good bass belongs to pentode amps with regulated G2 like the Audio Research amps but I also fancied the musicality and sweetness of ultralinear amps like the Dyna ST70.

It is really to each individual preference whether which configuration would be best.

I modified the biasing of the Dyna ST70 to individual bias and It ended up a speedier beast. And goodbye to a match quad EL34 purchase's and can prolong  tube hours due to optimal biasing option. The  biasing circuit of the Dyna ST70 is prone to bias current imbalance in the long run and can result to poor performance due to unequal cathode currents on the output tubes. Performance of pushpull amps is not limited alone to tranny output winding configuration but also to circuitry, core materials, wiring techniques, chassis, etc... but importantly Tube amps are known by their output tubes.

[ATJr.]

yes, with individual grid biasing, matched pairs or even quads are not nescessary.....