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SE Pentode output stage question

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Posted on November 19, 2014 at 22:35:58
DanK tubes
Audiophile

Posts: 414
Location: California
Joined: November 9, 2004
 Hi all,
I have a nice pair of single ended output transformers that are designed for parallel feed, and I was thinking of using them on a SEP output stage. However, I suspect a pentode won't work so well with choke loading. Is that correct?

I'm tinkling it might be better to use R-C coupling of a Pentode to a parallel feed output transformer, as Steve Bench shows in the link below. I'm OK with the high power supply voltage.

Any thoughts?

Thanks,
Dan

 

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RE: SE Pentode output stage question, posted on November 20, 2014 at 09:20:43
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 Unlike SS CCSes, choke loading a pentode's anode should work.

The damping factor issue remains, regardless of serial or parallel feed O/P coupling. Short loop NFB is essential.

Don't forget to regulate g2 B+.


Eli D.

 

+1, posted on November 20, 2014 at 13:03:41
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 The plate choke is (at audio frequencies) in parallel with the OPT, so as long as the inductance is high enough the load seen by the tube is the OPT primary reflection of the speaker impedance.

The feedback loop has more phase shift if you include the OPT inside the loop, so proper stability design takes on a different requirement - you can't just count on copying a series feed circuit.

 

Thanks guys! (nt), posted on November 20, 2014 at 15:03:49
DanK tubes
Audiophile

Posts: 414
Location: California
Joined: November 9, 2004
 nt

 

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