6CW5 / EL86 operating point

[lhgin]

Hi guys,

Hope you guys can share some of your experience with EL86 / 6CW5.

All EL86/6CW5 datasheet specifies Pa of 12W except RCA 6CW5 datasheet where it mentions that class A1 permits Pa of 14W. See below:

http://s22.postimg.org/n9ty7gnep/RCA_6_C5_W_data.png

All the others specify operating point of Pa >12W or at 100% of Pa, like follow from Mullard EL86 datasheet:
- Pentode Va 200V, Ia 64mA; Va 170V, Ia 70mA
- Triode Va 170, Ia 74mA

So, should the Pa be 14W for class A1 or it should be 12W? Has anyone run EL86 / 6CW5 at datasheet recommended points and it is working fine and ran for thousands of hours?

Thanks!
Ken

 

[lhgin]

Hmm... nobody knows the answer?

 

[aardvarkash10]

The majority of tube specifications should be regarded as general guidelines, not hard and fast laws. Try it and see.

 

[jazbo8]

To get maximum power output, Pd should be at 100%, so 14W I guess, but if you want long tube life, run it at 90% and give up a few watts. Since you are running it in the triode mode, we can assume that you are not interested in getting maximum power out of the tube, so you can lower it even more to get longer life.

What's your power supply voltage? Still can't read the schematic on the other thread...

Jaz

 

[lhgin]

Hi Jaz,

Thanks for the fast response. It is funny that all datasheet except RCA 6CW5 states 14W Pa with the classification of it running class A1. The rest all states 12W Pa only. So, I'm a bit concerned running it at recommended operating points stated in the datasheet.

My operating point for 6CW5/EL86 is 170V Va, 170V Vg2, 70mA Ia, -12.5V Vg1, 5~22mA Ig2.

Hi aardvarkash10,

Ya... thinking of giving it a go to use it at Pa at 100% (if Pa is 12W, to be confirmed). 6CW5 / EL86 are not expensive anyway.

Cheers!

 

[aardvarkash10]

I would (if I was building it) regulate the g2 supply for pentode mode. Even a simple zener string would help.

 

[jazbo8]

Hi Jaz,

Thanks for the fast response. It is funny that all datasheet except RCA 6CW5 states 14W Pa with the classification of it running class A1. The rest all states 12W Pa only. So, I'm a bit concerned running it at recommended operating points stated in the datasheet.

My operating point for 6CW5/EL86 is 170V Va, 170V Vg2, 70mA Ia, -12.5V Vg1, 5~22mA Ig2.

Hi aardvarkash10,

Ya... thinking of giving it a go to use it at Pa at 100% (if Pa is 12W, to be confirmed). 6CW5 / EL86 are not expensive anyway.

Cheers!

Sorry I missed it, you are running the 6CW5 in pentode mode and right at the 12W Pd limit per the GE datasheet I have - as you said they are not expensive anyway, so why not?!

Jaz

 

[lhgin]

Hi aardvarkash10 - yes sir, good idea.

Hi Jaz - just wondering why all the datasheets specifies 12W Pd limit but in the same datasheet itself it is recommending the operating points of exceeding the 12W Pd limit. Well, except the RCA 6CW5 as what's mentioned.

 

[jazbo8]

Hi aardvarkash10 - yes sir, good idea.

Hi Jaz - just wondering why all the datasheets specifies 12W Pd limit but in the same datasheet itself it is recommending the operating points of exceeding the 12W Pd limit. Well, except the RCA 6CW5 as what's mentioned.

I have not flip through all the datasheets, but GE's is right at 12W, if the other manufacturers recommend operating it at higher than the spec then perhaps their Pd ratings are a bit conservative and can be exceeded without damaging the tube.

Anyway, how does the amp sound?

Jaz

 

[Shoog]

I am running some PL84's at about 50mA and Va of 190V, in pentode with g2 at about 180V.
Sounds nice - but the amp has only just gone into service.

I discovered that these are hardy tubes which can take sustained red plating for quite some time without any serious harm.

Shoog

 

[lhgin]

Jaz - haven't built it yet, at the design stage. will report back to this forum when the amp is completed. from all the datasheet, only RCA specifies a Pd of 14W at class A1. the rest all say 12W.

Shoog - thanks for sharing! are all frame output tubes built hardy?

 

[Shoog]

I did get some cheap Telefunkens and they do sound considerably nicer than the Mazda ones I used for testing. They have a scary degree of turn on flash, but they settle down nicely.

Can't comment how durable the family of frame outputs are. Last time I used some EL84's I only got about a years service out of them in my LEAK Stereo 20 amp.

Shoog