It’s been a long and weird year with COVID-19. This evidently has kept me a bit distracted and changed priorities (as probably has done to you as well). Anyhow, here are the belated curves I was asked to publish.
The SRS-551 is a lovely powerful transmitting pentode from RTF. Similar (or close enough) to RS1003 and F3a. Much more accessible in price is the SRS-551. I have a nice stash of NOS valves somewhere lost in my attic storage. Either way, they sounded nice and could definitely live in my setup. The valve was intended for audio modulation in FM transmitters so it’s very reliable and linear device. Distortion was extremely low when I measured it but most importantly it could work really well with local feedback to squeeze out 14W in Single-Ended at nearly 490V/100mA bias point with an LL1623 OPT. The distortion was below 0.7% predominantly H2.