6L6, 6L6GT, 6L6GC, 5881, 7027, KT66...

[mr2racer]

Hello all,
Has anyone ever seen a comparison of these tubes? They seem to be listed as interchangeable by most sellers. Does one sound better than another? I mean is the variation between type greater or lesser than by manufacturer?


Kevin

 

[toprepairman]

There are differences in anode dissipation, and the KT66 requires slightly different bias.
Don't, for example, put 6l6's of any kind into a Quad II, unless you change the cathode bias resistor.

 

[DigitalJunkie]

...EL34/6CA7,KT88,KT90,6550,et al.

They all have the same socket/pinout (more or less),but I'm not sure I'd go as far as "interchangeable". They are all fairly similar tubes,and can be subbed into most circuits with some adjustment of the bias voltage,etc. !But not always!

Just be sure to do a little homework before you start swapping tubes around,you don't want to blow up your amp/tubes.
If you aren't quite sure,ask here and someone will steer you in the right direction.

 

[Eli Duttman]

Another thing about the KT66 is increased heater draw.

The best deal around in 6L6 family tubes may be the Russian 6П3С-Е (6p3s-e). Be sure to buy thoroughly tested stock from a reputable dealer.

 

[carbondated]

There are differences in anode dissipation, and the KT66 requires slightly different bias.
Don't, for example, put 6l6's of any kind into a Quad II, unless you change the cathode bias resistor.

Just curious, to what value? That's R12 (180R) for KT66s... the good ones are getting harder to find!

 

[mr2racer]

Hey all,
I have a collection of NOS 6sn7's. I need two good tubes for the amp I intend to build. I have two RCA GTB's, one CBS, one Sylvania, and one GE. I also have one GE GTA, one Sylvania GT and one Zenith GT. All these tubes are NOS and tested great. The obvious choice is to use the RCA GTB's because I have two. But if one of the others is inherently better it might make sense to buy one to match?
I found the attached review.
Kevin

 

[toprepairman]

Hi Carbon.
From memory optimum value would be around 240R.
You might get away with 220R if you made sure you used 6L6's with highest dissipation.
If you don't mind a small drop in power then 270R is a safe value.
Henry

 

[richwalters]

The 5881 with 20% higher dissipation than the 6L6, has in comparison been out of the race. On paper the 5881 should be better. Why hasn't it ?

richy

 

[toprepairman]

The few Russian 'short' base 5881's I've used have been really good.
Of course I don't thrash them to within an inch of their lives like some do.

 

[Borus]

And do not put a 6l6 in the socket labeled 7027 in an Altec amp. All well be lost.
The extra pin is hot.

 

[DigitalJunkie]

Yes,you will want to inspect the pin connections on your particular amp. The 'extra' (un-used) pins are sometimes used as tie-points for grid resistors or other stuff. This can be a serious problem in some cases! (Vg2 on the envelope of a metal 6L6 is not fun.) But,that can usually be re-arranged in an evening with some soldering.

Eli made a good point about heater draw,you'll want to double-check that too.

I'd say some guidelines would be..
-Make sure you can cover the heater current draw of the tubes you intend to use.
-Make sure the tubes you intend to use can take the B+ (Va/Vg2) that your amp will feed them.
-Make sure you can adjust the bias to a range suitable for the tubes you intend to use. Either the -Vg1 voltage for fixed bias,or the cathode resistor(s) for cathode/auto bias.

Once you've got those 3 things covered,I'd say you're free to experiment without major catastrophe.
The load impedance,etc. may not be right for the tubes you intend to use,but that shouldn't cause any MAJOR issues besides sounding different.

Another thing I seem to vaguely remember is that some tubes have G3 internally connected to the cathode,and some have it brought out to a separate pin -another reason to check the datasheets,and your socket wiring!
You may need to add a jumper to the cathode(or ground) for G3. 6CA7/EL34 seems to stick out in my mind,for this reason.

 

[ixe13]

Just curious, to what value? That's R12 (180R) for KT66s... the good ones are getting harder to find!

Carbondated,

If you're refering to the cathode resistor in a Quad II, I had to increase those resistors in my Quad II, (240 Ohms), to decrease the dissipation on the KT-66 I'm using.

I had to do that cause the main in Montreal is around 120Volts, instead of the 115/117 volts the amp were designed for.

I ended up with a higher B+ in both amp. Of course you would have to measure the values in yours.

Now the dissipation on the kt-66's is 19 watts (still a bit high to my taste).


As far as KT-66 goes, I'm using Gold Lion in both Quad II, they have 350 hours on them right now, and they are rock solid. The bias didn't move at all on any of the four tubes.

In these Quad, I tried electro-Harmonix 6l6gc, JJ 6l6GC, Sovtek KT-66, and the Gold Lion are the one I find (according to my ears) that sound the best.

Since, I already increase the cathode resistors, the 6L6GC were within their dissipation range. Even a bit low I'd say.

Anyway, the 6l6GC has a 30 Watts maximum dissipation , and the KT-66 is 25 Watts.

In any circuit, the thing to watch also is how much current the tube will draw and and make sure your power transformer can take it.

 

[TheGimp]

I realize this was not on the list, but can anyone tell me the difference between a 6V6GT and 6V6GTA?

The only listing difference I've found in spec sheets states there is a difference in filament ratings but does not elaborate.

Both contain similar heater warm up surge statements.

 

[chue]

6L6 tubes

hi, i'm new to diyaudio and am looking for information about substituting tubes in my mac mc60 monoblocks. my nephew sat on one of my amps and broke a tube, KT88. they are quite expensive to replace matched pairs so i was wondering if 6L6Gt tubes may be a good substitute b/c i have matched quads of these.
if i can just substitute these tubes would the only sacrifice be a little loss in power and maybe bass?

thanks, e

 

[mr2racer]

If you don't have an amp that uses the 6L6's why not sell them on Ebay? Then send the one tube you have that matches the broken tube and have someone match that? That way you only have to buy one tube and will probably come out ahead. I don't know where you are but Tube depot in Memphis could do it for you. And the shipping would be nominal.

 

[Rodeodave]

hi, i'm new to diyaudio and am looking for information about substituting tubes in my mac mc60 monoblocks. my nephew sat on one of my amps and broke a tube, KT88. they are quite expensive to replace matched pairs so i was wondering if 6L6Gt tubes may be a good substitute b/c i have matched quads of these.
if i can just substitute these tubes would the only sacrifice be a little loss in power and maybe bass?

thanks, e

No, a 6L6gt will not work in a McIntosh MC60. Only 6550 or KT88 will work.
AFAIK a 6L6gt has a max. plate voltage of 350V, but an output tube in an MC60 sees around 430V anode voltage. A 6L6gt won't survive that.

 

[toprepairman]

Definitly agree with Rodeodave there, a good 6L6 might just survive the volts, but not the dissipation.

 

[chue]

6L6 tubes

thanks for all your help. i had these tubes from long time ago for a pair of mc30's that i have stored away and forgotten about. you're all right that it would not work on my mc60's and thanks for your suggestions about getting matched tube to replace my one.

the reason i put away my mc30s was one day while playing some music one amp had a big blue flash across all the tubes. i powered down right away and put it aside. well, out-of-sight-out-of mind. then i came across a pair of mc60's and have been using them until the nephew problem.

i have some time now to pull out the mac30's to check. but they've been in storage for over 15 years. any suggestions how to proceed?
i do have a dvm and scope and a little electronicc background - mostly digital but would like to develop some skills in analog. i am aware of high voltage dangers. too bad they don't teach tubes in school anymore.

thanks,
ed