2/8/2023 

One of the most exciting adventures is the discovery of unknown tubes - tubes that few or no people use for audio. One such tube I recently found (again) is the 837 beam tetrode. Here's a DIYaudio.com thread on it, with triode curves for this tube:

https://www.diyaudio.com/community/threads/837-tube-for-se-amplifier.125076/

My thoughts on this tube: this tube appears to be a "smaller" version of the 807 with a graphite plate.  It is the same ST16 size, with plate cap, yet the maximum plate voltage is lower (400V plate vs 700V for 807), screen voltage also lower (200V vs 300V), and the plate dissipation is only 15W vs 25W of the 807. 

Also, the socket is 7 pin, and the supressor grid is not tied internally but available to tie to cathode outside - even better, to use the capacitor trick (G3-K connected via a capacitor, value / type not critical, seems not to impact sound quality, just make sure the voltage rating is sufficient to handle full B+ plus signal swing).

And then the filament voltage is 12.6V, at 0.7A. 

Tube data:

http://www.nj7p.info/Tubes/SQL/Tube_query.php?Type=837

https://frank.pocnet.net/sheets/049/8/837.pdf

Duncan amps simulation for 01A-71A direct coupled amplifier's power supply. 

This is with parts I have: a 115V pri, 350-0-350 (60mA) sec / 6.3V/4A & 5V/4A transformer. Approx 95VA core, 5V/2A can be used for Type 80 rectifier (plus drop voltage a little to 5.0VAC)  , or 6.3V/4A winding directly for a type 81 which needs 7.5VAC for fl.