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Proper location for the hotter power tube

Rambergwest

Member
Messages
914
Something I have been thinking about regarding unbalanced power tubes is, does it matter which side the hotter tube is in when one is producing more gain than the other? Assuming that the power tube closest to the phase inverter is going to produce the positive side of the waveform, should it get the hotter tube? What are the factors governing this relationship? Simply stated it would seem that the stronger tube would exert more control over the voicecoil and cone so this should result in something audible. Has anyone swapped the two to see if it can be heard?
 

Davo17

Member
Messages
2,170
Kinda like reversing the leads on a speaker, Im going to guess it makes little difference.
 

Rambergwest

Member
Messages
914
I hear what you are saying and that makes sense. I guess I could answer my own question but I just wondered if some of the members might have first hand experience. I will put in a set that is 2-3ma apart this evening and see if I can tell a difference when they are swapped.
 

Davo17

Member
Messages
2,170
I hear what you are saying and that makes sense. I guess I could answer my own question but I just wondered if some of the members might have first hand experience. I will put in a set that is 2-3ma apart this evening and see if I can tell a difference when they are swapped.
Its worth a shot, let us know.

Id also be interested in your findings with mismatched tubes.
 

zzmoore

Member
Messages
7,215
If there is a Phase INVERTER, both tubes see a positive wave, If not, one tube would go from quiescent (idle) to cut-off, and there would be no push-pull amplification.
It will not "matter" which socket it goes in.
Best
 

wyatt

Member
Messages
4,168
I hear what you are saying and that makes sense. I guess I could answer my own question but I just wondered if some of the members might have first hand experience. I will put in a set that is 2-3ma apart this evening and see if I can tell a difference when they are swapped.
Those are so close I can't see how there can be any perceivable difference.

If you wanted to test, I would test with a set beyond "matched" status (>5mA for large octals, >3mA for 6V6GT's and EL84's).
 

Rambergwest

Member
Messages
914
Very good feedback and fortunately I have an "ebay matched set" of 6v6s that are about 6ma apart ;-) they should do fine.
 

Rambergwest

Member
Messages
914
The test tubes were a set of very vintage Sylvania 6V6GT with plate voltage at 419Vdc and the tubes were biased at 19.8ma and 14.6ma. There was a noticable difference in headroom with the tubes in one way as opposed to the other. With the stiffer tube in the spot closest to the PI it seemed more clear and controlled overall.
 

pb641

Member
Messages
276
Those are so close I can't see how there can be any perceivable difference.

If you wanted to test, I would test with a set beyond "matched" status (>5mA for large octals, >3mA for 6V6GT's and EL84's).

Exactly. Unless something else has headed south, I can't imagine anyone noticing a difference at 2-3ma. I also agree with Wyatt's quoted specs. At ~2-3ma, those tubes would be "matched".
 

Rambergwest

Member
Messages
914
Bias is just a tiny bit different between sides 1-2 tenths of a ma so no reason to suggest any impact there. As I have it internalized, in a push pull configuration one tube works the positive half of the wave form and one works the negative. Crossover distortion is what happens at the transition between tubes. The proper description would be that one tube "sources" currrent and the other "sinks" current.
 

Blue Strat

Member
Messages
30,217
2-3mA isn't audible in any way in a blind test. I don't think it (which socket you put the hotter tube in) would matter even if the mismatch was much wider.
 

Rambergwest

Member
Messages
914
A little confusion in the last few posts, The two power tubes were 4.8ma apart as I indicted in my initial posting of results. At the suggestion of a member I went back and measured the difference in current draw of each tube in each location to eliminate a socket level difference in positions. My last post just followed up to indicate that each tube measured essentially the same regardless of position and they stayed 4.8ma apart.
 

MCK

Member
Messages
1,862
As a general rule I tend to put my hotter tube farthest from the PT / OT since it will be running hotter and heat from the PT/OT could make matters worse.
 

MCK

Member
Messages
1,862
Kinda like reversing the leads on a speaker, Im going to guess it makes little difference.
Oh but swapping speaker leads do make a lot of difference... Especially if you run multi-amp setups or play with others in a band setting etc. Read up on phase and phase cancellation. Its not a myth.
 

Davo17

Member
Messages
2,170
Oh but swapping speaker leads do make a lot of difference... Especially if you run multi-amp setups or play with others in a band setting etc. Read up on phase and phase cancellation. Its not a myth.
No question when it comes to multiple speakers, or when placed in nodes etc. I was referring to the supposed difference in reversing the speaker leads into a single speaker.
 

MCK

Member
Messages
1,862
No question when it comes to multiple speakers, or when placed in nodes etc. I was referring to the supposed difference in reversing the speaker leads into a single speaker.
I think it still makes a difference but lets not take it OT...
 






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