Prologue 2.0



topology:  single-ended Class A driver: Raytheon 5842Q sound quality: TBD
rated output:  ±750mW output: Hytron 1626 fun factor:  8/10
input sensitivity:  ±1Vrms rectifier: 5Y3 hernia scale:  9/10





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This is not a new amp, or cutting edge... It's a rehash of my old 1626 amp for the sake of being my first build after a 15 year break, so that I can get an easy start. Plus the not unimportant fact that I have all the parts still packed away in boxes; in other words almost zero investment needed.

It's a simple enough schematic with a single tube driver that has enough gain and drive capability to push the 1626 to full output with a ~1Vrms input signal. The 5842 is choke-loaded which means the gain will aproach the mu of the tube while offering a low DC resistance and allowing for a lower B+ voltage. I'm still wondering if that is a pro on this amp as I wanted to have a single supply per channel which would mean I need to add an RC stage to drop about 60V, kind of making the low Rdc of the choke a moot point.

The output stage is a little different from my old amps, that all used cathode bias. This amp will have a negative grid supply and will be an experiment for the future DHT amp. I'd like to tinker a little with this amp to get back into the groove so to speak. There might even be an altered driver stage to test what all the pentode fuss is about; substituting the 5842 with a D3a or russian 6Z9P in triode mode. Who knows.

The filament supplies are a little OP for this amp, as the IHT filaments aren't that fusy, but again this amp is a testbed for the future DHT amp rebuild and I'm thinking of having some PCBs made for the raw DC supplies.

With all the pointers to this being an experimental platform, it is unlikely I will be making a chassis for it until everything has crystalized and I have also started on the new amp system. I'd like this amp to stay together and act as a backup, and also the possibility to make a tri-amped system if/when I build the 3-way system with JBL/15"/tweeter.


Slowly taking shape. Have to get back into the swing of things.

Signal section

The signal section (preliminary design)


Raw DC for filaments

The raw DC supply for each channel's filaments. There will be seperate regulators behind this for the 1626 (12V) and 5842 (6V). It's a little over-engineered for the filaments of these tubes, but I might have some PCB's made for the future DHT amps, so I'm thinking ahead a bit and standardizing things (for how long that lasts).


Voltage rgulators

Here is the regulator circuit for each filament I've added a soft-start section to slowly raise the voltage on the filament.



B+ supply

The B+ supplies for both tubes and channels.