How to optimize sound if change from 6L6 to 6V6?

[Alan0354]

I did an experiment and posted a video comparing 6L6 to 6V6 in my Pro Reverb. I did comparison:

Compare sound of different power tubes with the same amp. - Fender Stratocaster Guitar Forum

My questions:

1) Do you think people are bias and think the 6L6 sounded better because it's "original"?
2) If you think the 6L6 did sound better, why? I even adjust the bias current as described. Yes, there is impedance mismatch, but from my experience, mismatch in impedance does not change the sound, just lower power some.

Any suggestion? I really want to adapt 6V6 into the amp to lower the power.

[big_teee]

6L6 and 6V6 tubes have different operating parameters.
They require different HT voltage requirements, and different tube HT primary inputs.
Use the one right for your needs.
Whatever tube that particular amp was designed for should sound best.
T
**Sorry, I took out the sentence Lame!
Don't want to offend anyone.

[Alan0354]

I did the comparison using switch to lower the +B to 400 volt for 6V6, it did not help, it make it even muddier. I adjust the bias current accordingly, I don't know what you mean about lame. The only thing I see is the load impedance mismatch. I did try to match back the impedance using 8ohm speaker instead of 4 ohm designed for 6L6. It did not help a single bit. What is not within the parameter?

In this comparison in post #143, I change the +B to 400V for 6V6. So I did try to fit the parameter for the 6V6:

http://www.strat-talk.com/forum/amp-...-reverb-8.html

[big_teee]

Sorry, I took out that sentence, I don't want to offend anyone!

[big_teee]

I listened to your clips again.
IMO, strictly my opinion, but a good set of custom Vintage type Pickups would do you more good than anything!
A good set of Single coils wound with heavy 42 AWG wire would bring out the tones of your Fender amp.
Like I said strictly IMO, and I have heard a lot of different Pickups.
T

[g1]

Yes, there is impedance mismatch, but from my experience, mismatch in impedance does not change the sound, just lower power some.

Impedance mismatch does change the sound and frequency response. It's like using the impedance switch on an amp to mismatch to a cabinet. The difference in tone will probably be more noticeable than the difference in power.
Some manufacturers that use robust OT's suggest experimenting with the impedance switch for tonal variation, or to "color the sound".
This is why you are not really getting a fair comparison of the tube types. You are hearing what a 6V6 sounds like in a 6L6 circuit.
Check with 6L6 only in the same amp on a scope. Take measurements at various frequencies, then check again with impedance mismatch. You will see there is quite a difference in frequency response.

[Alan0354]

I listened to your clips again.
IMO, strictly my opinion, but a good set of custom Vintage type Pickups would do you more good than anything!
A good set of Single coils wound with heavy 42 AWG wire would bring out the tones of your Fender amp.
Like I said strictly IMO, and I have heard a lot of different Pickups.
T

So you don't think the quality of sound is not much different between the tubes in the first video. I honestly think the only one I like less is the EL84 as it is quite stinging. The 6L6, JJ 6V6S and Ruby 6V6GT all sound very close and I think it can be adjusted out by slightly adjustment of the tone controls.

[Alan0354]

Impedance mismatch does change the sound and frequency response. It's like using the impedance switch on an amp to mismatch to a cabinet. The difference in tone will probably be more noticeable than the difference in power.
Some manufacturers that use robust OT's suggest experimenting with the impedance switch for tonal variation, or to "color the sound".
This is why you are not really getting a fair comparison of the tube types. You are hearing what a 6V6 sounds like in a 6L6 circuit.
Check with 6L6 only in the same amp on a scope. Take measurements at various frequencies, then check again with impedance mismatch. You will see there is quite a difference in frequency response.

I did compare by switch between one speaker( 8ohm) and two speakers in parallel(4ohm) for the 6V6, I don't hear any difference other than the two speaker sounded a little fuller for obvious reason........I had two speaker in front of me and it cover more area!!! The sound characteristics are the same. That's the reason I did not bother to change the impedance for the video. But I did adjust the bias of the tube.

