828 Triode Curves?

[lakeside]

Anybody know where I can find curves for a triode connected 828? I've done quite a bit of searching but no luck. Any help would be appreciated.

~Mike

[fbetti]

Never seen triode curves for those prewar transmitting tubes. To make things worse, can't even find their Ig2 curves. Probably never published. From available curves one can expect roughly one third of the transconductance of a 6550 or KT88. Those prewar transmitting tubes were intended to work at very high plate voltage voltage supplies up to 2kV. Triode connection would limit that to 750V. With 16W permissible g2 dissipation, should operate lazily at such ratings. Is it meant for a SE design?

[7N7]

I've just had a look at the data for this one; it looks quite interesting, though as noted above, the gm is a bit of a disappointment. Since RCA shows data for operation in AB1, I would be optimistic that it would operate OK as a triode for audio - i.e. should not have too high anode resistance.

I have never before seen a voltage specified for a suppressor grid - g3 - this is curious to me, perhaps someone with RF experience would care to comment? Perhaps there is an internal voltage inter-grid limit.

When running triode-strapped 813s I always strapped g3 to 0V - never got round to strapping it to the anode. I suppose with 828 this (a+g2+g3) may be the preferred method.

I would imagine that they may be safe to 1kV triode-strapped, but that is just a guess really. The small transmitting beam tetrode 6146B was rated at just 250V max on g2, but Philips published data which allowed 400V when triode strapped.

Of course at such elevated voltages it is best to be cautious!

I hope to hear more about this interesting valve.

Best of luck

[rdf]

They're a nice tube, I benched a few with good results using a big Hammond 5K OPT on the 4 ohm taps. ~900-950 Volts on the plate from memory without issue. I also recall data sheets varied in screen limits.