The filament PCBs arrived today and I soldered up two prototype boards. These have connectors at the voltage drop resistor pads so I can try different values and determine what values I will need for each tube to not give too much to the current regulators. The look absolutely gourgeous :)

Ordered some supply chokes and transformers for the 170V and 500V supplies. I've added four windings on each B+ transformer so I have some room to play with and not end up with more iron in the future that is a one trick pony. The filament windings have been moved to their own transformer to allow seperate switching to let the mercury diodes warm up before applying high voltage to the anodes in case of the 500V supply.

At the moment I am contemplating adding the Usagi preamp stage into the chassis of the Yokimbo output stage to save some desk space by having one preamp chassis and one or two power supply chassis  less as they could be integrated with one another. A high Dunker factor is nice and all, but not really wieldy or pratical.

A really nice tube on the datasheet, but after testing it seems there is a LOT of margin in the specs as you can see in the table below.

The current at the 150V/-1.5V bias has a range between 12 and 33mA, discounting the 45mA outlier. That is almost a factor of 3. The rp and µ are also all over the place.

Added the 4P1L configuration and curve data files.

Check here for the download link

Getting some parts in for upcoming amp builds. This box is still on it's way to me, but will keep my eTracer running for a while when it shows up :)

The 4P1L will get it's own dedicated amp at some point, and may make it into the preamp in a shootout vs the 26, or into the 801A amps. Who knows. Hoping it is as good as people say it is.

I had a 1626 laying on my desk, the eTracer within reach and a boring movie playing on the PC. I had to do something while watching. I tried lowering the filament voltage on the 1626 to see if there is any pattern to emission. Below are the results.

NOTE: This is a new tube right out of the box. It would be interesting to see the same test with an older tube.

Updates the eTracer files. Check here

This tube is very close to the 5842 and makes a nice affordable alternative, bias is just slightly off. Glass envlope is taller than the 5842, about the same as the regular 12A*7 noval tubes, although anode dissipation is rated lower than the 5842. The DR version is an extra long life (10.000 hours) and selected version of the regular 6S4P tube.

A really nice tube on paper; it's an E180F equivalent and when triode connected comes close the the specs of a 4852. I have two batches of these: one normal and one with thelong-life E variant which also has a taller glass envelope.

As you can see, despite having a large sample size, it is hard to match these tubes into pairs. Just like the 6Z11P, the specs vary enormously, making matched pairs hard to find.