"El Cheapo" with EL86-triodes?

[artosalo]

I’m curious if you have any thoughts on why you are able to run your EL86’s in UL mode with almost 300 Vdc across the tubes, while others seem to get screen current runaways at above the datasheet max screen voltage of 200 Vdc.

Actually (Philips EL86) max. Ug2 and Ua is 250 V, not 200 V.
In addition this is "Design centre rating", not "Absolute maximum".
The reason I have not had problems is obviously that have used tubes with total dissipation of less than 10 W, while max. is 12 W + 1.75 W.
My experience is that excessive plate/screen voltage alone with UL or triode mode is not harmful while total power dissipation is hold under limits.

 

[Francois G]

Thanks, artosalo.

You explanation makes sense and is encouraging. Indeed, I found a Philips data sheet that agrees vir your EL86 design centre rating of Ug2=250V. However, GE shows 220v, and Mullard 200V, and Philips itself shows 200v for UL84 tubes! I wonder if there really is a difference in the max screen voltage between these manufacturers. But I accept the notion that management of screen and plate dissipation is perhaps more important than the Ug2 voltage per se. I’m currently building a Baby Huey with EL86 outputs, and this gives me a bit more confidence in my intended operating conditions.

Just to be sure, you are also using Russian 6P43S tubes at these operating conditions?

 

[artosalo]

My Mullard data sheet shows also 250 V. If you feel that 300 V is excessive, just use 250 V and still get >15 W as UL.
However, I have used soviet 6P43P-E in all of my tests.
6P43P-E Russian Tubes - Old Schematics

 

[Francois G]

Thanks! I don’t mind trying Ug2=300V in UL at all, especially since you have proved it in practice (at the reduced dissipation) using 6P43S tubes that specifies Ug2 <185 V.

And I will not hold it against you if I blow up any . I have a lot of them.

 

[Kay Pirinha]

Isn't the 6P43S the same tube that was marketed by Svetlana under the SV83 moniker?
Best regards!

 

[Eli Duttman]

SV83 = 6Π15Π

 

[artosalo]

6P43S? I think you mean 6P43P-E. The specification is at the previous link I gave.
This has the same 250 V max. Ug2 as EL86. That 185V is sort of typical/suggested value.

 

[Francois G]

My apologies! I meant 6P43P. I have in fact the -E version. I had trouble understanding the Russian datasheets. Thanks for clarifying that their Ug2 = 250 V max.

Now I have to finish my 6P34P-E Baby Huey, and then build a 6P43P-E el Cheapo. Who knows if I will get to also do your schema, artosalo, but thanks a lot for sharing your experience with these, I think, under-appreciated tubes.