Measuring Triode-Connected Pentode Curves

[Tubes4e4]

Hi rdf,

those plate curves actually look quite good

Did you watch g2 dissipation? If it stays within reason, and you don´t want to trace higher plate voltages out of safety reasons, try to do a reasonable extrapolation at least, so actual plate voltage swing at an inductor (OPT primary) would be covered.

Tom

 

[rdf]

Hi Tom. The 814 is apparently part of the same family as 813, with lower ratings. From the strong similarity in pentode curves I had high hopes. Maximum screen voltage varies by spec sheet, one says 300 VDC, another 400 VDC. That's why the curves end soon. 900 VDC with a 560 ohm screen protection resistor showed nothing to cause alarm though, no funny glows. At lower voltages the harmonic series is pretty strong, cleaning up rapidly with rising B+. Pentode mode shows the same behaviour. I suspect with plate voltages deep into four-digits the 814 could be a corker.

Good point about the screen dissipation. I should have monitored current as well. However with my 5k, 500 VDC rated SE OPT the best I could achieve as a tremendous sounding, hideously inefficient 2 watts. With a pair of 813's and a box of 828's (hint, hint) waiting their turn I decided to leave the 814 aside for now. So many tubes, so little time!

 

[slowmotion]

And However the measured curves look very interesting so I'll post them with the warning they represent a single sample, albeit a new sample. They're also as far as I know the only 814 triode-mode curves to be found.

Thanks!

 

[aletheian]

Has anyone traced out any of the new Mullard & Tung-Sol re-issues and plotted them against the specs of the originals? Just curious-- that's one experiment I would LOVE to see.