6V6 has higher plate resistance, I know the Pro Reverb is designed for 4ohm. So if I cut one speaker, I double the load on the 6V6. I adjust the bias, I adjust the +B, I adjust the bias, I adjust the load impedance for the 6V6. I think my test is valid comparison. The only thing I did not do is I did not adjust the tone controls to optimize the sound for the tube.

[daz]

Yes, there is impedance mismatch, but from my experience, mismatch in impedance does not change the sound, just lower power some.

you sure about that? I have a amp that i use el34 in but i have also used 6l6 and 6v6. If I run 6v6 in it mismatched it sounds a hell of a lot different than if i drop it from 8 ohms to 4 for a more proper match. In fact, theres more difference between 6v6 when matched vs mismatched than there is between 6v6 and 6l6 in MY amp. That said, maybe it's very amp dependent, but in mine not only does the volume drop considerably when i don't drop the impedance selector, but the tone gets darker and fatter. Kinda nice actually, tho i'm not sure i'd feel good about running it like that.

[Alan0354]

you sure about that? I have a amp that i use el34 in but i have also used 6l6 and 6v6. If I run 6v6 in it mismatched it sounds a hell of a lot different than if i drop it from 8 ohms to 4 for a more proper match. In fact, theres more difference between 6v6 when matched vs mismatched than there is between 6v6 and 6l6 in MY amp. That said, maybe it's very amp dependent, but in mine not only does the volume drop considerably when i don't drop the impedance selector, but the tone gets darker and fatter. Kinda nice actually, tho i'm not sure i'd feel good about running it like that.

The main difference is two speakers sounds bigger. I tested it in a small room, so I am right in front of the amp. Two speaker gives a much wider wall of sound. But that's about it. Of cause the volume drop when I disconnect one speaker, but the sound is very much the same.

I understand impedance can affect the frequency response limit of the circuit, but guitar amp is only to 5KHz, I don't think it affect the frequency this low.

Bottom line, I personally do not hear there's a big difference in quality. Sure, they sound slightly different, but not better or worst. I question whether people are a little psychosomatic that they pick 6L6 in the comparison because it's supposed to be original.

[Alan0354]

I do notice the sound is a little darker with the Ruby 6V6GT at 400V. It's not necessary bad. But the JJ 6V6S is not darker.

But that is to be expected, different tubes has different sound. But I don't consider one inferior than the other. I am just showing you the result of others comment and want to find out is there anything that I missed other than impedance mismatch?

BTW, I don't see any danger running with load impedance double the plate impedance. Yes, the tube saturates faster, stressing the tube a little more. Other than slightly shortening the life of the tube, what else can go wrong?

[Dave H]

...is there anything that I missed other than impedance mismatch?

You should disconnect the output stage negative feedback to really hear the difference between tube types.

[Alan0354]

I did an experiment in the sound with matching impedance vs mismatch. I my experiment, I use 6V6GT with output transformer that has 4K primary and 4,8,16 ohm output. I know 6V6 match with somewhere around 8K ohm. So I use the 4 ohm tap and drive an 8ohm speaker will give 8K at the primary.

In my experiment, I used a switch to choose between the 4 ohm tap and the 8 ohm tap to drive the 8 ohm speaker. I notice there is a slight change in sound in favorite to the 4 ohm tap ( match condition). The sound is slightly more aggressive, like increase the bias current. So I agree the sound slightly improved with matching condition.

I cannot tell from before as switching speaker in and out itself make too much of a difference and cover up the real difference due to impedance alone. This experiment with switch enable me to switch in split second and have a much better comparison. But, still, the difference is very small to my ears. I had to switch back and fore many times to conclude there is a difference.

[daz]

Maybe it's amp dependent, but on my marshall style build it's the largest tonal difference i have ever noticed when using the selector to mismatch or mach any tube. Enough so that i have no doubt anyone would notice it easily. I have not however tested whether or not it is that different with or without NFB using my variable NFB knob which i made into a no load pot so it goes open for zero NFB at the end of it's throw. i probably haven't tested it with NFB since i use it w/o most of the time, or at least with minimal NFB.