EL34 pentode output in SSE

[Skorpio]

I am currently running my SSE with EL34 in triode connection. This is a very nice amp with approx. 5W output...

I have no UL connection on the OT and reading about Pentode connection of EL34 shown that this would be a step down in performance?

Therefore I was thinking of the possibility to use some feedback (like in Baby Huey) to lower the output impedance of the Pentode...is that a possible way to go?

What will be the penalty, besiden the need for more drive?

[Skorpio]

Here are an interesting alternative..."screen drive":

Screen Driven, DC Coupled, Single-ended EL509 Amp

[rknize]

Why not use the local, cathode feedback feature also supported by the SSE? That will clean up the pentode operation for you.

[Skorpio]

Yes, that seems to be a good idea, do you know what power to expect in pentode mode?

[rknize]

Expect around 10W with the EL34. Up to 14W is possible with a bigger tube, like KT88.

[w5jag]

Originally Posted by rknize

Why not use the local, cathode feedback feature also supported by the SSE? That will clean up the pentode operation for you.

I'm using Hammond 125ESE transformers on my SSE and, imo, cathode feedback by itself does little to tame pentode shrillness on the SSE, although it works great for linearizing (sp?) output transformers.

An additional local plate to grid (Schade) negative feedback loop has worked well for me on the SSE in pentode mode, and is easy to implement, but Schade feedback is not without its critics.

There is more of a discussion on the Schade feedback in the SSE in the 6146 SSE thread, three or four pages into it.

Win W5JAG

[rknize]

It's a different sound for sure. Not necessarily bad...just depends on your speakers and your tastes.

[Skorpio]

Thank you for your inputs!

I will look into the thread...

Do you have more detailed info about the difference in sound? What are the pros and cons....I am thinking on both Pentode/cathode feedback and pentode/Schade feedback versus a clean triode...?

[rknize]

How it sounds to you on your speakers is going to be different than how it sounds on mine. I have switches for triode/UL mode, cathode feedback, and even SS vs tube rectification. I also have a rotary switch that allows me to change the cathode resistor to run different tubes at different operating points. I don't normally run EL34s in my SSE. When I do I run them as triodes because to me that is where they seem to excel. As pentodes (UL in my case) EL34s don't sound any better than bigger tubes and lack the bass punch of something like a KT88. So when I have bigger tubes in there, they are usually in UL mode. There are a few exceptions to this, however.

Getting back to your question, I get that "warmer" tube sound with more subtle detail at lower volumes with tubes (especially EL34s) strapped as triode. In UL mode, I get more power and more bass with bigger tubes. This is great for playing rock or other beat-heavy music while doing other tasks. My speakers have horn tweeters and they get "shouty" at high volume. This is especially true on a PP amp. A triode SE amp tames them for those times when I am listening to music up close.

BTW, you will get a bit more power than I stated earlier. This numbers are for UL mode. Pure pentode mode would yield a bit more.

[Skorpio]

Thank you for you experiences!

I am at the time being satisfied with the troide connection with EL34 and I am using an active subwoofer below 50Hz, so the bass part is not handled by the tubes...

This is a Great little amp! Big thanks to George for his work!!