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Real power pentode recommendation

CijTele52

Member
2005-02-01 7:02 am
CA
Can anyone recommend real power pentode for audio other than EL84 and EL34? Ones that are not scarce like European's EL60 or 4699.

There are some threads that suggest beam power pentode but I'm looking for real pentode in affordable price. Thanks in advance for your help :)
 

Ketje

Member
2012-12-19 7:24 pm
Flanders

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Parafeed813

Member
2012-08-15 8:24 am
An old favorite of mine is the EL41. I tried it once in SE triode. Close to 1W output and I loved it :cool:. It is a smaller ancestor of the EL84, rated at 9W and just about every European factory made it. Rimlock base.
Haven't tried it yet, but the EL90 Is a 12W pentode in a 7pin miniature base. Often listed as equivalent to the 6AQ5, but that one is smaller and a beam tetrode.
Go big: EL156. 50W pentode made only by Telefunken. There is a Chinese copy with an octal base.
 
It's hard to beat the EL34 and EL84, when selecting true, 3 grid, power O/P tubes, for use in combination with ultralinear mode. They have tough screen grids. Another nice "12" W. true pentode is the 6CH6/EL821. Here, g2 is not especially tough. So, put 1 KOhm resistors in the lines leading to the UL taps on the O/P trafos, to ensure the g2 dissipation limit is not exceeded.

If you have the requisite "deep pockets", custom O/P "iron" with tertiary separate screen grid windings is THE way to go. You get the local NFB of UL mode and the benefit of regulated g2 B+. :yes:
 

tomchr

Member
Paid Member
2009-02-11 12:58 am
Calgary
www.neurochrome.com
If you have the requisite "deep pockets", custom O/P "iron" with tertiary separate screen grid windings is THE way to go. You get the local NFB of UL mode and the benefit of regulated g2 B+.

Do you mean suppressor grid (G3)? An UL OPT already has a wire for G2. G3 is normally connected to the cathode. Or am I missing something really fundamental here?

Which turns ratios do you recommend for the G2 and G3 taps?

~Tom
 
Tom,

With separate screen grid windings, regulating g2 B+ is feasible. It's still UL, as the tertiary g2 winding is a % of the plate winding. It's well known that max. open loop linearity in pentodes occurs, when g2 B+ is regulated at a fraction of anode B+. Having a separate tertiary g2 winding allows the cake to be eaten and retained, simultaneously. In "standard" UL "iron", g2 B+ can't be regulated. "Money talks and bull$hit walks."

The handling of the suppressor grids is unchanged.