• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

EF86 Sound

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#21
pentodes can have much higher voltage gains than say a 12ax7 can...
and that depends on cathode current and plate supply voltage...
gm*Rl is the universal gain formula for a pentode...

with today's signal sources, too much gain is no longer a big factor...
except for amplifier stability with global negative feedback...
 
#23
sony6060 said:
I know same brand can have entirely different sound.
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Its already been said, but in any competently built device this is demonstrably untrue.

sony6060 said:
Details like getter style, date codes, plate design, etc.
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I'll complete the sentence for you since you haven't. Details like getter style, date codes, plate design, etc. are largely irrelevant and make no difference to the operating characteristics of the tube which is designed to meet performance specifications, not construction specifications

sony6060 said:
I will buy a few different brands because tubes vary and my taste in sound nay be quite different than another audiophiles opinion.
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Again, to the extent you can actually differentiate in a blind test, no - output of tubes don't vary to an extent you can reliably identify. The rest of your sentence is a given.

sony6060 said:
But, good to get some direction vs buying every brand, particular year of manufacture, etc.
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Best you head over to AK or one of the sites that supports this belief system then.
 
#25
petertub said:
If the plate is significantly far from 100V the phase splitter will have a non-favorable working point. This might be the source of sound changes when testing different ef86 in this amp.
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Yes. This is similar to the Mullard 5-20 design and that can be quite fussy about EF86 anode voltage. If the LTP phase splitter grids are pulled too high (and hence anodes too low) you end up with grid current which loads the first stage and unbalances the LTP.

Given that, any attempt to select an EF86 is a wonderful illustration of how all you are doing is seeing how that particular sample (not brand, not getter, not year, not factory, not anode shape etc. etc.) takes current in that particular circuit.

The circuit has significant negative feedback so, apart from this voltage issue, you will not hear any difference between different EF86s. The best way to select an EF86 for this circuit is to put a voltmeter between the LTP anodes and choose the EF86 which gives the lowest voltage reading. Don't bother listening.

PS The mesh is a screen, not the anode. Why people call these 'mesh plates' is unclear.
 
#30
In an amp without nested or global feedback around the tube in question I can see how there might be sonic difference, particularly if the design is such that a 20% change in tube bias conditions could result in changes in the harmonic distortion profile.

With the large amount of feedback around the circuit including the EF86, and the competency of the original design, any perceived difference in sound when 'tube rolling' will be placebo effect.
 
#33
Are you kidding? Difference in the 12AX7 tubes I mentioned are night & day difference even on a lower resolution audio system (before my amplifier upgrades). Imagine I have a extremely upgraded audio amplifier playing into $2200 Revel speakers. I hear every micro detail.
 
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