GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Audio Discussions
In the Thread: How to get a LOT of SET power.

Post Subject: GU81 considerationsPosted by N-set on: 4/17/2011

Paul, don't get me wrong--normally I'm not choosing a tube by the power, but this situation is somehow special.
There are very few tubes which have the right electrical parameters (gm, mu, power, etc) to start with. In the
small tubes word one can glaze hours on the curves, trace them himself and then choose to whatever
factors. Here we have what we have. Few +/- aplicable tubes and the curves traced for class B-C opertion.
It's all a gamble. BTW, I've located a Dutch guy at DIYAudio who has been building around GU81M, and monsters like GU5b.

GU81M curves do not look that disastrous: observe that the knee (esp. 0V) seems softer.
I'm wondering how to drive it in A1. Will it need power?
I'd like a very linear triode with mu=30-33 at least and ideally 20W plate diss. SV572-30? 812A? 2x6E5P??
I'm wondering why Romy in his wishlist prohibited paralled
drivers but would happily accept paralled output tubes???

Below is something which may be breadboardable with a single 6E5P
(provided my power tranny can stand the current and I teleport 3000km).
I have no idea how to power the screen properly (500V wrt the cathode, 50mA!).
A separate supply with VR string to give 500V? Now is the RC circuit (no idea how to get C from the data).

With the 833 A2 idea I'm a bit stuck: i've spiced 6E5P -> EL34 (triode) -> 10:1 -> 833 and
EL34 will not give enough swing (the main limiting factor is 425V screen max, plate can stand 800V)

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