Just changed tubes: Ruby 6L6GC vs SED 6L6GC + Bias comparison

[::XeS::]

I've just finished to swap tubes in my 6505+ and of course I tested several things for you guys.
My amps had Ruby's as stock tubes and the specifics (measured today with bias probe) were:

V1: 30mA | 495V
V2: 17,3mA | 500V
V3: 16mA | 500V
V4: 27,4mA | 495V

As you can see they were totally unmatched, or maybe, bad matched pairs...and the plate voltage was different as well (not very important).
After this test, and after cleaning the tubes sockets I swap them for a matched quad set of Winged c SED.
Here are the SED specifics:

V1: 27,3mA | 494V
V2: 25,8mA | 494V
V3: 25,7mA | 494V
V4: 27,2mA | 494V

The values are very similar, identical plate voltage and they are close to a perfect matched quad.

The third test was about the bias. I tried to max the bias pot of the 6505+ (limited range) and I reach the 60% of the maximum plate dissipation

V1: 33,6mA
V2: 31mA
V3: 31mA
V4: 33,6mA

Here are the samples of the 3 test:

Ruby with standard bias: http://dl.dropbox.com/u/1436721/Ruby_Default.mp3
SED with standard bias: http://dl.dropbox.com/u/1436721/SED_Default.mp3
SED with maxed bias: http://dl.dropbox.com/u/1436721/SED_Hot.mp3

In my opinion, the difference between the 2 sets at standard bias are really unnoticeable....very subtle...maybe the SED are more defined in the bottom end area...but still very subtle.
With the bias maxed, the SED becomes more organic in every aspect...less cold.
Conclusion: don't know if buying SEDs instead of another brand worths the price they cost (120&#8364. Considering (apart the very good construction) the very subtle differences in terms of sound, maybe a set of Sovtek for half the price should be a better deal.

Let me know what you think

p.s.
Sorry for using another time these DI's

 

[::XeS::]

Brand new tubes

 

[TheWinterSnow]

Thats the thing about new amps, the manufactures don't care about how balanced the tubes are. Now you can actually get a sound closer to that the designer intended, with the gain stages working correctly the way they where designed.

It may be a subtle difference, but in the end, it seems much larger.

 

[::XeS::]

Yes...it's a subtle difference, but I like more the new sound (maybe placebo fx?)

 

[Pot]

V1: 33,6mA
V2: 31mA
V3: 31mA
V4: 33,6mA

hi there...small doubt here:

i know the T works in pairs, so the first one would be v1+v4 and the other v2+3.
So , in order to have the pairs balanced shoudln´t the tubes be arranged like this bellow?

V1: 33,6mA
V2: 31mA
V3: 33,6mA
V4: 31mA

that would make the 2 pairs like
v1+v4=64,6mA
v2+v3=64,6mA

instead of

v2+v3=62mA
v1+v4=67,2mA

Am i wrong?

Xes, i personally think the sovtek´s wxt+ are a great choice for these poweramps as demonstraded in another thread by guitarguru...so i´d stick with those for the next retube instead of the SED's

 

[nwright]

has this amp been bias modded before?

My 6505+ has no where near that hot of a bias, even with the stock bias adjustment set to max.

 

[mburton21]

has this amp been bias modded before?

My 6505+ has no where near that hot of a bias, even with the stock bias adjustment set to max.

Peavey sends them from the factory cold as fuck; like mine was 20mA before I biased it. I just added a pot to my 5150 - after years running cold - to adjust the bias and I'm running at 37mA. Beautiful.

 

[::XeS::]

No from what I know it was not bias modded...also because I checked the resistor values last year. I suppose it's a particular version because it has an unpluggable power chord (and also a green led in the red channel and viceversa).

Pot, I don't know if you're wrong or not...I supposed they have to be considered by pairs...so V1,V4 with the same values and V2,V4 with the same values. But I'm not sure

 

[Pot]

maybe someone more knowlegdeable chimes in and clears this little doubt ...wintersnow or omegavoid ?!

Let me elaborate:
i have a stock 6505 and i retubed it with a quad of sovtek´s wxt+
the plate voltage was 522, which meant that using 6l6 tubes 70% of plate dissipation is 25.4mA
if i were tu use 6l6gc that would mean that the "optimal" value would have been 40.2mA
Refer to this link bellow
http://www.webervst.com/tubes1/calcbias.htm

the readings were as follows

V1: 24.4mA
V2: 21mA
V3: 27.9,6mA
V4: 21mA

I´ve arranged the tubes like that becuase then one pair would read 48.9mA and the other 45.4mA. (v1+v4 , v2+v3)
there´s only a 3.5mA difference but it´s the way that both pairs are more closely balanced.
I believe this is correct but i am not totally sure.
However, by using 6l6 tubes instead of 6l6gc i´m running close to "optimal" 70% plate dissipation, without having to do any biasmodding.


Maybe that´s why these sovtek tubes come along as being refered as sounding good in these amps?!

Again i´m not totally suire this is correct so, if anyone knows better please chime in.
THX

 

[::XeS::]

Yes I'm very interested too...hope any of the expert guys could chime in

 

[Omega_Void]

I´ve arranged the tubes like that becuase then one pair would read 48.9mA and the other 45.4mA. (v1+v4 , v2+v3)
there´s only a 3.5mA difference but it´s the way that both pairs are more closely balanced.

It's not necessary that both pairs draw the same current. It is best if both tubes in the same pair draw equal current.

Technical reason:

Both "push" tubes share one side of the output transformer primary, both "pull" tubes share the other.

Ideally you want the DC current to be equal in both halves of the transformer primary. Otherwise there is DC offset in the magnetic flux in the core, which would reduce the headroom before the core saturates. A small imbalance isn't a big deal, though.

 

[Omega_Void]

i have a stock 6505 and i retubed it with a quad of sovtek´s wxt+
the plate voltage was 522, which meant that using 6l6 tubes 70% of plate dissipation is 25.4mA
if i were tu use 6l6gc that would mean that the "optimal" value would have been 40.2mA

Sovtek 6L6WXT+ = 6L6GC.
See here.

Your calculation for 6L6 dissipation is corect, but you've forgotton something: max voltage on 6L6__ is 360V on the anode and 270V on the screen. Only 6L6GC is rated for 500V. You wouldn't want to put 6L6GB or similar on a 522V B+.

 

[Pot]

Thanx Omega Void

"It's not necessary that both pairs draw the same current. It is best if both tubes in the same pair draw equal current"

Ok, so Xes had his tubes arranged correctlly...i though it should be the same current has u refered (always learning)
I messed up on that wxt/6l6 thing (noob), so the rest of my line of thought crumbles...i may have confused myself with the sovtek´s 5881,6l6wgb , although they aren´t 6l6´s also...

Might have to consider a bias mod on mine sometime in the future

 

[Omega_Void]

i may have confused myself with the sovtek´s 5881,6l6wgb , although they aren´t 6l6´s also...

If it's Sovtek, who knows what's in the tube. Their KT66s are apparently just 6L6GC in a bigger bottle. I nearly bought a pair of them!